Investigation of effects of process parameters on microstructure and fracture toughness of SLM CoCrFeMnNi

Abstract

Selective Laser Melting (SLM) of multi-component alloy (MCA) such as CoCrFeMnNi is gaining significant attention due to its potential to exhibit an intriguing blend of mechanical properties, particularly strength-ductility combinations. However, limited attention has been directed toward the critical aspect of fracture toughness, which is indispensable for various engineering applications. This study delves into obtaining the fracture toughness of SLMed CoCrFeMnNi MCA, with a focus on the influence of microstructure, densification, and key printing parameters (volumetric energy density (VED), laser power, and scan speed). Experimental findings revealed that individual printing parameters rather portray better insights on the densification as opposed to the VED. Notably, slow scan speed of 800 mm/s significantly enhances densification irrespective of the VED. The alloy presents complex cellular structures with the morphology reflecting a non-linear dependence on VED. The presence of cellular dislocations analogous in scale to the cellular structures was observed with dark nanoprecipitates, recognized as Mn-rich oxides. Microhardness evaluations portrayed a non-linear relationship with varying VED, with values spanning between 230 HV and 280 HV. The fracture toughness did not exhibit a linear correlation also with VED, but better fracture toughness values were achieved at 200 W. Additionally, a notable observation of late crack initiation was observed on the load-displacement curves, indicative of the material's intrinsic ductility. The fracture toughness values ranged between 320 and 220 MPa.m−0.5. A correlation between the microstructure and densification with the fracture toughness was made. The paper also presents a comprehensive discussion on the mechanisms underpinning microstructure formation and their consequential effects on the fracture toughness of the material.