镍基高温合金以其优异的高温强度、蠕变抗力及抗氧化耐腐蚀性能，广泛应用于航空发动机和燃气轮机等高端装备的热端部件[1,2]。然而，传统铸锻工艺在复杂构件成形和性能集成方面存在局限性[3,4]。作为一种高精度的增材制造技术(图1a)，激光粉末床熔融(LPBF)为镍基高温合金的制备提供了新途径，不仅能实现复杂结构的近净成形，还能通过高冷却速率显著细化晶粒，优化微观组织[5,6]。通过精确调控激光参数，可以影响熔池热历史，进而调控第二相的析出行为，但LPBF工艺的高温度梯度和快速凝固带来了第二相非平衡析出、空间分布不均等挑战[7,8]。从第二相类型与机制上看，镍基合金的典型第二相包括γ′相(Ni3(Al, Ti)，L12有序、与γ基体共格)、γ″相(Ni3Nb，D022，片/针状、常呈半共格)、δ相(Ni3Nb，正交，主要用于晶粒调控而非直接强化)、MC/M23C6等碳化物以及弥散氧化物颗粒(如Y2O3)；其强化机制主要包括有序剪切与反相畴界(APB)能强化、相干错配应变强化、位错Orowan绕过以及Zener钉扎晶界等。相反，拓扑密排(TCP)/η等脆性相会削弱基体连续性并诱发热裂纹，需加以抑制。
图1
图1
激光粉末床熔融(LPBF)制造过程及第二相作用机制
Fig.1
Schematic of manufacturing process (a) and mechanisms of secondary phases (b) of laser powder bed fusion (LPBF)
在镍基合金中，γ′相通过位错剪切机制主导高温强化，γ″相通常以盘状/透镜状纳米析出物形式存在，通过阻碍位错运动(切过或绕过)实现强化，弥散分布的碳化物和氧化物能抑制晶界滑移与裂纹形成[9~12] (图1b)。具体而言，γ′相与γ基体通常保持共格或半共格关系，其APB能与相干失配应变共同决定位错与沉淀相的相互作用；当γ′相尺寸超过临界半径时，强化机制可由位错剪切转变为Orowan绕过，并在蠕变条件下发生筏化而重排强化通道。γ″相依赖Nb富集形成盘/针状析出物，通过相干应变场强钉扎位错，对650~750 ℃区间的屈服强度与低周疲劳性能尤为敏感；δ相可稳定晶界与调控晶粒度，但会消耗Nb、削弱γ″强化。MC、M23C6碳化物在晶界起到Zener钉扎和抑制晶界滑移的作用，适量碳化物有利于提高蠕变抗力，但连续网状分布的碳化物可能诱发晶界脆化；弥散氧化物颗粒通过Orowan机制提高合金的高温强度，并对晶界提供稳定化钉扎，有助于提升合金的抗氧化/耐腐蚀和持久性能。综合而言，γ′/γ″相沉淀主导中高温强度和蠕变性能，碳化物和氧化物提升晶界稳定性与疲劳抗裂能力，而过量TCP/η等相显著降低塑性、持久寿命并劣化抗腐蚀/抗氧化性能。需要强调的是，LPBF工艺的非平衡热历史引入短路扩散通道(位错/胞壁/亚晶界)与层间再加热效应，使形核势垒、扩散通量与界面能演变动态耦合，从而改变沉淀相的析出顺序和竞争关系。同时，LPBF的非平衡冷却环境使这些第二相的形核和长大行为更为复杂，热应力循环可能导致碳化物粗化或溶解，元素偏析则可能影响相变动力学和相稳定性[13]。
1 激光粉末床熔融过程中合金的组织特征与非平衡行为
LPBF过程通过高能激光逐层熔化金属粉末，其极高的冷却速率和温度梯度显著改变了镍基高温合金的凝固机制，进而形成了高度非平衡的微观组织和织构特征[19,20]。热处理后，样品中的第二相形成路径示意图如图2a所示，其经历了形核与粗化的过程。具体而言，激光熔化过程中熔池瞬时温度可超2000 ℃，冷却速率高达105~107 K/s，这种极端条件促使合金形成过饱和固溶体，并导致择优取向的柱状晶生长[21~23]。进一步地，从凝固动力学看，高温度梯度/凝固速率(G / R)和大R使溶质边界层难以建立，产生溶质俘获和成分过冷，诱发胞状/枝晶生长和强微观偏析；随之形成的过饱和固溶体与化学势梯度为后续沉淀提供了高驱动力与优先形核位点。
图2
图2
LPBF镍基高温合金第二相的形成与调控：形成路径示意图，相演变，及热处理调控[7,24,29,40]
Fig.2
Formation and regulation of secondary phases in nickel-based superalloys by LPBF
(a) schematic of the formation path of secondary phases (TCP—topologically close-packed)
(b) evolution of secondary phases[7,24,29]
(c) regulation of secondary phases through heat treatments[40] (HT1, HT2—aging heat treatments; w—mass fraction)
为更直观地阐释工艺参数对沉淀相的影响，可以从形核、长大、粗化及相变耦合的角度加以说明。在位错密集区和位错胞壁处，高应变能和高扩散通量降低了临界形核功，从而促使γ′/γ″优先形核。γ′相在形核早期与基体保持共格，其APB能与由晶格失配引起的相干应变能共同决定了其形貌由球形向立方的演化，同时也控制着位错剪切向Orowan绕过的转变。γ″相依托Nb富集形成盘状或针状析出物，通过相干应变场钉扎位错，但在层间再加热过程中易向δ相转变，从而削弱强化作用。沉淀相的粗化大体遵循Lifshitz-Slyozov-Wagner (LSW)动力学，而周期性加热则会加速其粗化，并在层高方向上形成尺寸梯度。MC碳化物的形成和分布受C、Ti、Nb等元素的局部富集以及熔池对流和界面迁移速率的共同影响，当其呈链状或网络化分布时，会显著增加晶界脆化的敏感性。此外，随着热输入和停留时间的增加，由于枝晶间Nb过饱和往往首先析出Laves相，随后在热暴露下溶解并重新分配为γ″/δ相，从而为后续沉淀相析出提供溶质来源[46]。
此外，缺陷的形成主要源自热应力的积累和凝固过程中成分(元素)分布的不均匀性。这些缺陷不仅降低了材料的致密性，还破坏了第二相的空间均匀性，表1列出了常见的缺陷类型及其成因。具体来说，非均匀性主要来源于：晶界元素偏析诱导σ相析出，进而降低了合金的结合力[13]；熔池边界热循环造成的再结晶区会导致第二相显著细化[47]；强织构造成的各向异性可能导致弹性模量各向差值达到15%[48]。因此，系统地识别缺陷的来源并有效调控缺陷的形成，是实现第二相稳定析出及组织均匀性的重要保证[49]。并且，应注意缺陷-沉淀的双向耦合：孔隙/未熔合缺陷的应力集中可促进局部再析出/粗化与相转变，而连续碳化物/脆性相网络又会降低断裂韧性并放大裂纹驱动力，需通过HIP +合适的热处理工艺联合抑制。
表1 LPBF镍基高温合金的缺陷类型、成因及化学不均匀性(元素偏析)
Table 1
| Defect type | Characteristic size | Main cause | Impact on secondary phase |
|---|---|---|---|
| Porosity | 20-200 μm | Entrapment of protective gas / keyhole collapse | Localized accumulation of γ′ |
| Hot cracking | Length 500 μm | Shrinkage stress of the liquid film | Blocking the distribution of carbides |
| Element segregation | Segregation bandwidth 50 μm | Solute trapping between dendrites | Promoting coarsening of γ″ |
对于γ′相，首层快速冷却形成细小球状γ′/原子团簇。层间再加热过程中，Gibbs-Thomson效应优先驱动较小的γ′相回溶，溶质富集至周围基体。随后的再冷却会导致重新析出，并与存活的大颗粒共同进入Ostwald粗化阶段，形成双峰分布。随着Ω的累积，γ′相形貌由球状逐渐转变为立方状，并可能发生择向粗化或初始筏化，特别是由残余应力与各向异性界面能驱动。此时，位错-沉淀相互作用逐步由剪切转向Orowan绕过机制[56]。
在碳化物的链化与演变过程中，MC (TiC、NbC)碳化物优先在晶界或胞状晶组织壁析出。随着温度的升高，溶质的再分配与界面迁移主导其生长。当Ω较高时，MC碳化物可能向M23C6等转变，并沿晶界形成链化或网络结构。适量的碳化物有助于抑制晶界滑移和Zener钉扎效应，而过度链化则会降低材料的断裂韧性，成为裂纹源[59]。对于弥散氧化物颗粒(如Y2O3、Al2O3)，它们在循环升温过程中通常保持稳定，但可能存在团聚和粗化的风险。颗粒与位错之间的Orowan钉扎与对晶界迁移的Zener阻力随颗粒半径和间距的变化而发生变化。若热峰温度超过颗粒的稳定窗口，可能导致颗粒与基体之间的界面解耦，进而降低钉扎效应[60]。
在构建高度方向的梯度和热影响层厚度方面，由于上部多层的持续沉积，靠近基板和早期沉积区的Ω较大，表现为更粗大的γ′/γ″颗粒和更高的碳化物连续度。相较之下，顶部的层数较少，再加热次数较少，因此沉淀相颗粒更为细小且非平衡度较高。这种自下而上的粗化梯度与扫描轨迹以及道间停留时间共同作用，决定了沉淀相尺寸和体积分数随高度的变化[61]。
