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本文用变温X射线衍射和电阻方法研究了NiTi和NiTiCo形状记忆合金在低温产生的“预马氏体”转交(R相变)。合金经750℃1h+水冷处理后,均发生可逆且几乎无滞后的R相变.R相是B2型结构的母相经低温畸变的产物,具有菱形晶体结构,其菱形畸变随温度下降而增大,在-185℃,晶胞参数为:a_0=9.03(?),a=89.1~°。 透射电镜观察进一步表明,R相呈条状,在T_R和M_S以下,R相和单斜畸变的B19型马氏体共存于合金之中,呈相对的稳定状态。
In this paper, the “pre-martensitic” transformation (R-phase transformation) of NiTi and NiTiCo shape memory alloys at low temperature was studied by means of temperature-dependent X-ray diffraction and electrical resistance. The reversible and almost non-lagged R phase transformation of the alloy occurs at 750 ℃ for 1h + water cooling, and the R phase is the product of the low temperature distortion of the parent phase of the B2 structure with a rhombohedral crystal structure. The diamond distortion increases with decreasing temperature , At -185 ℃, unit cell parameters: a_0 = 9.03 (?), A = 89.1 ~ °. Transmission electron microscopy further showed that the R phase was strip. Under the conditions of T_R and M_S, the B19 martensite with R phase and monoclinic distortion coexisted in the alloy, showing a relatively stable state.