Influence of hot isostatic pressing on mechanical response of as-built SLM titanium alloy

Abstract

Hot Isostatic Pressing (HIP) can be used to increase the fatigue limit of additively manufactured metals. However, with no further surface treatment, its contribution might be restricted by a rough surface. We thus tested Ti6Al4V alloy prepared by selective laser melting in the as-built surface condition to evaluate the utility of HIP. The influence of HIP on microstructure, static mechanical properties and fatigue was evaluated in comparison with untreated and conventionally heat treated state.

Selective Laser Melting of Ti-6Al-4V: The Impact of Post-processing on the Tensile, Fatigue and Biological Properties for Medical Implant Applications

“…HIP was effective in collapsing the internal porosity that may be caused by lack of fusion, entrapped argon in the feedstock powder during gas atomisation or from any stochastic gas entrapment during SLM. Entrapped gas pores result in near-spherical voids, within the solid matrix of the build [4], like those observed in the as-fabricated samples (Figure 3a). Application of HIP after SLM is necessary to reduce the presence of internal pores that are associated with AM, as the pores create stress concentration points and fatigue crack initiation sites [9,13,14].…”

“…This strategy relies on 3D printing of the part from digital models in a layer-by-layer fashion in an attempt to add new implant functionality with better specifications in less time and at a lower cost. Several investigations are being performed to evaluate the capacity of these techniques in comparison with the conventional routes [3][4][5]. Selective laser melting (SLM), one of the most common AM techniques, has been recently used in various studies to exploit the design flexibility of this technique in 2 of 16 manufacturing patient-particular metallic implant parts.…”

“…Recently, Cox et al demonstrated that the surface finishing of SLMed Ti-6Al-4V parts significantly alters surface topography, resulting in a direct influence on the cellular and biofilm adhesion [3]. Hot isostatic pressing (HIP), polishing, sandblasting and chemical etching are among the post-processing methods that are routinely used as standard procedures to improve the mechanical properties and surface topography of SLMed components [4][5][6]. For example, HIP, in which the materials go through pressurised heat treatment, is reported by various studies to be a necessary step for SLMed Ti implants due to its positive impact on the mechanical properties [7].…”

“…Roudnicka et al [4] demonstrated that the effect of the surface condition on the fatigue behaviour is more important than the influence of the internal defects, suggesting that the role of HIP on the fatigue performance of SLM Ti-6Al-4V alloy is secondary to the influence of surface treatment. Nonetheless, it appears that the post-processing methods such as HIP, machining and polishing are all essential steps to create AM implants with high structural integrity [10][11][12].…”

Correlation of microstructural with corrosion behaviour of Ti-6Al-4V specimens developed through selective laser melting technique

“…This needle-like structure is said to be rich in the α’-martensite phase and this diffusionless martensite transformation is due to the effect of the greater cooling rate followed by subsequent solidification during the SLM printing process. 41,42 The α’-martensite phase may exist in primary, secondary, tertiary α’ forms along with a few lamellar phase growths. 43 Regarding the β-phase, there is a distribution of bright spots throughout the microstructure.…”