【摘要】 利用相场模型研究了Ni₄Ti₃沉淀相自催化效应的产生机制,基于体系各种能量的变化规律研究了自催化生长效应中合理的Ni₄Ti₃变体群的排列方式.模拟研究结果表明,在模拟最初的时间内,为缓解球形Ni₄Ti₃相与NiTi基体相形态上的不匹配,体系的化学自由能逐渐增大,弹性能和界面能逐渐减小;当Ni₄Ti₃相与NiTi基体相达到最佳匹配后,相变过程中化学自由能逐渐减小,弹性能和界面能逐渐增大;整个相变过程中体系向低能量态发展.同取向变体的梯形排列模式具有最大的优先性,其次是同取向变体的水平排列方式,再次是不同取向变体的边-面排列方式,最不具优先性的是同种变体的垂直排列模式.相场模拟结果深化并拓展了已有实验结论.更多还原

【Abstract】 The precipitation behavior and distribution of Ni₄Ti₃ particles in NiTi alloys have a significant influence on the subsequent martensitic transformation,which may consequently affect shape memory effect and superelasticity of NiTi alloys.The latest experimental studies confirmed that in single crystal NiTi alloy,the Ni₄Ti₃ particles nucleate and grow as an autocatalytic way leading to a step-like configuration.The autocatalytic nucleation known as collective manner has been widely studied in martensitic transformation while causing relatively less attention in diffusion transformation such as precipitation.Previous studies have been launched to investigate the nucleation and orientation issues of M₄Ti₃ precipitate mainly by analyzing the stress or concentration field around the Ni₄Ti₃ particle.However,the coupling between stress and concentration field is necessary in Ni₄Ti₃ precipitation due to its diffusion nature,also the coupling and cross influence of each energy in the simulation system should be taken into account.In this paper,the mechanism of autocatalytic effect of Ni₄Ti₃ precipitate has been studied by means of phase field method,the favorable Ni₄Ti₃ precipitates array has been investigated through the variation of each energy in the simulation system. The simulation results show that in the initial short time of Ni₄Ti₃ precipitation,due to the morphological accommodation of Ni₄Ti₃ and NiTi phases,the system chemical free energy gradually increases,while the elastic and interfacial energy decrease;after the self-accommodation stage,each energy shows the inverse trend compared with the initial stage;in the whole phase transformation process,the system total energy develops toward the lower energy state.In all of the feasible precipitate arrays,it is found that the step-like array formed by same orientation Ni₄Ti₃ variants has the supreme priority,secondly the horizontal array followed by the edge-face array formed by different orientation variants,the vertical array constituted by same orientation variants was confirmed as the least possible way,these simulation results have deepened and expanded the understanding obtained in previous experiment studies.更多还原