Microstructure of Ni / WC surface composite layer on gray iron substrate

Abstract

The surface infiltrated composite (Ni/WC) layers on gray iron substrate were fabricated through a vacuum infiltration casting technique (VICT) using Ni-based composite powder with different WC particles content as raw materials. The microstructures of surface infiltrated composite layer, the interface structures between surface composite layer and the substrate, the changes of macro-hardness with the increasing of WC content and the micro-hardness distribution are investigated. The infiltrated composite layer includes a surface composite layer and a transition layer, and the thickness of the transition layer decreases with the increasing content of WC. The thickness of transition layer with 20%WC content in the surface infiltrated composite layer was 170 μm which was the thickest for all transition layers with different WC content. The surface composite layer was mainly composed of WC, W₂C, FeB and NiB, along with Ni-Cr-Fe, Ni (Cr) solid solution, Ni (Si) solid solution and Ni (Fe) solid solution. The transition layer was composed of Ni (Cr) solid solution, Ni (Fe) solid solution, Ni (Si) solid solution, Fe (Ni) solid solution and eutectic. The surface macro-hardness and micro-hardness of the infiltrated layer had been evaluated. The macro-hardness of the surface composite layer decreases with the WC content increasing, and the average macro-hardness is HRC60. The distribution of micro-hardness presents gradient change. The average micro-hardness of the infiltrated layer is about HV1000.

Keywords

Ni/WC surface composite layer / vacuum infiltration casting technique / gray iron substrate

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