Phase evolution of ductile iron during laser cladding processing

Abstract

Ductile cast iron is a ferrous alloy characterized by carbon-rich phase in form of spheroidal graphite, but it is difficult for ductile cast iron to be remanufactured owning to the complicated phase evolution during the remanufacturing process. Nickel based alloys were also used to repair invalid ductile cast iron components with various defects like abrasion and corrosion. In this research work, laser cladding using Ni-Cu based alloy powders as the cladding material with a single pass and multi-layer cladding has been carried out. The related phase evolution, migration of different elements near the interface zone and microhardness in partially melted zone (PMZ) and heat affected zone (HAZ) by single pass and multi-layer cladding have been investigated. Scanning electron microscopy (SEM), electron microprobe analysis (EMPA) and X-ray diffraction (XRD) were used to determine the microstructure and phase composition of the cladding layers and interfaces. Microhardness of the samples was evaluated after laser cladding. The result revealed that entirely distinct phases were formed by single pass and multi-layer cladding process. Carbon, nickel and copper element migrated apparently across the interface. It was also noted that the microhardness of the cladding layers, PMZ and HAZ was higher than that of the substrate. The hardness in the interface of the samples processed with multi-layer process decreased obviously compared with that of the single pass process, which was due to the multi thermal cycles.