2 多类型第二相的形成机制与调控路径
在LPBF特有的高温梯度与非平衡凝固环境下，镍基高温合金中可形成多种第二相，包括γ′相、γ″相、MC类碳化物、TCP/η相以及引入的弥散氧化物颗粒(图3a)。由于各类第二相在热力学稳定性和扩散行为上的差异，其演化路径复杂且相互耦合，显著影响最终组织和性能。因此，其形成和调控不仅取决于热力学驱动力，还受到界面能、相干应变能、扩散通量和缺陷结构的共同控制，表现出显著的非平衡特征与路径依赖性。
图3
具体而言，γ′相为典型的L12有序结构，是镍基合金中主要的强化来源之一(图3b[64])。在LPBF的快速凝固条件下，γ′相倾向以亚稳、细小形态富集于位错或亚晶界附近[3,8]。同时，其析出行为受到Al / Ti比(质量比)及晶格缺陷的显著影响。机理上，γ′相的形成遵循过饱和固溶体、异质形核、尺寸长大与粗化链条：快速凝固提供了过饱和溶质，位错与胞状结构壁作为低能界面降低了形核势垒，晶格失配导致的相干应变能与颗粒尺寸共同作用，控制沉淀的共格保持与演化；当尺寸超过临界半径时，γ′相与位错相互作用机制由剪切转变为Orowan绕过。在调控层面，针对γ′相的调控策略主要包括：① 在成分设计中优化Al / Ti比，并引入Ta元素以抑制有害的TCP相形成[65]；② 通过优化激光功率和扫描速率等参数，降低偏析程度，改变形核条件[64,66]；③ 采用双时效等热处理方式，控制γ′相的尺寸，从而提升蠕变性能和组织均匀性[67]。
与γ′相互补，γ″相作为亚稳相在约650 ℃以下贡献显著；在更高温度下易粗化并向δ相转变，其强化作用随服役温度/时间增加而衰减，其强化机制来源于对位错运动的强钉扎效应[68]。γ″相在γ基体中的分布如图3c[69]所示。然而，LPBF过程中Nb的偏析常导致γ″相以细小但分布不均的形式析出，易诱发Laves相的析出，从而降低材料的韧性[7,70]。并且，γ″相的形成依赖于Nb的局部富集与长程扩散，其亚稳特征决定了在循环加热条件下容易向δ相转变；该相变本质上是由相干应变能积累超过临界值触发的有序和无序转变过程。据此，其调控策略包括：① 通过引入V、Ti等微合金化元素调节Nb的分布行为[7]；② 设计合理的热处理制度(如950 ℃固溶+ 720 ℃时效)促进γ″相的均匀析出[55]；③ 采用短时预时效以实现γ′/γ″相的协同析出并优化沉淀相的尺寸和分布[71,72]。
除γ′/γ″等金属间化合物相外，MC型碳化物(如TiC、NbC)沿晶界链状析出，是提升晶界强度与蠕变抗力的关键因素之一[73]，碳化物在γ基体中的分布如图3d[74]所示。其形成主要源于C、Ti、Nb元素的局部富集以及熔池内部的热对流驱动[75]。在机制方面，碳化物优先在晶界形成，是由于晶界作为高能界面可降低形核功；其长大依赖于溶质扩散速率和界面迁移速率，链状/连续分布则源于溶质在液/固界面处的富集、偏聚与连锁效应。然而，若碳化物分布过于连续，易引发晶界脆化现象[76]。近年来，引入陶瓷纳米颗粒或利用原位碳化物成为实现碳化物尺寸可控、均匀弥散分布的有效手段，能够在强度与延展性之间实现较好平衡[77~80]。
在提升合金高温服役性能方面，弥散氧化物颗粒(如Y2O3)也展现出独特优势。它们不仅可增强高温强度、细化晶粒，还可有效抑制位错积累[81]。氧化物在基体中的分布如图3e[82]所示。其强化机理主要为Orowan绕过与Zener钉扎双重效应：前者抑制位错攀移，后者稳定晶界迁移，因此在高温下能显著延缓组织粗化。需要指出的是，LPBF过程中存在高温和局部过热问题，可能导致氧化物溶解、团聚或偏析[83]。针对这一挑战，优化策略包括：① 通过合金化设计引入Y元素，促进多尺度氧化物的原位生成[84]；② 采用预合金粉末或构建原位反应路径以实现氧化物的空间均匀分布[81,85]；③ 优化激光工艺参数，抑制颗粒粗化，促进等轴晶形成，增强组织稳定性[43]。
然而，在上述第二相析出的同时，LPBF过程中高能量输入和元素偏析亦会促使脆性相如TCP (σ、μ、P)和η相的形成(图3f[86])，这将显著削弱基体连续性并诱发热裂纹等缺陷[86~90]。TCP/η相的形成本质上是镍基高温合金体系中元素分布失衡的结果：W、Mo和Re等元素在枝晶间的长期偏聚，降低了局部相稳定性，从而触发复杂金属间化合物相的析出。TCP相主要由Re、W、Mo等元素富集形成，而η相多在热积累区由Ti / Al比过高驱动析出[91]。针对这些脆性相，主要的调控方法包括：① 通过成分优化控制Re + W + Mo总量，同时引入Ru以提高相稳定性[92,93]；② 控制Ti / Al比低于0.9、提高扫描速率以抑制热积累诱导析出[41,90,94]；③ 采用均质热处理与HIP技术溶解已有TCP相，从而显著提升延展性和组织稳定性[92,95]。值得指出的是，当前尚缺乏针对LPBF条件下TCP/η相析出的定量模型，这限制了其精准预测与过程优化能力[96]。
总体而言，在LPBF制备过程中，γ′相、γ″相、MC碳化物与弥散氧化物常以协同或竞争方式析出，其相互作用最终决定材料的综合性能[48]。例如，在IN718合金中，双时效工艺可实现γ′/γ″相的协同析出，从而显著增强其蠕变性能[97]；进一步引入WC颗粒不仅促进了第二相细化至约20 nm，还可构建三重强化体系，使其屈服强度提升约42%[98,99]。因此，为实现第二相的协同优化与性能最大化，当前研究提出了系统的调控策略(图3[64,69,74,82,86])，包括：① 采用固溶、塑性变形和再时效三阶段路径实现第二相有序析出与晶粒稳定[69,100]；② 结合相场模拟与机器学习方法，精确预测第二相析出行为并优化热处理制度[101,102]。该策略不仅为多目标性能调控提供理论基础，也为智能化合金设计奠定了基础。需要强调的是，多类型第二相的形成并非孤立过程，而是由溶质偏聚、界面应变、循环热历史以及相互竞争析出的耦合共同主导。未来研究亟需发展跨尺度动力学模型，将热力学驱动力与非平衡扩散和界面迁移动力学相结合，才能实现从机理层面对多类型第二相形成路径的预测与精准调控。
3 第二相对合金组织稳定性与性能的影响
LPBF工艺中极高的热梯度和快速非平衡凝固行为显著改变了镍基高温合金中各类第二相的形核和生长机制。因此，本节聚焦于第二相对合金组织稳定性和性能的影响，并讨论其随LPBF热历史的演化规律(图4[6,103~105])。具体而言，从第二相的类型、形貌、尺寸与空间分布出发，阐明其对合金性能的因果作用链。可见，这些第二相的类型、形貌和分布(及其演化)直接决定了合金的组织稳定性及合金性能。因此，系统揭示不同第二相在LPBF过程中的演化规律，并分析其对组织-性能耦合的作用机理，对于高性能构件的设计及服役可靠性提升具有重要意义。在此基础上，在LPBF过程中的层间循环加热作用下，γ′/γ″相的等效半径(
图4
第二相γ′在LPBF成形后以细小的球状或立方状形式析出，主要富集于位错区和亚晶界。其通过位错钉扎机制显著提升初始强度，但在高温服役条件下易发生粗化，进而导致蠕变抗力下降[108]，热处理中的相演变规律如图4b[6]所示。热处理后，生成了大量γ′和M23C6相。同时，γ′相的形貌差异也显著影响强化效果：立方状γ′相更易通过位错剪切实现强化，而球状形态则更可能被位错绕过，降低整体强度[109~111]。因此，为增强其热稳定性，常采用多级热处理精确控制其尺寸与形貌演化，同时通过引入高密度位错网络，提升γ′相在高温下的稳定性[8,47]。此外，稳定的γ′相还可为后续第二相(如γ″)的协同析出提供有利形核环境，进一步提升合金组织与性能的协同水平。
综上所述，LPBF制备的镍基高温合金中，多类型第二相在不同时空尺度上实现协同演化，不仅构建了多层次组织稳定性体系，也直接提升了合金的多维综合性能。这种从第二相出发的因果表达更清晰地支撑了工艺-组织-第二相-性能耦合调控理论体系的构建，并为高性能合金的智能设计奠定了坚实基础。
4 工艺参数与热处理对第二相的多尺度调控
图5
图5
工艺参数-组织演化-性能响应三者之间的对应关系
Fig.5
Correspondence diagram of process parameters, microstructure evolution, and performance response (TB—twin boundary, Tonset—onset temperature, Tpeak—peak temperature)
首先，激光功率和扫描速率作为影响熔池热输入的核心参数，是调控第二相初始形成行为的基础变量。它们共同决定单位体积能量密度，影响熔池尺寸、冷却速率和温度梯度，从而显著影响第二相的初始析出特征[130]。较高激光功率及低的扫描速率将增强能量密度，有利于形成完整熔池，但也易导致元素偏析和第二相粗大析出；而较低能量密度则促使快速凝固和细化组织，为后续第二相的均匀析出提供有利条件[7,24]。合适的激光参数能够在组织致密性和第二相调控之间实现良好平衡，显著改善组织均匀性和沉淀相分布[24,82]。在实际应用中，激光能量输入的微调还需兼顾致密度的控制。例如，在双激光LPBF成形GH3536合金过程中，搭接区域激光功率过高反而导致致密度下降[131]；而通过优化能量密度参数，高功率激光熔融制备GH4169合金可实现致密度超过99.80%的致密组织[132]。因此，激光参数的精确调控不仅关系到第二相的初始析出行为，也为后续微观结构演化和热处理路径构建了稳定可控的热历史基础，构成第二相空间分布调控的前置条件。
