Normal and dwell fatigue behavior of a near-alpha titanium alloy - IMI 834

K.U Yazar,Satyam Suwas,Anish Karmakar,Vivek Kumar Sahu ,Anup Kumar Bhattacharjee

doi:10.1051/matecconf/202032104005

Abstract

Dwell sensitivity of titanium alloys at ambient temperature (~250 C) is a well-known phenomenon, although the question about the exact micromechanical reasons responsible for this still remains open. In this work, the normal and dwell fatigue response of a near-alpha titanium alloy, IMI 834, is studied. Samples with three different microstructures, namely, fully lamellar, fully equiaxed and bimodal, are evaluated for their dwell fatigue behaviors. A reduction in fatigue life by at least an order of magnitude is seen in all the three microstructures. Large plastic strain accumulation (almost equal to the monotonic ductility) was observed during the dwell fatigue loading condition and this is held responsible for this large debit in fatigue life. The normal fatigue lives decreased in the order, bimodal > fully equiaxed > fully lamellar, while the dwell fatigue lives decreased in the order, fully equiaxed > fully lamellar > bimodal. Bimodal microstructure showed a dwell fatigue debit of 17, while fully lamellar and fully equiaxed showed a debit of 9 and 10, respectively.

Highlights

Near alpha and alpha-beta titanium alloys are extensively used in the aerospace industry due to their excellent specific strength and creep-fatigue properties
It is known that the crack initiation rather than the propagation life is affected by the dwell period [1]
Starting material The material used in the current study is a near α titanium alloy that was received as a gift from Defense Metallurgical Research Laboratory, Hyderabad, India in the form of rods of 26 mm diameter

Summary

Introduction

Near alpha and alpha-beta titanium alloys are extensively used in the aerospace industry due to their excellent specific strength and creep-fatigue properties. The stress redistribution arising at a ‘soft-hard’ grain interface and the resulting crack nucleation was studied by Hasija et al [8] and Dunne et al [9] using crystal plasticity modelling. Their predictions were consistent with the experimental observations made by Sinha et al [10] which was based on quantitative tilt fractography. The presence of microtextured zones (macrozones) are presumed to aggravate the issue and this fact has percolated throughout the dwell fatigue literature [11]

Methods

Results

Conclusion