材料期刊网

利用轴对称单向压缩法研究了纯钛在变形温度从723~873 K范围内、应变速率从0．001~1 s－1下的热压缩行为,并通过背散射电子衍射技术对不同热变形条件下的微观组织进行表征.研究结果表明,高温轴对称单向压缩下的纯钛经历从应变硬化阶段到稳态变形阶段的过程,在低的应变速率条件下材料流变应力出现平台,高的应变速率条件下,流变应力随变形过程逐渐增加.该合金流变应力的大小受变形温度、应变速率的强烈影响,随变形温度升高而降低,随应变速率提高而增大,高纯钛是一种具有正应变速率敏感性的材料.该合金高温流变应力σ可采用 Zener-Hollomon参数的函数来描述,函数表达式中参数A、α和n 的值分别为1．84×1024 s－1、0．013 MPa－1、12．66,其热变形激活能Q为415．69 kJ/mol.不同Z参数条件下微观组织对比分析表明在高的Z 参数条件下,材料未发生动态再结晶,在低的Z 参数条件下,材料发生明显的动态再结晶,在Z 值介于两者之间时材料发生部分再结晶.

Isothermal compression tests of high purity titanium were performed on a Gleeble-1500 system in the temperature range between 723 and 873 K at strain rates between 0.001 and 1 s-1 .The flow behavior was de-scribed by a hyperbolic sine constitutive equation and the microstructures of samples were observed by electron back scattering diffraction (EBSD).The results show that during hot deformation pure titanium experienced from strain hardening to steady state deformation and the corresponding softening mechanism changes from dy-namic recovery to dynamic recrystallization;peak stress levels decreased with deformation temperature increas-ing and strain rate decreasing.High purity titanium was positive strain rate sensitive material.The flow stressσwas represented by the Zener-Hollomon parameter in an exponential equation withparameter A,αand n in ex-pression were 1.84×1024 s-1 ,0.013 MPa-1 and 12.66,with activation energy Q of 415.69 kJ/mol.The micro-structure of specimens with different Z values show that dynamic recrystallization was responsible for softening of low Z value sample,which dynamic recovery was the main reason for dynamic softening of high Z values sample,dynamic recrystallization occurred in the sample with middle Z value.Z value can be used to j ustified the dynamic softening mechanism for high purity Ti material.