高Ni-Ti合金およびFe,Coを添加したNi-Ti合金の変態特性におよぼす加工・熱処理の影響

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The effects of cold work and heat treatment on the transformation behavior of 56.2%Ni-Ti, 53.5%Ni-Ti-2.0%Fe and 54.6%Ni-Ti-2.2%Co alloys have been studied by means of differential scanning calorimetry (DSC) and observation of optical microscopy.The results are summarized as follows:(1) Only R-phase appeares in 56.2%Ni-Ti alloy annealed at less than 450°C, and transformations proceed upon cooling as B2→R→M or B2→M in the specimens annealed above 500°C.The Af point of 56.2%Ni-Ti alloy annealed at the temperature range from 400 to 500°C is in between about 30°C and 50°C and is not influenced by cold work.(2) In 53.5%Ni-Ti-2.0%Fe the transformations proceed upon cooling as B2→R over the test temperature range and cold reduction rage.The Af point is in between approximately -10°C and 30°C at the annealing temperature range from 400°C to 500°C, but the temperature difference (As-Af) is as large as about 30°C(3) In 54.6%Ni-Ti-2.2%Co the transformations proceed upon cooling as B2→R in the specimens annealed at less than 500°C, and proceed upon cooling as B2→R→M or B2→M in the specimens annealed above 550°C.The Af point is in between 3°C and 40°C at the annealing temperature rang from 400°C to 500°C, and the temperature difference (As-Af) is as small as about 10°C, Therefore, Ni-Ti-Co alloy may be used for the practical applications of the shape memory effect at the low temperature.
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