NiTiCu合金コイルばね特性に及ぼす熱処理と熱サイクルの影響

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In order to clarify the effects of heat treatments and thermal cycles on helical spring properties which are essential to practical use, spring (force-temperature) test, differential scanning calorimetry (DSC) and X-ray diffraction measurement have been performed on Ni48.9-xTi50.2Cux alloys.The force-temperature curve was measured at a constant spring height and the shear modulus G303K and G363K were calculated from the force on the curves at 303K and 363K, respectively. The G303K at the martensitic phase was 0GPa in either case of annealing at 673 and 773K, having a tendency of increasing with rise in annealing temperature of 873 and 973K. Meanwhile, the G363K at the parent phase with a value of G363K=20 to 30GPa was not affected by annealing temperature. Transformation temperature was increased with rise in annealing temperature, but transformation range (Af-Mf) temperature did not agree between the spring test and DSC measurement. The (Af-Mf) temperature was about 20K on the former and about 40K on the latter. Thermal cycles of 5000 times between 293 and 363K resulted in decrease in the force of the spring and the ratio of the force at 363K after the 5000 cycles to no cycle showed a tendency to decrease with rise of annealing temperature and increase with rise of Cu concentration.X-ray diffraction measurement made it clear the martensitic phase was monoclinic system in X=7 and orthorhombic system in X=10, 12.
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