The Effect of Building Direction on Microstructure and Microhardness during Selective Laser Melting of Ti6Al4V Titanium Alloy

D Palmeri,G Buffa,G Pollara,L Fratini

doi:10.1007/s11665-021-06039-x

Abstract

During the last few years, additive manufacturing has been more and more extensively used in several industries, especially in the aerospace and medical device fields, to produce Ti6Al4V titanium alloy parts. During the Selective Laser Melting (SLM) process, the heterogeneity of finished product is strictly connected to the scan strategies and the building direction. An optimal managing of the latter parameters allows to better control and defines the final mechanical and metallurgical properties of parts. Acting on the building direction it is also possible to optimize the critical support structure. In particular, more support structures are needed for the sample at 0°, while very low support are required for the sample at 90°. To study the effects of build direction on microstructure heterogeneity evolution and mechanical performances of selective laser melted Ti6Al4V parts, two build direction samples (0°, 90°) were manufactured and analyzed using optical metallographic microscope (OM) and scanning electron microscopy (SEM). Isometric microstructure reconstruction and microhardness tests were carried out in order to analyze the specimens. The obtained results indicate that the build direction has to be considered a key geometrical parameter affecting the overall quality of the obtained products.

Highlights

Additive manufacturing (AM) technologies are increasingly widespread in the production of metal components used in various engineering sectors because the significant advantages related to the possibility to obtain complex geometries, difficult to achieve with other technologies, together with the reduction in production waste, energy costs and assembly costs (Ref 1)
Small sample sizes in the building direction cause low thermal gradients and slower cooling that promote the formation of dark bands with a high aluminum content that may lead to the formation of Ti3Al precipitates, resulting in longitudinal lack of homogeneity of the mechanical and microstructural properties of the final part
It can be stated that the orientation of the sample, directly affecting the size of the material surface deposited in each layer, for a given specimen geometry, can be considered a main factor for the formation of porosity

Summary

Introduction

Additive manufacturing (AM) technologies are increasingly widespread in the production of metal components used in various engineering sectors because the significant advantages related to the possibility to obtain complex geometries, difficult to achieve with other technologies, together with the reduction in production waste, energy costs and assembly costs (Ref 1). There are significant advantages associated with additive manufacturing technologies, it should be considered that there are a few shortcomings, related to the fact that the production phases result in strong thermal gradients and high cooling rates that give rise to thermal stresses, phase segregation phenomena and the development of metastable phases. Such phenomena cause microstructural anisotropies which in turn produce anisotropies of mechanical properties in the final piece.

Methods

Results

Conclusion