Design rules to develop solute lean α+β titanium alloys exhibiting high work-hardening by reorientation induced plasticity

Abstract

While work-hardening is typically considered in Ti as a prerogative of the β-metastable alloys, this paper introduces a novel perspective, presenting a set of alloy design rules to develop solute lean α + β titanium alloys exhibiting increased work-hardening capabilities. More specifically, reaching this goal is made possible through the development of α + α′ microstructures exhibiting Reorientation Induced Plasticity (RIP) within the α′ martensitic phase. The microstructural requirements for activating RIP and maximizing mechanical properties (i.e., combining high work-hardening, yield strength and ductility levels) are derived from an analysis of the microstructures/mechanical property relationships of various α + α′ samples. A set of design rules is provided. Emphasis is laid on the pivotal role of the chemistry of the α′ martensitic phase in RIP activation and a Molybdenum equivalent chemical criterion is proposed. The α phase is here suggested as a mean to reduce the prior β grain size and the resulting size of the martensite plates. This approach reveals that the versatile thermal treatments leading to α+α’ structures broaden the mechanical property landscape, achieving large work-hardening capabilities (typically over 500 MPa) that can be combined with high yield strength (over 800 MPa).