在热输入控制的基础上，扫描策略作为调节局部热场与组织取向的重要手段，进一步决定第二相的空间分布均匀性和析出一致性[133]。多向旋转扫描或90°交错扫描可破坏柱状晶优先生长方向，促进等轴晶形成，显著改善第二相分布的均匀性[134,135]。同时，合理的扫描路径还能有效降低局部温度梯度和残余应力，抑制热裂纹的形成[134,136]。而不当扫描策略可能导致第二相溶解-再析出，增加组织异质性并降低力学性能稳定性[134]。针对增材制造中常见的结构缺陷问题，扫描策略的优化表现出重要的工艺潜力。例如，在MAR-M247合金中，孔洞和热裂纹是典型缺陷类型，通过调整能量密度与扫描间距可显著降低孔洞数量，而引入间歇沉积策略可显著提升抗裂纹能力[137]。因此，扫描策略的合理制定在第二相空间控制和缺陷抑制中具有不可忽视的重要作用。
尽管上述工艺参数对第二相的初始演化具有显著调控效应，但由于LPBF过程本身引发的快速凝固和强烈元素偏析，第二相的沉淀行为往往难以达到稳定态。因此，热处理作为LPBF合金第二相调控的核心环节，在激活第二相析出、调节其尺寸和分布方面发挥着决定性作用。传统的固溶+双时效制度虽广泛用于铸态IN 738合金，但在LPBF制备条件下，常因晶粒异常长大而无法获得理想性能，需要对固溶温度和时效参数进行系统优化[115,138,139]。针对非平衡组织特征，热处理不仅影响γ′、γ″等沉淀第二相的析出行为、尺寸演化和界面结构，还可显著调控碳化物和氧化物的析出形貌，进而改善合金的力学性能与高温稳定性[109,140,141]。进一步地，在高γ′含量合金中，采用分级时效可诱导形成双尺度γ′相，兼顾高温稳定性与位错钉扎能力[129,139,140]。此外，基于胞状晶组织特征的发展路径，如固溶-温轧-再时效处理，也可实现第二相分布的有序化，提升组织稳定性与第二相一致性[142,143]。为了实现多类型第二相的协同调控，热处理过程中还需关注碳化物、Laves相等第二相的演变行为，并通过精准的温度控制防止有害相生成[144~147]，通常需严格控制时效温度在γ′相固溶线以下[139,148]。如在DD491单晶合金中，复合热处理工艺可有效抑制再结晶，保证组织稳定性[149]。近年来，液态金属辅助LPBF技术的发展也为热处理方式带来创新，通过逐层原位热处理实现组织连续优化，突破传统路径下的强-塑性协同调控瓶颈[142]。
在完成热处理精细调控的基础上，进一步提升组织致密性和第二相稳定性的重要后处理手段是HIP技术。该工艺通过高温高压条件促使孔隙闭合、元素再分布与局部再结晶，显著改善组织致密性与晶粒结构[47,117,130]。经过HIP处理后，第二相(如γ′和γ″)的稳定析出行为得到提升，其尺寸分布变异系数可显著降低至15%以下[140,149]。同时，HIP处理促使碳化物由网状结构转为离散颗粒，有效降低裂纹萌生风险[140,144,150]。复合处理路径亦展现出显著优势，例如在GH3536合金中，预热-HIP复合处理使材料的室温和高温延伸率分别提升62.6%和243.6%[131]；在IN738LC合金中，HIP处理诱导γ′相粗化，并在阶梯时效后进一步析出细小的二次γ′相，使其持久寿命提升高达300%[145,148]。特别是对于单晶镍基合金，采用超固相线条件下的HIP处理技术，通过瞬时液相生成可实现微孔愈合，显著提升疲劳寿命和组织稳定性[150]。
综上所述，LPBF工艺中涵盖的多尺度调控机制，依托激光参数、扫描策略与后续热处理及HIP路径的精确协同，不仅有效优化了第二相的析出行为和空间分布，还显著提升了组织一致性和服役稳定性。该体系为高性能镍基合金构件的微结构设计和性能构建提供了坚实的理论基础和系统工艺支持。
5 总结与展望
随着LPBF技术在镍基高温合金制造中的不断深入，其非平衡凝固特性为第二相的精准调控提供了前所未有的可能。多类型第二相的可控析出不仅显著提升了构件的服役性能，也促使传统组织设计理念发生根本性转变。然而，尽管在这一领域取得了诸多进展，现阶段仍面临一系列技术和机制层面的挑战，主要集中于模拟预测、组织控制、性能优化以及标准体系建立等方面，制约了其在高性能构件设计中的广泛应用。
在模拟预测方面，宏观熔池行为与微观相变动力学之间的耦合尚不完善，导致非平衡凝固过程下第二相的形成路径难以精确预测。尤其是元素间溶质分配与偏析的竞争析出机制缺乏定量模型支持，使得合金成分设计仍依赖经验积累和大量实验迭代。尽管已有研究尝试引入机器学习方法用于第二相的形成预测，但由于缺乏系统性的服役数据支撑，目前的模型仍难以在实际工程中推广应用。在组织控制方面，熔池热历史的剧烈波动使得第二相析出存在一定随机性，难以实现可控调节。尤其在能量密度较高的工艺窗口下，虽然致密度得以提高，但也更容易形成Laves相等脆性相，加剧了强度与塑性之间的性能矛盾，反映出在多性能协同优化方面仍有较大改进空间。
面向未来，研究的重点应转向多类型第二相之间的协同演化机制和稳定构建策略。例如，通过位错工程诱导γ″相有序排列，结合界面功能化调控与核/壳结构碳化物的引入，可在微观尺度上增强界面稳定性并抑制裂纹扩展。此外，固溶-变形-再时效等动态热处理路径有望拓展γ′/γ″相协同强化的温度-时间窗口，提升组织稳定性和适应性。同时，推动LPBF合金设计从依赖经验的路径向智能化和标准化转型也愈发迫切。一方面，需要依托高通量与多场耦合的原位测试平台，系统筛查第二相稳定性和界面演化行为；另一方面，应发展以图神经网络为核心的四维图谱工具，实现微观机制到宏观服役寿命的跨尺度预测，为工艺路径设计和热处理方案提供精准指导。
从已有研究来看，LPBF技术通过高速扫描和非平衡凝固，显著改变了镍基高温合金中第二相的析出行为和界面结构。快速凝固有助于形成细小且均匀分布的γ′/γ″相，提升中温蠕变性能；但也容易导致元素偏析并促使Laves相、δ相等有害相生成，削弱整体材料性能。在此背景下，第二相之间的协同关系显得尤为重要。例如，γ′/γ″相协同析出在中温强度方面具有显著优势，碳化物和氧化物则通过晶界钉扎机制增强材料的热稳定性和抗裂性。尽管如此，第二相析出过程中的元素竞争与界面失稳等问题仍未彻底解决。HIP处理在1120 ℃下可有效闭合孔隙并保留胞状亚结构，为γ″相的有序析出提供了结构基础；进一步结合多阶段动态热处理路径，可在保持强度的同时提升延展性，实现组织与性能的协同优化。然而，当前多尺度设计方法尚不完善，性能均衡优化的策略不足，同时缺乏系统性的高温服役数据库，成为制约高性能镍基合金发展的核心障碍之一。
为破解上述难题，未来研究需从以下三个方面取得突破：一是基础理论深化，构建从电子结构到宏观性能的多尺度建模体系，借助第一性原理计算与高通量模拟技术，量化第二相析出和元素偏聚行为，并结合原位表征揭示高温演化过程中的界面迁移动力学；二是智能工艺开发，融合图神经网络、数字孪生和机器视觉等先进手段，构建可实时感知、在线反馈与自适应控制的数字化制造系统；三是工程标准构建，围绕材料-工艺-性能-检测的全流程，建立统一的数据平台与评估体系，加快实验室成果向工程应用的高效转化。
综上所述，精准调控与协同演化的第二相体系构成了LPBF镍基高温合金高性能化的核心支撑。未来，应充分发挥材料学、计算科学与智能制造等多学科优势，推动数据驱动型材料设计范式的建立，为先进制造与高端装备提供稳定、可靠的材料基础。
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Heat treatments-induced wear resistance of Inconel 718 superalloy fabricated via Laser Based Powder Bed Fusion
[J].
Liquid-induced healing of cracks in nickel-based superalloy fabricated by laser powder bed fusion
[J].
Small punch creep test reveals the differences of high-temperature creep behaviours for laser powder bed fusion and Rolled Inconel 718 alloys
[J].
Gamma prime formation in nickel-based superalloy IN738LC manufactured by laser powder bed fusion
[J].
Effect of printing parameters and heat treatments on microstructure development of LPBF manufactured Inconel 718 alloy
[J].
Achieving well-balanced strength and ductility in laser powder bed fusion additively manufactured nickel-based superalloys by doping multiple oxides
[J].
On the thermomechanical aging of LPBF alloy 718
