Effect of incremental equal channel angular pressing (I-ECAP) on the microstructural characteristics and mechanical behaviour of commercially pure titanium

Muhammad Jawad Qarni,Giribaskar Sivaswamy,Andrzej Rosochowski,Sonia Boczkal

doi:10.1016/j.matdes.2017.03.015

Abstract

Incremental equal channel angular pressing (I-ECAP) is one of the continuous severe plastic deformation (SPD) processes. This paper presents the processing of commercial purity titanium (CP-Ti) using a double billet variant of I-ECAP process. Ultrafine-grain (UFG) structure was successfully achieved after six passes of I-ECAP at 300°C. Microstructural evolution and texture development were tracked using EBSD. Analysis revealed continuous dynamic recrystallization (CDRX) as one of the grain refinement mechanism during processing. Room temperature tensile tests carried out before and after six passes, shows significant increase in strength with acceptable levels of ductility. The yield strength was increased from 308 to 558MPa and ultimate tensile strength from 549 to 685MPa. Compression tests conducted at different strain rates shows considerable increase in strength and enhanced strain rate sensitivity after processing. A distinct three-stage strain hardening was observed during compression. However the processed material displayed a loss in strain hardening ability during tensile as well as in compression tests. Detailed microhardness measurements show the evolution of hardness after subsequent passes with a reasonable level of homogeneity after the sixth pass. It is demonstrated that I-ECAP is an effective method for grain refinement in CP-Ti and subsequently improving its mechanical properties.

Highlights

Owing to its high specific strength, low density, outstanding corrosion resistance and excellent biocompatibility; titanium is the material of choice in biomedical devices [1,2]
This paper presents the processing of commercial purity titanium (CP-Ti) using a double billet variant of Incremental equal channel angular pressing (I-equal channel angular pressing (ECAP)) process
The feasibility of using the I-ECAP process for refining grain structure in CP-Ti with the objective of improving its strength characteristics has been presented in this article

Summary

Introduction

Owing to its high specific strength, low density, outstanding corrosion resistance and excellent biocompatibility; titanium is the material of choice in biomedical devices [1,2]. The addition of alloying elements such as Al and V significantly enhance the mechanical characteristics of titanium, these are considered toxic and undesirable for full bio-integration [4]. An attractive alternative is to improve the mechanical properties of CP-Ti via nano-structuring or grain refinement and the use of these harmful alloying elements can be eliminated altogether. In CP-Ti, after attaining ultrafine grain structure (UFG, grain size less than ~1 μm with high angle grain boundaries), improves its yield and tensile strength and improves the fatigue and corrosion resistance considerably [7,8]

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