CC BY
38HiLASE-O-5
Effect of laser shock peening on the microstructure, residual stress, hardness, and fatigue behavior of additive manufactured CoCrMo alloy
M. Kattoura1, B.T. Donkor1, J. Song1, J. Kaufman2, S.R. Mannava1, V.K. Vasudevan1 University of Cincinnati, Mechanical and Materials Engineering, Cincinnati, USA 2HiLASE, Centre, Institute of Physics of the Czech Academy of Sciences, Dolni Brezany, Czech Republic
Laser Shock Peening (LSP) is a process where high energy nanosecond laser pulses are used to modify surface characteristics of treated materials. In this work, the effects of LSP on the microstructure, residual stress, hardness and fatigue behaviour of Additive Manufactured (AM) CoCrMo Alloy was investigated. The CoCrMo alloys is commonly utilized in biomedical industry due to its high wear-resistance and biocompatibility. It is used in manufacturing of medical tools, various artificial joints including dental partial bridge work, hips and knee implants. Three processing parameters were studied to optimize the laser peening process: 1) sacrificial layer: black vinyl tape versus aluminum tape, 2) shift between two peening layers, and 3) laser wavelength: infrared laser (1064 nm) versus its second harmonic (532 nm). In all studied laser peening conditions, laser peening induced a Strain-Induced Martensitic Transformation (SIMT) shifting the initially FCC structure to HCP+FCC structure at the surface. The initially high tensile residual stresses created by the AM process were converted to high compressive stresses that protect the material against different type of metal failures. The laser peened samples showed increase in the yield strength by around 15%, the surface hardness was increased roughly by 15% and the fatigue life was improved 10x to 15x when compared to the unpeened samples.
