Effect of Heat Treatments on Fatigue Properties of Ti–6Al–4V and 316L Produced by Laser Powder Bed Fusion in As-Built Surface Condition

Abstract

Over the last decade, additive manufacturing (AM) techniques have been expanding rapidly due to their ability to produce complex geometries with an efficient use of material. In order to design reliable AM parts, the mechanical properties resulting from the manufacturing process need to be understood. The present study investigates the fatigue of AM Ti-6Al-4V and 316L. Miniaturized Ti-6Al-4V and 316L specimens were manufactured using laser powder bed fusion (L-PBF). The geometry, process parameters, and loading conditions were kept constant and the specimens were tested in as-built surface condition. The S-N curves of as-built, stressrelieved and HIP'ed specimens were measured, and an analysis of the microstructure, relative density and surface roughness was performed. The effect of fatigue influencing factors (residual stresses, surface roughness, porosity and microstructure) was systematically investigated. In order to understand the fatigue failure mechanism, identification of crack initiation point, via fracture surfaces analysis, was performed.

On the advances to obtain excellent and repeatable mechanical properties and build quality of LaserForm® Ti gr23 (A) across whole build platform

“…It could be noticed from the graph that the fatigue limit is at around 657 MPa (5x10 -6 cycles). This results is very much comparable or even better than cast Ti-6Al-4V results reported in Li et al [2] and one of the best that could be seen from literature for L-PBF processed Ti-6Al-4V [2,3].…”

“…Therefore the combination of robust, repeatable part quality and tailored heat treatment provide good fatigue properties. Cutolo et al [3] reports this finding and even concludes that the SR treatment helps in achieving a better fatigue properties than HIP. The other important parameter for fatigue properties is surface roughness.…”

“…Although the AM technology has matured well in the last decades with significant progresses made on the L-PBF process optimization, literature still shows a significant scatter of ductility as well as fatigue performance of L-PBF Ti-6Al-4V [1,2]. This scatter has been mostly attributed to the presence of material defects such as pores and surface roughness, residual stresses and the presence of harmful brittle phases or undesired microstructural morphologies [1][2][3]. The review article by Li et al [2] reported ductility values ranging from 4% to 13% and fatigue limits (R=0.1, 10 6 cycles) ranging from 400 MPa to 600 MPa for L-PBF Ti-6Al-4V samples which underwent heat treatment and concomitant surface treatment [2].…”

Post‐treatment selection for tailored fatigue performance of 18Ni300 maraging steel manufactured by laser powder bed fusion

“…This geometry was used in other published and internal studies, and no significant deviations were found in the fatigue behaviour compared with standard-sized samples. [28][29][30][31] Highly stressed volume approach as mentioned by Van Hooreweder et al 32 was utilised in designing the sample geometry. This design ensures that maximum stress is concentrated at the gauge section while maintaining fatigue notch factor K f of unity.…”

Effect of Solution Treatment and Cooling Rate on the Microstructure and Hardness of Ti-6Al-4V Alloy Manufactured by Selective Laser Melting Before and After Hot Isostatic Pressing Treatment

“…Many studies on the mechanical properties like hardness, tensile, and fatigue of SLM samples before and after solution heat treatment have been carried out by different authors (Ref 12,20,21). In addition, hot isostatic pressing (HIP) treatment also was applied on as-built SLM samples in numerous studies to improve the fatigue property of the SLM part and reduce porosity (Ref 22,23). However, combination of HIP with different post-heat treatments on the microstructure and mechanical properties of SLM specimens, aimed at improving structural integrity, microstructural and mechanical capability for different applications, has not been thoroughly investigated.…”