β单相区固溶温度对Ti-55531合金组织及性能的影响

Influence of solution temperature in β phase region on microstructure and performance of Ti-55531 alloy

摘要:

采用OM、SEM及拉伸测试方法,结合系列的热处理工艺,研究了β单相区不同的固溶温度对Ti-55531合金片层组织参数及力学性能的影响规律。结果表明,β单相区不同温度固溶,再经相同的时效处理后,合金的组织均为片层状的次生α_s、残余β片和微量晶界α组成的片层组织,但不同温度固溶后合金的β晶粒尺寸改变,进而影响时效析出次生α_s片的含量及尺寸,最终导致合金力学性能的差异。固溶温度在830~900 ℃之间时,随固溶温度的升高,原始β晶粒尺寸增大,后续时效析出的次生α_s长、宽及长宽比均先增大后减小,数量越来越多,合金强度直线下降,塑性先降低后增加。固溶温度为860℃时合金对应的强塑性匹配最好。合金的断裂失效机制为以微孔聚集为主,沿晶开裂和穿晶断裂并存的混合断裂机制。

Abstract:

In order to research the influence rule of solution temperature above β transformation temperature on the microstructural parameters and mechanical properties of Ti-55531 alloy, series heat treatments, OM, SEM and tensile testing methods were carried out. Results indicate that all microstructures of the alloy consist of lamellar α_s, residual β laths and a few grain boundary α after solution at different temperatures in β phase region and aging treatment. Different solution temperature affects the original β grain size of Ti-55531 alloy, and then the content and size of aging precipitated α_s phase, which ultimately results in mechanical properties of the alloy. When the solution temperature is ranging from 830 ℃ and 900 ℃, with the increase of solution temperature, the size of original β grain increases, and the length, width and length-width ratio of α_s phase precipitated by subsequent aging increase at first and then decrease. Meanwhile, the volume fraction of α_s phase increases, the strength of the alloy gradually decreases, and the plasticity decreases first and then increases. As the solution temperature is 860 ℃, the alloy could obtain the good cooperation between strength and plasticity. Fracture mode of lamellar microstructures is a mixed mode, including microvoids accumulation, transgranular cleavage and intergranular fracture.