TC11钛合金形变热处理工艺参数的控制及其对亚稳组织的影响

Control of Process Parameters and Their Effect on the Metastable Microstructures in Thermomechanical Treatment for TCll Titanium Alloy

本文对含热矫正的TC11钦合金形变热处理工艺试验结果进行了回归分析,建立了工艺参数与合金中初生α大小及有关拉伸性能的经验关系式,可用于性能的预测及工艺的优化。同时,分析了矫正温度对组织的影响,并指出在较高温度下矫正所得的组织形态有利于合金综合性能的改善。

There have been many studies on the influence of deformation temperature,cooling mode, strain rate and deformation amount on the final microstructuresand properties of titanium alloys [1-3, 5]. However, if a process of thermomecha-nical treatment is used in the course of forging of the semifinished products(for example, jet engine blades, which must be of an accurate size and shapeafter forging), the effect of the heat correction, which is an important para-meter on microstructures and mechanical properties of titanium alloy, mustbe studied. The author has not found any paper in the open literature on theeffect of heat correction on titanium alloy. In the author's previous paper [6], the influence of the heat correction onthe microstructures and properties of titanium alloy has been studied to a cer-tain degree, but how to control the process of thermomechanical treatment, in-cluding the heat correction under different conditions and the effect of theheat correction on metastable microstructures after deformation followed bywater quenching, requires further study. In this paper, such a further study on TC11 titanium alloy, i.e. alloy Ti-6.5Al-3.5Mo-1.5Zr-0.25Si is presented. The author's new findings are believedto be the following: (1) The empirical formulas which relate the process parameters to thesize of primary α and some tensile properties about the alloy have been derived(Tab. 4) by the statistical method of regression. Based on these empirical for-mulas, the 'equiscalar curves' are prepared and given in fig.1. (2) There is an obvious influence of correction temperature on the mor-phology of the phase precipitated from martensite and metastable β in the alloy deformed and followed by water quenching. The effect of variation of correc-tion temperature on the size of primary α is unnoticeable. (3) If the correction temperature is about 850℃, the properties of thealloy will worsen. If the correction temperature is higher and equal to theforging temperature, i. e. 950℃, the properties will be improved and the dis-tribution of secondary α appears as fine and crossed (such a distribution issimilar to the morphology of microstructure under customary double annealing). (4) As the products are aged in a temperature range from 530℃ to 600℃after the heat correction, the variation of microstuctures and mechanical pro-perties with the ageing temperature is almost unnoticeable except that the re-duction in area, i.e. ψ, of the tensile specimens at 500℃ varies noticeably.