| Mould whose surface is so easily wore by the molten steel and casting powder that the service life is reduced is an important part of modern continuous casting equipment. At present, the plating is a common method of surface modification for mould, and it mainly includes Ni-Fe and Ni-Co coating. It is restricted due to the problems of low hardness, long production cycle and the environmental pollution of plating. People began to use the thermal spraying process to improve abrasion resistance along with the development of thermal spraying technology. Metal matrix composite(MMC’s)were widely used as abrasion-resistant coating structure, high hardness and high toughness. Nickel base self melting alloy has a excellent wear resistance and a good spraying performance, and is widely used to prepare abrasion-resistant coating. In addition, it is also a suitable matrix material for MMC’s. The Cr3C2has a high hardness and similar physical and chemiscal properties to metals, and is widely used as coating reinforcement materials.In this paper,10%,20%,30%content of Cr3C2p were mixed with NiCrBSi and Ni-Fe respectively, two kinds of composite coatings named NiCrBSi and Ni-Fe strengthen by Cr3C2p were prepared by plasma spraying method. Micro-chemical composition and structure were analysised by X-ray diffraction, SEM and EDAX; the hardness and porosity of coating were measured; wear test was done by ML-10abrasive wear machine to study wear resistance and the micro-hardness and wear resistance of these composite coatings were compared with Ni-Fe,Ni-Co plating layer; at last, to test the thermal fatigue of the composite coatings. The results show that:the structures of two composite coatings were all layered, NiCrBSi strengthen by Cr3C2p was consisted by y-Ni, eutectic phase Ni3B,CrB,Cr2B, hard phases Cr7C3,and Cr23C6. Ni-Fe strengthen by Cr3C2P was consisted by matrix phase γ-Ni, α-Fe and hard phases Cr7C3,Cr23C6. Coatings clearly showed a pattern of recrystallization, brittle-fractured fracture which clearly showed typical lamellar structure with some pores and cracks. Two common characteristics were showed by EDS analysis:different shapes of the dark gray chromium carbide phase was distributed in continuous matrix phase, and porosity was to be larger and the dark gray chromium carbide increased as content of Cr3C2P increasing.Hardness of the cross-section of the coatings was wavy curve, the hardness and wear resistance of their increased as the content of Cr3C2P increasing. NiCrBSi coatings strengthen by Cr3C2P have high hardness and wear resistance compared with Ni-Co, Ni-Fe plating layer, the rang of hardness is from950-1020HV, but the hardness of Ni-Fe coatings strengthen by Cr3C2P equals plating layer’s which is about400HV averagely. The wear test showed that the wear rates of30%Cr3C2p/NiCrBSi and20%Cr3C2p/Ni-Fe coatings were0.3075mg/mm and0.3667mg/mm, those were53%and42%of the Ni-Co plating layer,55%and46%of Ni-Fe. Coating thermal fatigue tests showed that the number of thermal shock NiCrBSi coating was only25times, while30%Cr3C2p/NiCrBSi’s was190times, Ni-Fe coating’s was63times,20%Cr3C2p/Ni-Fe’s was427times. |
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