Influence of the Structure and Asymmetry of Loading Cycles on the Cyclic Crack Resistance of Ti–Si Composites

We analyze fatigue-crack growth rate diagrams for various modifications of a Ti–Si cermet alloy in the initial (as-cast) state and after thermomechanical treatment plotted for beam specimens subjected to three-point bending. It is shown that, for different asymmetries of the loading cycle, the maximum stress intensity factor Kmax better describes the behavior of the growth rate of fatigue macrocracks in the high-amplitude part of the diagrams than the range of the stress intensity factor ΔK. The threshold crack resistance of the Ti–Si composite under cyclic loading is 2–5 times lower than under long-term static loading. For highly asymmetric loading cycles (R = 0.6), the maximum cyclic crack-growth resistance is exhibited by a modification with the structure of grains of pseudo-α-titanium matrix 20–40 μm in size and 15–30 wt.% of dispersed precipitations of titanium and intermetallic silicides 5–10 μm in size.