热处理及预拉伸对TC4-0.55Fe合金组织和力学性能的影响

Effect of Heat treatment and Pre-stretching on Microstructure and Mechanical Properties of TC4-0.55Fe Alloy

摘要:

本文研究了具有双态组织的钛合金Ti-6Al-4V-0.55Fe(TC4-0.55Fe)在不同热处理制度（固溶时效、双重退火）和引入预拉伸对微观组织及力学性能的影响，并分析了合金显微组织与力学性能之间的联系。通过对双态组织的 TC4-0.55Fe采用固溶时效和双重退火热处理后微观组织和力学性能进行比较，发现两种热处理方式下随着时效和低温退火温度升高合金中微米级的片层α相厚度均逐渐增大、强度降低、塑性提高。固溶时效热处理下随着时效温度的升高合金屈服强度从530℃的873MPa下降到590℃的862MPa，而延伸率提高3.2%。双重退火热处理试样的屈服强度随着低温退火温度的升高逐步降低，但是延伸率相比于固溶时效有了很大提高，最好可达到23.6%。由于普通热处理对钛合金强度提升不明显，时效和低温退火温度均为590℃时，双重退火试样塑性更优于固溶时效，所以选择该试样引入预拉伸强化，对其在固溶和低温退火中间进行预拉伸。引入预拉伸后，晶粒发生了明显的变形，进行时效强化后合金组织无沉淀区（PFZ）中析出大量细小的二次α相（αs），引入预拉伸后进行时效可以在提升钛合金屈服强度的同时只降低极少的塑性，其中预拉伸形变1%的试样等轴晶含量最高，强度较引入预拉伸前提高68MPa，延伸率仅下降4%，力学性能最优。通过本文研究可知，TC4-0.55Fe钛合金在经过固溶处理后继续进行预拉伸和时效处理，可以有效提升合金的综合力学性能。

Abstract:

This paper investigated the effects of different heat treatment processes (solution aging and double annealing) and pre-stretching on the microstructure and mechanical properties of Ti-6Al-4V-0.55Fe (TC4-0.55Fe) alloy with duplex microstructure and the relationship between microstructure and mechanical properties of TC4-0.55Fe alloy was analyzed. The microstructure and mechanical properties of the duplex microstructure after solution aging and double annealing were compared and it can be found that the thickness of the micron scale lamellar α phase gradually increased with the increase of aging and low temperature annealing temperature under the condition of two kinds of heat treatments, which reduced the strength and increased the plasticity of the alloy. Under the solution aging treatment, the yield strength of the samples decreases from 873MPa at 530℃ to 862MPa at 590℃ and the elongation increases by 3.2% with the increasing aging temperature. The yield strength of the double annealing heat treatment sample decreases gradually with the increase of the low temperature annealing temperature, but the elongation has been greatly improved compared with the solution aging, and the best is 23.6%.Because the strength of titanium alloy is not significantly improved by ordinary heat treatment, the plasticity of the double annealing sample is better than that of the solution aging when the aging and low temperature annealing temperature is 590 ℃, so the sample is selected to introduce the pre-stretching strengthening and pre-stretch it between the solution and low temperature annealing. After the introduction of pre-stretching, the grain deformation is obvious. And a large number of fine secondary α phase (αs) are precipitated in the precipitation-free zone (PFZ) of the alloy structure after aging strengthening. The aging after the introduction of pre-stretching can improve the yield strength of titanium alloy and only reduce a little plasticity. Among them, the sample with 1% pre-stretching deformation has the highest content of equiaxed grains, the strength is increased by 68MPa compared with that before the introduction of pre-stretching, and the elongation is only decreased by 4%, the mechanical properties are the best. According to this study, the comprehensive mechanical properties of TC4-0.55Fe titanium alloy can be improved by pre-stretching and aging strengthening after solution strengthening.