Effect of microstructure on the formability of Ti21S alloy

Cai Hu,Dominique Guines,Lionel Leotoing,Philippe Castany,Thierry Gloriant

doi:10.25518/esaform21.1630

Abstract

Titanium alloys find a wide range of uses, especially in the aeronautic industry because of a combination of favorable specifications in terms of strength-to-weight ratio, corrosion resistance and performance at high temperature. If many works are interested in mechanical properties, as well as microstructure, few of them studied the effect of microstructure on formability. The aim of this work is to study the influence of the microstructure on the formability of β metastable titanium alloys (Ti21S) which are increasingly used in aeronautical applications. For this purpose, two different heat treatments are performed on Ti21S alloy in order to propose different microstructures. Based on uniaxial tensile tests, the elastoplastic hardening behavior and the limit strain in the uniaxial tension state are obtained and allow to determine one point of the forming limit curve (FLC). From these experimental observations, it is shown that the microstructure has an important effect on the formability: precipitation of α phase reduces the formability in comparison with full β phase microstructure. Finally, a finite element M-K model is used and calibrated to predict the whole FLC for the different investigated microstructures.

Highlights

Ti21S is a metastable β titanium alloy that has wide use in the aviation industry
Several conclusions can be drawn: 1. The formability calculated for the tensile specimens along the longitudinal direction is better than for the transverse direction
The aging treatment (STA) drastically lowers the formability compared to the solution treatment state (ST)

Summary

Introduction

Ti21S is a metastable β titanium alloy that has wide use in the aviation industry. It exhibits high strength, good resistance to corrosion, and good performance at high temperature. Sheet forming process is commonly used in the manufacturing of many components in aerospace [1]. The onset of necking during forming is usually described by the Forming Limit Curve (FLC). This curve is a standard method to characterize the formability of sheet metals and is used to avoid the failure of materials while the manufacturing process [2][3]. M‐K model is presented as an analytical method to calculate the forming limit curves [6]

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