# Microstructural Evolution and Mechanical Properties of LPBF Ti-6Al-4V with Different Process Parameters

## TL;DR

This study explores how different laser parameters affect the microstructure and mechanical properties of 3D-printed Ti-6Al-4V, showing that factors beyond energy density influence material behavior.

## Contribution

The paper reveals distinct roles of laser power, scanning speed, and hatch distance in microstructural evolution and mechanical response of LPBF Ti-6Al-4V.

## Key findings

- Lower scanning speeds and smaller hatch distances promote continuous <001>β epitaxial growth.
- α’ lath thickness is most influenced by scanning speed, with secondary effects from hatch distance.
- Residual stress is more sensitive to scanning speed, while bulk stress varies with hatch distance.

## Abstract

Although processing windows have been widely reported for LPBF Ti-6Al-4V, the distinct roles of laser power, scanning speed, and hatch distance remain unclear beyond VED-based comparisons. In this work, the distinct effects of laser power, scanning speed, and hatch distance on the microstructural evolution and mechanical response of laser powder bed fusion (LPBF) Ti-6Al-4V (Ti64) are investigated within a stable processing window with comparisons among different parameter combinations at a comparable VED. A total of 56 processing conditions were designed, and microstructure/texture and properties were characterized by OM/SEM, EBSD, microhardness (HV0.5), and hole-drilling residual stress measurements. Within the selected processing window, prior-β grain morphology, α’ martensite thickness, texture, microhardness, and residual stress exhibit distinct sensitivities to different processing parameters. Specifically, lower scanning speeds and smaller hatch distances promote more continuous <001>β epitaxial growth, whereas higher scanning speeds or larger hatch distances produce fragmented prior-β grains. The α’ lath thickness shows the strongest dependence on scanning speed with a secondary influence from hatch distance, while laser power mainly provides an overall thermal modulation. Furthermore, the macroscopic α (0002) texture is mainly governed by the β solidification texture, with α-variant selection playing a secondary, amplifying role. In addition, microhardness correlates with α’ martensite thickness following a Hall–Petch equation. The peak residual stress is more sensitive to scanning speed, while bulk residual stress varies more significantly with hatch distance. These findings demonstrate that process parameters, in addition to VED, can guide microstructural control and mechanical optimization in LPBF Ti64 alloy.