[J].
Residual stress mapping in heat-assisted additive manufacturing of IN 718: An X-ray diffraction study
[J].Laser powder bed fusion (LPBF) is a type of additive manufacturing (AM) technique characterized by multiple localized thermal processes that result in rapid heating and cooling. The thermal variations observed in the LPBF process can generate residual stress (RS) inside the fabricated part, impacting the surface integrity and geometric tolerances of the manufactured components. To reduce thermal variation during manufacturing, heat-assisted AM was employed, thereby minimizing RS and any thermal distortion that could occur during the fabrication of materials. The present research utilizes non-destructive x-ray diffraction to analyze the influence of an in-situ heated building plate and processing parameters on the RS distribution in Inconel 718 (IN718) fabricated by LPBF. This study examines the impact of two scanning procedures and three laser power levels and offers critical insights into both measurement techniques and RS characterization. By understanding the effect of the processing parameters on RS, we aim to enhance the quality of manufactured parts through process optimization. Post-processing heat treatment consistently reduced RS in all samples, regardless of laser power levels or scanning strategies. Combining a chess scanning strategy with 270 W laser power resulted in the most significant RS reduction in IN718.
On the current research progress of metallic materials fabricated by laser powder bed fusion process: A review
[J].
Microstructure evolution and mechanical properties of additively manufactured Ni-based GH4099 superalloy via hot isostatic pressing and heat treatment
[J].
Fine grains with high-density annealing twins and precipitates inducing favorable strength and excellent plasticity in laser powder bed fusion-fabricated Inconel 718 via deep cryogenic and heat treatments
[J].Tailoring high-density annealing twins in laser powder bed fusion (LPBF)-fabricated alloys based on their intrinsic residual stress requires high annealing temperatures and/or long-term annealing, resulting in the abnormal growth of large recrystallized grains, which is detrimental to mechanical properties. This work proposes a new strategy for achieving a favorable strength-plasticity synergy of the LPBF-fabricated Inconel 718 superalloy by performing a deep cryogenic treatment (DCT) with the subsequent heat treatment (including annealing and double aging) to tailor fine grains with “high-density annealing twins + precipitates” architectures and compares the obtained material with an alloy subjected to a direct heat treatment without a prior DCT. The obtained results reveal that the additional internal stress generated during DCT increases the stored energy and dislocation density, which provide a sufficient driving force for activating high-density annealing twin boundaries (63.2 %) with fine grains (31.6 μm) within a short annealing time. The more homogeneous tailored microstructure with the “finer grains + high-density twins + precipitates” architectures decreases the mean free path of slipping dislocations, promoting intensive interactions with dislocations and inducing a strong strain hardening effect. The multiple deformation modes of stacking faults coupled with Lomer-Cottrell locks, thin primary deformation twins, and secondary twins activated during tensile loading, sustaining a strong work hardening ability and delaying the plastic instability, which exhibits a high strength (yield strength of 1088 MPa and tensile strength of 1369 MPa) and excellent plasticity (elongation of 30 %). This work not only describes a feasible method for simultaneously enhancing the strength and plasticity in additively manufactured (AM) alloys but also provides new insights into increasing the fraction of twins at a small grain size to improve the grain boundary-related properties without destroying the AM alloy shape.
