Ti-5.8Al-4.8Sn-2Zr-1Mo-0.35Si-0.70Nd合金中富钕稀土相研究

Nd-rich Rare Earth Phases in Ti-5.8Al-4.8Sn-2Zr-1Mo-0.35Si-0.70Nd Alloy

针对Ti-5.8Al-4.8Sn-2Zr-1Mo-0.35Si-0.70Nd粉末冶金高温钛合金中富钕稀土相的形成、尺寸、分布、形态、长大及结构特征进行了系统研究。结果表明：快速凝固态高温钛合金粉末中稀土相为液态析出相,其尺寸大部分在50-250 nm之间,弥散分布在基体中;晶内稀土相多为球状,晶界稀土相多为椭球状,其长轴平行于晶界;TEM观察到的稀土相的尺寸和分布与理论计算相符合;快速凝固高温钛合金粉末经过700-1000℃/110 MPa/0.5 h热等静压成形后,快速凝固过程中已析出的稀土相尺寸变化不大;同时细小的稀土相从过饱和的基体中大量固相析出;经过1200℃/140 MPa/3 h热等静压成形后,稀土相颗粒尺寸大部分在150-500 nm之间,有明显长大;稀土相的高分辨图像及同心衍射环花样表明,快速凝固高温钛合金粉末中的稀土相由5-10 nm的纳米晶组成,经过1200℃热等静压成形处理后的稀土相仍由纳米晶组成,而且纳米晶的尺寸没有明显变化;但是稀土相的＂基体＂上明显出现富Sn元素的＂第二相＂颗粒,结构变得复杂。

The formation, morphology, size, distribution, growth and structure of Nd-rich rare earth（RE） phases in powder metallurgy（PM） high temperature titanium alloy were investigated. The results show that the RE-rich phases in as-rapidly-solidified high temperature titanium alloy powder precipitate in the process of powder droplet solidification, and the particle size is 50-250 nm in diameter. The majority of the particles are uniformly distributed in the alloy matrix. The particles are nearly spherical within the grains and ellipsoidal along the grain boundary. The major axes of the ellipsoidal particles are lying nearly parallel to the grain boundary. The calculated size and distribution of the second phase particles are in agreement with the TEM experimental results. The diameters of RE-rich phases are largely smaller than 50 nm precipitated from the supersaturated matrix after hot isostatic pressing（HIP） between 700 and 1000 ℃ in a short time. The size variation of the original RE-rich phases is minimal. However, the particle size including the original and the precipitated is 150-500 nm in diameter after HIP at 1200 ℃for 3 h. The HRTEM image and SAED pattern of the RE-rich phases indicate that they are composed of many nanocrystallines while they are still composed of nanocrystallines whose size grows up minutely after HIP at high temperature. Maybe the later nanocrystalline is different from the former one because the tin-rich phases appear on the RE-rich phases ＂matrix＂, resulting in the complex microstructure of the RE-rich phases.