Laser production of B–Ni complex layers

The paper presents the results of modification with nickel and laser treatment of boronized layers produced on C45 steel. The objective of the study was to investigate the microstructure and selected properties of the new layer. The boronized layer modified with nickel was produced by the galvanic-diffusion method. Galvanic coating was produced first; next the galvanic-coated sample was diffusion boronized at 950 °C for 4 h. This resulted in a two-zone microstructure consisting of a continuous subsurface zone and underlying needle-like iron borides. In the continuous zone microhardness was in the range of 1100–1200 HV0.1 while in the second zone of the needle-like microstructure the microhardness was between 1600 HV0.1 and 1400 HV0.1. Galvanic-diffusion boronickelized layers were modified by using CO2 laser technology. As a result of the laser beam impact the presence of three zones was observed: remelted (MZ), heat affected (HAZ) and the substrate. Laser heat treatment was carried out by two methods. The first method consisted of remelting the galvanic-diffusion layer. The second method consisted of alloying galvanic coating with boron. Microhardness measurements of the surface layers were made before and after laser modification. An advantageous effect of laser modification on the microhardness of boronickelized layers was found. Microhardness profiles of boronickelized layers after laser modification were characterized by a smooth transition from the remelted zone through the heat affected zone to the substrate. In the remelted zone the microhardness was approximately 1100 HV0.1. In this study, also an X-ray phase analysis was carried out. Nickel boride phases Ni3B and Ni4B3 were detected in the nickel modified boronized layer. In addition, the nonequilibrium phase of iron boride Fe3B occurred in the laser-modified layers. Laser modification had a positive effect on the wear resistance of nickel modified boronized layers.