DEVELOPMENT OF PERMANENT-MOLD CAST TIAL AUTOMOTIVE VALVES

This paper presents the results of an EMTEC funded project to develop low-cost TIAl automotive valves. The alloy studied was Ti-47Al-2Nb-1.7 5Cr (at %). Over 800 valves were cast, using several variations of the permanent-mold process, in a multi-cavity steel mold. Applying pressu re during solidification improved the casting fill. However, none of t he permanent-mold casting methods produced pore free as-cast valves. T he as-cast microstructures of valves produced by permanent-mold castin g were much finer than investment castings of similar section sizes. O f the permanent-mold casting methods, the injection cast method exhibi ted the finest as-cast structure showing a potential for a new high ou tput method for producing fine-grained TiAl components. Room temperatu re tensile properties of the permanent-mold material were superior to those of investment castings with a similar microstructure. Two sets o f valves were road tested for a total of 50 000 km with average 2% fue l savings and no valve damage. There is a need to overcome few challen ges before this technology can be implemented in the automotive indust ry. (C) 1998 Elsevier Science Limited. All rights reserved.