Abstract
Fatigue life estimation of Ti-6Al-4V parts produced by additive manufacturing (AM) technologies has received increasing interest during the last decade. Recent studies focused mostly on the fatigue performance of Ti-6Al-4V considering a fixed stress ratio ( R ), usually 0.1 or −1. However, in order to properly design structural components subjected to variable loads, the effect of different stress ratios on the fatigue performance has to be carefully investigated. This research studies the stress ratio influence on the fatigue properties of Ti-6Al-4V specimens produced by laser powder bed fusion (L-PBF). Miniaturized Ti-6Al-4V samples were tested with the step procedure for different R values. A constant life Haigh's diagram ( 2 · 1 0 6 cycles) was generated for L-PBF Ti-6Al-4V in as-built, electro-polished, and machined surface condition. The results present for the first time the relations between alternating and mean stresses for L-PBF Ti-6Al-4V with a fine α + β microstructure when different surface posttreatments are used to enhance the coupons’ final surface quality.
Highlights
Among the additive manufacturing (AM) processes, the laser powder bed fusion (L-PBF) technique is currently one of the most widely used manufacturing technology for functional part production [1], no longer restricted to mainly prototyping
The results present for the first time the relations between alternating and mean stresses for L-PBF Ti-6Al-4V with a fine α + β microstructure when different surface posttreatments are used to enhance the coupons’ final surface quality
The main findings of the present study can be summarized as follows: (i) Ti-6Al-4V specimens produced by L-PBF are very sensitive to the stress ratio R, with fatigue strength becoming lower and lower with increasing R; (ii) Given the same stress ratio R, machined coupons exhibited the higher fatigue resistance, followed by electro-plasma-polished and as-produced samples; (iii) The relation between the mean and stress amplitude can be described by the Soderberg's equation for both machined and electro-plasma-polished coupons, whereas an exponential Walker's equation has to be adopted for as-produced parts; (iv) The Walker's relation has been adopted to predict the fatigue behaviour of as-built L-PBF Ti-6Al-4V coupons in the life range 104 − 106 cycles for a stress ratio R = 0:5
Summary
Among the additive manufacturing (AM) processes, the laser powder bed fusion (L-PBF) technique is currently one of the most widely used manufacturing technology for functional part production [1], no longer restricted to mainly prototyping. To meet the more and more stringent requirements of part integrity in the aerospace, automotive, and biomedical industries, detailed mechanical behaviour investigations of L-PBF Ti-6Al-4V components are required. In this respect, there has been a growing interest in the fatigue characterisation of this alloy created using AM methods in recent years [2,3,4,5,6]. The literature on conventionally manufactured Ti-6Al-4V fatigue performance reports a variety of mean stress relations [7,8,9,10,11] highlighting the need to extend this research to L-PBF Ti-6Al-4V
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