U-Nb形状记忆合金热弹性马氏体相变的相场模拟

U-Nb形状记忆合金具有优异的抗腐蚀性和力学性能,其中亚稳α?相的典型微观组织为多层级孪晶马氏体。利用相场法模拟α?相热弹性马氏体的形成过程。结果表明,在弹性应变能最小化的驱动下,获得了多种自协调马氏体组织,也发现了多种自协调模式。对比本研究模拟结果和文献中的实验结果,认为相变变形梯度矩阵的反对称性和界面兼容性显著影响变体结对和孪晶面。另外,基于变体重排过程,预测了相变态组织在变形初期的织构演化。     

微观相场模型及其在合金固态相变中的应用

材料科学与工程领域中,相场法是计算材料学的重要分支。相场法在模拟与预测材料微观组织、形貌演化等方面的作用越来越突出。材料微观组织决定其宏观服役性能。商业合金材料性能的改变与控制,在很大程度上依赖于精细调控固态相变过程以期获得理想的微组织图斑。实验对于合金材料固态相变的分析侧重于结果的观测与讨论,对于相变动力学过程研究较少。基于微观扩散理论的相场模型在原子尺度上研究合金固态相变过程,这显著不同于其它的相场模型。本文系统阐述了微观相场模型在合金固态相变方面的研究思路及研究成果。在此基础上,阐述了当前研究的难点,展望了微观相场在固态相变领域的发展前景,最后特别指出了微观相场在合金相变方面未来的研究方向。     

Convective Flow and Its Effect on the Liquid-liquid Phase Transformation of Monotectic Alloys

建立了偏晶合金液--液相变过程中的两相流动模型, 发展了偏晶合金凝固理论模型; 以Al-Pb合金为例, 模拟研究了偏晶合金凝固时的组织演变进程, 考察了流动对凝固组织形成的影响. 结果表明, 对流影响液--液相变的形核特性, 提高凝固界面前沿最高弥散相液滴数量密度、最大液滴半径和最高弥散相 体积分数, 促进宏观偏析组织的形成.     

零件厚度对激光相变硬化温度场的影响

以GCr15钢为例,采用有限单元法对激光相变硬化过程进行了数值模拟研究,建立激光相变硬化过程温度场的数学模型,分析了工件厚度及其下表面在自然散热和辅助水冷条件下对激光相变硬化温度场的影响。     

零件厚度对激光相变硬化温度场的影响

以GCr15钢为例,采用有限单元法对激光相变硬化过程进行了数值模拟研究,建立激光相变硬化过程温度场的数学模型,分析了工件厚度及其下表面在自然散热和辅助水冷条件下对激光相变硬化温度场的影响.     

Mo-Pd二元合金边际固溶度的MAEAM模型研究

用改进分析型嵌入原子模型（MAEAM）计算了Mo-Pd二元合金在2个典型温度的边际固溶度。在淬火温度为1473K时，Pd在Mo（a相区）中的边际固溶度为0．6％（原子分数，下同）：Mo在Pd（声相区）中的边际固溶度为26．8％；在包晶温度2028K附近，Pd在Mo（a相区）中的边际固溶度为1．1％；Mo在Pd（声相区）中的边际固溶度为29．5％。计算结果与已有理论和实验结果大体上是吻合的。     

应变能对Ni75Al15V10合金预析出相影响的微观相场研究

采用微观相场方法,以Ni75Al15V10合金为例研究了应变能对预析出相的影响。研究发现：合金沉淀早期的应变能影响预析出相L10的析出。无应变能作用时,体系中没有预析出相L10相出现;应变能越大,L10预析出相的孕育期越短,析出量增加,稳定存在时间越长,且体系所析出的L10相的结构特征越明显。应变能较小时,无序基体有些区域先析出L10相,随后所析出的L10相转变为L12相,而在有些区域却直接析出L12相;当应变能较大时,基体大范围先析出L10相,随后部分L10预析出相溶解,只有未溶解部分最终能转变为L12相。     

Microalloying Effect of Sn on Phase Transformation During Heat Treatment in Mg–Y–Zn–Zr Alloys

