Mechanical properties and corrosion resistance of cobalt-chrome alloy fabricated using additive manufacturing

Abstract

Recent progress in metal additive manufacturing methods allowed fabrication of parts with complex geometry while attaining comparable or superior to parts fabricated using conventional methods. Considering its efficient use of material, potential for light-weighing and role in closing the digital to physical gap, additive manufacturing emerged as a promising technology. In AM, the commonly used methods are selective laser melting (SLM) and Electron Beam Melting (EBM). Cobalt Chrome (CoCr) is gaining popularity as a biomaterial parts produced via AM. In this study, mechanical and corrosion properties of additively manufactured CoCr alloy are investigated and compared to those of the same alloy produced via casting. Samples produced using AM (SLM & EBM) and casting are compared in terms of mechanical properties (tensile strength, yield strength & hardness) and corrosion resistance. The microstructures were observed using SEM and corrosion resistance were tested using EIS. The mechanical properties of SLM printed parts are found to be more superior than cast produced part due to the smaller grain size of SLM printed parts. The grain size for SLM printed part is 30 µm while for cast is 4000 µm. For yield strength, the values were 840 MPa and 730 MPa for both SLM & EBM as-built samples while for cast sample was at 450 MPa. The yield strength values decreased to 622 MPa and 560 MPa for both SLM & EBM respectively post HIP-ing. For tensile strength, the values were 1070 MPa and 960 MPa for both SLM & EBM respectively while for cast samples, the value was at 655 MPa. As for hardness values (HRC), they were at 38 and 47 for both SLM & EBM respectively while for cast samples, the value was at 30. Post HIP-ing, hardness values (HRC) decreased to 36 and 34 respectively. Meanwhile, the corrosion resistance, Rct value for AM sample is at 6.21 ± 3.91 MU cm−2 while for cast sample is at 3.74 ± 1.86 MU cm−2. In conclusion, AM produced parts fare better than conventional cast part in terms of mechanical properties (tensile strength, yield strength & hardness) and corrosion resistance.