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将镍钛形状记忆合金Ni50.9Ti49.1(摩尔分数)在1123 K固溶处理2 h,然后分别在573、723和873 K时效2 h。采用透射电镜、高分辨率透射电镜、扫描电镜和压缩实验,系统研究固溶处理和时效对镍钛合金组织演化及力学性能的影响。结果表明:固溶处理有助于消除原始镍钛样品中的Ti2Ni相,但不能消除TiC相。固溶处理导致镍钛合金中原子排列的有序畴界。在所有时效镍钛样品中,Ni4Ti3析出相、R相和B2奥氏体相共存于室温下的镍钛基体上,然而在873 K时效的镍钛样品中,可以观察到马氏体孪晶。在573和723 K时效的镍钛样品中,细小密集的Ni4Ti3相均匀分布在镍钛基体上,而且与B2基体保持共格关系。然而,在873 K时效的镍钛样品中,Ni4Ti3相尺寸非常不均匀,和B2基体保持共格、半共格和非共格关系。在723 K时效的条件下,细小均匀的Ni4Ti3相阻碍位错运动,导致最大的位错滑移临界分切应力,因此镍钛样品表现出最高的屈服强度。
Nickel-titanium shape memory alloy Ni50.9Ti49.1 (mole fraction) was solution treated at 1123 K for 2 h and then aged at 573, 723 and 873 K for 2 h, respectively. The effects of solution treatment and aging on the microstructure evolution and mechanical properties of Ni-Ti alloy were investigated systematically by TEM, high-resolution transmission electron microscopy, scanning electron microscopy and compression experiments. The results show that the solution treatment helps to eliminate the Ti2Ni phase in the original NiTi sample, but it can not eliminate the TiC phase. Solution treatment leads to an ordered domain of atoms in the nitinol. In all aged NiTi samples, Ni4Ti3 precipitates, R phase and B2 austenite coexist at room temperature NiTi matrix, however martensite twins can be observed in 873K NiTi samples. In the NiTi samples aged at 573 and 723 K, the fine and dense Ni4Ti3 phases are uniformly distributed on the NiTi matrix and are in a coherent relationship with the B2 matrix. However, the Ni4Ti3 phase size is very inhomogeneous in 873 K aged NiTi samples, which maintains a coherent, semi-coherent and non-coherent relationship with the B2 matrix. At 723 K aging, the Ni4Ti3 phase hinders dislocation motion, resulting in the largest critical shear stress for dislocation slip, so the NiTi sample exhibits the highest yield strength.