Effect of Hot Isostatic Pressing on Microstructures and Mechanical Properties of Ti6Al4V Fabricated by Electron Beam Melting

Changyong Liu,Pei Wang,Mingguang Jiang,Deng Yan,Zhuokeng Mai,Zhangwei Chen,Yuhong Dai,Changshi Lao

doi:10.3390/met10050593

Abstract

This study investigated the effects of hot isostatic pressing (HIP) on the microstructures and mechanical properties of Ti6Al4V fabricated by electron beam melting (EBM). The differences of surface morphologies, internal defects, relative density, microstructures, textures, mechanical properties and tensile fracture between the as-built and HIPed samples were observed using various characterization methods including optical metallography microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) and tensile tests. It was found that the main effects of HIP on microstructures include—the increase of average grain size from 7.96 ± 1.21 μm to 11.34 ± 1.89 μm, the increase of α lamellar thickness from 0.71 ± 0.15 μm to 2.49 ± 1.29 μm and the increase of β phase ratio from 4.7% to 10.5% in terms of area fraction on the transversal section. The combinatorial effects including densification, increase of grain size, α lamellar thickness, β phase ratio, reduction of dislocation density and transformation of dislocation patterns contributed to the improvement of elongation and ductility of EBM-fabricated Ti6Al4V. Meanwhile, these effects also resulted in a slight reduction of the yield strength and UTS mainly due to the coarsening effect of HIP.

Highlights

Ti6Al4V is an important titanium alloy that has been widely used in aerospace engineering and biomedical engineering due to its high specific strength and excellent biocompatibility [1,2,3]
The surface roughness of as-built and HIPed samples was Ra 16.56 μm and Ra 18.32 μm respectively. These values indicated that electron beam melting (EBM)-fabricated Ti6Al4V parts typically had a relatively coarser surface and hot isostatic pressing (HIP) had little effects on the surface roughness
Greatly reduced the internal defects especially pores and voids and thereby increased the relative density from (98.98 ± 0.03)% to (99.73 ± 0.04)%; (3) HIP did not alter the fundamental features of microstructures

Summary

Introduction

Ti6Al4V is an important titanium alloy that has been widely used in aerospace engineering and biomedical engineering due to its high specific strength and excellent biocompatibility [1,2,3]. It has been a great challenge to process Ti6Al4V parts with complex geometries using conventional processing technologies such as machining and forging processes due to its limited machinability and deformation capacity [4]. With the development of various metal additive manufacturing technologies such as selective laser melting (SLM) and electron beam melting (EBM), complex Ti6Al4V parts can be fabricated in a convenient way [5]. Additive manufacturing of Ti6Al4V by EBM has been extensively investigated by many research groups [5]. As for the microstructures of EBM-fabricated Ti6Al4V, it was found that transformed Widmanstätten-like α + β microstructures with acicular α-plate was formed within the epitaxillay grown columnar β grain [5,7,8,9].

Methods

Results

Conclusion