Graded hierarchical microstructure and mechanical property of electron beam melted Ti–5Al–5Mo–5V–3Cr–1Zr

Abstract

Abstract The layer-wise additive manufacturing process offers a unique approach to achieve a novel graded microstructure which can fulfill the conflicting requirement of contradictory properties. The present study investigated microstructure evolution and mechanical properties of a near β alloy Ti–5Al–5Mo–5V–3Cr–1Zr fabricated by additive manufacturing using electron beam melting. In combination, the high preheating temperature in electron beam melting, the low β transus (850\xa0°C) in Ti–5Al–5Mo–5V–3Cr–1Zr, and the increasingly accumulated heat with build height resulted in an in-situ formed graded hierarchical microstructure from an α+β lamellar microstructure at the specimen bottom to an αp+αs bi-lamellar microstructure at the specimen top. Such a gradually changing microstructure was obtained by the same electron beam melting parameter set, and its formation was related to the controlled secondary α precipitation through manipulating the stability of metastable β-phase at different specimen heights. The resultant hardening effect in the bi-lamellar microstructure was attributed to the precipitation of fine secondary α.