엔도 파일용 Ti-Ni계 합금의 상변태 및 초탄성 특성에 미치는 열처리 영향

Abstract

The effects of annealing temperature and thermal cycling on the martensitic transformation and stress-strain characteristics have been studied Ni-rich Ti-Ni binary alloy for endodontic files. The stress-strain behavior with loading-unloading temperature also has been investigated to clarify superelasticity with the change in oral cavity temperature for pratical application. The results obtained are as follows;

(1) When the specimen NT-3 is cooled to –100℃ and then ~ 100℃anv the B2→R→B19' forward transformation occurs on cooling and B19'→B2 reverse transformation undergoes on heating in specimen NT-3. In the case of specimens NT-5 and NT-6, only B2→R transformation occurs on cooling but endothermic peak on heating is divided two peaks. This means that R→B19' transformation undergoes below –100℃.

(2) Plateau stress of specimen NT-3 is lower than those of specimens NT-5 and NT-6. Stress hysteresis of specimen NT-3, which is the difference between loading stress and unloading stress, is also lower than those of specimens NT-5 and NT-6. The stress for inducing stress-induced martensite from parent phase decreases with rising in annealing temperature while plastic deformation occurs.

(3) When the specimen NT-5(Rs=17℃) is tensile-deformed and undefored at the range of 15∼55℃, the stress for inducing stress-induced martensite from parent phase increases while plateau stress also increases. An increase in stress with increasing of deformation temperature can be explained Clausius-Clapeyron equation ().

(4) Heat flow of as-received specimen NT-3 decreases with increase in the number of cycling. However, the stress for inducing stress-induced martensite and the amount of superelasticity increases with increase in the number of cycling because of higher dislocation density inducing during thermal cycling.