Akira Nozue1, Kenji Kasuga1, Tomoo Watanabe1 and Tadatsune Okubo1
1Department of Mechanical Engineering, Faculty of Science and Technology, Sophia University, Tokyo
A transformation toughening method has been known to enhance fracture toughness for ceramics. In the present study, nearly the same type of method has been developed to increase the fracture toughness of a material. A near beta type of Ti alloy was utilized as a model of the transformation toughening. For its Ti alloy, specimens consist of fine alpha precipitates within the beta matrix, after solution-treated and aged. The present method is taken as follows: Specimens were cathodically charged at 303 K and then baked at 473~673 K in a vacuum furnace in order to form hydrides only on alpha precipitates. Fracture toughness tests were carried out with CT specimens of 10 mm thickness. At almost the same strength levels, only the fracture toughness was increased up to about 20% mainly due to the transformation of the alpha phase to hydrides. The hydrides were confirmed by a transmission electron microscope and hydrogen content measurement. Therefore, the present method made it possible to increase the fracture toughness and to retain the high strength.
titanium alloy, mechanical properties, fracture toughness, hydrogen, transformation toughening
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