Study On Air Spray WC-x%Co Coating For 45 Steel Prepared By Electric Contact Strengthening

The failures of roller are usually caused by three modes of peeling,fracture and crack due to its harsh working conditions.The production efficiency and quality of rolling are highly influenced by its surface quality.Therefore it is especially important to improve the surface quality and service period of roller.WC-x%Co cemented carbide could effectively improve the roller surface quality because of its high hardness,intensity and wear resistance.In this work,with the purpose of using surface modification technique to improve operating life of roller,micron WC-17%Co and WC-12%Co powder were used to be the coating raw materials.Air spray technology was used to prepare a pre-coating on the surface of the 45 steel substrate,which it could directly deposit coating on the substrate surface,so that the granulation and thermal spraying process were eliminated.Then the electrical contact strengthened was used to remelt coating and form an enhancement layer,which leads to the metallurgic combination between enhancement layer and substrate.So the bonding strength as well as the mechanical properties were improved.Then contented performance requirements and low costs of coating could be obtained.Main content and conclusions of this work are summarized and presented as follows:Firstly,air spray coating technology was used to prepare a pre-coating on the surface of the 45 steel substrate with the raw materials powder of micron WC-17%Co and WC-12%Co respectively.Then the electrical contact strengthened equipment was used to remelt the coatings by different parameters and the enhancement layers were formed on the substrate surface.Secondly,optical microscope(OM)and scanning electron microscopy(SEM)were employed to analyze the microstructure of the enhancement layers.Energy disperse spectroscopy(EDS)and X-ray diffracmeter(XRD)were employed to analyze the chemical composition and phase constitution of the enhancement layers,respectivelyLastly,the hardness of the enhancement layers was characterized by Micro-hardness tester Thermal shock resistance and mechanical properties were also measured.The experimental results of WC-17%Co and WC-12%Co enhancement layers were finally compared.The experimental results demonstrated that a certain thickness coating on the surface of 45 steel can be prepared by the method of cold spraying and electric contact strengthening technology.The microstructure of enhancement layer of WC-x%Co was compacted with high density.And the metallurgic bonding was formed between enhancement layers and matrix.The element diffusion occurred in the interface between substrate and coating.Some new phases were formed by electrical contact strengthened process.Hardness testing and thermal shock measurement results revealed that the enhancement layers possessed high hardness and excellent thermal shock resistance.Considering the integrated process conditions,WC-12%Co layer had higher hardness and equal thermal shock result than WC-17%Co layer under the methods of preparing coating using electrical contact to strengthen twice.