Titanium alloys are key materials for applications in major engineering areas, such as aerospace and marine equipment. Studies on structural titanium alloys focus on strengthening and toughening the alloys, especially the latter. The mainstream structural titanium alloys comprise both α and β phases. The optimization of the strength and toughness balance relies on the control of the compositions, volume fractions, and morphologies of both phases. In this study, some recent advances along the above line are reviewed, focusing on studies on the composition design, plastic-deformation mechanism, and microstructure tuning. Rational design of the compositions of both phases improved the deformation coordination within the α phase and across the α/β interface, suppressed the precipitation of brittle ω and α2 phases, and resulted in improved plasticity and toughness through the α-deformation twin and β-deformation-triggered phase transformation. The multiscale microstructure enhanced the strength and toughness of the titanium alloy. Using the abovementioned approaches, a series of titanium alloys with an improved strength-toughness combination were developed and fabricated. Finally, an attempt was made to predict the prospect of technology development in the field of high-strength and high-toughness titanium alloys for various applications.

Microstructure- and texture-evolution of Ti65 Ti-alloy plate were investigated, and the tensile deformation mechanism of the plate after heat treatment with different texture were discussed. The results show that heat treatment has a significant influence on the evolution of microstructure and texture of the plate. Equiaxed-, duplex- and lamellar-microstructure would be obtained after different heat treatment. The plate with equiaxed microstructure presented a B/T texture, while the c-axis of the α-phase and the rolling direction (RD) met at a 70°~90° angle; similar texture could be found in duplex- and lamellar-microstructure, meanwhile a new texture that the c-axis of the α-phase paralleled to RD could be found in the alloy. Room temperature tensile strength of plates with duplex microstructure could be enhanced by the dislocations and sub-structures, while had little effect on tensile properties at high temperature. Texture was found to be the main factor affecting the anisotropy of tensile properties of Ti65 plates, the plate would possess good tensile properties without obvious anisotropy in tensile strength after heat treatment of 980℃/1 h/AC+700℃/4 h/AC.

研究了不同热处理条件下Ti65钛合金板材的显微组织和织构的变化规律，分析了板材织构的类型和热处理影响拉伸强度的机制。结果表明，热处理对板材的显微组织和织构类型具有显著的影响。通过热处理可分别得到具有等轴组织、双态组织或片层组织的板材。等轴组织板材的织构为晶体c轴与板材RD方向呈现70°~90°夹角的B/T型织构，双态组织和片层组织板材的主要织构类型与等轴组织类似，且出现晶体学c轴与RD方向平行的织构。双态组织板材内的位错和亚结构使板材的室温拉伸强度提高，但是对高温拉伸变形的阻碍能力有限。板材中的织构是影响合金力学性能各向异性的主要因素。经980℃/1 h/AC+700℃/4 h/AC热处理后的板材横、纵向拉伸强度的差异最小，且都具有较高的室温拉伸性能和最佳的650℃拉伸性能。

The evolution of microstructure and texture at different temperatures and its effect on room temperature strength in Ti60 Ti-alloy plates were investigated in the present work. There was no perceivable change of the microstructure or texture after heat treatment at 700?C compared with those of the as-rolled plate. In α+β and β phase regions equiaxed primary α grains shrank and ultimately transformed to secondary α phase, and T-type texture was replaced by a new type of texture with temperature increasing. It was indicated that whether new texture formed or not was significantly affected by the percentage of primary α phase during α→β→α phase transformation: by high percentage, the primary α phase strongly induced the secondary α phase to be with the similar orientation, thereby nearly no change of the texture; by low or zero percentage, part of the formed secondary α phase with new orientation, which was hardly affected by the primary α phase and was inferred as results of α variants selection dominated by texture of β grains formed during rolling at high temperature. Room temperature strength was mainly affected by the substructure: heat treatment in the α phase region didn't eliminate the substructure, the room temperature strength is comparable to that of the as-rolled plates; heat treatment in/above α+β phase field eliminated the substructure, resulting in large reduction of room temperature strength compared with the as-rolled plates. After eliminating the substructure, the room temperature strength was impacted by the microstructure: similar room temperature strength of plates heat treated in low and high α+β phase region is related to the limited effect of the percentage of equiaxed primary α phase on the strength; the room temperature strength decreased after heat treatment in β phase region, and the decrease amplitude in certain direction was remarkably affected by texture. The degree of room temperature anisotropy was influenced by the texture and substructure: higher strength exhibited along the crystallographic c axis; while the substructure weakened the influence of the texture on anisotropy, resulting in stronger anisotropy in plates heat treated in/above α+β phase region.

