添加Co对Ti-Ni形状记忆合金组织和性能的影响

Effect of adding Co on microstructure and properties of Ti-Ni shape memory alloy

以400和600℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金为对象,用示差扫描热分析仪、光学显微术、X射线衍射仪和拉伸试验研究了添加Co对退火态Ti-Ni形状记忆合金相变、组织和形状记忆行为的影响。结果表明,400℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金冷却时皆发生A→R→M(A-母相,R-R相,M-马氏体)两阶段相变;加热时Ti-49.8Ni合金发生M→A一阶段相变,Ti-49.8Ni-1.0Co合金发生M→R→A两阶段相变;600℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金冷却加热时皆发生一阶段AM相变。400℃退火态Ti-49.8Ni和Ti-49.8Ni-1.0Co合金的组织呈纤维状,塑性较差;600℃退火态合金的组织呈等轴状,塑性良好。Ti-49.8Ni合金室温组成相为马氏体,呈形状记忆效应;Ti-49.8Ni-1.0Co合金的室温组成相为母相B2,呈超弹性特性。退火时间对Ti-Ni合金的组织和性能影响不大,合金的相变温度随退火时间延长缓慢升高。形变温度显著影响Ti-Ni合金的超弹性特性,随形变温度升高合金的超弹性应力增加,超弹性滞回面积减小。

The effects of Co microalloying and annealing technology on the transformation,microstructure and shape memory effect （SME） of Ti-Ni shape memory alloy were investigated by differential scanning calorimetry,optical microscopy,X-ray diffraction and tensile test for Ti-49.8Ni and Ti-49.8Ni-1.0Co alloys annealed at 400 and 600℃,respectively.The results are described as follows.The A→R→M （A-parent phase,R-R phase,M-martensite） two-stage transformations takes place in Ti-49.8Ni and Ti-49.8Ni-1.0Co alloys during cooling from 400℃ annealing,while during heating the M→A one stage and M→R→A two-stage transformations takes place in Ti-49.8Ni and Ti-49.8Ni-1.0Co alloys,respectively.The 400℃ annealed Ti-49.8Ni and Ti-49.8Ni-1.0Co alloys show fiber microstructure and poor plasticity,and the 600℃ annealed alloys shown equiaxed grains and good plasticity.Since Ti-49.8Ni alloy at room temperature consist of a single martensite,the alloy exhibits SEM,while Ti-49.8Ni-1.0Co alloy consist of a single parent phase B2,and thus shows superelasticity （SE）.The effect of the annealing time on microstructure and properties of Ti-Ni alloy is not obvious.The transformation temperature of the Ti-Ni alloy increases slowly with increasing annealing time.The deforming temperature obviously affects the SE of Ti-Ni alloy.The SE stress increases and the SE loop area decreases in Ti-Ni alloys with increasing deformation temperature.