Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金β晶粒生长及片层组织转变

β-grain growth and lamellar microstructure evolution of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

利用可控冷却速度热处理装置研究了Ti-6. 5Al-3. 5Mo-1. 5Zr-0. 3Si合金β热处理过程中的β晶粒生长及片层组织转变规律。结果表明,合金在β单相区固溶时,随着温度升高和保温时间延长,β晶粒尺寸增大,且加热温度高于1140℃时,β晶粒快速生长。计算了β相区晶粒生长激活能为129. 6 k J·mol-1,并建立了β晶粒生长模型。随冷却速度变化,合金出现全马氏体组织和(α+β)片状组织。原始β晶界在全马氏体组织和(α+β)片状组织中均清晰可见,原始β晶粒呈等轴状特征。(α+β)片以取向各异"集束"形式存在于原始β晶粒内,(α+β)集束内的α片几乎相互平行。(α+β)片层组织特征参数(原始β晶粒尺寸、α片厚度及(α+β)集束尺寸)均随冷却速度降低而增加。α片层可在β晶界和晶内形核,以集束形式生长,但不能穿过β晶界。原始β晶界能对α片层的生长起到约束作用。

Theβ-grain growth and the lamellar microstructure evolution of Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy were investigated byβheat treatments on a heat treatment machine with controllable cooling rate.The results indicate that theβ-grain size increases with the increase of the heating temperature and holding time duringβsolution treatment,and increases rapidly when heated over 1140℃.Theβ-grain growth activation energy was calculated as 129.6 k J·mol-1,and aβ-grain growth model was developed.As the cooling rate changes,two types of transformation phases(martensite and(α+β)lamellar microstructure)are observed.The originalβ-grain boundaries are clearly visible in the martensite and the(α+β)lamellar microstructure,and the originalβ-grain is equiaxed.The(α+β)plate exists in the originalβ-grain with a form of clusters with different orientations,while theαplates in(α+β)cluster are almost parallel to each other.With the decrease of the cooling rate,all the lamellar characteristic parameters including the initialβ-grain size,αplate thickness andαcluster size increase.Theαplate nucleates at theβ-grain boundary or grain interior,but cannot cross through theβgrain boundary.Theαplate grows in the form of‘cluster’,and is restrained by originalβ-grain boundaries.