A microstructure and sonic fatigue investigation of Ti-TiB functionally graded materials

The microstructure and high-cycle sonic fatigue behavior of 3- and 25-mm-thick titanium-titanium boride (Ti-TiB) functionally graded plates were evaluated. The TiB content had a significant effect on the microstructure. A needle-like TiB phase existed at low TiB phase volume percentages (< 33.8%), while higher volume percentages resulted in TiB-phase clustering. For larger layer thicknesses, the transition or interface region between the layers was more evident. Fracture surface images of the fatigue specimens indicated that high TiB content regions exhibited brittle fracture characteristics while the Ti-rich layers exhibited ductile failure characteristics. A Ti-85%TiB alloy was also investigated and this material exhibited TiB clustering and sporadic fatigue lives as well as brittle fracture characteristics.