WSTi3515S阻燃钛合金大晶粒超塑性及组织演变研究

发布时间：2018-06-05 19:07

  本文选题：阻燃钛合金 + 大晶粒　； 参考：《长安大学》2017年硕士论文

【摘要】：钛合金因具有良好的耐热性和高的比强度而广泛应用于航空航天领域,但常规的钛合金部件在高温高压等苛刻的工作环境下,会发生严重的燃烧事故。针对于“钛火”现象,我国在Alloy C合金的基础上研发了WSTi3515S阻燃钛合金,该合金具有良好的阻燃和综合性能,但因其晶粒粗大,高温变形易开裂,采用常规加工手段难以满足产品性能的要求。超塑性成形技术是加工难变形材料的有效方法之一,但对于具有粗大晶粒的阻燃钛合金超塑性的力学行为及组织演变规律尚缺乏系统地研究。因此,本文以热轧退火态WSTi3515S阻燃钛合金为研究对象,通过等温恒应变速率超塑拉伸试验,对该合金在不同变形条件下的超塑性力学行为及粗大晶粒的组织演变规律进行了深入地研究。主要研究内容和结果如下:研究了WSTi3515S阻燃钛合金的超塑性力学行为及热力学参数对超塑性特征的影响规律。发现在选定实验范围(温度为800℃~920℃、应变速率为5×10-4s-1~1×10-2s-1)内,延伸率均接近于或大于200%,具有良好的超塑性能,最大延伸率556%出现在920℃,5×10-4s-1条件下;揭示了大晶粒WSTi3515S阻燃钛合金应力-应变曲线变化规律,且流变应力曲线变化的实质是加工硬化与动态软化相互作用的结果;采用等应变速率拉伸法测定了WSTi3515S钛合金应变速率敏感指数m值,在所选定应变速率范围内,试样m值的平均值均大于0.3,表明合金具有良好的超塑性;基于应力-应变曲线,分别利用双曲正弦型Arrhenius模型与多项式法建立WSTi3515S钛合金本构方程,通过误差分析表明多项式方程精度较高;分析了WSTi3515S阻燃钛合金在超塑性拉伸变形时的动态再结晶机制及组织演变规律。发现原始大晶粒被拉长压扁,在晶界处发生动态再结晶,原始组织得到细化,随着温度的升高或者应变速率的降低,再结晶晶粒不断长大,显微组织呈等轴状且均匀分布;在高应变速率(≥5×10-3s-1)及低温(≤840℃)时发生动态再结晶,主要机制为不连续再结晶(DDRX)。在低应变速率(≤1×10-3s-1)及高温(≥880℃)时发生动态再结晶,主要机制为连续动态再结晶(CDRX)。但在不同条件下发生动态再结晶过程均伴随粒子刺激形核(PSN)。揭示了不同变形条件对动态再结晶平均晶粒大小及体积分数的影响规律。结果表明,随着变形温度的升高或者应变速率的降低,动态再结晶平均晶粒大小和体积分数均增大;基于Avrami模型,分别建立了动态再结晶临界应变模型和动态再结晶体积分数模型,动态再结晶临界应变模型为,动态再结晶体积分数模型为。
[Abstract]:Titanium alloy is widely used in aerospace field because of its good heat resistance and high specific strength. However, the conventional titanium alloy parts will occur serious combustion accidents under harsh working conditions such as high temperature and high pressure. In view of the phenomenon of "titanium fire", the flame retardant titanium alloy WSTi3515S was developed in China on the basis of Alloy C alloy. The alloy has good flame retardancy and comprehensive properties, but because of its coarse grain size, it is easy to crack during high temperature deformation. It is difficult to meet the requirements of product performance by conventional processing methods. Superplastic forming technology is one of the effective methods for processing refractory materials, but the mechanical behavior and microstructure evolution of flame retardant titanium alloys with coarse grain are not studied systematically. Therefore, the hot rolled annealed WSTi3515S flame retardant titanium alloy was studied by isothermal constant strain rate superplastic tensile test. The superplastic mechanical behavior and microstructure evolution of the alloy under different deformation conditions were studied. The main contents and results are as follows: the superplastic mechanical behavior of WSTi3515S flame-retardant titanium alloy and the influence of thermodynamic parameters on superplasticity were studied. It is found that in the selected experimental range (temperature 800 鈩，

本文编号：1983101