Erosion Wear Characteristics And Mechanism Of Cr₃C₂-kNiCr Modified Coatings Under Multi-angle Impact

Large centrifugal compressors,widely used in petrochemical,metallurgical,and the WestEast gas transmission project,are costly,with high added value,high downtime costs,and complex.Erosion wear of the blade caused by the impact of the gas-solid two-phase flow is one of the important forms of damage.Depositing erosion wear resistant cermet coating Cr3C2-NiCr on blade surface by thermal spraying technology is of great significance to carry out surface strengthening of new products and remanufacturing of used parts such as impeller blades.However,the impact angle at each position of the complex blade surface is very different,and the Cr3C2-NiCr coating,as a typical brittle material,shows significant degradation of the erosion wear performance at the leading edge of the large blade under medium and high impact angles.It is necessary to carry out plasticization modification in combination with the excellent erosion resistance of the plastic material at high impact angle.Supported by National Natural Science Foundation of China'Design of tangential gradient coating and remanufacturing of blades for erosion wear' and the Key Research and Development Program of Shandong Province 'Tangential gradient coating design and process equipment development for remanufacturing of gas booster equipment',facing the multi-angle impact,this dissertation proposed a plasticizing modification method of Cr3C2-NiCr coating by adding ductile metal to regulate the fracture damage of brittle materials to deformation wear damage of plastic materials at high angles.The modified formulation system of the coating was established through experimental studies,the quality of the modified coating was evaluated,and the main mechanical property parameters were tested.The erosion behavior of Cr3C2-NiCr coating,substrate FV520B,and modified materials(NiCr and NiCrAl)at different impact angles was studied with 45 steel as the reference group.The Cr3C2-kNiCr modified coating formulation system with NiCr as the modified material was determined based on the principle of consistency of the scale of the erosion rate.The Cr3C2-kNiCr coatings with different DBR(Ductile Brittle Ratio)were prepared by HVOF.The microstructure of the coatings was evaluated and the results showed that the coatings had good intra-,inter-layer,and interfacial quality,with porosity below 0.46%and uniform distribution.The microhardness,elastic modulus,and fracture toughness changed stably with the change of DBR.Erosion wear law of Cr3C2-kNiCr was studied and the erosion wear mechanism was revealed.The mapping relationship of erosion rate-impact angle-DBR of the modified coating was obtained,which verified the feasibility of plasticizing modification.Combined with the analysis of erosion wear characteristics,it is clear that the essence of coating modification under multi-angle impact is to regulate the damage form and damage degree.By analyzing the generation and evolution of four types of damage,namely microcutting,deformation wear,stress fatigue fracture,and brittle fracture,the mechanism of erosion wear of Cr3C2-kNiCr coatings was revealed,and it was found that the mechanisms of resistance to erosion wear at low and high impact angles are high hardness and high toughness,respectively.The effect of mechanical properties on erosion rate was explained and the erosion rate model of modified coating was established and verified.The combined effect of coating hardness Ht,the ratio of erosion particle to coating hardness HP/Ht,coating fracture toughness Kic,and the product of coating fracture toughness and hardness KIC1.5�Ht0.5 on total erosion wear and the independent effect mechanism on normal/tangential erosion wear were analyzed,respectively,to further explain the effect of high hardness and toughness on erosion resistance at low and high impact angles,which was the effect on tangential and normal erosion resistance.Based on the deformation wear theory,four key variables in the modified coating erosion rate model,elastic limiting velocity Vel,material attribute factor K,normal wear factor ?0 and tangential wear factor ?0,were analyzed and solved.By introducing DBR,the model of modified coating erosion rate based on deformation wear theory was constructed and validated.Deformation wear theory applicable to brittle-plastic composites was developed,which can provide theoretical guidance for the on-demand regulation of modified coating formulations under multi-angle impact.A novel structure and fabrication method of modified coating for multi-angle impact were proposed.For the multi-angle impact conditions of impeller blades and other complex surfaces,a method of matching different DBR coatings under different impact angles was proposed,and then a new structure of TFGC was proposed.To address the need of this structure for bidirectional transition between the functional layer and the transition layer in the normal and tangential directions,the normal/tangential bi-directional gradient transition layer structure was proposed.Based on the constraints of channel width and interval,structure design and performance prediction method for the lap zone of TFGC was built.A method of spraying process path planning based on equal-impact angle line was established to transform variable DBR coating on complex curved surface into constant DBR coating along equal-impact angle line.The TFGC containing homogeneous zones and lap zones was fabricated on plates,and the microstructure and mechanical properties were characterized.Plasticizing modification provides a new idea for improving the erosion resistance of brittle coatings under multi-angle impact and a new method for on-demand regulation of surface modification.