Effect of forging on microstructure and tensile properties of Ti-45Al-(8-9)Nb-(WB,Y) alloy

The effect of canned forging on microstructure and tensile properties of high Nb containing TiAl alloy, with the nominal composition of Ti-45Al-(8-9)Nb-(W,B,Y) was studied in this paper. The microstructure of the as-cast material was near lamellar (NL) microstructure composed of lamellar colony, 70 mu m in size, and 15% gamma and beta phase. There existed many boride ribbons longer than 40 mu m with high aspect ratio. After canned forging the material exhibited fine, homogeneous duplex (DP) microstructure, with grain size less than 20 mu m, and the borides were crushed to rods shorter than 6 mu m. Both microstructures of the alloy had excellent strength at room and high temperatures. The as-forged material was stronger and much more ductile than the as-cast material, exhibiting a brittle-ductile transition with an elongation 2.29% at room temperature (RT) increasing to 59.14% at 815 degrees C. A much less pronounced brittle-ductile transition existed for the as-cast material, with a increase elongation from 0.49% at RT to only 1.42% at 815 degrees C. The inferior tensile properties of the as-cast material were attributed to the NL microstructure which included detrimental P phase, boride ribbons and porosities, while the superior tensile properties of the as-forged material were attributed to finer DP microstructure resulting from canned forging. (c) 2005 Elsevier B.V. All rights reserved.