FATIGUE OF IN-SITU REINFORCED TI-8.5AL-1B-1SI

The effect of temperature on the fatigue and fracture properties of an in situ reinforced super alpha alloy Ti-8.5Al-1B-1Si (wt. %) was inve stigated. At room temperature the as-extruded composite has a strength of 631 MPa with limited ductility. On increasing the temperature to 7 00 degrees C only a marginal drop in strength to 610 MPa was observed along with a significant improvement in ductility to 5.9%. Low-cycle f atigue results indicate a marginal decrease in fatigue life as tempera ture is increased from room temperature to 700 degrees C. Fatigue crac k growth studies in the as-extruded microstructure indicate a strong i nfluence of R-ratio on both the threshold for fatigue crack growth and crack growth rates in the Paris regimes. At elevated temperatures, th e resistance to fatigue crack growth increases with temperature below approximately 500 degrees C. At 600 degrees C, however, there is an in crease in the near threshold crack growth rate due to embrittlement ef fects. At higher Delta K values (Delta K > 9 MPa root m), the resistan ce to fatigue crack growth at elevated temperatures is always better t han that at room temperature. This improvement is attributed to the in crease in the inherent resistance of the matrix to fatigue crack growt h.