Fracture Strength at Ambient Temperature and High Temperature Self-healing Capability of Titanium Aluminide Coatings Produced by IR Laser Fusion Reaction

Abstract

Fracture strength and dynamics of three titanium aluminide coatings (Ti₃Al, TiAl and Al+TiAl₃) at ambient temperature were examined by AE source inversion processing during cantilever bending. Mode I cracking (vertical crack) occurred prior to the Mode II cracking (exfoliation). Threshold stress to cause a first Mode I micro-cracking decreases with the increase of aluminum concentration in the aluminide. Vertical cracking through the coating was observed for Ti₃Al and TiAl coatings, whereas microcracking was found in the TiAl₃ layer for TiAl₃+Al composite coating. Very few exfoliation was observed at higher stresses. The cracks through the coating was found to be filled with alumina and titania after the subsequent exposure at high temperature, while the cracks locked in the composite coating was filled with TiN. Oxidation performance of these coatings was kept at high level by the self healing capability of cracks.