Microstructural Tailoring and Enhancement in Compressive Properties of Additive Manufactured Ti-6Al-4V Alloy through Heat Treatment.

Byungmin Ahn

doi:10.3390/ma14195524

Abstract

Among laser additive manufacturing, selective laser melting (SLM) is one of the most popular methods to produce 3D printing products. The SLM process creates a product by selectively dissolving a layer of powder. However, due to the layerwise printing of metal powders, the initial microstructure is fully acicular α′-martensitic, and mechanical properties of the resultant product are often compromised. In this study, Ti-6Al-4V alloy was prepared using SLM method. The effect of heat treatment was carried out on as-built SLM Ti-6Al-4V alloy from 650–1000 °C to study respective changes in the morphology of α/α′-martensite and mechanical properties. The phase transition temperature was also analyzed through differential thermal analysis (DTA), and the microstructural studies were undertaken by optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties were assessed by microhardness and compressive tests before and after heat treatment. The results showed that heat treated samples resulted in a reduction in interior defects and pores and turned the morphology of the α′-martensite into a lamellar (α + β) structure. The strength was significantly reduced after heat treatment, but the elongation was improved due to the reduction in columnar α′-martensite phase. An optimum set of strength and elongation was found at 900 °C.

Highlights

A phase transition point was found near 730 ◦ C before the β-transus temperature and, the heat treatment was performed at five different temperatures starting from the temperature corresponding to the two-phases (α + β) region
We have studied the effect of heat treatment on the microstructure and mechanical properties of selective laser melting (SLM) Ti-6Al-4V alloys
The important conclusions drawn from this study are summarized as follows: 1

Summary

Introduction

SLM additive manufacturing technology produces parts by stacking powders layer by layer from a metal powder bed [1]. The immediate fusion of powder particles provides superior efficiency in large sized and complex manufacturing of products. SLM has been extensively applied in the manufacturing of near net shape design and high-performance products, representative aircraft parts, and medical and dental implants, etc. There is no fear of a reduction in precision due to tool wear and a large number of samples can be produced in the same batch manufacturing with the possibility of a fully automatic process. Due to the difference in shapes and sizes of human body tissues and organs of each person, 3D printing is highly utilized in the medical field and future designs of personalized implants seem to be growing very fast in medical technology [4,5]. The most widely studied and used alloy in the above field is Ti-6Al-4V alloy as, among them, it has superior strength, toughness, and corrosion resistance [6]

Methods

Results

Conclusion