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用X射线衍射、电阻、形状变化、内耗等方法研究等原子NiTi合金在150℃以下发生的相变与记忆效应。X射线衍射结果表明,在45℃左右,合金出现两类相变:马氏体相变与R相变,具有B_2型结构的母相分别转变成单斜畸变B_(10)型马氏体和畸变B_2结构的R相。R相变不是预转变,R相在-185℃仍保持稳定。合金在相变时,电阻和内耗增加。出现电阻峰和内耗峰。在相变温度进行不完全热循环时,开始只出现一个马氏体内耗峰。多次热循环,在马氏体内耗峰的高温侧分裂出一支小内耗峰。这是R相变引起的。升温时,在50～60℃,R相和马氏体开始向B_2相逆转变。在等原子NiTi合金中,相变依下列次序进行,B_2(?)B_2+R+B_(19)(?)R+B(19)。 NiTi合金的记忆效应是降温时B_2相向R相和马氏体转变及随后升温时,R相和马氏体向B_2相逆转变造成的。
The phase transformation and memory effect of allomorphous NiTi alloys at temperatures up to 150 ℃ were investigated by X-ray diffraction, resistance, shape change and internal friction. X-ray diffraction results show that there are two types of phase transitions at about 45 ℃: martensitic transformation and R phase transformation, and the parent phase with B 2 structure is transformed into B 10 type martensite and monoclinic martensite Distortion B 2 structure of the R phase. R phase transition is not pre-transition, R phase remains stable at -185 ℃. Alloy in the phase transition, the resistance and internal friction increase. Resistance peaks and internal friction peaks appear. In the phase transition temperature for incomplete thermal cycling, the beginning of only one martensitic peak. Multiple thermal cycles, in the martensitic peak of the high-temperature side of the split a small internal friction peak. This is caused by R phase change. When the temperature rises, the phase R and martensite start to reverse to B_2 phase at 50 ~ 60 ℃. In equiatomic NiTi alloys, the phase transformation is performed in the following order, B 2 (?) B 2 + R + B 19 (?) R + B (19). The memory effect of NiTi alloy is caused by the phase transformation of B phase to R phase and martensite and the reverse phase transformation of R phase and martensite to B 2 at the time of temperature decrease and subsequent temperature increase.