Localization of Plastic Deformation in Ti-6Al-4V Alloy

Vladimir A. Skripnyak,Vladimir V. Skripnyak

doi:10.3390/met11111745

Abstract

This article investigated the mechanical behavior of Ti-6Al-4V alloy (VT6, an analog to Ti Grade 5) in the range of strain rates from 0.1 to 103 s−1. Tensile tests with various notch geometries were performed using the Instron VHS 40/50-20 servo hydraulic testing machine. The Digital Image Correlation (DIC) analysis was employed to investigate the local strain fields in the gauge section of the specimen. The Keyence VHX-600D digital microscope was used to characterize full-scale fracture surfaces in terms of fractal dimension. At high strain rates, the analysis of the local strain fields revealed the presence of stationary localized shear bands at the initial stages of strain hardening. The magnitude of plastic strain within the localization bands was significantly higher than those averaged over the gauge section. It was found that the ultimate strain to fracture in the zone of strain localization tended to increase with the strain rate. At the same time, the Ti-6Al-4V alloy demonstrated a tendency to embrittlement at high stress triaxialities.

Highlights

The alloy Ti-6Al-4V (VT6) is widely used for the manufacture of light, reliable, and corrosion-resistant parts of mechanisms and machines, and structural elements of aerospace and transport systems [1]
It was found that the fracture of Ti-6Al-4V was initiated on boundary edges of the localized bands, while the highest magnitude of plastic strain was realized in the zone of shear band intersection
The formation of shear bands at high strain rates influences the fracture behavior of the Ti-6Al-4V alloy

Summary

Introduction

The alloy Ti-6Al-4V (VT6) is widely used for the manufacture of light, reliable, and corrosion-resistant parts of mechanisms and machines, and structural elements of aerospace and transport systems [1]. It has been found that mechanical properties and failure mechanisms of Ti-6Al-4V depend on strain rate and stress triaxiality [3,4]. The localization takes place by the formation of two-dimensional interfacial regions, which are commonly referred to as shear bands [5,6]. The formation and widening of shear bands is a complex phenomenon, which is influenced by mechanical properties of the material such as work hardening, strain rate sensitivity, and thermal softening [5,7]. These properties depend on the thermodynamic state of the material and its grain structure. The similarity of regularities between the stress triaxiality and ultimate strain to fracture under quasi-static and dynamic loading conditions is questionable

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