Melting, casting, and forging problems in titanium alloys

Titanium alloys exhibit a number of problems at the billet evaluation stage that are connected to the melting and casting processes used in their preparation. Some of these, such as the alpha I and high-density inclusions defects, originate principally in the raw materials used: others, such as alpha II and beta fleck, are connected with the melting practice. The importance of the defect incidence in relation to final product quality depends on a complex interaction of property requirements, inspection techniques, and alloy structure. This interaction is specific to the alloy concerned. Conventional melting provides a product having a reliability with respect to these defects that is uncomfortably close to the limits imposed by probabilistic design and fracture mechanics analysis. Efforts to improve this situation should center around the increased use of electron-beam techniques and the use of forging sequences designed to increase the inspectability of the billet product.