Ni-Ti 합금의 산화거동에 영향을 미치는 열처리 온도의 영향

초록

Variation in oxidation behavior with heat treatment temperature is investigated for a Ni-Ti alloy using X-ray diffraction, DSC(differential scanning calorimetry) and Auger electron spectroscopy. And the effect of oxidation on transformation behavior and superelasticity is characterized. A cold-worked 50.6Ni-Ti alloy is oxidized at 300-700℃ for 1hr in the air atmosphere. With an increase in heating temperature, the structure of TiO2 changes from amorphous(300 and 400℃) to anatase(500℃), and to rutile(700℃). Activation energy of oxidation for NiTi is measured to be 51Kcal/mol when heating temperature is 500℃ or above. Since Ti reacts preferably with oxygen, Ni content increases between matrix and oxide, forming Ni3Ti compounds. The resultant of oxidation decreases significantly Ms and As temperature in the specimen oxidized at 900℃ with B2 → M transformation path. An extra is found on cooling between two peaks in the specimen with B2 → R → M one which is oxidized at 900℃ and aged at 500℃. Oxidation deteriorates superelasticity due to formation of Ni-rich compound.

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