Texture evolution during ARB (Accumulative Roll Bonding) processing of Ti–10Zr–5Nb–5Ta alloy

Abstract

Titanium alloys are extensively used in a variety of applications due to their good mechanical properties, high biocompatibility and corrosion resistance. In the last decade, α-type Ti alloys containing Zr, Nb and Ta have received much attention, because they exhibit not only high strength but also bio-corrosion resistance and high biocompatibility. A α-type Ti–10Zr–5Nb–5Ta alloy was processed by Severe Plastic Deformation (SPD) – Accumulative Roll Bonding (ARB) procedure and investigated with the aim to observe the texture development during ARB processing. Texture data for the (0 0 0 2), ($10\overline{1}0$), ($10\overline{1}1$) and ($10\overline{1}2$) Pole figures (PFs) were obtained by X-ray experiments and Inverse Pole Figures (IPFs) and Orientation Distribution Functions (ODFs) were determined. The results showed presence of $\{02\overline{2}3\}〈10\overline{1}0〉$ and $\{01\overline{1}1\}〈10\overline{1}0〉$ texture components, {0 0 0 1} basal fibre and {$01\overline{1}0$}, {$11\overline{2}0$}, {$11\overline{2}3$}, {$11\overline{2}6$} fibres.

Introduction

During the last decades titanium alloys due to their high strength, high biocompatibility and high corrosion resistance were commonly used in aerospace, biomedical and energy applications. In all these fields, a way to obtain materials with desired material characteristics is represented by the crystallographic texture developed controlling during thermo-mechanical processing [1], [2], [3]. For this reason, texture evolution, in titanium-based alloys, during thermo-mechanical processing represents an interesting research topic [4], [5], [6], [7]. At ambient temperatures the microstructure of α-type Titanium alloys, may consist of an equiaxed (hexagonal close-packed, hcp) primary-alpha phase (α-Ti), which may also contain middle-like secondary-alpha (α″-Ti) phase.

Ultra-Fine Grained (UFG) and Nano Crystalline (NC) materials showed outstanding mechanical properties, such as high strength, toughness, superelasticity, etc., compared with their coarse-grained counterparts [8], [9], [10], [11]. An effective way to produce UFG/NC materials is represented by the Severe Plastic Deformation (SPD). Various SPD production procedures have been developed, such as: Accumulative Roll-Bonding (ARB) [12], High Pressure Torsion (HPT) [13], [14], [15], Severe Torsion Straining (STS) [16], equal channel angular pressing/extrusion (ECAP/ECAE) [17], [18], [19] and repetitive corrugation and straightening (RCS) [20].

The ARB processing is a method for production of large bulk multi-layered sheets, used in different industrial applications. The ARB processing consist in rolling of two metal sheets (ARB precursor sheets) with equal dimensions using a 50% thickness reduction, in one pass, resulting one single bonded sheet which has the same thickness with the originals sheets. The ARB cycle is repeated until desired multi-layered sheets stacks are obtained. Using ARB processing is possible to achieve an extremely high plastic strain, because theoretically, the number of ARB passes can be repeated without a limit.

In previous studies it was showed that the ARB processing has succeeded in producing elongated UFG and NC structures. The formation mechanism of UFG/NC structure during ARB processing can be explained in terms of grain subdivision at submicron scale [21], [22], [23], [24] where initial coarse-grains have been subdivided by deformation-induced in high-angle grain boundaries [24].

The properties of crystalline materials depend, among others, on the parameters characterizing the polycrystalline state. Since preferred orientations of the grains are very common phenomena, crystalline texture plays an important role in terms final desired properties. During thermo-mechanical processing (plastic deformations, heat treatments, etc.) the crystalline texture suffer changes. In polycrystalline material, due to the high number of grains, many typical texture components can be present. The crystallographic texture can be analyzed by means of Pole Figures (PFs) or Inverse Pole Figures (IPFs), both being usually used in order to characterize the texture evolution in polycrystalline materials. A more precise way to analyze crystallographic texture, in terms of individual texture components, is represented by the Orientation Distribution Function (ODF) analysis.

Texture evolution during thermo-mechanical processing of α-Ti based alloys have attracted much interest over the last decades because of the use of these alloys in aerospace and automotive industry and also in medical applications [25], [26], [27], [28], [29].

The aim of the present research was to assess the Ti–10Zr–5Nb–5Ta alloy’s capacity to form UFG/NC structures through Accumulative Roll Bonding (ARB) processing and to identify the main texture components and texture fibres developed during ARB processing.