Effect of Heat Treatment on the Properties of CoCrMo Alloy Manufactured by Selective Laser Melting
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Effect of Heat Treatment on the Properties of CoCrMo Alloy Manufactured by Selective Laser Melting Zhang Guoqing, Li Junxin, Zhou Xiaoyu, Li Jin, and Wang Anmin (Submitted August 3, 2017; in revised form December 12, 2017) To obtain medical implants with better mechanical properties, it is necessary to conduct studies on the heat treatment process of the selective laser melting (SLM) manufacturing parts. The differential scanning calorimetry method was used to study the heat treatment process of the phase transition of SLM CoCrMo alloy parts. The tensile properties were tested with a tensile test machine, the quantity of carbide precipitated after heat treatment was measured by energy-dispersive x-ray spectroscopy, and the tensile fracture morphology of the parts was investigated using SEM. The obtained results were: Mechanical properties in terms of elongation and tensile strength of CoCrMo alloy manufactured by SLM that had been heat-treated at 1200 °C for 2 h followed by cooling with water were not only higher than the national standard but also higher than the experimental results of the same batch of castings. The mechanism of fracture of parts manufactured by SLM without heat treatment was brittle fracture, whereas parts which had been heattreated at 1200 °C for 2 h combined with water cooling and at 1200 °C for 1 h with furnace cooling suffered ductile fracture. This study provides the basis for defining the applications for which CoCrMo alloys manufactured by SLM are suitable within the field of medical implants. Keywords
CoCrMo alloy, fracture mechanism, microstructure, selective laser melting, tensile strength
1. Introduction Additive manufacturing (AM) technology cuts three-dimensional models into pieces by using special software in order to obtain the cross-section data, and the data of the assembly components are led into rapid prototyping equipment for layerby-layer assembly. The manufacture of parts with arbitrary geometric shapes can be realized through the AM technology by adopting layer-by-layer accumulation, demonstrating its advantages in single-piece processing, small batch, complex geometric structure, and densified structure after processing (Ref 1, 2). Selective laser melting (abbreviated as SLM) is an AM technology based on laser-melted metal powder (Ref 3). Because of its special advantage, SLM is gradually approved in the field of medical implants, manufacturing mandible, femur, skull, zygomatic bone, joint, and other artificial substitute organs for different defects and occluded shapes in human bone; these parts with a complex shape are customized for superior performance (Ref 4, 5). Forgeable CoCrMo alloy has been applied in dentistry for dozens of years and was successfully used to produce artificial joint in 1950s (Ref 6). However, metal materials are required to possess good biomechanical property before applying in clinic, and researches on quality and performance of medical materials are essential in aspect of biomechanics (Ref 7, 8). Zhang Guoqing
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