含W钛铝合金的枝晶偏析和晶粒细化.docVIP

 n Dendrite core grain refining and interdendrtic coarsening behaviour in W-containing γ-TiAl based Alloys# SUN Hongliang, HUANG Zewen** 5 10 15 20 25 30 35 (Key laboratory of advanced technologies of materials(ministry of education), Southwest JiaoTong University, ChengDu 610031) Abstract: Two W-containing γ-TiAl based alloys were studied in as-cast ingot condition. Pronounced partitioning of heavy-metals and light-metals were found to occur, causing segregation of W and Nb into dendrite core and Al in interdendritic region. The average Al content in α2+γ lamellae was close to 46 % in interdendritic region, and below 44 % in dendrite cores, regardless of the nominal Al content of the alloy. About 15% coarse colonies formed in alloy 44Al and 60 % in alloy 46Al. Effective grain refinement can be achieved in the dendrite core where both the Al depletion and Nb, W and Ti enrichment ensured a L→β ?solidification route. In contrast, the solidification in interdendritic regions involves a peritectic reaction L+β→?α p. As a result, unusually large ap? grains α2+γ ?lamellar colonies) formed in the interdendritic regions. Keywords: Titanium aluminides; Phase transformation; Casting; Segregation; grain refining and coarsening 0 Introduction In the recent years, significant efforts have been devoted to development of high strength TiAl-based alloys containing W, aiming to increase creep resistance and oxidation resistance [1-9], and to refine lamellar structure by producing more uniform and continuous??2 lamellae. This could lead to improving tensile properties and thermal stability [4, 9-11]. This is because, as a solid solution strengthener, integration of W into????2 lamellae can reduce the stacking fault energy and diffusion rates so as to stabilize the??2+? lamellar structure. Also well documented is that the formation of small B2 particles retained by W can impede the motion of dislocations and prevent dissolution of??2 lamellae, which is beneficial for improving c