Tailoring of the microstructure of laser powder bed fused Inconel 718 using solution annealing and aging treatments
[J].Inconel 718 (IN718) is a nickel-based superalloy with high weldability and is thus ideal for being processed via laser powder bed fusion (LPBF). Unlike traditional casting, LPBF IN718 develops a complex microstructure due to the rapid solidification that characterizes this manufacturing process. As a result, LPBF microstructures are different from those expected in equilibrium conditions, and for this reason, specific heat treatments should be designed. This paper, using differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), and a field emission scanning electron microscope (FESEM), aims to develop a complete heat treatment that maximizes the material strength, thereby enhancing its microstructure. The paper shows that high-temperature annealing followed by two aging steps is the most suitable way to achieve the abovementioned task. More specifically, a complete dissolution of the δ phase via solution annealing at 1080 °C is the key factor in gaining an even and intense precipitation of γ′ and γ″ during the subsequent aging treatments. The microstructural analyses showed the elimination of needle-like δ particles and detrimental Laves phases. At the same time, intense precipitation of spherical and of discoidal reinforcing particles was achieved by performing the aging treatments at 720 and 630 °C, respectively.
Simulation and experimental analysis of nanoscale precipitation during ageing treatment of laser powder-bed fusion fabricated IN718 Ni-based superalloy
[J].
Material extrusion thermal model mapped across polyetheretherketone isothermal and continuous cooling transformation charts
[J].
Kinetics of phase change. I General theory
[J].The theory of the kinetics of phase change is developed with the experimentally supported assumptions that the new phase is nucleated by germ nuclei which already exist in the old phase, and whose number can be altered by previous treatment. The density of germ nuclei diminishes through activation of some of them to become growth nuclei for grains of the new phase, and ingestion of others by these growing grains. The quantitative relations between the density of germ nuclei, growth nuclei, and transformed volume are derived and expressed in terms of a characteristic time scale for any given substance and process. The geometry and kinetics of a crystal aggregate are studied from this point of view, and it is shown that there is strong evidence of the existence, for any given substance, of an isokinetic range of temperatures and concentrations in which the characteristic kinetics of phase change remains the same. The determination of phase reaction kinetics is shown to depend upon the solution of a functional equation of a certain type. Some of the general properties of temperature-time and transformation-time curves, respectively, are described and explained.
The kinetics of precipitation from supersaturated solid solutions
[J].
The temperature dependence of relaxation mechanisms in amorphous polymers and other glass-forming liquids
[J].
Kinetics and mechanisms of γ′ reprecipitation in a Ni-based superalloy
[J].The reprecipitation mechanisms and kinetics of gamma' particles during cooling from supersolvus and subsolvus temperatures were studied in AD730TM Ni-based superalloy using Differential Thermal Analysis (DTA). The evolution in the morphology and distribution of reprecipitated gamma' particles was investigated using Field Emission Gun Scanning Electron Microscopy (FEG-SEM). Depending on the cooling rate, gamma' particles showed multi or monomodal distribution. The irregularity growth characteristics observed at lower cooling rates were analyzed in the context of Mullins and Sekerka theory, and allowed the determination of a critical size of gamma' particles above which morphological instability appears. Precipitation kinetics parameters were determined using a non-isothermal JMA model and DTA data. The Avrami exponent was determined to be in the 1.5-2.3 range, suggesting spherical or irregular growth. A methodology was developed to take into account the temperature dependence of the rate coefficient k(T) in the non-isothermal JMA equation. In that regard, a function for k(T) was developed. Based on the results obtained, reprecipitation kinetics models for low and high cooling rates are proposed to quantify and predict the volume fraction of reprecipitated gamma' particles during the cooling process.
Laser powder bed fusion additive manufacturing of metals; physics, computational, and materials challenges
[J].
Additive manufacturing of metallic components—Process, structure and properties
[J].
Strengthening and embrittlement mechanisms in laser-welded additively manufactured Inconel 718 superalloy
[J].Although laser-welded additively manufactured Inconel 718 joints find numerous high-temperature industrial applications, their strengthening and embrittlement mechanisms remain underexplored. To bridge this gap, we herein prepared such joints by the laser welding of the as-built material (built-LW), laser welding of double-aging heat-treated as-built material (DAT-LW), and double-aging heat treatment of laser-welded as-built material (LW-DAT). The microstructures of the joint fusion zones (FZs) were examined using scanning electron microscopy (electron backscatter diffraction and secondary electron imaging), while nanoscale features were probed by transmission electron microscopy, and mechanical properties were evaluated using microindentation hardness (HIT) measurements and tensile tests. The FZs of the built-LW and DAT-LW joints contained no strengthening precipitates, such as the Laves phase and γ′ and γ″ nanoparticles. In stark contrast, the FZ of the LW-DAT joint contained spherical nanoparticles of the γ′ and γ″ phases responsible for precipitation hardening. The DAT-LW joint displayed base metal (BM) strengthening and FZ softening (HIT = 6.47 and 3.6 GPa, respectively), whereas the LW-DAT joint demonstrated BM and FZ strengthening (HIT = 6.2 and 6.5 GPa, respectively). The built-LW joint exhibited the lowest ultimate tensile strength (UTS) of 833 MPa, primarily because of the absence of strengthening precipitates. The DAT-LW joint, despite experiencing FZ softening, exhibited a higher UTS of 1086 MPa and a limited elongation of 2%, while the LW-DAT joint featured the highest UTS of 1440 MPa, primarily because of the enhancement of nanosized γ′ and γ″ strengthening phases facilitated by postwelding double-aging heat treatment.
Structure and properties of LW 4280, a new high γ′ Ni-based superalloy fabricated by laser powder bed fusion
[J].
Unique yttria nanoparticle strengthening in an inconel 718 superalloy fabricated by additive manufacturing
[J].
Effect of building-height-dependent heat accumulation on microstructure and properties of Super Invar alloy fabricated by laser powder bed fusion
[J].
Prediction of epitaxial grain growth in single-track laser melting of IN718 using integrated finite element and cellular automaton approach
[J].The mechanical properties of selective laser melting (SLM) components are fundamentally dependent on their microstructure. Accordingly, the present study proposes an integrated simulation framework consisting of a three-dimensional (3D) finite element model and a cellular automaton model for predicting the epitaxial grain growth mode in the single-track SLM processing of IN718. The laser beam scattering effect, melt surface evolution, powder volume shrinkage, bulk heterogeneous nucleation, epitaxial growth, and initial microstructure of the substrate are considered. The simulation results show that during single-track SLM processing, coarse epitaxial grains are formed at the melt–substrate interface, while fine grains grow at the melt–powder interface with a density determined by the intensity of the heat input. During the solidification stage, the epitaxial grains and bulk nucleated grains grow toward the top surface of the melt pool along the temperature gradient vectors. The rate of the epitaxial grain growth varies as a function of the orientation and size of the partially melted grains at the melt–substrate boundary, the melt pool size, and the temperature gradient. This is observed that by increasing heat input from 250 J/m to 500 J/m, the average grain size increases by ~20%. In addition, the average grain size reduces by 17% when the initial substrate grain size decreases by 50%. In general, the results show that the microstructure of the processed IN718 alloy can be controlled by adjusting the heat input, preheating conditions, and initial substrate grain size.
Experimental investigation into microstructure, mechanical properties, and cracking mechanism of IN713LC processed by laser powder bed fusion
[J].
Printability, microstructures and mechanical properties of a novel Co-based superalloy fabricated via laser powder bed fusion
[J].High levels of Al and Ti in superalloy compositions normally lead to cracking formation during the laser powder bed fusion process, while these elements are key constituents of strengthening phases. In the current study, a novel Co-based superalloy with the basic chemical composition of Co-Al-W-Ta-Ti resolved this contradiction, indicating that the part was formed without cracking and simultaneously contained a large amount of strengthening precipitates in the microstructure fabricated via laser powder bed fusion. The printability, microstructures, and mechanical properties of the sample were analysed before and after heat treatment, providing a potential superalloy that can replace Ni-based superalloys fabricated by additive manufacturing in aerospace and other industries with higher temperature and more efficiency.
