Precipitate size and number density are two key factors for tailoring the mechanical behavior of nanoscale precipitate-hardened alloys. However, during thermal aging, the precipitate size and number density change, leading to either poor strength or high strength but significantly reduced ductility. Here we demonstrate, by producing nanoscale co-precipitates in composition-optimized multicomponent precipitation-hardened alloys, a unique approach to improve the stability of the alloy against thermal aging and hence the mechanical properties. Our study provides compelling experimental evidence that these nanoscale co-precipitates consist of a Cu-enriched bcc core partially encased by a B2-ordered Ni( Mn, Al) phase. This co-precipitate provides a more complex obstacle for dislocation movement due to atomic ordering together with interphases, resulting in a high yield strength alloy without sacrificing alloy ductility.

High strength low alloy (HSLA) steels are widely used in the construction of ship structures, oil pipelines, offshore platforms and so on because of their good strength, toughness and weldability. HSLA steel is generally designed with low carbon and Cu alloying. Tempered lath bainite or martensite and nano-precipitate phase of Cu can be obtained by quenching and ageing process after rolling to ensure the excellent matching of strength, low temperature toughness and weldability of HSLA steel. At present, increasing attention has been focused on the precipitation behavior and strengthening mechanism of Cu particles in HSLA steel which was aged at the peak hardness of ageing curve. However, in practical engineering applications, overageing heat treatment is generally used to make HSLA steel achieve a good match of strength and toughness. In this work, the microstructure and nano-sized Cu precipitates of an industrial production HSLA steel plate with thickness of 35 mm were characterized by SEM, EBSD, HRTEM and APT. Meanwhile, the strengthening mechanism of the tested steel was investigated. The results show that Cu precipitates in the tested steel processed by overageing are mainly in the range of 6~50 nm, Cu particles exhibiting short rod or spherical shape within 30 nm are 9R structure, and other particles size larger than 30 nm exhibiting long rod or spherical shape are fcc structure. The segregation of trace Mn and Ni in rod particles on the interface between Cu particles and matrix is more obvious. After ageing at a higher temperature range, the yield strength of the tested steel decreases linearly with the increase of tempering temperature. The main strengthening mechanism of the HSLA steel is fine grain strengthening, followed by dislocation strengthening and precipitation strengthening. The calculated results show that every 1%Cu added in the tested steel can produce about 90 MPa precipitation strengthening increment under the condition of overageing heat treatment. The strength difference between the surface and the center of the tested steel plate is about 40 MPa, which is mainly due to the difference of grain size and dislocation density of steel.

对含Cu低合金高强度钢板淬火并经高温时效后，采用SEM、EBSD、HRTEM和APT等手段对其微观组织和纳米尺度Cu的析出相进行了表征，对其厚度截面的室温拉伸性能进行了测定，并对钢板厚度方向近表面和心部的强化机理进行了分析。结果表明，高温时效后钢中Cu的析出相尺寸在6~50 nm范围内，30 nm以内的为9R结构的短棒状或球状粒子，30 nm以上的为fcc结构的长棒状粒子，棒状粒子中微量的Mn、Ni在Cu粒子与基体界面上的偏聚更明显。在较高温度范围内进行时效后，钢的屈服强度随着时效温度的升高而呈大致线性下降趋势，钢的主要强化机制为细晶强化，其次为位错强化和析出强化，经计算，钢中每1% (质量分数)的Cu在过时效状态下能够产生约90 MPa的析出强化增量。钢板厚度截面存在强度差异，表面与心部强度相差约40 MPa，这主要是由于晶粒尺寸及位错密度差异所导致。

采用循环干/湿模拟腐蚀增重实验、动电位极化曲线、电化学阻抗谱和XRD方法, 研究了模拟海岸-工业大气中SO₂对Q235B钢腐蚀行为的影响. 结果表明, 在腐蚀初期SO₂抑制了Q235B钢的腐蚀; 在腐蚀后期, SO₂促进了Q235B钢的腐蚀. 当SO₂的浓度较低时, 腐蚀速率随SO₂浓度的升高而增大; 当SO₂的浓度较高时, 腐蚀速率随SO₂浓度的升高而减小. 工业-海岸大气中的SO₂组分可以抑制腐蚀产物中g -FeOOH和b-FeOOH的生成, 而促进a-FeOOH生成. 低碳钢腐蚀速率随SO₂浓度变化出现的极值现象与SO₂导致的锈层相组分变化密切相关.

