Understanding the effects of PBF process parameter interplay on Ti-6Al-4V surface properties

Abstract

Ti-6Al-4V is commonly used in orthopaedic implants, and fabrication techniques such as Powder Bed Fusion (PBF) are becoming increasingly popular for the net-shape production of such implants, as PBF allows for complex customisation and minimal material wastage. Present research into PBF fabricated Ti-6Al-4V focuses on new design strategies (e.g. designing pores, struts or lattices) or mechanical property optimisation through process parameter control–however, it is pertinent to examine the effects of altering PBF process parameters on properties relating to bioactivity. Herein, changes in Ti-6Al-4V microstructure, mechanical properties and surface characteristics were examined as a result of varying PBF process parameters, with a view to understanding how to tune Ti-6Al-4V bio-activity during the fabrication stage itself. The interplay between various PBF laser scan speeds and laser powers influenced Ti-6Al-4V hardness, porosity, roughness and corrosion resistance, in a manner not clearly described by the commonly used volumetric energy density (VED) design variable. Key findings indicate that the relationships between PBF process parameters and ultimate Ti-6Al-4V properties are not straightforward as expected, and that wide ranges of porosity (0.03 ± 0.01% to 32.59 ± 2.72%) and corrosion resistance can be achieved through relatively minor changes in process parameters used–indicating volumetric energy density is a poor predictor of PBF Ti-6Al-4V properties. While variations in electrochemical behaviour with respect to the process parameters used in the PBF fabrication of Ti-6Al-4V have previously been reported, this study presents data regarding important surface characteristics over a large process window, reflecting the full capabilities of current PBF machinery.

Process Parameters Optimisation for Mitigating Residual Stress in Dual-Laser Beam Powder Bed Fusion Additive Manufacturing

“…The laser beams offset distance (∆x and ∆y, Figure 2) is designed based on the laser spot diameter of 0.1 mm [11], e.g., the parallel scanning case (e) in Table 2 has a y offset of 0.2 mm, which is two times of the laser spot diameter. The applied process parameters in Table 2 are expected to produce nearly fully dense Ti-6Al-4V samples [29].…”

Uncertainties Induced by Processing Parameter Variation in Selective Laser Melting of Ti6Al4V Revealed by In-Situ X-ray Imaging

“…Each one of these parameters will influence the resulting shape and size of the depression zone, the melt pool, and the spatter behavior. Previous publications show that the processing parameters are critical factors that contribute to the resulting microstructural features and mechanical properties since they influence the thermal history and cooling rates for Ti6Al4V and other AM materials [1,2,[6][7][8][9][10][11][12][13][14]. Additional works highlight the importance of the powder layer thickness on the resulting properties of the manufactured part [15][16][17][18].…”

“…Additional works highlight the importance of the powder layer thickness on the resulting properties of the manufactured part [15][16][17][18]. These works make use of energy density to describe the effects of laser processing parameters on the dynamics of the AM process [8][9][10][11]. Other works use simulations which utilize thermal and fluid flow models to describe heat and mass transfer during the AM process [2,8,9].…”

Ti6Al4V scaffolds fabricated by laser powder bed fusion with hybrid volumetric energy density

“…They altogether affect volumetric energy density (VED) of the melt pool, represented by equation (1). Higher VED values are suitable for obtaining denser parts with superior strength owing to proper melting of the melt pool – surfaces as well as the interiors, leaving no room for porosity (Khorasani et al , 2019; Majumdar et al , 2019; Qiu et al , 2015; Tsopanos et al , 2010). Further, higher VED raises the temperature of the melt pool and its surrounding, allowing slow solidification and cooling.…”