因子设计法分析TiNi合金形状记忆效应的研究

采用因子设计法分析了TiNi合金的形状记忆效应．试验设计了5个影响因子：丝材直径、热处理温度、热处理时间、冷却速率和训练次数，每个因子分别取高低2个水平值．以马氏体逆相变完成温度Af作为试验观测值．研究发现：热处理温度对试验观测值的影响最为显著，试样丝材直径和冷却速率也有较大的影响，而热处理时间和训练次数的影响较小．     

Microstructures evolution and phase transformation behaviors of Ni-rich TiNi shape memory alloys after equal channel angular extrusion

Ni-rich TiNi shape memory alloys were subjected to the effect of equal channel angular extrusion (ECAE) processes at 773 K by Bc path. The effects of ECAE processes on microstructures evolution and phase transformation behaviors were investigated. The initial 60-80 μm equiaxed coarse grains of samples were elongated along the shearing force direction of ECAE and refined to 300-400 nm after eight passes ECAE. The R phase transformation of Ni-rich TiNi shape memory alloys was stimulated by ECAE processes within a larger temperature range. The martensite transformation peak temperature (Mp) dropped in previous 1-3 ECAE treatments, but the dropped Mp increased gradually with the increase of ECAE processes. Ti₃Ni₄ phase was observed in the regions with high density of dislocations after ECAE treatment. Reasons for microstructures evolution and phase transformation changes were also discussed.     

TiNi形状记忆合金与不锈钢的瞬时液相扩散焊

采用AgCu金属箔作中间过渡层,对TiNi形状记忆合金与不锈钢进行了瞬时液相扩散焊,分析了接头的显微组织、元素分布和物相组成等,研究了接头的抗剪强度和断裂方式。结果表明:接头界面区由TiNi侧过渡区,中间区,不锈钢侧过渡区组成,主要相分别为Ti(Cu,Ni,Fe),AgCu,TiFe等。连接温度为860℃,保温时间为60min,连接压力为0.05MPa时,接头最大抗剪强度为239MPa。断裂发生在TiNi母材和AgCu中间层扩散界面上,断口为混合断裂形貌。通过中间层等温凝固过程动力学模型,结合界面形貌和元素扩散分析,认为TiNiSMA与不锈钢异种材料瞬时液相扩散焊过程存在明显的非对称性。     

TiNi形状记忆合金片激光微焊接接头的组织性能

采用脉冲激光实现了0.2mm厚TiNi形状记忆合金的对接焊,研究了焊接接头的抗拉强度、断裂形貌、组织和相变过程。结果表明,脉冲激光能够实现薄片状TiNi形状记忆合金的良好对接焊,焊接接头的抗拉强度可达683MPa,为冷轧态母材的97%,断口形貌与母材相似,均为延性断裂。根据晶粒尺寸和显微组织的不同,接头可分为4个区。焊缝中心区为细小的等轴晶,而焊缝边缘为柱状晶组织。对焊接接头进行焊后退火处理后其相变过程与退火态TiNi形状记忆合金的接近。     

Separation of the Martensite in TiNi Fiber Reinforced Aluminum Matrix Composite

The reverse martensitic transformation of TiNi shape memory alloy fibers embedded in a pure aluminum matrix was studied in this paper. Results showed that the phase composition of the TiNi alloy fibers prior to prestraining at the room temperature had a significant influence on the differential scanning calorimetry (DSC) results of the composites. By a comparison to the high temperature X-ray diffraction (XRD) results, it was confirmed that the martensite was divided into two groups: the self-accommodating martensite (SAM) and the preferentially oriented martensite (POM). The evolving process of the separation of martensite was discussed.     

Effects of Yttrium Addition on Microstructure, Hardness and Resistance to Wear and Corrosive Wear of TiNi Alloy

TiNi alloy has a high resistance to wear and could be an excellent candidate for various tribological applications. In this paper, it was demonstrated that by addition of yttrium, hardness properties and resistance to wear and corrosive wear of TiNi alloy were improved. New yttrium rich regions were formed in microstructure of TiNi alloy. The improved properties of this alloy by the yttrium addition could be attributed to the formation of these regions. The results showed that there was an optimum content for addition of yttrium between 2% and 5% (in wt%), and above this content the improvement in properties of TiNi became minor.     

Ti49.2Ni50.8合金在等径角挤压过程中Ti3Ni4析出相的演化规律

采用透射电子显微镜研究Ti49.2Ni50.8合金中Ti3Ni4析出相在等径角挤压及中间退火过程中的演化规律。固溶态Ti49.2Ni50.8合金在450℃时效处理10~60 min以获得尺寸为37~75 nm的Ti3Ni4析出相。在450℃等径角挤压处理1道次后,时效处理10 min和30 min试样中Ti3Ni4析出相完全溶解;而在时效处理60 min试样中Ti3Ni4析出相尺寸减小。Ti3Ni4析出相完全溶解的临界尺寸范围为37~68 nm。等径角挤压态试样的位错密度取决于Ti3Ni4析出相的初始尺寸。随初始时效时间从10 min延长至60 min,试样的位错密度先增加然后降低。     

Stress-dependent deformation behaviour in bulk nanocrystalline titanium–nickel alloys

In this study, the deformation mechanisms operating with stress in bulk nanocrystalline (NC) titanium–nickel with an average grain size below a critical size of 10–20?nm have been investigated. We demonstrate a sequential variation of the deformation mechanism from grain boundary (GB) sliding and grain rotation to grain growth and dislocation activity with the increase of the deformation stress. These deformation mechanisms are different from the previous understanding that below a critical grain size of 10–20?nm, GB sliding and grain rotation govern plastic deformation of NC materials.     

Experimental study on the dynamic behavior of TiNi cantilever beams with rectangular cross-section under transversal impact

The experimental investigation of TiNi alloy cantilever in the PE state and R-SME state, respectively, was conducted under transversal impact by using a modified Hopkinson bar apparatus. For comparison, the impact response of A3 steel cantilevers with the same geometry was also studied. The results show that at an early stage the elastic flexible waves dominate the wave response of the beam. After about 1 ms the dynamic structural response will be the main response. Under impact the “phase transformation hinge (TH)”, which differs from the conventional plastic hinge (PH), may form and undertake the main deformation and energy absorption in a cantilever. The impact position has a great influence on the location, time and number of the formation of TH, hence the response mode of a cantilever. After impact there is no residual deformation for a PE cantilever, there is a small residual deformation for an R-SME cantilever due to the R transition and large residual deformation for steel cantilevers due to the plasticity. The energy absorption efficiency of cantilevers for different materials and impact conditions are discussed.