细晶TiAl基铸造合金的制备及其凝固特征

Synthesis and Solidification Characterization of TiAl Based Alloy with Fine Grain Structure

摘要:

采用非自耗电弧熔炼铸造方法，制备了Ti-Al-Nb基铸造合金。通过X射线衍射、金相观察、扫描电镜及透射电镜等实验方法，研究了Al含量对基体合金显微组织与凝固特征的影响。结果表明，适当降低铸造合金中铝的含量，能制备出晶粒细小的Ti-44Al-2Nb-1Cr-1W-1B合金，其平均晶粒尺寸为50 mm。细晶TiAl基铸态合金中b 相与g 相存在“伴生”现象；同时，该合金中一定量b相稳定元素W和Nb的加入，使高温b 相得以在凝固过程中保留到室温，这种少量b相的存在也限制了a 相晶粒的长大。

Abstract:

Ti-Al-Nb based alloys were prepared by a non consumable skull melting. The effect of Al content on the microstructure and the solidification characterization of as-cast alloys were investigated using X-ray diffraction, optical microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that a fine grain structure Ti-44Al-2Nb-1Cr-1W-1B alloy with average grain size 50 mm could be got by proper decreasing of Al content, and the companion phenomenon of co-existence of b and g phases in the fine grain structure as-cast alloy was found. Moreover, the proper additions of alloying elements such as W and Nb increased the stability of b phase, and thus b phase was retained to low temperature. The presence of b phase was found to restrict a grain growth at the temperatures above the a transus temperature.