Herein, three-dimensional graphene-like nanosheet network (3D-GLNN)/copper (Cu) materials were synthesized using hop-pressing (HP) and hot-rolling (HR) methods and their corrosion resistance and mechanism were investigated using polarization curves, electrochemical impedance spectroscopy (EIS), and weight loss data after a cavitation corrosion test. Microstructural characterization results revealed that the 3D-GLNN structure was intact in the bulk composites, thereby restricting the effective grain growth of the Cu matrix. Compared with pure Cu, the Vickers hardness of 3D-GLNN/Cu fabricated using the HP and HR methods improved by 8% and 46%, respectively. Polarization curve results indicated that the anodic dissolution current of 3D-GLNN/Cu was considerably lower than that of pure Cu, indicating that 3D-GLNN/Cu exhibited better corrosion resistance. EIS measurements under a corrosion potential revealed that the electrode process kinetics was complex, with both charge and mass transfer controlling it. By extending the immersion time from 1 h to 9 d, the corrosion potential first became positive and then became negative. The capacitance arc at a high-frequency EIS range first increased and then decreased, attributed to the formation and detachment of a CuCl salt film. Diffusion impedance was observed in the low-frequency EIS range, with a phase angle of 18°-23°, indicating that the mass transfer process was not attributed to a single species but controlled by anodic and cathodic reactants. The constant phase angle element (CPE) behavior of the electrochemical system was further evaluated using the ohm-corrected phase angle and impedance modulus. The high-frequency phase angle was greater than -90 °, while the slope of impedance modulus was approximately -0.9; thus, the CPE was used to model the EIS data. The CPE behavior was attributed to the surface distribution of the charge transfer resistance and interface capacitance, implying a time-constant dispersion on the surface. Weight loss data after the cavitation corrosion test indicated that pure Cu showed better cavitation resistance than 3D-GLNN/Cu fabricated using the HR and HP methods. This is because of the difference in the elastic modulus between the graphene and Cu matrix that caused deformation dissonance during cavitation erosion.

采用热压和热轧方法制备了三维石墨烯纳米片网络/Cu复合材料(3D-GLNN/Cu),组织表征结果表明,在块体复合材料中石墨烯网络结构保持完整,有效限制了Cu基体晶粒长大,热压态和热轧态3D-GLNN/Cu的硬度分别较纯Cu提高了8%和46%。采用电化学方法和空蚀失重分析研究了其在模拟海洋环境中的腐蚀和空蚀行为。极化曲线测试结果表明,3D-GLNN/Cu的阳极溶解电流与热压态纯Cu相比显著降低,热轧处理对复合材料的耐蚀性影响不大。腐蚀电位下的电化学阻抗谱(EIS)及电化学等效电路拟合分析结果表明,3D-GLNN/Cu的电极过程动力学较为复杂,主要受电荷转移和扩散过程共同控制。欧姆电阻校正后的Bode图结果表明,高频区的相位角大于-90°而阻抗模斜率约为-0.9,Cu及2种3D-GLNN/Cu复合材料在模拟海水中均存在常相位角元件(CPE)特征,这主要是因为电极表面材料结构和成分不均一性导致的局部界面电容和电荷转移电阻存在差异。随着浸泡时间延长(从1 h到9 d),EIS高频区容抗弧均是先增加后减小,主要是因为腐蚀生成的CuCl盐膜在表面的覆盖与局部脱落有关,EIS低频区出现扩散阻抗特征,且低频区相位角为18 °~23 °,说明电极过程不是单一反应物的Warburg扩散阻抗特征,而是受阴阳极传质过程共同控制。空蚀失重结果表明,热轧后的3D-GLNN/Cu与热压态的材料相比,耐空蚀性能显著下降,这主要是因为石墨烯与Cu基体的弹性模量的差异,在空蚀机械冲击力作用下形变不协调,易产生凹坑。