Synchronously enhanced printability and properties of additively manufactured nickel-based superalloys via alloying minor Sc
[J].
On selective laser melting of Inconel 718: Densification, surface roughness, and residual stresses
[J].
Fatigue crack growth characterization of Inconel 718 after additive manufacturing by laser powder bed fusion and heat treatment
[J].
Precipitation kinetics of γ″ phase and its mechanism in a Nb-bearing nickel-based superalloy during aging
[J].
Outstanding strength-ductility synergy in Inconel 718 superalloy via laser powder bed fusion and thermomechanical treatment
[J].
Multi-phase field model of laser powder bed fusion based additive manufacturing of IN718 superalloy
[J].
Thermal processing strategies enabling boride dissolution and gamma prime precipitation in dissimilar nickel-based superalloys transient liquid phase bond
[J].
Surface integrity and superelastic response of additively manufactured Nitinol after heat treatment and finish machining
[J].
Hierarchical architecture and mechanical behavior of K418 Ni-based superalloys manufactured by laser powder bed fusion
[J].
Effect of Ta addition on primary MC carbide in Ti-Nb-Mo-W-alloyed superalloy
[J].
Effect of laser energy density on temperature field, forming quality, and performance of LPBF-fabricated nickel-based superalloy composites
[J].
Effect of solution heat treatment on microstructure, mechanical and electrochemical properties of Hastelloy X fabricated by laser powder bed fusion
[J].
Investigation of a novel laser powder bed fusion nickel-based superalloy with Hf, Y addition: Melt characteristic, microstructure and mechanical properties
[J].
The role of ceramic particles on the crack inhibition and mechanical properties improvement of Haynes 230 alloy fabricated by laser powder bed fusion
[J].
Controlling WC/Co two-phase microstructure of cemented carbides additive-manufactured by laser powder bed fusion: Effect of powder composition and post heat-treatment
[J].
Boron effect on phase transformation of σ and M23C6 in nimonic 105 superalloy
[J].
Effects of Y2O3 nanoparticles on the high-temperature oxidation behavior of IN738LC manufactured by laser powder bed fusion
[J].
Mitigating microstructural heterogeneity in laser-directed energy deposition Ni-based superalloys by heat accumulation in-situ heat treatment
[J].
Laser powder bed fusion of oxide dispersion-strengthened IN718 alloys: A complementary study on microstructure and mechanical properties
[J].
Synergistic improvements of strength and ductility of laser powder bed fusion Inconel 718 with higher carbon content at 650 oC by adding yttrium
[J].
Additive manufacturing of nickel-based superalloys: A state-of-the-art review on process-structure-defect-property relationship
[J].
Creep prediction model for nickel-based single-crystal superalloys considering precipitation of TCP phase
[J].The microstructure of nickel‐based single‐crystal (SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long‐term creep properties of nickel‐based SC superalloys, but also results in the formation of a topologically close‐packed (TCP) phase which is a harmful and brittle hard phase. Here, high‐temperature creep interruption tests of a nickel‐based SC superalloy that contains 4.8 wt% Re were performed under various temperatures and stress conditions, and the evolution of microstructure during creep was observed by scanning electron microscopy (SEM). The volume fraction of the TCP phase was also extracted to explore the mechanism that controls the impacts of the TCP phase on the creep properties. According to the microstructure evolution mechanism, the influence of the TCP phase was attributed to the initial damage and critical shear stress of the material. A creep performance prediction model for nickel‐based SC superalloys considering the precipitation of the TCP phase that is based on the crystal plasticity theory and a modified creep damage model was established. The simulation curves fit well with the experimental results and the errors between prediction creep life with test results are within 5%.
Precipitation of TCP phases with R/P intergrowth structure during directional solidification in a Ru-containing nickel-based single crystal superalloy
[J].
Hot isostatic pressing elimination of process-induced defects in laser powder bed fusion fabricated DZ125 superalloy: Microstructure evolution and mechanical property enhancement
[J].
Structural evolution of topologically closed packed phase in a Ni-based single crystal superalloy
[J].
Crack types, mechanisms, and suppression methods during high-energy beam additive manufacturing of nickel-based superalloys: A review
[J].
Asymmetric cracking in Mar-M247 alloy builds during electron beam powder bed fusion additive manufacturing
[J].
A review on microstructural stability regulation in nickel-based superalloys: Synergistic effects of alloying elements and phase stability optimization
[J].
A multi-component diffusion multiple approach based synergistic regulation of γ' phase stability and mechanical properties in CoTiVNi-based superalloys
[J].
Advances in crack formation mechanisms, evaluation models, and compositional strategies for additively manufactured nickel-based superalloys
[J].
Nucleation and transition sequences of TCP phases during heat-exposure in a Re-containing Ni-based single crystal superalloy
[J].
Microstructure and tensile properties of Y2O3-dispersion strengthened CoCrFeNi high entropy alloys prepared via mechanical alloying using pre-alloyed powder
[J].
Role of the γ′′ precipitation at the cell boundaries in enhancing the creep resistance of additively manufactured Inconel 718 alloy using the laser powder bed fusion technique
[J].
Achieving balanced mechanical properties in laser powder bed fusion processed Inconel 718 superalloy through a simplified heat treatment process
[J].Laser additively manufactured (LAM) Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state, requiring post-heat treatment to improve mechanical properties. We propose a modified heat treatment (MHT) process that only involves a single-step aging at 650 °C for 4 h to achieve high strength, high ductility, and low residual stress simultaneously in a laser powder bed fusion (LPBF)-processed Inconel 718 (IN718) alloy. The MHT treated alloy exhibits comparable tensile strength (1368 MPa) to the conventional solution plus two-step aging (SA) treated alloy (1398 MPa), while the tensile elongation (∼21.7 % for MHT treated alloy and 13.4 % for SA treated alloy) is 60 % higher and the residual stress (∼195 MPa) is 20 % lower than the SA treated alloy. The balanced high performance of the MHT IN718 alloy was mainly attributed to the precipitation of abundant γ'' phase with a size of ∼5 nm, while the original nano-sized Laves precipitates and dislocation cells were mostly retained. The finer size and higher fraction of γ'' of the MHT sample mainly result from the dislocation structure and compositional variations in the as-built IN718, which promotes precipitation during aging. The retention of Laves phase, and cellular dislocation network in the MHT alloy also contributes to work hardening during tension and suspends the occurrence of necking. This study unveils a unique strengthening and toughening mechanism in the Ni-based superalloy produced by LAM with the presence of abundant Laves precipitates and provides a simple, low energy-consumption and cost-effective heat treatment route for achieving desirable mechanical properties.
Laser powder bed fusion of WC-reinforced Hastelloy-X composite: Microstructure and mechanical properties
[J].
Dissolution of the Laves phase and δ-precipitate formation mechanism in additively manufactured Inconel 718 during post printing heat treatments
[J].
Phase-field simulation of microstructure evolution of Inconel 718 alloy by laser powder bed fusion solidification and homogenization heat treatment
[J].
Process optimization of Inconel 718 alloy produced by laser powder bed fusion
[J].To cut the cost of the laser powder bed fusion (LPBF) process, which is much higher than that of the traditional manufacturing process, an effective implementation of optimization analysis is needed. The study investigated the optimization of the LPBF Inconel 718 alloy with the Taguchi method and principal component analysis (PCA), covering four control factors at three levels in the manufacturing process. It focused on four mechanical properties, namely tensile strength, elongation, impact energy, and hardness. The results show that the highest tensile strength is obtainable at a laser power of 140 W, scanning speed of 800 mm/s, scanning pitch of 70 μm, and interlayer angle of 45 degrees. The optimal combination of process parameters for multiobjective optimization is just the same as that for single-objective optimization for tensile strength. The difference between the predicted and experimental average tensile strength is 1.2%, and the error of the predicted optimal strength index is 12.6%. The most important control factor for tensile strength and multiple responses is the angle between layers, with a contribution rate exceeding 90%. With a given volume energy density of the LPBF process, the higher the power and scanning speed, the higher the accumulated energy and the larger the amount of dendritic or cellular crystals formed.