The microstructure and mechanical properties of the as-cast and heat-treated Mg-4.6 Y-2.5 Zn-0.6 Zr-x Sn(x = 0, 0.2 and0.5 wt%) alloys were investigated in this work. The results showed that the eutectics have been refined with 0.2% Sn addition and it has no effect on the phase category of the alloys. However, Sn3 Y5 phase was found in 0.5% Sn-added alloy.After heat treatment at 520 °C, the transformation of the long-period stacking ordered(LPSO) phase takes place in the Mg-Y-Zn-Zr alloy, but the transition is not completed in the alloys containing Sn. In addition, during the heat treatment, the mechanical properties of Sn-free alloys are significantly improved, and the strength of alloys containing Sn does not change much. Through observation and analysis of the microstructure and mechanical properties, it is found that Sn addition hinders the process of a0-Mg ? a-Mg ? 14 H and the process is the key to the transition of 18 H-LPSO to 14 H-LPSO.     

Isothermal Phase Diagrams of Binary Alloys and Two Oxidants

An example of an isothermal thermodynamic phase diagram of a quaternary system composed of a binary alloy and two oxidants has been calculated under appropriate values of the stability of the corresponding compounds, assuming that each metal forms only one compound with each oxidant. Initially, two-dimensional sections of the complete three-dimensional diagram made along planes corresponding to constant values of one of the variables involved were examined in detail. The actual structure of this type of three-dimensional diagram was then discussed by analyzing the shape and the boundaries of the various regions corresponding to the conditions of stability of each phase taken separately or in combination with other phases.     

Continuum Separation of Nanoscale Phase in Thermal Aging Fe-Cr Alloys: Phase-Field Simulation and Experiment

JOM - The separation of Cr-enriched α′ phase in Fe-(25–45) at.% Cr alloys is studied from the metastable region to the unstable region. The three-dimensional phase-field...     

Thermodynamic Characteristic and Phase Evolution in Immiscible Cr–Mo Binary Alloys

This paper systematically reports the thermodynamic characteristic and phase evolution of immiscible Cr–Mo binary alloy during mechanical alloying(MA) process. The Cr–35Mo(in at%) powder mixture was milled at 243 and258 K, respectively, for different time. For comparative study, Cr–15Mo and Cr–62Mo powder mixtures were milled at 243 K for 18 h. Solid solution Cr(Mo) with body-centered cubic(bcc) crystal structure and amorphous Cr(Mo) alloy was obtained during MA process caused by high-energy ball milling. Based on the Miedema's model, the free-energy change for forming either a solid solution or an amorphous in Cr–Mo alloy system is positive but small at a temperature range between 200 and 300 K. The thermodynamical barrier for forming alloy in Cr–Mo system can be overcome when MA occurs at 243 K, and the supersaturated solid solution crystal nuclei with bcc structure form continually, and three supersaturated solid solutions of Cr–62Mo, Cr–35Mo and Cr–15Mo formed. Milling the Cr–35Mo powder mixture at 258 K, the solid solution Cr(Mo) forms firstly, and then the solid solution Cr(Mo) transforms into the amorphous Cr(Mo)alloy with a few of nanocrystallines when milling is prolonged. At higher milling temperature, it is favorable for the formation of the amorphous phase, as indicated by the thermodynamical calculation for immiscible Cr–Mo alloy system.     

强磁场对Bi-6%Mn合金中MnBi相形态和相变的影响

在无磁场的条件下,降温过程中Bi—Mn合金在340℃发生包晶相变,顺磁性Mn1．08Bi相转变为铁磁性MnBi相,同时伴随着相的形态变化,由块状转变成片状;在10T磁场中,Mn1．08Bi相发生包晶相变的温度升高至介于360—370℃之间,且MnBi相晶体发生了分裂,分裂后的小晶体沿磁场方向定向排列和聚合．从磁场诱发应变的角度分析了磁场对相变温度和MnBi相形态的影响．     

Ni含量和时效对TiNi形状记忆合金相变热的影响

用示差扫描热分析仪（ＤＳＣ）、光学显微镜、扫描电镜和ＥＤＸ能谱仪系统研究了Ｎｉ含量和时效对ＴｉＮｉ合金Ｒ、马氏体（Ｍ）相变热（Ｑ）的影响。揭示了ＱＭ、ＱＲ与Ｎｉ含量和时效工艺的关系。     

热处理参数对Ti-50.8Ni钛镍合金相变点的影响

研究了不同热处理制度对Ti-50.8Ni钛镍记忆合金丝材性能的影响.实验结果表明,试样经固溶处理后,随温度的升高,Af值变化不大,仅为20℃左右.试样经固溶加时效处理后,随时效时间延长,Af值虽略有上升,但变化不大;时效温度对Af值影响较大,低于480℃随时效温度升高,Af点升高;高于480℃随时效温度升高,Af点下降.试样经固溶时效处理后,水淬的Af值最高;经固溶加时效处理后,炉冷和水淬的Af值较空冷显著提高,但炉冷和水淬2种方式的Af值差别不大.     

