Variable amplitude loading of additively manufactured Ti6Al4V subjected to surface post processes

M Kahlin,H Ansell,A Kerwin,B Smith,J Moverare

doi:10.1016/j.ijfatigue.2020.105945

Abstract

The fatigue life of additively manufactured metals need to be improved before they can be introduced to flight critical aerospace structural applications. In this study, laser powder bed fusion (L-PBF) and electron beam powder bed fusion (E-PBF) Ti6Al4V material were therefore subjected to four different surface post processes. Furthermore, variable amplitude fatigue testing were performed and compared to fatigue life predictions based on constant amplitude fatigue tests using a cumulative damage approach. The predictions were in good accordance with the experimental results and post processed L-PBF and E-PBF material showed an increase in fatigue life with >5 times.

Highlights

Additive manufacturing (AM), referred to as 3D-printing, in metal has gained a lot of interest within the aerospace industry in the recent years
Manufactured materials with rough asbuilt surfaces were subjected to either centrifugal finishing, linishing, shot peening or laser shock peening. It was investigated how well the fatigue life for vari able amplitude loading could be predicted with the use of constant amplitude test results and cumulative damage calculations
A considerably longer fatigue life could be achieved by surface post processing for both electron beam powder bed fusion (E-PBF) (x 5.4 fatigue life by linishing) and laser powder bed fusion (L-PBF) (> x 7.1 fatigue life by centrifugal finishing) material compared to as-built conditions

Summary

Introduction

Additive manufacturing (AM), referred to as 3D-printing, in metal has gained a lot of interest within the aerospace industry in the recent years. There are different AM processes which all have in common that they manufacture parts by adding material layer-by-layer in con trast to a subtractive manufacturing process in which material is re moved. Metals manufactured with AM do not always exhibit the same material properties as conventionally manufactured metals This is true for fatigue properties which are influenced both by different microstructure, due to repeated heating and quick cooling, and internal defects [2,3]. Previous studies of additively manufactured Ti6Al4V, using either L-PBF or E-PBF, have shown that fatigue properties similar to wrought Ti6Al4V can be achieved if the rough as-built surface is re moved by machining and the internal defects are closed by hot isostatic pressing (HIP) [4,6,7]. The effect of many of these surface pro cesses, on additively manufactured Ti6Al4V, have been investigated in several previous studies, both with the focus on surface roughness im provement [8,9,10] and with the focus on fatigue improvements [11,12,13] even though fewer studies have had the latter focus

Results

Discussion

Conclusion