| Title |
The Effect of External Stress on Phase Transformation of Ni - Ti Shape Memory Alloy |
| Authors |
성윤막(Yun Mo Sung); 지광구(Kwang Koo Jee); 갑명철(Myung Chul Shin); 홍종휘(Jong Hwi Hong) |
| Abstract |
The effect of external stress on the phase transformation behavior of annealed and aged Ni-Ti alloys has been studied by the tensile test and the measurement of electrical resistance. Martensitic (M_s) and austenitic transformation starting temperatures (A_s) increased gradually with increasing stess up to 129 MPa and increased rapidly at a rate of 0.2℃/MPa above this stress level. However, incommensurate (T`_R) and commensurate phase transformation starting temperatures (T_R) increased very slowly at a rate of 0.06℃/MPa with the increasing stress. Martensitic transformation temperature range, ΔT(M_s∼M_f), and the stress at which ΔT was kept constant were larger for the aged specimen than for the annealed specimen. The stress at which the strain accompanied by incommensurate and commensurate phase transformation began to decrease (ε-1c) was higher for the annealed specimen than for the aged specimen. these facts imply that the incommensurate and commensurate phases are more stable in the annealed specimen than in the aged specimen. While the residual stress (ε_p) in the annealed specimen remained low regardless of the stress level, ε_p in the aged specimen began to increase rapidly at 240 MPa. This means that slip deformation is more difficult for the annealed specimen than for the aged specimen. |