Developments in Titanium Alloy Casting Technology

Improved life and performance of aerospace, marine, and corrosion-resistant systems can in many cases be achieved by increased use of titanium alloys. However, titanium alloys have shown only a modest increase in use in recent years mainly due to the combination of basic material expense and the high cost of component fabrication. One approach used to circumvent this problem is net-shape technologies which minimize costly material wastage. Titanium alloy casting technology is an attractive net-shape approach which lately has been receiving increased attention. The various aspects of the two main casting methods, the rammed graphite and the investment casting techniques, are discussed, including size, shape-making, and resulting properties, and ways to improve them. The comparison of mechanical properties of castings to ingot metallurgy (cast and wrought) parts indicates that not only is casting technology cost competitive, but many properties such as fracture toughness and fatigue crack growth rate are equivalent to those exhibited by ingot metallurgy (IM) material. This results from both the as-cast microstructure and the ability to completely close internal porosity in titanium alloys by hot isostatic pressing (HIP). It is suggested that the casting factor, which is currently applied to titanium castings, is inappropriate, and serious thought should be given to eliminating this factor. Current R&D work in titanium alloy casting technology is highlighted, and some thoughts for future developments are presented.

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