Laser alloying of 316L steel with boron and nickel

Abstract

Purpose: The aim of the study was to improve the hardness and tribological properties of austenitic 316L steel by laser alloying with boron and nickel. Design/methodology/approach: The relatively low wear resistance of austenitic 316L steel could be improved by an adequate surface treatment. Laser alloying was developed as an alternative for time- and energy-consuming thermo-chemical treatment, e.g. diffusion boriding. In the present study, laser alloying of 316L steel with boron and nickel was carried out as the two-stage process. Firstly, the outer surface of the sample was coated with the paste, consisting of the mixture of boron and nickel powders, blended with a diluted polyvinyl alcohol solution. Second stage consisted in laser re-melting of the paste coating together with the base material. Laser treatment was carried out with the use of the TRUMPF TLF 2600 Turbo CO2 laser. The multiple laser tracks were formed on the surface. The microstructure was observed with the use of an optical microscope (OM) and scanning electron microscope (SEM) Tescan Vega 5135. The phase analysis was carried out by PANalytical EMPYREAN X-ray diffractometer using Cu Ka radiation. Hardness profile was determined along the axis of laser track. Wear resistance was studied using MBT-01 tester. Findings: The use of the adequate laser processing parameters (laser beam power, scanning rate, overlapping) caused that free of cracks and gas pores and the uniform laseralloyed layer in respect of the thickness was produced. In the microstructure, only two zones were observed: laser re-melted zone (MZ) and the substrate. There were no effects of heat treatment below MZ. Heat-affected zone (HAZ) was invisible because the austenitic steel could not be hardened by typical heat treatment (austenitizing and quenching). The produced laser-alloyed layer was characterized by improved hardness and wear resistance compared to the base material. Research limitations/implications: The application of proposed surface treatment in industry will require the appropriate corrosion resistance. In the future research, the corrosion behaviour of the produced layer should be examined and compared to the behaviour of 316L steel without surface layer. Practical implications: The proposed layer could be applied in order to improve the hardness and tribological properties of austenitic steels. Originality/value: This work is related to the new conception of surface treatment of austenitic steels, consisting in laser alloying with boron and some metallic elements.