Journal Article

The Martensitic Transformation and Mechanical Properties of Ti6Al4V Prepared via Selective Laser Melting

Qin, Guohua, Jiang, Wugui, Qin, Qinghua, He, Junjie, Qiu, Dachuang, Ke, Liming, Li, Duosheng, Ye, Yin

2019

Overview

This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent β phase, martensite (α’) and newly generated β phase that formed in the present experiments were elucidated. The primary X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile test were combined to discuss the relationship between α’, β phase and mechanical properties. The average width of each coarse β columnar grain is 80–160 μm, which is in agreement with the width of a laser scanning track. The result revealed a further relationship between β columnar grain and laser scanning track. Additionally, the high dislocation density, stacking faults and the typical ( 10 1 ¯ 1 ) twinning were identified in the as-built sample. The twinning was filled with many dislocation lines that exhibited apparent slip systems of climbing and cross-slip. Moreover, the α + β phase with fine dislocation lines and residual twinning were observed in the stress relieving sample. Furthermore, both as-built and stress-relieved samples had a better homogeneous density and finer grains in the center area than in the edge area, displaying good mechanical properties by Feature-Scan. The α’ phase resulted in the improvement of tensile strength and hardness and decrease of plasticity, while the newly generated β phase resulted in a decrease of strength and enhancement of plasticity. The poor plasticity was ascribed to the different print mode, remained support structures and large thermal stresses.

• Publisher: MDPI AG,MDPI
• Subject: Additive manufacturing / Advanced manufacturing technologies / Argon / Beta phase / Construction / Cross slip / Crystal structure / Dislocation density / Dislocation mobility / Fault detection / Friction welding / Hardness tests / Heat / Indentation / Investigations / Laser beam melting / Lasers / Martensite / Martensitic transformations / Mechanical properties / Microstructure / Morphology / Optical instruments / Particle size / Plastic properties / Porosity / Process parameters / Rapid prototyping / Residual stress / Scanning / Scanning electron microscopy / Solid solutions / Stacking faults / Stress relieving / Surface roughness / Tensile tests / Thermal stress / Thickness / Titanium alloys / Titanium base alloys / Transmission electron microscopy / Twinning / X-ray diffraction