Ultra-High Strength and Specific Strength in Ti61Al16Cr10Nb8V5 Multi-Principal Element Alloy: Quasi-Static and Dynamic Deformation and Fracture Mechanisms

TL;DR

This paper studies a titanium-based alloy with high strength and explores how it deforms and fractures under different compression speeds.

Contribution

The study reveals unique deformation mechanisms in a Ti61Al16Cr10Nb8V5 alloy under quasi-static and dynamic conditions.

Findings

The alloy shows a strain-rate-strengthening effect with a sensitivity coefficient of ~0.0088 at low strain rates.

At higher strain rates, the alloy activates additional slip planes and increases its sensitivity to strain rate.

The alloy resists adiabatic shear localization and forms recrystallized shear bands through dynamic recrystallization.

Abstract

This study investigates the deformation and fracture mechanisms of a Ti61Al16Cr10Nb8V5 multi-principal element alloy (Ti61V5 alloy) under quasi-static and dynamic compression. The alloy comprises an equiaxed BCC matrix (~35 μm) with uniformly dispersed nano-sized B2 precipitates and a ~3.5% HCP phase along grain boundaries, exhibiting a density of 4.82 g/cm3, an ultimate tensile strength of 1260 MPa, 12.8% elongation, and a specific strength of 262 MPa·cm3/g. The Ti61V5 alloy exhibits a pronounced strain-rate-strengthening effect, with a strain rate sensitivity coefficient (m) of ~0.0088 at 0.001–10/s. Deformation activates abundant {011} and {112} slip bands in the BCC matrix, whose interactions generate jogs, dislocation dipoles, and loops, evolving into high-density forest dislocations and promoting screw-dominated mixed dislocations. The B2 phase strengthens the alloy via dislocation shearing, forming dislocation arrays, while the HCP phase enhances strength through a dislocation bypass mechanism. At higher strain rates (960–5020/s), m increases to ~0.0985. Besides {011} and {112}, the BCC matrix activates high-index slip planes {123}. Intensified slip band interactions generate dense jogs and forest dislocations, while planar dislocations combined with edge dislocation climb enable obstacle bypassing, increasing the fraction of edge-dominated mixed dislocations. The Ti61V5 alloy shows low sensitivity to adiabatic shear localization. Under forced shear, plastic-flow shear bands form first, followed by recrystallized shear bands formed through a rotational dynamic recrystallization mechanism. Microcracks initiate throughout the shear bands; during inward propagation, they may terminate upon encountering matrix microvoids or deflect and continue when linking with internal microcracks.

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