Metallographic Study on Nucleation of Martensite in Ti-Ni Shape Memory Alloys

1. 用原位电镜观察了Ti-40Ni-10Cu（%）附近合金中马氏体的形核和生长，在室温下由B2母体热弹性转变为正交马氏体。结果表明，马氏体在某些应力集中的地方，如位错缠结、表面台阶处形成核。我们还尝试了高分辨率的电镜实验，但由于相变引起的图像漂移，虽然我们获得了相变后马氏体的高分辨率图像，但到目前为止还没有成功地在现场观察到成核。通过光学和电镜观察，研究了Ti-Ni-Fe和Ti-Ni-Al形状记忆合金中r相的转变和自调节机制。利用电视摄像机，用录像带成功地记录了变换事件的序列。我们发现r相转变是通过非均相的形核和生长方式发生的。成核发生在应力集中的地方，如基体夹杂界面和位错。单个位错的应力场可使r相形核。讨论了自调节机理。通过会聚束电子衍射证实了r相的空间群为P31m。然而，这个结果似乎有些模棱两可，因为观测结果在几何上相当有限。本研究的目的是研究r相的晶体结构。为了在室温下观察r相，我们选择Ti-47.8Ni-1.5Fe（at%）合金，进行1273K， 3.6ks固溶处理。,智商)。电镜下得到了单变异r相各带轴的衍射图。对P3模型和P31m模型的衍射图强度进行了比较。观测结果均支持P3空间群，而非P31m空间群。

1. In situ electron microscope observations were made on the nucleation and growth of martensite in a few alloys near the composition Ti-40Ni-10Cu(at%) which transform thermoelastically from a B2 parent to an orthorhombic martensite near room temperature. We found that martensite nucleate at certain stress concentrated places, e.g. dislocation tangles, surface steps. We alsotried high resolution electron microscopy experiments, but were so far no success in observing in situ the nucleation due to the image drift caused by the transformation, although we obtained high resolution image of martensite after the transformation.2. Transformation and self-accommodation mechanisms of the R-phase in Ti-Ni-Fe and Ti-Ni-Al shape memory alloys were studied by means of optical and electron microscope observations. Sequences of transformation events were recorded successfully with video tapes using a TV camera. We found that the R-phase transformation takes place by nucleation and growth in a heterogeneous manner. Nucleation takes place at stress concentrated places, e.g. matrixinclusion interfaces and dislocation. The R-phase can nucleate from the stress field of a single dislocation. Self-accommodation mechanism was also discussed.3. The space group of the R-phase was reported to be P31m by means of convergent beam electron diffraction. However, there seemed to be some ambiguity about this result, because observations were rather limited geometrically. The purpose of this study is to investigate the crystal structure of the R-phase. To observe the R-phase at room temperature, we chose Ti-47.8Ni-1.5Fe(at%) alloy and made a solution treatment(1273K, 3.6ks., I.Q.). Diffraction patterns from various zone axes in single variant R-phase were obtained by electron microscopy. Comparison of the intensities in diffraction patters were made between P3 model and P31m model. The observation results all support the space group P3 rather than P31m.