A TiNi-alloy is solution-treated in a vacuum furnace of 6.7×10^-3 Pa at 1 223 K for 3.6 ks, and then aged at 773 K for 1.8 ks. The differential scanning calorimetry （DSC） measurements show that after the heat-t...A TiNi-alloy is solution-treated in a vacuum furnace of 6.7×10^-3 Pa at 1 223 K for 3.6 ks, and then aged at 773 K for 1.8 ks. The differential scanning calorimetry （DSC） measurements show that after the heat-treatment, takes place a two-step reverse Martensitic transformation, from which results the two-stage recovery strain in a prestrained Martensitic TiNi-alloy wire during heating. The Vickers microhardness indentation test in cross-sectional areas of the TiNi-alloy wire indicates the compositional heterogeneity between its surface layers and its inside. The fact that the sizes of the indentation in surface layers smaller than those in the inside bears witness to the existence of slightly harder surface layers. It is believed that these phenomena are related to the compositional fluctuation caused by the evaporation and oxidization of Ti-element during the solution-treatment and heterogeneity formed during the subsequent aging treatment.展开更多
Effect of solution treatment temperature on transformations and two way memory, effect in a Ti- 55.2 wt-%Ni alloy was investigated. The results show that with increasing the solution treatment temperature (T_s), two w...Effect of solution treatment temperature on transformations and two way memory, effect in a Ti- 55.2 wt-%Ni alloy was investigated. The results show that with increasing the solution treatment temperature (T_s), two way memory effect (TWME) decreases continuously and temperatures of martensite and reverse, martensite transformations (MR) rise, but the temperature of R start trans- formation (parent→R) does not change. The results of the internal friction measurements indicate that when T_s=1073 K, internal friction peaks of MR and P→R transformations are larger than those of the specimens after solution-treatments at 973 and 1173 K. With increasing T_s, the de- crease of TWME can be attributed to that the defect stress field caused by the rolling fades out grad- ually and preferential martensite variants, which fit into the defect stress field, decrease. The changes of transformation temperatures and internal friction peaks with T_s are closely related to the change of defect numbers.展开更多
基金National Natural Science Foundation of China (50471021)Beijing Municipal Program of Education Committee.
文摘A TiNi-alloy is solution-treated in a vacuum furnace of 6.7×10^-3 Pa at 1 223 K for 3.6 ks, and then aged at 773 K for 1.8 ks. The differential scanning calorimetry （DSC） measurements show that after the heat-treatment, takes place a two-step reverse Martensitic transformation, from which results the two-stage recovery strain in a prestrained Martensitic TiNi-alloy wire during heating. The Vickers microhardness indentation test in cross-sectional areas of the TiNi-alloy wire indicates the compositional heterogeneity between its surface layers and its inside. The fact that the sizes of the indentation in surface layers smaller than those in the inside bears witness to the existence of slightly harder surface layers. It is believed that these phenomena are related to the compositional fluctuation caused by the evaporation and oxidization of Ti-element during the solution-treatment and heterogeneity formed during the subsequent aging treatment.
文摘Effect of solution treatment temperature on transformations and two way memory, effect in a Ti- 55.2 wt-%Ni alloy was investigated. The results show that with increasing the solution treatment temperature (T_s), two way memory effect (TWME) decreases continuously and temperatures of martensite and reverse, martensite transformations (MR) rise, but the temperature of R start trans- formation (parent→R) does not change. The results of the internal friction measurements indicate that when T_s=1073 K, internal friction peaks of MR and P→R transformations are larger than those of the specimens after solution-treatments at 973 and 1173 K. With increasing T_s, the de- crease of TWME can be attributed to that the defect stress field caused by the rolling fades out grad- ually and preferential martensite variants, which fit into the defect stress field, decrease. The changes of transformation temperatures and internal friction peaks with T_s are closely related to the change of defect numbers.