将一种Fe-Ni基沉淀强化奥氏体合金在980 ℃固溶后水淬,在620 ℃经过不同时间时效。利用硬度测试及原子探针层析技术(APT)研究时效过程中γ'相的析出行为及其对材料硬度的影响。结果表明,当时效时间小于6 h时,合金硬度增加较快,由时效前的145 HV迅速增加至205 HV,随后硬度增加速率缓慢;时效120 h时,硬度为251 HV。APT结果表明,合金经固溶处理后,合金元素均匀分布在基体中。在时效最初阶段,Ti发生了较为明显的偏聚,形成含有Fe、Ni和Al等元素的富Ti纳米团簇。随着时效时间延长,富Ti纳米团簇中的Ni和Al原子的含量逐步增多,而Fe、Cr及Mo等原子的含量不断减少;当时效至120 h时,团簇中Ni与Ti+Al比值近似于3,即已完全形成γ'相,表明γ'相析出是形核-长大过程。合金硬度的变化与时效过程中γ'相的数量密度和体积分数有关。

High-Mn austenitic Fe-Mn-C twinning-induced plasticity (TWIP) steels are prospective candidates in many industrial fields, owing to their excellent mechanical properties. However, these steels show poor corrosion resistance, which affects their performance and prevents their applications particularly in aqueous environment. In this study, an effective way to improve the corrosion resistant property of TWIP steels was described by understanding the corrosion behavior of TWIP steel that was alloyed with Cr. A series of Fe-25Mn-xCr-0.3C (x = 0, 3, 6, 9, and 12, mass fraction, %) TWIP steels were prepared in a vacuum arc melting furnace using high purity raw materials (≥ 99.8%). Thereafter, the resulting steels were solution treated at 1200oC for 2 h under an argon atmosphere. The effect of Cr addition on the corrosion behavior of the prepared TWIP steels was investigated using various analytical techniques including XRD, potentiodynamic polarization, electrochemical impedance spectroscopy, and XPS. XRD results showed that the TWIP steels with Cr content that ranged from 3% to 12% retained their single austenite phase. Moreover, increasing the concentration of Cr in the alloys substantially increased and decreased the corrosion potential and corrosion current density, respectively. These resulted in an improvement in the corrosion resistant property of the alloys, which was verified by the increase in the charge transfer resistance found in the Nyquist plots. Meanwhile, XPS results revealed that the prepared quasi-passive oxide film was composed of FeO, Fe2O3, FeOOH, MnO, MnO2, Cr2O3, and Cr(OH)3. Furthermore, these results showed the progressive enrichment of Cr oxides and decrease of both Fe and Mn oxides in the outermost oxide as the Cr content was increased. The improved corrosion resistance of the prepared TWIP steels was caused by the protective Cr oxide film.

通过动电位极化曲线、电化学阻抗谱(EIS)测试和X射线光电子能谱(XPS)分析等研究了Cr添加对Fe-25Mn-xCr-0.3C (x = 0、3、6、9、12，质量分数，%)孪生诱发塑性(TWIP)钢腐蚀行为的影响。结果表明，TWIP钢基体中Cr含量增加导致腐蚀电位显著增加和腐蚀电流密度明显降低。耐腐蚀性能改善还通过Nyquist图中电荷转移电阻随着Cr含量的增加而增加得到证实。XPS结果表明，准钝化膜由FeO、Fe₂O₃、FeOOH、MnO、MnO₂、Cr₂O₃和Cr(OH)₃等组成，并且随着Cr含量增加，Cr氧化物在最外层氧化物中逐渐富集，同时Fe氧化物和Mn氧化物逐渐减少。正是这种保护性Cr氧化膜提高了TWIP钢的耐腐蚀性能。