Novel additive manufacture and hot forging technique for titanium alloy

Abstract

Hot forging is investigated as a method of improving the mechanical behaviour of additive manufactured (AM) titanium alloy Ti64. An initial study using AM 316L stainless steel is used to show that the hot forging of the additive material can reduce, and in some cases eliminate, porosities and defects within the material. Testing shows that the mechanical properties such as strength and ductility can be improved by this method. Initial tests were then made on AM Ti64 through the isothermal compression of cone shaped specimens. This geometry enabled a single sample to display the effects of forging over a wide range of plastic strain. This work identified a suitable range of temperature and deformation for use in the hot forging of AM Ti64. A series of AM Ti64 samples were then built to a dog-bone geometry and hot forged between flat anvils. This open die forging allowed the determination of the changes in structure and behaviour over the range of conditions. Following the series of tests to determine tensile strength and ductility, a further study was undertaken to evaluate the fatigue behaviour of the forged material against that of un-forged AM Ti64 and commercial Ti64 wrought sheet. The result results indicate that the forging operation has the capacity to bring the fatigue performance of the AM material up to that of standard (non-AM) Ti64, indicating commercial possibilities. As an illustrative test of the practical application of AM + hot forging, a representative component was made from an AM Ti64 blank using a closed die forging technique. Analysis of the strength and structure of the resulting forging indicated that the properties were compatible with the standards requirement for commercial forgings. The conclusion is that hot forging is a viable method of improving mechanical performance in AM metals.