Effect of Aging Treatment on the Initiation and Propagation of Fatigue Cracks in the Ti-15V-3Al-3Sn-3Cr Metastable β Titanium Alloy

Abstract

The scope of this study is the investigation of the effect of microstructure on fatigue behavior of Ti-15V-3Al-3Sn-3Cr (Ti 15–3) metastable beta titanium alloy. Aging treatment was applied to Ti 15–3 alloy at low and high aging temperatures. The fatigue crack initiation and propagation behavior of the alloy was determined by applying fatigue crack propagation tests under constant amplitude loading. Fatigue crack propagation in the solution treated sample showed a propagation due to grain boundaries, while the aging treated samples were affected by the homogeneous distribution and size of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> phases. The fatigue crack propagation rate decreased with increasing aging time due to the formation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> phases at low temperatures for long periods. At high aging temperatures, the increase in the aging time caused the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> phases to grow and the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> platelets amount to decrease. This situation created an inhomogeneous distribution of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> phases in the microstructure and adversely affected the fatigue behavior of the sample. The highest rate of fatigue crack propagation was observed in 450°C 10 hour sample, while the lowest rate of fatigue crack propagation was obtained in 300°C 10 hours sample.