Processing, properties, and ballistic performance of titanium-aluminum titanium metal-intermetallic laminate (MIL) composites

A systematic investigation into the processing of Ti-Al₃Ti metal-intermetallic laminate (MIL) composites from elemental titanium and aluminum foils in open air by a novel one step technique, and subsequent characterization, physical, mechanical and ballistic testing was carried out. Al₃Ti is the only intermetallic phase to form, and no oxides or other phases are formed. Composites with Ti volume fractions of ∼0, 14, 20, 35, and 57 percent can be processed consistently, with measured density agreeing well with calculated density. The intermetallic reaction occurs in two parts that are linear with respect to Al₃Ti growth with time: oxide controlled diffusion of Al, and the order of magnitude faster chemical reaction that occurs after the oxide layer breaks down and transient liquid phases are formed. A reaction model based on the production of Al₃Ti spheroids that are ejected from the Ti reaction surface has been developed, and is titled reactive foil sintering. Quasi-static and dynamic compression tests resulted in maximum yield stresses for the 20Ti composite, and end-confined quasi-static and dynamic compression tests, tension tests, and 3-point bend tests resulted in maximum yield stresses and bending loads for the 35Ti composite. Maximum yield stresses occurred in specimens tested with layers parallel to the load. Arrester orientation R-curve testing was completed for the 14Ti composite under large-scale bridging conditions, with initiation toughness values obtained for 20Ti and 35Ti which developed cracks in the intermetallic layer growing perpendicular to the load axis. Divider orientation R-curves were obtained, with the 20Ti and 35Ti curves closely approaching calculated steady-state toughness values. Ballistics testing of bonded Ti, bonded Ti-Al, 5Ti, 14Ti, 35Ti, 57Ti, and Al₃Ti at projectile velocities of 500–700 m/s resulted in the 14Ti and 35Ti having the best ballistic performance based on mass efficiency. Ballistics testing of 14Ti, 20Ti, and 35Ti composites at 950 m/s resulted in the 20Ti and 35Ti composites having excellent performance, corresponding to mechanical property trends. There is never debonding of the Ti/Al₃Ti interface, and failure modes in quasi-static and dynamic testing are similar, with greater damage in the dynamic testing.