A multiscale constitutive model for metal forming of dual phase titanium alloys by incorporating inherent deformation and failure mechanisms

Abstract

Ductile metals undergo a considerable amount of plastic deformation before failure. Void nucleation, growth and coalescence is the mechanism of failure in such metals. α–β titanium alloys are ductile in nature and are widely used for their unique set of properties such as specific strength, fracture toughness, corrosion resistance and resistance to fatigue failures. Voids in these alloys have been reported to nucleate on the phase boundaries between α and β phase. Based on the findings of crystal plasticity finite element method investigations of the void growth at the interface of α and β phases, a void nucleation, growth, and coalescence model has been formulated. An existing single-phase crystal plasticity theory is extended to incorporate underlying physical mechanisms of deformation and failure in dual phase titanium alloys. Effects of various factors [stress triaxiality, Lode parameter, deformation state (equivalent stress), and phase boundary inclination] on void nucleation, growth and coalescence are used to formulate a phenomenological constitutive model while their interaction with a conventional crystal plasticity theory is established. An extensive parametric assessment of the model is carried out to quantify and understand the effects of the material parameters on the overall material response. Performance of the proposed model is then assessed and verified by comparing the results of the proposed model with the RVE study results. Application of the constitutive model for utilisation in the design and optimisation of the forming process of α–β titanium alloy components is also demonstrated using experimental data.

A new framework for the assessment of model probabilities of the different crystal plasticity models for lamellar grains in α+β Titanium alloys

“…In more sophisticated modeling efforts, the finer details of the α − β colony are explicitly incorporated into the CPFE models. Prior works that utilized this approach have analyzed the effects of salient microstructural characteristics of the lamellar grains, such as β-phase volume fraction, lamellae thickness, the relative orientation of the primary slip direction in the α phase, the number of prior β grains, and the number of α colonies per grain, on the effective ductility, yield strength, strain-rate sensitivity, resistance to dwell fatigue, strain localization, formability and resilience to void growth and coalescence [19][20][21][22][23][24][25][26].…”

Regulation of Microstructure to Optimize Mechanical Properties of Ti-15Mo-3Al-2.7Nb-0.2Si via Solution-Duplex Ageing

“…In addition, researchers found that the α phase microstructure with a scale gradient obtained during heat treatment was conducive to improving the comprehensive matching of the strength and toughness of titanium alloys [19,20]. For titanium alloys, the multiscale lamella structure exhibits an improved strength-fracture toughness combination that is better than that of the single lamella structure and bimodal structure, which is mainly attributed to the more tortuous crack propagation path caused by the multiscale lamella microstructure [21].…”