Influence of Inherent Surface and Internal Defects on Mechanical Properties of Additively Manufactured Ti6Al4V Alloy: Comparison between Selective Laser Melting and Electron Beam Melting.

Karel Doubrava,Matěj Daniel,Michaela Fousová,Chiu-Feng Lin,Dalibor Vojtěch

doi:10.3390/ma11040537

Abstract

Additive manufacture (AM) appears to be the most suitable technology to produce sophisticated, high quality, lightweight parts from Ti6Al4V alloy. However, the fatigue life of AM parts is of concern. In our study, we focused on a comparison of two techniques of additive manufacture—selective laser melting (SLM) and electron beam melting (EBM)—in terms of the mechanical properties during both static and dynamic loading. All of the samples were untreated to focus on the influence of surface condition inherent to SLM and EBM. The EBM samples were studied in the as-built state, while SLM was followed by heat treatment. The resulting similarity of microstructures led to comparable mechanical properties in tension, but, due to differences in surface roughness and specific internal defects, the fatigue strength of the EBM samples reached only half the value of the SLM samples. Higher surface roughness that is inherent to EBM contributed to multiple initiations of fatigue cracks, while only one crack initiated on the SLM surface. Also, facets that were formed by an intergranular cleavage fracture were observed in the EBM samples.

Highlights

Over the past 20 years, titanium and titanium alloys production has developed more rapidly than perhaps any structural material in the history of metallurgy
Our goal was to provide a complex study of Ti6Al4V that was obtained by both technologies, selective laser melting (SLM) and electron beam melting (EBM), in a similar state of the microstructure
The microstructure exerts similar lamellar morphology consisting of thin α-lamellae that are separated by a small amount of interlamellar β phase

Summary

Introduction

Over the past 20 years, titanium and titanium alloys production has developed more rapidly than perhaps any structural material in the history of metallurgy. That enabled the use of titanium materials in many safety-critical structures, such as those in aircraft, engines, or biomedical applications. Because of the high price of titanium and its costly and difficult manufacturing, there is still a focus on cost-effectiveness and reduction of product development time. There is a high demand for light-weight materials of high specific strength and high quality, and a quest for pertinent technological approaches [1,2]. Additive manufacturing (AM) seems to be the most promising technological approach to prepare sophisticated light-weight structures and cost-effectively [3].

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Conclusion