镁造孔多孔NiTi合金的微波烧结制备与表征

为了获得轻质、高强和高阻尼的多孔NiTi合金,采用微波烧结协同镁造孔技术制备多孔NiTi合金。考察多孔NiTi合金的显微组织、力学性能、相变行为、超弹性和阻尼性能。结果表明:当烧结温度低于或等于900℃时,多孔NiTi合金主要由B2 NiTi相和少量B19'NiTi相组成。随着烧结温度的升高,多孔NiTi合金的孔隙率逐渐降低,而压缩强度先增加后下降,在900℃时获得最大值。随着造孔剂Mg的含量从1%增加到7%(质量分数),多孔NiTi合金的孔隙率从37.8%增加到47.1%,而压缩强度从2058 MPa降低至1146 MPa。与碳酸氢铵造孔多孔NiTi合金相比,镁造孔多孔NiTi合金的相变行为发生变化,而压缩强度、超弹性、形状记忆效应和阻尼性能均获得极大的提高。

热处理和球磨对Ni-Mn-Ga-Nb合金显微组织和相变的影响（英文）

为了揭示时效和球磨后Nb掺杂Ni-Mn-Ga合金的相变演化,采用SEM、EDS、XRD、DSC和交流磁化率测试等技术研究时效和球磨双相Nb掺杂Ni-Mn-Ga合金的显微组织和相变。铸态合金主要由层状第二相组成,随着第二相含量增加,合金的马氏体相变逐渐减弱。1173 K淬火后第二相从层状转变为致密的棒状,且合金的马氏体相变增强。经673和873K时效后,含有较少第二相的3%Nb合金表现为一步相变,而含有较多第二相的6%Nb和9%Nb合金表现为两步马氏体相变和居里转变。球磨双相颗粒的马氏体相变和居里转变消失,1073 K退火后基体的高有序结构得到恢复,从而导致双相颗粒的马氏体相变和居里转变恢复。

深冷轧制制备高强、高电导率CuMg合金（英文）

利用透射电子显微镜观察(TEM)、电子背散射衍射(EBSD)技术、硬度测试、拉伸测试与电导率测试研究室温轧制与深冷轧制Cu-0.2wt.%Mg合金的显微组织、力学性能与电导率。结果表明,与室温轧制样品相比较,深冷轧制样品的晶粒尺寸减小了41%。随轧制变形量增加,合金的显微硬度持续增加而电导率下降。对于深冷轧制样品,当厚度减小90%时,其抗拉强度和电导率分别达到726 MPa和74.5%IACS。抗拉强度的提高主要归因于晶界强化与位错强化。

SPS制备NiMnGa/Cu复合材料的显微组织、相变和力学性能

采用SEM、EDS、XRD、交流磁化率测试和力学测试研究放电等离子体烧结法制备NiMnGa颗粒/Cu复合材料的显微组织、相变和力学性能。研究发现,NiMnGa颗粒与Cu基体发生反应,复合材料具有与Cu基体相似的晶体结构。由于反应导致NiMnGa颗粒发生成分变化,因此,复合材料的马氏体相变和居里转变被弱化。随着NiMnGa颗粒含量增加,复合材料的马氏体相变和居里相变在一定程度上得到增强。与原始NiMnGa颗粒相比,复合材料的马氏体相变温度和居里转变温度降低约50 K。随着NiMnGa颗粒含量增加,复合材料的压缩强度得到提高,但压缩应变逐渐降低。

电脉冲处理对激光沉积Ti-6Al-4V合金强度各向异性的影响

为消除激光沉积Ti−6Al−4V合金的强度各向异性,利用拉伸试验、光学显微组织观察、扫描电子显微观察、电子背散射衍射分析和透射电子显微观察研究电脉冲对激光沉积Ti−6Al−4V合金显微组织与强度的影响。结果显示,随着施加电压从0增加到130 V,β柱状晶内的显微组织按如下顺序演化:α′马氏体→集束α组织→网篮α组织。130 V电脉冲处理会弱化β柱状晶内马氏体织构。沉积态Ti−6Al−4V合金表现出约6.2%的屈服强度各向异性;经130 V的电脉冲处理后,屈服强度各向异性减小到0.6%。这主要是由于沿不同方向变形时,130 V电脉冲处理样品表现出近似相同的施密特因子分布。

Martensitic Transformation and Its Thermal Cycling Stability in Ni_(56)Mn_(21)Cu_4Ga_(19)High-Temperature Shape Memory Ribbon

The microstructure, martensitic transformation, and thermal cycling stability of Ni56Mn21Cu4Ga19 high-tem- perature shape memory ribbons subjected to different annealing conditions were investigated and compared with that of the bulk master alloy. It was shown that 7 phases precipitated in the bulk and the ribbons annealed for 5 h at 800 and 900 ℃, which lead to the same poor thermal cycling stability. However, the formation of 7 phase was inhibited in the ribbons annealed at 700 ℃ for 30 rnin and 5 h, which remarkably improved the thermal cycling stability and also shifted the martensitic transformation to a lower temperature with a drop of about 60 ℃ than other three samples.

New Formulas of Shear Strain during Equal-channel Angular Pressing Process with Consideration of Influences of Velocity and Motion Trajectory

The influences of die parameters on shear strain were investigated by using two-dimensional finite element simulation.New formulas of shear strain were proposed.According to the results of formulas,the shear strain showed a linear dependence on the difference between internal and external fillet radius and the slope was determined by the intersection angle.The simulation results indicated that the velocities of the points from different zones were different in the specimen and the motion trajectories of different points did not follow geometrical laws.The influences of the average velocity and the motion trajectory on shear strain were incorporated in the formula to calculate the shear strain produced during equalchannel angular pressing process.The reliability of simulation results has been partially validated by experiments.

Martensitic transformation and magnetic properties of Ti-doped NiCoMnSn shape memory alloy

Martensitic transformation, microstructure, and magnetic properties of Ti-doped Ni43-xTixCo7Mn43Sn7（at%）（x = 0, 0.5, 1.0, 2.0, and 4.0） shape memory alloys were investigated. The results show that transformation temperatures of Ni43Co7Mn43Sn7 can be efficiently adjusted by the substitution of Ti for Ni. For example, the martensitic transformation starting temperature（Ms） is reduced by about 278 K with 4 at% addition of Ti. Room temperature microstructure evolves from single tetragonal martensite for the Ti-free alloy to dual phases（tetragonal martensite ＋ second phase） with 0.5 at%, 1.0 at%, and2.0 at% addition of Ti to dual phases（cubic austenite ＋ second phase） for 4.0 at% Ti-doped alloy. The mechanical properties can be obviously improved by adding an appropriate amount of Ti. A noteworthy point is that magnetic-field-induced reverse transformation is observed in Ni39Ti4Co7Mn43Sn7 alloy.

Achieving High Strength and High Electrical Conductivity in a CuCrZr Alloy Using Equal-Channel Angular Pressing

In the present work, a CuCrZr alloy characterized by ultrafine grains and nanoscale particles was prepared by equalchannel angular pressing （ECAP） at 450℃. A desired combination of a tensile strength （580 MPa） and an electrical conductivity （81% International Annealed Copper Standard） is simultaneously obtained in the as-ECAP-processed CuCrZr alloy without additional aging treatment. The improved properties can be mainly attributed to the ultrafine grains and nanoscale precipitates. This processing may pave a way to develop the CuCrZr alloys having high strength and high electrical conductivity for engineering applications.