Influence of HPT and Accumulative High-Pressure Torsion on the Structure and Hv of a Zirconium Alloy

Dmitry Gunderov,Veta Mukaeva,Andrey Stotskiy,Yuri Lebedev

doi:10.3390/met11040573

Abstract

The authors previously used the accumulative high-pressure torsion (ACC HPT) method for the first time on steel 316, β-Ti alloy, and bulk metallic glass vit105. On low-alloyed alloys, in particular, the zirconium alloy Zr-1%Nb, the new method was not used. This alloy has a tendency to α → ω phase transformations at using simple HPT. When using ACC HPT, the α → ω transformation can be influenced to a greater extent. This article studies the sliding effect and accumulation of shear strain in Zr-1%Nb alloy at various stages of high-pressure torsion (HPT). The degree of shear deformation at different stages of HPT was estimated. The influence of various high-pressure torsion conditions on the micro-hardness and phase composition by X-ray diffraction (XRD) of Zr-1%Nb was analyzed. It is shown that at high-pressure torsion revolutions of n = 2, anvils and the specimen significantly slip, which is a result of material strengthening. It was found that despite sliding, regular high-pressure torsion resulted in the high strengthening of Zr-1%Nb alloy (micro-hardness more than doubled), and after high-pressure torsion n = 10, up to 97% of the high-pressure ω-phase was formed in it (as in papers of other researchers). Accumulative high-pressure torsion deformation leads to the strongest transformation of the Zr-1%Nb structure and Hv and, therefore, to a higher real strain of the material due to composition by upsetting and torsion in strain cycles.

Highlights

This paper intended to determine, using a method from [19], the degree of shear strain achieved in Zr-1%Nb alloy during high-pressure torsion (HPT), to study the structure and micro-hardness of the zirconium alloy subject to accumulative high-pressure torsion (ACC HPT), and to compare ACC HPT and HPT effects in various conditions
Lower surfaces of the halves, it can be evaluated that the specimen has received the the achieved of lower strain than by torsion, halves ofbythe alloy disk degreeTo offind shear strain γ = 4, which isdegree
According to the relative shear of the upper and lower surfaces of the halves, it can be evaluated that the specimen has received the degree of shear strain γ = 4, which is 20 times lower than γ = 80 as predicted by formula (1) (γ is evaluated in point R = 1, h = 1 mm)

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. As is known [3,4], there are several SPD methods—high-pressure torsion, equal-channel angular pressing, multiaxial forging, differential velocity sideways extrusion, etc They allow increasing the mechanical properties of many metals and alloys to the required level, which is undoubtedly an alternative to the search for new materials and their subsequent approbation. A new method was proposed in [20]—accumulative high-pressure torsion (ACC HPT) deformation to achieve high strains in hard and hardened materials. This paper intended to determine, using a method from [19], the degree of shear strain achieved in Zr-1%Nb alloy during HPT, to study the structure and micro-hardness of the zirconium alloy subject to ACC HPT, and to compare ACC HPT and HPT effects in various conditions

Materials and Methods

Method

Results and Discussion

Conclusions