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Ti-6Cr-5V-5Mo-4Al-1Nb合金的晶粒长大动力学 被引量:2

Grain Growth Kinetics of Ti-6Cr-5V-5Mo-4Al-1Nb Alloy
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摘要 以新型亚稳β钛合金Ti-6Cr-5V-5Mo-4Al-1Nb为研究对象,对其晶粒长大动力学进行研究。用Beck方程描述了晶粒的长大过程,用Arrhenius方程计算了晶粒长大激活能,对晶粒尺寸的均匀性(ω值)随固溶温度与时间的变化规律进行了总结并进行相关机制分析,得到了合金适宜的固溶温度区间。研究表明:Ti-6Cr-5V-5Mo-4Al-1Nb合金在890℃以下固溶时,晶粒的尺寸稳定性较好;而在890℃以上热处理,晶粒急剧粗化,故该合金适宜的固溶温度在890℃以下。且随着固溶时间的延长,晶粒的长大速度减缓。固溶后ω值随时间的延长先降低又逐渐升高,而且温度越高达到ω最小值的时间越短,晶粒尺寸的均匀性越差。合金的生长指数(n值)随温度升高而增大,范围在0.22~0.39之间,均小于纯钛在相变点上保温时的生长指数,这是由于该材料合金化程度高,大量的溶质原子形成的杂质气团会对晶界的迁移产生阻碍作用。晶粒长大激活能随着保温时间的延长而增加,其值在46.2~100.6 kJ·mol^(-1)之间。 Because of its excellent specific strength,hardenability and heat treatment strengthening effect,metastable β titanium alloy has become the key material for some structural parts such as fasteners and frames of aircraft.For metastable β titanium alloy,a suitable solution treatment process above the β phase transition point can obtain metastable microstructure,which lays the organizational foundation for the subsequent aging strengthening treatment of the material.However,due to the cubic structure of titanium alloy in β phase region,the diffusion of β phase is enhanced,and the grains are easy to grow.In addition,the grain size is also closely related to the fracture toughness of titanium alloy.When the crack propagates along the grain boundary,if the grain size is too large or too small,the path will be straighter.Only the appropriate grain size can make the crack path tortuous,so that the alloy can obtain excellent fracture toughness.Therefore,in-depth study of grain growth behavior and growth mechanism is the premise of designing and regulating process parameters,and then obtaining excellent mechanical properties.In this paper,a new metastable β titanium alloy Ti-6Cr-5V-5Mo-4Al-1Nb was taken as the research object.At present,there were few reports on the matching of strength and toughness of the alloy.The fracture toughness of titanium alloy was closely related to grain size,so in this paper,the grain growth kinetics of the alloy during solid solution in β single phase region was studied from the perspective of grain size influencing factors.According to the grain growth mechanism of the alloy,theoretical reference was provided for the formulation of solid solution process parameters of the alloy,so as to obtain excellent strength and toughness matching of the alloy and broaden the engineering application range of the alloy.After solid solution treatment of new metastable β titanium alloy,coarse grinding,fine grinding and polishing were carried out to make metallographic samples.The microstructure evolution process was observed by metallographic microscope(OM)and the grain size was counted by image processing software.The microstructure evolution process was described by kinetic and thermodynamic knowledge.The variation of grain size with solution time was quantitatively described by Beck equation,and the growth exponent of grain at each solution temperature was obtained.The activation energy of grain growth was calculated by Arrhenius equation.A parameterωwas defined to measure the uniformity of grain size after solid solution,so as to explore the variation of grain size uniformity with holding time during grain growth.After the above experimental process,the following experimental results could be obtained and conclusions:The growth exponent at 860,890,920 and 950℃ were 0.21,0.27,0.33 and 0.38.It could be seen that the higher the solution temperature was,the larger the growth exponent was.The growth exponent increases slightly from 860 to 890℃,while the growth exponent increased greatly above 890℃,but it was smaller than that of pure titanium at the phase transition point.This was because the material had a high degree of alloying.After solution treatment,a large number of impurity gas clusters formed by solute atoms would hinder the migration of grain boundaries.The suitable solution temperature of the alloy was below 890℃,and the grain coarsening above 890℃ was serious,which was not conducive to the control of material properties.The parameterωdefined to measure the uniformity of grain size after solution decreases first and then increases gradually with time.Moreover,the higher the solution temperature was,the shorter the time for reaching the minimum value of uniformityωwas,and the worse the uniformity of grain size was.The grain boundary moved to the curvature center under the action of driving force,which would lead to the further growth of large grains and the gradual disappearance of small grains.This change process led to the change of the uniformityωvalue of solid solution grain size.The grain growth activation energy of the new metastableβtitanium alloy was between 46.2~100.6 kJ·mol^(-1) in the solid solution temperature range of this experiment,which increased with the extension of time,but all in the range of grain activation energy of some commonly used titanium alloys.This was because at the initial stage of solid solution,the moving speed of grain boundary was faster than the diffusion speed of solute atoms.At this time,the drag effect of dragging solute atoms was weak.With the extension of holding time,the grain boundary energy decreased,and the migration speed of grain boundary was smaller than the diffusion speed of solute atoms.The drag effect of solute atoms was enhanced,showing an increase in activation energy.In the early stage of heat preservation,the defects of microstructure(vacancies,dislocations,etc.)provided driving force for the movement of grain boundaries,so the movement speed of grain boundaries was faster than the diffusion speed of solute atoms.At this time,the drag effect of solute atoms was weak.With the extension of heat preservation time,the grain size increased,and the grain boundary energy decreased.The migration speed of grain boundaries was less than the diffusion speed of solute atoms.The solute atoms were enriched at the grain boundaries.At this time,the drag effect of solute atoms increased and the activation energy increased.
作者 宋越 崔雪飞 于洋 宋晓云 叶文君 惠松骁 Song Yue;Cui uefei;Yu Yang;Song Xiaoyun;Ye Wenjun;Hui Songxiao(State Key Laboratory of Nonferrous Metals and Processes,GRINM Group Co.,LTD.,Beijing 100088,China;GRIMAT Engineering Institute Co.,LTD.,Beijing 101407,China;General Research Institute for Nonferrous Metals,Beijing 100088,China;AECC Guizhou Liyang Aviation Power Co.,LTD.,Guiyang 550014,China)
出处 《稀有金属》 EI CAS CSCD 北大核心 2023年第6期908-914,共7页 Chinese Journal of Rare Metals
基金 国家重点研发计划项目(2017YFB0306204)资助。
关键词 亚稳Β钛合金 晶粒长大动力学 长大激活能 晶粒均匀性 metastable beta titanium alloy kinetics of grain growth growth activation grain uniformity
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