Laser-deposited CoCrMo alloy: Microstructure, wear, and electrochemical properties
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Mitun Das and Vamsi K. Ballaa) Bioceramics & Coating Division, CSIR-Central Glass and Ceramic Research Institute (CGCRI), Kolkata 700032, India
Ch. Srinivasa Rao and V.V.S. Kesava Rao Department of Mechanical Engineering, Andhra University College of Engineering, Visakhapatnam 530003, India (Received 2 April 2014; accepted 16 June 2014)
CoCrMo alloy was deposited on a metallic substrate using laser engineered net shaping (LENS™) – a laser-based additive manufacturing technique. Several samples with five layers of deposit were fabricated at different combinations of laser power, powder feed rate, and scan velocity to study their influence using L4 Orthogonal array. The deposits were evaluated for their microstructure, hardness, wear resistance, and electrochemical performance. Grey relational grade analysis and analysis of variance were applied to identify optimum process parameters. The x-ray diffraction and microstructural analysis of the deposits showed uniform and fine microstructural features. Our experimental results revealed that the coatings fabricated using high laser power (350 W), low powder feed rate (5 g/min), and high scan velocity (20 mm/s) provide the highest hardness (446 6 2.87 Hv) and wear resistance (1.80 6 0.0007 mm3/Nm). However, the corrosion resistance was observed to be high for the deposits fabricated using low laser power (200 W), low powder feed rate (5 g/min), and low scan velocity (10 mm/s).
I. INTRODUCTION
CoCrMo alloys are known for their high wear resistance and corrosion resistance, and are also one of the best known alloys exhibiting high strength and biocompatibility.1–3 These alloys have been shown to exhibit unique property of self-polishing ability during articulation against CoCrMo alloy thus reducing accelerated wear.1 Significant research has been done on conventionally processed CoCrMo alloys for a variety of applications. Detailed microstructural analysis of cast and wrought CoCrMo alloys showed M23C6 and M6C type (M 5 Cr, Mo, Co) carbides primarily along the grain boundaries and interdendritic regions,2,3 which are responsible for high strength and wear resistance of these alloys. Julian et al. studied corrosion and wear performance of high carbon CoCrMo alloy in simulated body fluids.4 They found that post-fabrication heat treatment can significantly change their electrochemical and tribological properties particularly fine grains with large grain boundary area found to accelerate the corrosion.4 Further, recent tribocorrosion study on high carbon
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.163 J. Mater. Res., Vol. 29, No. 17, Sep 14, 2014
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CoCrMo alloy demonstrated strong influence of electrode potential on tribocorrosion rates.5 Reports on fabrication of CoCrMo alloy structures and coatings using laser-based additive manufacturing are very limited.6–9 Using laser engineered net shaping (LENS™), España et al.6 successfully fabri
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