Thermal fatigue crack growth behaviours of laser deposited Ti60A near α titanium alloy

Abstract

Thermal fatigue damage of high temperature titanium alloys and thermal fatigue crack growth (TFCG) behaviours are of great concern for severe temperature fluctuating environments. Cyclic thermal fatigue tests of heating to 700°C for 55 s followed by water cooling for 3 s at 20°C per cycle were performed with laser deposited Ti60A (Ti–5·54Al–3·38Sn–3·34Zr–0·37Mo–0·46Si) alloy. Thermal fatigue crack growth paths including crack length and crack growth directions were examined, as were their correlations with microstructure changes during the thermal fatigue process. Results show that local coarsened lamellar α developed by the interaction between cyclic thermal stress and oxygen atom interstitial solution effect occurs in the alloy after 800 cycles. Thermal fatigue cracks initiate after 800 cycles. Subsequently, total crack length increases with the volume fraction of local coarsened lamellar α from 800 to 2000 cycles. The enhanced oxygen penetration process plays a key role in the TFCG process.