A study on surface morphology and tension in laser powder bed fusion of Ti-6Al-4V

Mahyar Khorasani,Guy Littlefair,Umar Shafique Awan,Martin Leary,Elahe Hadavi,Milan Brandt,Ian Gibson,Amirhossein Ghasemi,William O’Neil

doi:10.1007/s00170-020-06221-w

Abstract

When reporting surface quality, the roughest surface is a reference for the measurements. In LPBF due to recoil pressure and scan movement, asymmetric surface is shaped, and surface roughness has different values in different measurement orientations. In this research, the influence of the laser powder bed fusion (LPBF) process parameters on surface tension and roughness of Ti-6AI-4 V parts in three orientations are investigated. To improve the mechanical properties, heat treatment was carried out and added to the designed matrix to generate a comprehensive data set. Taguchi design of experiment was employed to print 25 samples with five process parameters and post-processing. The effect and interaction of the parameters on the formation of surface profile comprising tension, morphology and roughness in various directions have been analysed. The main contribution of this paper is developing a model to approximate the melting pool temperature and surface tension based on the process parameters. Other contributions are an analysis of process parameters to determine the formation and variation of surface tension and roughness and explain the governing mechanisms through rheological phenomena. Results showed that the main driving factors in the variation of surface tension and formation of the surface profile are thermophysical properties of the feedstock, rheology and the temperature of the melting pool. Also, the results showed that while the value of surface tension is the same for each test case, morphology and the value of roughness are different when analysing the surface in perpendicular, parallel and angled directions to laser movement.

Highlights

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) method for the process of metal alloys by fusing and melting the metallic powder with a laser beam [1, 2]
Delfs et al [5] showed that the surface roughness and porosity of LPBF-fabricated parts are determined by the dimensions, stability and behaviour of the melt pool
We developed a physical model to estimate the melting pool temperature and surface tension of LPBF Ti6Al-4V by using the process parameters, including laser power, scan speed, hatch space and pattern angle

Summary

Introduction

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) method for the process of metal alloys by fusing and melting the metallic powder with a laser beam [1, 2]. Chen et al [6] showed that the surface roughness of Ti6Al-4V manufactured by LPBF is dependent on the sample’s location on the build platform and powder size distribution. Yadroitsev et al [8] reported that to reduce surface roughness, the maximum hatch space should not exceed the average width of continuous tracks. They reported that for onepass thin wall fabrication by LPBF (fixed laser power), layer thickness and scanning speed play important roles. This research showed that heat treatment in beta phase and laser power had the highest influence on the value of average surface

Methods

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Discussion

Conclusion