Effect of subsequent Hot Isostatic Pressing on mechanical properties of ASTM F75 alloy produced by Selective Laser Melting

Abstract

The Co-based alloy ASTM (Co -28.5 wt.-% Cr -6.3 wt.-% Mo) is widely used for medical implants, e.g. knee prostheses, and is commonly processed by investment casting. Selective laser (SLM) melting is supposed to be an efficient alternative for the production of individually designed knee implants regarding production time and production costs. The mechanical properties, in particular the fatigue strength, of the material have been studied in different states of the material. The mechanical properties of investment casted ASTM F75 and PM-SLM produced ASTM F75 were investigated. The focus in this study was on the PM-SLM material, the specimens were initially produced by selective laser melting and a part of the specimens were further processed by hot isostatic pressing (HIP). The PM-SLM material was mechanically tested in the as-SLM state as well as in the SLM þ HIP state. It was found that the mechanical properties of the as-SLM material did not reach the level of the fatigue strength of as cast material. The post-densification treatment by HIP offers distinct improvements regarding the fatigue strength compared to the as-SLM material.

Microstructures, properties, and applications of laser sintered 17‐4PH stainless steel

“…This significant increase in the ultimate tensile strength of the water‐atomized L‐PBF parts after the HIP treatment could be attributed to the increase in density of L‐PBF parts (3%‐6%; Figure ). This relation between the ultimate tensile strength and the porosity of the L‐PBF parts after the HIP treatment was observed in previous studies …”

“…Metallographic specimen preparation was carried out following standard procedures for microstructure characterization. The carpenter's etchant was used as an etchant to reveal the austenite and martensitic phases typically found 17‐4PH stainless steel parts . The tensile testing of the L‐PBF parts and microstructural characterization of the polished and etched L‐PBF parts were performed in the horizontal plane perpendicular to the build direction.=…”

“…This relation between the ultimate tensile strength and the porosity of the L-PBF parts after the HIP treatment was observed in previous studies. 21,23,24,[26][27][28]35,36 The gas-atomized L-PBF parts after the HIP treatment showed significantly higher tensile strength (~1100 MPa) when compared to the tensile strength water-atomized L-PBF parts before and after the HIP treatment as shown in Figure 7. However, at the high-energy density of 104 J/ mm 3 , the ultimate tensile strength of water-atomized L-PBF parts (~950 MPa) after the HIP treatment was higher than the tensile strength as-printed gas-atomized L-PBF parts (~950 MPa) but lower than the as-printed water-atomized L-PBF parts.…”

“…Tillmann et al discussed the efficiency of the HIP in decreasing the porosity and enhancing the mechanical properties of IN718 L‐PBF parts. Many research groups performed HIP studies on various materials such as HastealloyX, 316L stainless steel, CoCr, and Ti–6Al–4V alloys . However, there has been limited work performed on the elimination of the defects in 17‐4 PH stainless steel L‐PBF parts using HIP process …”

Characteristics of Biometallic Alloy to Additive Manufacturing Using Selective Laser Melting Technology

“…For D2 powder particle because of its smaller specific surface area, it obtained the highest result of beat density (equal to 5.26 g/cm 3 ). According to Haan et al [19], powder flow time and apparent density of the alloy Co-Cr-Mo study showed relevant results to those obtained respectively for powders with D90 diameter equal to 39 µm, the flow time was 18.60 s/cm 3 and bulk density was 4.38 g/cm 3 .…”