| Abstract:Valve-valve seat is a pair of key components in the internal combustion engine and hardfacing alloy coating is usually employed to improve its wear-resistance. PTA hardfacing technique is widely used in industrial production due to its advantages including high powder utilization, low dilution rate, etc. In this work, two Fe-based alloy coatings with different compositions and a Co-based alloy coating for comparison were produced using PTA hardfacing, and the compositions, microstructures and mechanical properties of them were investigated. Meanwhile, the influence of annealing on the microstructures and micro-hardness of coatings were also investigated. Furthermore, in order to improve the properties of Fe-based hardfacing alloy, the hardfacing alloy with hypereutectic structure and the hardfacing alloy with Boron addition were designed and produced according to the results of thermodynamic modeling. The microstructures, micro-hardness and wear-resistance were investigated and compared with the other three hardfacing alloys produced from commercial powders. The main conclusions of this work are given as below:1) The metallographical structures of hardfacing coatings consist of fusion area, near fusion area and surface area, and all the three coatings belong to hypoeutectic structure, in which the eutectic net-like carbides with high hardness act as the skeleton of coatings while the matrix phase with good ductility supports the carbide phase, Co-based coating has better mechanical properties in comparison to the two Fe-based coatings;2) Annealing at800℃has strong influence on the microstructures and phase compositions of coatings, and the Cr7C3carbides would partially decompose and transform into Cr23C6carbide, leading to an increase in the hardness of coatings; on the contrary, annealing at500℃would have effect on the types and amounts of alloy elements which exist in the solution of matrix phase while no distinct changes happened in the hardness of coatings; 3) Boron addition could optimize the distribution of carbides in the hardfacing alloys, and the wear-resistance of hardfacing alloy could be improved and surpass that of the Co-based hardfacing alloy. |
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