Advanced computer models improve the quality of titanium alloys.

AFRL scientists developed advanced computer models to improve the processing and quality of titanium alloys used in manufacturing gas turbine engine parts and critical structural components for military aircraft. AFRL transferred both the models and the basic materials knowledge to titanium mill suppliers to help them eliminate strain-induced porosity (SIP)—also known as cavitation—in billet products (see Figure 1) and finished parts. The models also increase product yield by reducing the amount of scrap material, which helps lower production costs.

Titanium is a very durable, lowdensity element (about 60% the density of iron) that gains considerable strength when processed as an alloy or mechanically altered via deformation processing. Because titanium alloys reduce weight and operate very effectively at low to moderately elevated temperatures, engineers have used them as replacements for iron alloys in aerospace applications for many years.

Corrosion-resistant parts and lowweight, high-specific- strength structures represent two typical applications for titanium and its alloys. In aircraft gas turbine engines, rotating components such as turbine disks and blades require titanium alloys in order to maximize strength-to-weight ratio, metallurgical integrity, and reliability at service temperatures. These alloys must exhibit good fatigue resistance and low creep rates. Stringent user requirements ensure controlled homogeneous microstructures and freedom from imperfections. Melting-related imperfections include alloy segregation, high- or lowdensity inclusions, and ingot porosity, while flaws associated with thermomechanical processing include SIP, shear bands, and undesirable residual stresses.