研究了Ti60合金板材的组织、织构随热处理温度的变化规律及其对室温强度的影响。结果表明：对于Ti60合金板材,与轧制态相比,在α单相区热处理后显微组织和织构基本不变;随着热处理温度由α+β两相区升高到β单相区,等轴初生α相体积分数减少直至完全转变为片层次生α相,T型织构成分逐渐消失,并形成新的织构。在热处理温度下初生α相的体积分数,是决定是否形成新织构的主要因素：初生α相大量存在时次生α相的取向与之相近;初生α相体积分数减少对次生α相取向的影响减弱,次生α相的{0001}晶面易形成新的集中取向,与高温轧制变形后形成的β相织构有关。板材同一方向(TD或RD)的室温强度变化主要受晶内亚结构的影响：α单相区热处理后未消除晶内亚结构,板材的室温强度与轧态接近;α+β两相区和β单相区热处理消除了晶内亚结构,使强度明显降低。消除晶内亚结构后,板材相同方向的室温强度受显微组织的影响较小：初生α相体积分数的减少对室温强度没有明显的影响,在两相区不同温度热处理的板材其室温强度相当,β单相区热处理后板材的室温强度呈降低趋势,但是不同方向上的降低幅度受织构的影响较大。织构和晶内亚结构共同影响板材室温强度的各向异性,在晶体学c轴集中取向的方向上强度较高,晶内亚结构的存在弱化织构对拉伸强度各向异性的影响,在两相区和β单相区热处理消除了晶内亚结构,使板材的各向异性增强。

The trade-off relationship between the strength and the electrical conductivity has been the bottleneck restricting the development of conductive metallic materials with high strength and high electrical conductivity. In this study, commercially pure Al wires and commercially pure Cu wires with various grain characteristics were prepared by the cold-drawing process to investigate the influencing mechanisms of grain on strength and electrical conductivity. Surprisingly, the synchronous increase in strength and electrical conductivity may be achieved both for the commercially pure Al wires and commercially pure Cu wires in the later stage of cold-drawing deformation, which shatters the traditional constrictive relationship between the strength and the electrical conductivity. Additionally, the microstructure investigation demonstrates that with the increase of drawing deformation, the axial grains were lengthened, the radial grains were increasingly polished, and the radial <001> texture was transformed to <111> texture. Finally, the heterogeneous microstructures, including heterogeneous grain formation and heterogeneous crystal orientation were formed. The theoretical analysis reveals that the grain width and texture mainly influence the strength, and the grain length primarily influences the electrical conductivity. Consequently, the axial long grain, the radial fine grain, and radial hard orientation texture are proved to be the primary mechanisms causing the synchronous improvement of strength and electrical conductivity of commercially pure Al wires and commercially pure Cu wires. This suggests that the heterogeneous grain design may be considered a useful method to create conductive metallic materials with high strength and high electrical conductivity.