钛合金固态相变的研究进展

综述了近年来国内外学者在钛合金固态相变理论和实验研究方面的进展情况，介绍了几种钛合金固态相变的研究实验方法，并对钛合金中马氏体、硼、亚稳脚分解等相变动力学、晶体学以及组织的演变、形核生长等进行了总结和归纳。     

微观相场法计算Fe含量对NiAlFe三元合金中反位缺陷的影响

采用三元微观相场模型,对铝含量大于25%(原子分数,下同)与镍含量大于75%(原子分数,下同)的NiAlFe三元合金中反位缺陷NiAl、AlNi随Fe含量变化的规律进行模拟计算,其中NiAl(AlNi)表示Ni(Al)原子占据Al(Ni)格点产生的反位缺陷。结果表明:在一定温度范围内,随着Fe含量的增大,铝含量大于25%的NiAlFe合金中AlNi浓度明显上升,NiAl浓度略有上升,但小于AlNi浓度,相反在镍含量大于75%的NiAlFe合金中NiAl浓度明显上升且远大于AlNi浓度;同一温度下比较铝含量大于25%与镍含量大于75%的NiAlFe合金中反位缺陷受Fe含量影响的程度差异,发现前者的AlNi浓度比后者受Fe含量影响大,而后者的NiAl浓度比前者受Fe含量影响大。此外,反位缺陷NiAl和AlNi浓度随时间的演化规律均是逐渐由初始值降低至平衡值;温度升高促使反位缺陷演化变缓慢以及平衡时浓度增大。     

基于热和相变应变模型的齿轮合金钢渗碳淬火畸变分析

目的研究热和相变应变各自在渗碳淬火畸变中的作用,分析渗碳淬火工艺对齿轮合金钢畸变的影响。方法通过考虑相变和不考虑相变两种模型,对齿轮合金钢17CrNiMo6C形开口畸变试样渗碳淬火的畸变机理和变形过程进行数值模拟,并设计正交试验,量化工艺参数对畸变的影响程度,最后利用渗碳淬火实验测定表面含碳量和畸变量,验证分析结果。结果初始工艺下热应变约为相变应变的2倍。正交试验各工艺参数的F比结果从大到小顺序为:渗碳温度(1.74)、淬火温度(1.546)、碳势(1.448)、预热温度(0.603)和油温(0.473)。优化工艺参数为:渗碳温度880℃,淬火温度790℃,预热温度500℃,碳势0.8%,油温80℃。优化后畸变率减少了28.5%,畸变分析结果与实验结果对应较好。结论由热膨胀引起的热应变对试样的畸变占据主动,抵消并超过相变应变,渗碳温度、碳势和淬火温度对齿轮合金钢畸变影响较大。     

TiAl基双相合金等温转变的动力学

利用定量金相和Ｘ射线衍射的方法研究厂过饱和有序α２相等温转变的动力学。两种方法所测得的γ相析出量与等温处理时间的关系相互吻合。Ｔｉ－４５Ａｌ合金的等温转变速度明显高于Ｔｉ－４２Ａｌ合金。在相图中的共析转变温度以下，转变速度随温度的降低而减小，没有出现Ｃ字形等温转变曲线的可能性。     

Strain/Oxidation Interactions in Steels and Model Alloys

Strain/oxidation interactions in steels and model alloys The strains generated in oxide films on a number of materials of interest to the power generation industry are considered in relation to their operating conditions. Topics discussed the growth of nuclear canning alloys, oxide spalling, the formation of multilayer oxides during internal boiler corrosion and low ductility failures in austenitic stainless steels. The strains induced during thermal cycling are considered in detail and the temperature changes required to cause film craking are estimated and compared with observed spalling behaviour.