Crystallography and reorientation mechanism upon deformation in the martensite of an α-α′ Ti-6Al-4V dual-phase microstructure exhibiting high work-hardening rate

The present study provides a fundamental understanding of the crystallography and the microscale behavior of the V-enriched and Al-depleted alpha' martensite taking place during the microstructure formation and the deformation of the dual phase alpha+alpha' microstructure produced in Ti-6Al-4V. This particular microstructure exhibits much larger work-hardening capabilities than the conventional wrought product. The as-quenched structure of the martensite is analyzed using the Phenomenological Theory of the Martensite Crystallography (PTMC) coupled with EBSD analyses. This approach sheds new light on the microstructure configuration obtained during the dual-phase treatment and its fine-scale mechanical behavior. The martensite preferentially forms into parallel groups of 3 self-accommodating variants separated by a misorientation of 63.26 degrees /[(10) over bar 5 5 (3) over bar](alpha'). TEM analyses additionally show that the variants of a same group are separated by a hitherto unobserved {13 (4) over bar1}(alpha') type twin plane. Postmortem analyses after tensile testing demonstrate that this twinning plane is mobile under deformation. This allows the martensitic microstructure to exhibit the remarkable property to reorient under uniaxial tension. This unique property is shown to be intimately related to the mobility of the {13 (4) over bar1}(alpha') twinning plane thereby evidencing for the first time that twin boundary motion is not uniquely associated to the orthorhombic alpha ''' martensite but can also occur in hexagonal alpha' martensite. Quantification of the Interaction Energy (IE) appears relevant to rationalize and predict the reorientation of the martensite. The critical influence of the parent beta-grains texture on the reorientation is evidenced, while the impact of this deformation mechanism on the ductility of the martensite is debated. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study investigates the crystallography and microscale behavior of V-enriched and Al-depleted alpha' martensite in the dual phase alpha+alpha' microstructure produced in Ti-6Al-4V. The martensite exhibits larger work-hardening capabilities than conventional products, possibly due to the mobility of twinning planes.