【作者】 胡益丰；

【导师】 邓文；

【作者基本信息】 广西大学 ， 理论物理， 2006， 硕士

【摘要】 近等原子比的NiTi合金由于具有良好的形状记忆效应、超弹性、抗腐蚀性和生物相容性，被广泛应用于航空航天和生物医学等领域，已经成为应用最多、最有成效的一种记忆合金。在降低温度或应力诱变下，NiTi合金将发生马氏体转变，晶体结构由CsCl(B2)型转变为单斜畸变的B19’型，当温度升高时，又能回到母相的结构，从而表现出形状记忆效应。大量的研究表明，NiTi合金中的微观缺陷和电子结构状态对于它的形状记忆效应和马氏体转变有着重要影响。目前，虽然这方面的研究比较多，但是对于NiTi合金马氏体转变过程中的微观缺陷和电子结构随温度变化的微观机制还不是很清楚。 本工作分别测量了NiTi、NiAl合金、Si单晶、纯Fe、Co、Al、Nb、Cu、Ni、Ti金属的符合正电子湮没辐射多谱勒展宽谱，并从谱线中提取金属及合金中3d电子的信号。测量了NiTi合金在降温过程(295K降至25K)和升温过程(25K升至295K)的正电子寿命谱。利用正电子寿命谱参数研究了NiTi合金马氏体转变及其奥氏体转变过程中的微观缺陷和电子密度的变化，从而揭示NiTi合金马氏体转变的微观机制。本文的研究结果表明： 1．当Ni原子和Ti原子形成NiTi合金时，两原子中的部分3d电子被局域化并形成共价键，导致合金基体中的自由电子密度相对较低。更多还原

【Abstract】 Near-equiatomic binary NiTi alloys have been widely applied in many fields of aviation and biomedicine and have become the most successful of the shape memory alloys as a result of their combination of good shape memory effect, superelasticity, anticorrosion and biocompatibility. When the temperature decreases or the stress induces, the martensitic transformation will happen in NiTi alloys with the crystal structure changing from CsCl(B2) to monoclinic B19’.When being heated, the parent phase will be restored, showing shape memory effect consequently. A variety of methods have been used in the studies of NiTi alloys. It has been shown that the microdefect and electronic structure in NiTi alloys play an important role on shape memory effect and martensitic transformation. More experimental evidences are needed to understand the micromechanism on the variation of microdefects and electron densities with the temperature in NiTi alloys.In present work, the coincidence Doppler broadening spectra of positron annihilation radiation of NiTi, NiAl alloys, single crystal of Si, and pure metals, such as Fe, Co, Al, Nb, Cu, Ni, Ti have been measured. The signal of 3d-shell更多还原