Fatigue crack growth and mechanical properties of laminated TC4/TB8 titanium alloys fabricated by diffusion bonding

Laminated TC4/TB8 titanium alloys with heterogeneous microstructures of lath and equiaxed shape are fabricated by diffusion bonding and heat treatment to enhance the fatigue crack growth (FCG) resistance with high tensile strength. It is worth noting that the forward direction of fatigue crack can be changed due to different alloy layers and bonded interfaces, which can reduce the FCG rate along the main direction. In contrast, heat treatment accompanied by active & alpha; precipitates in TB8 layer can remarkably improve the tensile strength of laminated alloys. The strain distribution of TC4 and TB8 layers upon tension is also characterized by the digital image correlation (DIC). In addition, a generalized Paris model describing steady state FCG is established based on the tensile properties of two monolithic alloys. This study can provide guidance that diffusion bonding process is available to fabricate the heterogeneous laminates with as many interfaces as possible for the improvement of FCG resistance and tensile strength.