Effect of laser energy density on microstructure, wear resistance, and fracture toughness of laser cladded Mo2FeB2 coating

Abstract

To expand the applications of Mo2FeB2 ternary borides in industry, laser cladding technology was utilized to prepare Mo2FeB2 coating to improve the properties of the AISI 1045 medium steel substrate. The influence of cladding laser energy density (75–175 J⋅mm−2) on the obtained coating properties was studied, such as geometric characteristics, microstructure, microhardness, wear resistance, and fracture toughness. It can be found from the results that width and dilution rate increased with the increase of laser energy density when the coating had the same scanning speed or laser power, while the wetting angle had an opposite result. The ability of Marangoni convection was increased with the increase of laser energy density, and the hard phase particles became coarse and formed needle-like structures and herringbone structures. An excellent bonding zone was formed between the coating and the substrate. The direction of crystal structures in the bonding zone grew along the direction of heat dissipation. Based on the results of the mechanical properties of the coating, it can be concluded that the coating fabricated with 90 J⋅mm−2 laser energy density had the highest microhardness (1283.7 HV0.5) and excellent wear resistance (0.34 coefficient of friction, 2.9 mg wear mass loss). The wear forms were typical abrasive and adhesive wear, where a smooth worn surface was formed, and only pits or shallow grooves existed. The coating obtained with the highest laser energy density (175 J⋅mm−2) had a high fracture toughness value (16.73 MPa⋅m1/2). Besides, the coatings had typical transgranular fractures with different laser energy densities. Hence, a coating with perfect properties can be fabricated by adjusting laser cladding parameters.