Microstructure and Soil Wear Resistance of a Grey Cast Iron Alloy Reinforced with Ni and Cr Laser Coatings

The goal of the presented investigation was to assess the impact of surface laser modification with the implementation of nickel and chromium on the microstructure and tribological behaviour of grey iron. Surface laser modification consisted of remelting the surface layer with simultaneous implementation of selected elements. In the first variant of treatment only nickel was implemented and in the second one, a combination of nickel with chromium together. This treatment was performed on an agriculture machine part made of grey iron and working in intensive friction conditions. The constituted surface layer was characterized by about 0.45 mm of depth and a 160 mm(2) area of the most exposed to wear of the treated part. In the case of both types of variants, the achieved surface layer microstructure was identified as homogenized with small grains. It involved nickel in the first variant of modification and nickel and chromium in the second one. The attained microstructure with nickel addition was characterized by nearly 800 HV0.1 of hardness (a 3.6-fold increase in comparison to its core material). The approximate hardness of 900 HV0.1 was achieved in the case of the microstructure enriched with nickel and chromium (over a 4-fold increase in comparison to the core material). The roughness of the surface after laser modification was reduced (nearly 3-fold) in comparison to the original surface of the part that was characterized by quite substantial coarseness. The wear test showed that Ni and Cr laser coatings increased resistance to abrasive wear resulting from the modification of the microstructure by the formation of martensite and grain fragmentation. Laser modified parts had a 2.5-fold smaller mass loss than untreated parts. Both types of performed variants: with the implementation of nickel and a combination of nickel and chromium gave comparable effects.