Microstructure and mechanical properties of additive manufactured Inconel 718 alloy strengthened by oxide dispersion with 0.3 wt% Sc addition
[J].
Influence of heat treatments on microstructure evolution and mechanical properties of Inconel 625 processed by laser powder bed fusion
[J].
Investigation on different additions as candidates for nano-oxide particles in nickel-based ODS superalloys
[J].
Influence of hot isostatic pressing on the microstructure and mechanical properties of Hastelloy X samples manufactured via laser powder bed fusion
[J].This study investigates the effects of Hot Isostatic Pressing (HIP) treatment on the microstructural evolution and mechanical properties of Laser Powder Bed Fusion (LPBF)-manufactured Hastelloy H. This research evaluates the trade-offs between defect elimination, anisotropy reduction, and strength retention in well-optimized LPBF components. Specimens were manufactured using optimized LPBF parameters, achieving 99.85% density, and then subjected to HIP treatment at 1160 °C/100 MPa for 4 h. The analysis includes porosity analysis, grain size measurement, crystallographic texture evaluation, and tensile tests in two principal orientations. The results show that HIP treatment provides minimal benefits for defect elimination in already high-quality LPBF material, reducing porosity from 0.15% to <0.01%—a negligible improvement that does not translate to proportional mechanical enhancement. Tensile tests show that as-built specimens exhibited orientation-dependent strength, with XY-oriented samples reaching a yield strength (YS) of 682 MPa, ultimate tensile strength (UTS) of 864 MPa, and elongation of 17%, while XZ-oriented samples showed lower strength (YS = 621 MPa, UTS = 653 MPa) but superior ductility (elongation = 47%). After HIP treatment, anisotropy was largely removed, with both XY and XZ orientations showing comparable strength (YS ≈ 315–317 MPa, UTS ≈ 682–691 MPa) and elongation (38–41%). This indicates that HIP significantly improves ductility and isotropy at the cost of reduced strength. HIP treatment effectively eliminates the anisotropy of LPBF components, achieving uniform hardness across all orientations while reducing crystallographic texture intensity from 12.3× to 3.2× random orientation. This isotropy improvement occurs through grain-coarsening mechanisms that increase the average grain size from 7.5 μm to 13.5 μm, eliminating cellular–dendritic strengthening structures and reducing hardness by 32% (254 HV2 to 170 HV2) following Hall–Petch relationships. The conducted research confirms that HIP treatment allows for modification of the microstructure of Hastelloy X alloy, which may lead to the improvement of its mechanical properties in high-temperature applications and a significant increase in the isotropy of the material.
Hot isostatic pressing in metal additive manufacturing: X-ray tomography reveals details of pore closure
[J].
Kinetic analysis for high-temperature coarsening of γ'' phase in Ni-based superalloy GH4169
[J].The growth of precipitates in Ni-based superalloy GH4169 is critical as it controls the mechanical properties and long-term stability of the alloy. In this paper, the coarsening behavior of the main strengthening phase γ″ in the temperature range from 800 °C to 900 °C is investigated. Two heat treatment steps, i.e., pre-precipitation of γ″ phase and coarsening of precipitates at high temperatures, were performed on the GH4169 alloy. It was found that there were three morphological forms of γ″ phase in chronological order: lip-shape, disc-shape, and irregular rectangle-shape with larger size. The coarsening kinetics of γ″ phase followed the Lifshitz-Slyozov-Wagner (LSW) time-law for diffusion-controlled growth, and the activation energies of γ″ phase before and after losing the coherent relationship with matrix were 261 kJ mol−1 and 271 kJ mol−1, respectively.
Effects of the γ″-Ni3Nb phase on fatigue behavior of nickel-based 718 superalloys with different heat treatments
[J].The effects of the γ″-Ni3Nb phase on fatigue behavior of nickel-based 718 superalloys with standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging were investigated by scanning electron microscope, transmission electron microscopy, and fatigue experiments. The standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging resulted in the formation of more and smaller γ″ phases in the matrix in the nickel-based 718 superalloys. However, the grain boundaries of the hot isostatic pressing + direct aging sample showed many relatively coarse disk-like γ″ phases with major axes of ~80 nm and minor axes of ~40 nm. The hot isostatic pressing + direct aging sample with a stress amplitude of 380 MPa showed the longest high cycle fatigue life of 5.16 × 105 cycles. Laves phases and carbide inclusions were observed in the crack initiation zone, and the cracks propagated along the acicular δ phases in the nickel-based 718 superalloys. The precipitation of fine γ″ phases in the matrix and relatively coarse γ″ phases in the grain boundaries of the hot isostatic pressing + direct aging sample can hinder the movement of dislocation.
Quantitative and qualitative characterization of the damage, deformation mechanisms, and failure modes of a nickel-based GH3536 alloy prepared via laser powder bed fusion after various heat treatments
[J].
Molecular dynamics simulation of twin nucleation and growth in Ni-based superalloys
[J].
Influence of isothermal holding on the microstructure and mechanical properties of electron beam welded dissimilar Inconel 718/ATI 718Plus® joint
[J].Microstructural changes of the Inconel 718 and ATI 718Plus(R) base materials and the fusion zone caused by the isothermal hold at 760 degrees C for up to 500 h were investigated. The evaluation was performed using a scanning electron microscope with backscattered electrons detector and scanning transmission electron microscopy supported by energy-dispersive x-ray spectroscopy. Furthermore, to evaluate the effect of microstructural changes on mechanical properties Vickers microhardness measurements were performed. Exposure of welded joint at high temperature led to coarsening and/or dissolution of main strengthening phases' particles and nucleation and growth of plate-like precipitates. In the interdendritic region of the fusion zone, the transformation of the Laves phase to a complex cluster of precipitates contained sigma phase had taken place. Analysis of microstructure and microhardness measurements showed that ATI 718Plus has better mechanical properties and microstructural stability at elevated temperature than Inconel 718.
Effects of heat treatment and carbon element invasion on microstructure and mechanical properties of Inconel 718 alloys fabricated by selective laser melting
[J].
Improvement of tensile properties of laser directed energy deposited IN718/316L functionally graded material via different heat treatments
[J].
On the detailed morphological and chemical evolution of phases during laser powder bed fusion and common post-processing heat treatments of IN718
[J].
Two-step heat treatment for laser powder bed fusion of a nickel-based superalloy with simultaneously enhanced tensile strength and ductility
[J].
Enhanced strength and ductility of laser-directed energy deposition repaired IN718 superalloy via a novel tailored heat treatment
[J].High-quality repair of damaged Inconel 718 (IN718) superalloy components can achieve great economic benefits. However, the directly double aging (DA) treatment by industrial standards, yields an inferior ductility on the repaired component than that of the wrought base metal. In this work, wrought IN718 components were repaired by laser-directed energy deposition (LDED), a novel tailored heat treatment (THT) schedule consisting of a short-term low-temperature homogenization, and subsequent DA was subsequently conducted to strengthen the repaired IN718 alloys. The microstructure evolution and mechanical properties of the DA and THT-treated repaired alloys were comparatively investigated. The results indicated that the THT effectively dissolved most of the hard brittle Laves precipitates in the deposition region with only slight coarsening of the grains in the substrate. As compared to the DA sample, the elongation of the THT sample increased remarkably by 88% with only a slight reduction of 19.2 MPa in yield stress. Moreover, the strain distribution of the THT sample was overall more even but then destabilized in a narrow abnormal coarsened grain region caused by the static recrystallization. In general, this study breaks through the limitation of the low ductility of the DA-treated repaired IN718 alloys and provides a promising way to further improve the mechanical properties.
