Electron beam powder bed fusion of Ti–6Al–4V: Augmenting mechanical properties with low porosity and fine microstructure

Abstract

Electron beam powder bed fusion (PBF-EB) is a distinct class of additive manufacturing technique, capable of fabricating high-strength material, such as Ti–6Al–4V. Precise control of the process parameters plays a fundamental role in achieving the desired characteristics and process optimization has been extensively studied. However, discrepancies persist in the optimization of PBF-EB printed Ti–6Al–4V due to variations in machine configurations, study scopes, and parameter combinations. To address this issue, we herein investigate the individual effects of key parameters-scan speed, line offset, focus offset, and preheating temperature-on surface morphology, porosity, microstructure, and mechanical properties. While focus offset had a limited impact on the microstructure, increasing scan speed or line offset, thus decreasing the energy density, led to a refined microstructure and improved microhardness. However, excessive scan speed, line offset, or focus offset led to insufficient bonding, which compromised the tensile properties. In contrast, reducing scan speed and line offset, thus increasing the energy density, ensured sufficient fusion but yielded a coarse microstructure, which diminishes hardness and tensile strength. The lowest scan speed caused surface distortion and large spherical pores. These results culminated in a process map, which expounded the intricate relationships between the parameters in PBF-EB. These findings not only facilitated the optimization process to achieve fine microstructure and low porosity but may also serve as an anchoring framework for developing new material systems.