采用冷拉拔工艺制备了具有不同晶粒特征的工业纯Al线和工业纯Cu线,研究了晶粒对强度和导电率的影响机制。性能测试结果表明,拉拔变形后期,工业纯Al线和工业纯Cu线的强度和导电率同步提高,打破了强度和导电率传统的倒置关系。微观组织观察发现：随着拉拔变形量增大,轴向晶粒被拉长,径向晶粒逐渐细化,径向&lt;001&gt;织构向&lt;111&gt;织构转变,形成了晶粒形状异构和晶体取向异构的微观组织结构。理论分析表明：晶粒宽度和织构主要影响强度,晶粒长度主要影响导电率；提出了轴向长晶粒、径向细晶粒和径向硬取向织构是工业纯Al线和工业纯Cu线强度和导电率同步提高的根本原因。

<p>Microstructure and texture of titanium alloy are determined by thermomechanical and heat treatments and can significantly affect the mechanical properties of the final products. In this work, the microstructure and texture evolution during the heat treatment in <em>&alpha;</em>/<em>&beta;</em> and <em>&beta;</em> phase field in Ti60 precision forging bars were investigated. The results implied that the actual deformation temperature gradually decreased during precision forging processes. The microstructure and texture of Ti60 bar were determined by the finish forging temperature and the diameter, and strong microtexture macrozones existed in the forged Ti60 bar. For the bar with diameter of 45 mm (D45), the finish forging temperature fell in the lower temperature region of the <em>&alpha;</em>/<em>&beta;</em> phase field, and the main <em>&alpha;</em> textures in these bars were <0001> and <inline-formula></inline-formula><mml:math xmlns="http://www.founder.com/PDMLSchema/2009/main" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtable><mml:mtr><mml:mtd><mml:mrow><mml:mo><</mml:mo> <mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mstyle displaystyle="true"> <mml:mover accent="true"><mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:mrow> <mml:mo>?</mml:mo> </mml:mover></mml:mstyle><mml:mn>0</mml:mn> <mml:mo>></mml:mo></mml:mrow></mml:mtd> </mml:mtr></mml:mtable></mml:math>fiber texture components in initial Ti60 bar. The similarity of the microstructure and texture were found after heat treatment at 950 ℃. The intensity of <inline-formula></inline-formula><mml:math xmlns="http://www.founder.com/PDMLSchema/2009/main" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtable><mml:mtr><mml:mtd><mml:mrow><mml:mo><</mml:mo> <mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mstyle displaystyle="true"> <mml:mover accent="true"><mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:mrow> <mml:mo>?</mml:mo> </mml:mover></mml:mstyle><mml:mn>0</mml:mn> <mml:mo>></mml:mo></mml:mrow></mml:mtd> </mml:mtr></mml:mtable></mml:math>fiber texture gradually decreased while that of <0001> fiber texture increased with the increase of the heat treatment temperature. Heat treatments have little influence on the strength of forged Ti60 bars of D45, while their ductility was reduced after <em>&beta;</em> heat treatment. For the bar with diameter of 30 mm (D30), the finish forging temperature was below the <em>&alpha;</em>/<em>&beta;</em> phase field, and the main <em>&alpha;</em> texture in those bars was <inline-formula></inline-formula><mml:math xmlns="http://www.founder.com/PDMLSchema/2009/main" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtable><mml:mtr><mml:mtd><mml:mrow><mml:mo><</mml:mo> <mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mstyle displaystyle="true"> <mml:mover accent="true"><mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:mrow> <mml:mo>?</mml:mo> </mml:mover></mml:mstyle><mml:mn>0</mml:mn> <mml:mo>></mml:mo></mml:mrow></mml:mtd> </mml:mtr></mml:mtable></mml:math>fiber texture component. The intensity of <0001> fiber texture in those bars increased while that of <inline-formula></inline-formula><mml:math xmlns="http://www.founder.com/PDMLSchema/2009/main" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtable><mml:mtr><mml:mtd><mml:mrow><mml:mo><</mml:mo> <mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mstyle displaystyle="true"> <mml:mover accent="true"><mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:mrow> <mml:mo>?</mml:mo> </mml:mover></mml:mstyle><mml:mn>0</mml:mn> <mml:mo>></mml:mo></mml:mrow></mml:mtd> </mml:mtr></mml:mtable></mml:math>fiber texture gradually decreased with the increase of the heat treatment temperature. Their room temperature strength significantly increased with the increase of the heat treatment temperature, and yield strength and tensile strength reached to 1086 and 1144 MPa, respectively, but the elongation only 3.3% after <em>&beta;</em> heat treatment.</p>

