The effect of surface oxidation behavior on the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy

In this study, the effect of surface oxidation behavior on the fracture toughness of Ti-5Al-5Mo-5V-1Cr -1Fe alloy suffered oxidation treatments at the temperatures of 500 degrees C, 600 degrees C, 700 degrees C and 800 degrees C is studied by means of OM, SEM and EDS analysis. For comparison, the fracture toughness of this alloy suffered vacuum annealing treatments at the temperatures of 550 degrees C, 600 degrees C, 650 degrees C and 700 degrees C are also investigated. The results show that at the heating temperatures below 600 degrees C, the fracture toughness values of Ti-5Al-5Mo-5V-1Cr-1Fe alloy suffered vacuum annealing treatments and oxidation treatments show no obvious difference. However, at the heating temperature of 700 degrees C, the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe alloy undergone oxidation treatment is almost 50 MPa m(1/2) lower than that undergone vacuum annealing treatment. This is due to that at the oxidation temperature of 700 degrees C, the oxide layer thickness is above 5 mm. In this situation, its influence on the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe alloy cannot be ignored. The existence of oxide layer can decrease the total area of shear lips on the fracture surface, decrease the crack propagation tortuosity and limit the formation of secondary cracks on the side surface of K-IC specimen. This can result in a big decrease of fracture resistance, which is detrimental to the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe alloy. (C) 2015 Elsevier B.V. All rights reserved.