Microstructures And Properties Of Hard Phases Reinforced Wear-resistant Layers Prepared By Plasma Spray Welding

Plasma spray welding, as a new surface strengthening and repairing technology, has advantages such as energy concentration, low heat input, low dilution ration and widely applied materials. Base on the advantages, plasma spray welding has been a hot research area in the fields of surface engineering. The hard phase reinforced wear-resistant layers prepared by in-situ plasma spray welding and reactive plasma spray welding have excellent mechanical properties.In this study, hot work die steel(H13) and Ni60 B powders were selected as the substrate materials and base alloy powders, respectively. Firstly, microstructures of Ni60 B layers and solidification process of molten pool were investigated. The results showed that the Ni60 B layers consisted mainly of CrB, Cr7C3, Cr23C6,(Cr,Fe)7C3,(Cr,Fe)23C6 hard phases, and the main phase in the layers was FeNi3 and eutectic structure(γ-Ni+?1-Ni3Si). Due to the energy and composition fluctuation in the weld pool, the precipitation sequence of phase in Ni60 B layers may be different.Secondly, effects of content of NiCr-Cr3C2 powders and on microstructures and properties of layers prepared by plasma spray welding with mixed powders(Ni60B+NiCr-Cr3C2) were investigated. The results showed that microstructures of layers were refined by Cr5B3 and Cr3C2 as new hard phase appearing in the layers. When the addition of NiCr-Cr3C2 was 15%, the microhardness of the layer reached the maximum value over 1000HV0.5 and the wear resistance of the layer was 6 times as that of Ni60 B layers. Mechanical properties improvement of layers was restricted by uneven microstructures. The homogeneity of structure was worse with increasing number of layers, resulting in the performance degradation such as microhardness.Hard phase, such as TiC+TiB2, TiC+TiB2+TiCo2, TiB2+TiC+TiSi2, were in-situ synthesized in the layers prepared by in-situ plasma spray welding with mixed powders(Ni60B+Ti(Cu), Ni60B+Ti+Co60, Ni60B+Ti+Si). Microstructures of layers were refined. The growth mechanism of TiB2 was screw dislocation growth. When the addition of Ti was 6%, the microhardness of the layer reached the maximum value over 1000HV0.5 and the wear resistance of the layer was 2 times as that of Ni60 B layers. The addition of Cu decreased the porosity of layers. When the addition of Ti and Co60 were both 9%, the microhardness of the layer reached the maximum value over 900HV0.5 and the wear resistance of the layer was 4 times as that of Ni60 B layers. When the addition of Ti and Si were both 15%, the microhardness of the layer reached the maximum value over 1000HV0.5 and the wear resistance of the layer was 6 times as that of Ni60 B layers.Hard phase, such as TiN, TiB2, TiC1-xNx, TiC, were in-situ synthesized by gas-solid reaction and solid-solid reaction in the layers prepared by reactive plasma spray welding with Ni60B+Ti(+N2). The microhardness of the layer was up to 700HV0.5, and the wear resistance of the layer was 1.8 times as that of Ni60 B layers. A mount of TiN and TiC were synthesized in the layers prepared with mixed powders(Ni60B+TiN). However, the grain sizes and porosity of layers both increased with increasing addition of TiN. Mechanical properties improvement of layers was restricted by uneven microstructures.