将&alpha;+&beta;两相区精锻, 直径为30和45 mm (分别定义为D30和D45)的Ti60棒材分别在950, 1000和1050 ℃进行固溶+时效热处理, 研究了热处理温度对棒材织构和拉伸性能的影响. 结果表明, D45棒材锻态组织中, 棒材轴向与&alpha;相的或 10 1 ? 0 > 方向平行的丝织构较强; 950 ℃热处理后显微组织和织构变化不明显. 随固溶温度升高, &alpha;相的丝织构增强, 而 10 1 ? 0 > 丝织构密度减弱. 固溶温度对棒材强度的影响不大. D30棒材锻态组织中主要存在 10 1 ? 0 > 方向的丝织构; 随固溶温度升高, 丝织构逐渐增强, 棒材的室温强度显著升高.

The microstructure evolution and phase composition of an α + β titanium alloy, Ti-3Al-5Mo-4.5V (wt.%), have been investigated. Electron probe micro analysis (EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β → ω phase transformation does occur when quenching at 750 °C and 800 °C. The ω-reflections change from incommensurate ω-spots (750 °C) to ideal ω-spots (800 °C) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α′′ martensite, which has the following orientation relationships: [111]β//[110]α′′, [100]β//[100]α′′ and [-110]β//[00-1]α′′ with respect to the β matrix.

研究了两相区固溶温度及固溶后冷速对Ti-6Al-4V (TC4)合金元素再分配行为的影响，利用EPMA技术表征了初生α相(α_p)以及β转变区域(β_t)的元素浓度，考察了β_t显微组织尺寸随固溶温度及元素浓度的变化。结果表明：随着固溶温度升高，β_t区域元素浓度变化显著，表现为Al含量升高、V含量降低，而α_p晶粒中元素浓度变化较小，导致两区域元素浓度差异减小；同一固溶温度下，以不同冷却方式(水冷、空冷及炉冷)冷却的显微组织及元素分布显示，冷却速率越低，α_p比例越高，α_p与β_t之间元素浓度差异越明显。合金经固溶水冷、空冷后，β_t分别为淬火马氏体、次生α相(α_s)+残余β相，2种冷速下β_t的显微组织尺寸均与高温β相内的元素浓度水平有关，即β_t内部显微组织尺寸受固溶温度的显著影响。利用纳米压痕技术表征了不同固溶温度下微区域(α_p、β_t)的力学特征，结果表明，密排六方(hcp)晶格α_p本身呈现的力学行为的各向异性对其纳米压痕性能起决定性作用，而β_t的弹性模量及硬度主要受α_s片层尺寸的影响。最后讨论了“固溶温度-微区元素浓度-微区显微组织-微区力学性能”之间的关系。

Effect of cooling rates, i.e., air cooling and furnace cooling, after solution in α+β phase-field on variant selection, coarsening behavior of α phase and microstructure evolution were investigated in α+β TC21 alloy. The textures of primary α (αp) and lamellar α (αL) in β phase transformation microstructure (βt) were analysed separately, and the orientation relationship among αp, αL and the parent β phase were studied. In addition, the influence of the microstructure characteristics on the tensile properties was investigated. The results showed that all parent β grains, despite their different orientations, produced 12 ideal αL variants with the same texture components and interweave to form a basketweave βt structure under the air-cooling condition. The αp without Burgers orientation relationship (BOR) with β phase exhibited obviously texture component without overlapping the αL texture component. The volume fraction of αp in the furnace-cooled sample (about 50%) was higher than that of the air-cooled sample (about 12%), while the size of it slightly increased with decreasing the cooling rate. In each β grain, the thick αL in the same orientation formed an α colony. A typical 3 variant colonies which were related to each other were observed. Consequently, the αL spatial orientation distribution showed more heterogeneity. Moreover, the BOR between αp and β and the same orientation of some αL and the surrounding αp grains resulting in the overlapping of αp texture component and αL texture component. At last, the relationship between microstructure and tensile properties was analysed.