Effects of hot processes on microstructure evolution and tensile properties of FGH4096 Ni-based superalloy processed by Laser Powder Bed Fusion
[J].
Microstructure and mechanical properties of in-situ oxide-dispersion-strengthened NiCrFeY alloy produced by laser powder bed fusion
[J].
Improvement of high temperature mechanical properties of Ni-based oxide dispersion strengthened alloys by preferential formation of Y-Ti-O complex oxide
[J].
Optimizing the thermomechanical process of nickel-based ODS superalloys by an efficient method
[J].Thermo-mechanical process of nickel-based oxide dispersion strengthened (ODS) superalloys is critical to produce desired components. In this study, an efficient method of consolidating powder is introduced to optimize the preparation process, microstructure and properties of nickel-based ODS superalloys. The influences of consolidation temperature, strain rate and ball milling time on the hardness of nickel-based superalloys were studied. The relationship among process, microstructure and hardness was established, the nanoparticles strengthening and grain boundary strengthening in nickel-based ODS superalloys were discussed. The results indicate that long ball milling time, moderately low consolidation temperature and high strain rates are beneficial to improving properties of nickel-based superalloys. Moreover, dispersion strengthening of nanoparticles and grain boundary strengthening play important roles in enhancing nickel-based ODS superalloys.
The effect of hot isostatic pressing and heat treatment on the microstructure and properties of EP741NP nickel alloy manufactured by laser powder bed fusion
[J].
Inhomogeneous planar distribution of γ′ precipitates in waspaloy caused by local spatial consumption of MC carbides
[J].
Transformation of oxide nanoparticles in a nickel-based ODS alloy aged at 1000 oC
[J].
Failure-mode dependence on the formation of deformation twinning in the fourth-generation single crystal Ni-based superalloy at high temperatures
[J].
Tailoring thickness debit for high-temperature fatigue resistance of Inconel 718 superalloy fabricated by laser powder bed fusion
[J].
Influence of solution temperature on microstructure and mechanical properties of DZ411 alloys with different Ta compositions
[J].
Multi-scale calculation-aided composition optimization design of low-density and high-strength nickel-based superalloy
[J].
Tailoring microstructure and mechanical properties of IN738LC fabricated by laser powder bed fusion through processing parameter optimization
[J].
Temperature field analysis and process optimization research of selective laser melting of nickel-based superalloys
[D].
激光选区熔化镍基高温合金温度场分析及工艺优化研究
[D].
Study on the defect suppression and property optimization of GH3536 alloy processed by multi-laser powder bed fusion
[D].
多激光粉末床熔融GH3536合金搭接区域缺陷抑制及性能优化研究
[D].
Microstructure and mechanical properties of GH4169 superalloy via high-power laser powder bed fusion
[J].
高功率激光粉末床熔融成形GH4169高温合金的显微组织与力学性能研究
[J].
Study on the manufacture of nickel-based superalloy gradient materials by laser additive manufacturing and its heat treatment process
[D].
激光增材制造镍基高温合金梯度材料及其热处理工艺研究
[D].
Experimental study and neural network model based prediction of layer thickness influence on LPBF IN625 single track geometry
[J].
Process defects knowledge modeling in laser powder bed fusion additive manufacturing: An ontological framework
[J].
Effect of scan strategy and substrate preheating on crack formation in IN738LC Ni-based superalloy during laser powder bed fusion
[J].
Investigation on crystallographic transformation and solidification structure of a nickel-based superalloy produced by additive manufacturing
[D].
镍基高温合金增材制造的晶形转变和凝固组织研究
[D].
Advances in additive manufacturing of nickel-based high-temperature alloys
[J].Nickel-based superalloys have attracted significant attention due to their outstanding high-temperature strength, corrosion resistance, and oxidation resistance, and are widely used in aerospace and other fields. This article provides a comprehensive review of the preparation methods, common grades, and microstructure and properties of additive manufactured nickel-based superalloys, summarizes the current issues, and proposes future areas for exploration. Nickel-based superalloys prepared by metal additive manufacturing technology have excellent performance, can achieve precise forming of complex components, and have minimal material waste during the manufacturing process. They are expected to become an important production process for nickel-based superalloys components in fields such as aerospace. Common methods for additive manufacturing of nickel-based superalloys include laser powder bed melting, directed energy deposition, and arc additive manufacturing. Powder bed melting is widely used for manufacturing high-precision and complex parts, but it has a relatively slow manufacturing speed and higher equipment and material costs. Directed energy deposition has higher degrees of freedom and flexibility and can be used to prepare functional gradient materials, but it has lower accuracy. Arc additive manufacturing has lower equipment and material costs and is suitable for rapid manufacturing of large parts, but the surface roughness of the alloy produced by this method is poor and requires additional processing or post-treatment. Nickel-based superalloys widely studied in the additive manufacturing process include IN625, Hastelloy X, and other solid solution strengthened alloys, as well as IN718, CM247LC, IN738LC, and other precipitation strengthened superalloys. Compared with traditional casting and forging methods, the unique layer-by-layer forming and rapid cooling and heating process of additive manufacturing result in a coarse columnar grain structure and a unique microstructure with a large number of fine grains. It also forms unique melt pool structures and dislocation cell structures. However, the alloys obtained by additive manufacturing generally require heat treatment to control grain structure and precipitated phases, which affects the mechanical properties of the alloy. In addition, the mechanical properties of additive manufactured nickel-based superalloys are also related to specific preparation methods and alloy types. Although additive manufacturing has been widely used in the preparation of nickel-based superalloys, there are still issues such as anisotropy in microstructure and properties, high sensitivity to alloy cracking, and a lack of corresponding specifications and standards. In the future, further exploration is needed in areas such as heat treatment, customization and development of specialized alloys, investigation of the process-structure-function relationship, and computational modeling.
镍基高温合金增材制造研究进展
[J].镍基高温合金因其优异的高温强度及耐腐蚀、抗氧化性能而备受关注, 被广泛应用于航空航天等领域。本文对增材制造镍基高温合金的制备方法、常见牌号以及合金的组织与性能进行了综述, 总结了当前存在的问题, 提出了未来值得探索的研究领域。金属增材制造技术制备的镍基高温合金具有良好性能, 能实现复杂构件精密成形, 且制备过程中材料浪费少, 有望成为未来航空航天等领域中镍基高温合金构件的重要制备工艺。常见的镍基高温合金增材制造方法有粉末床熔化、定向能量沉积和电弧增材制造等, 粉末床熔化被广泛用于制造高精度和复杂零件, 但制造速度相对较慢, 且设备和材料成本较高。定向能量沉积自由度和灵活性更高, 可用于制备功能性梯度材料, 但精度较低。电弧增材制造具有较低的设备成本和材料成本, 适用于大型零件的快速制造, 但其制备的合金表面粗糙度较差, 需要进行额外的加工或后处理。在增材制造过程中被广泛研究的镍基高温合金包含IN625, Hastelloy X等固溶强化型和IN718, CM247LC, IN738LC等沉淀强化型高温合金。与传统的铸造和锻造方法相比, 增材制造独特的逐层成型、快冷快热的制备过程带来了粗大的柱状晶粒组织和大量细小晶粒的独特微观组织, 还形成了独特的熔池组织及位错胞结构。但是, 通过增材制造得到的合金一般还需要进行热处理, 对晶粒组织、析出相等进行调控, 从而影响合金的力学性能。此外, 增材制造镍基高温合金的力学性能还与具体制备方法和合金种类有关。尽管目前增材制造已被广泛用于镍基高温合金的制备, 但仍面临组织与性能存在各向异性、高性能合金开裂敏感性高以及缺乏相应的规范和标准等问题, 将来需要在热处理、专用合金的定制与开发、探索工艺-结构-功能关系以及计算建模等方面深入探索。
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激光粉末床熔融DD491镍基单晶高温合金的组织与高温性能研究
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