Preparation Of β-Sialon Material With Aluminum Dross And Its Wear Characteristics

In agricultural machinery,wear failure accounts for more than 70%of mechanical parts failure,resulting in huge economic losses.In order to improve the wear resistance of key parts of agricultural machinery,the research and development of new wear-resistant materials with high performance and the application of wear-resistant coating technology on the surface of parts are two important solutions.Sialon is a typical NOx ceramic,which is considered as one of the most promising high-temperature structural ceramics due to its superior mechanical properties,thermal properties and chemical stability.At present,the synthetic Sialon technology requires high technical requirements,mostly using pure raw materials to prepare,high cost,difficult to achieve large-scale industrial production,restricting its practical application in engineering.In this study,Sialon powders were prepared from aluminum dross.The effects of raw material composition and process parameters on the phase composition and microstructure of Sialon were systematically studied.Further,the effects of discharge plasma sintering（SPS）and laser cladding technology on the formation of Sialon compact body and the structure and properties of Sialon coating were studied.The delamination phenomenon and growth mechanism ofβ-Sialon powders were discussed,which provided theoretical basis for the preparation of single-phaseβ-Sialon powders.The forming mechanism of Sialon ceramic body and coating was studied,and the influences of macroscopic morphology,cross-section morphology,phase composition and microstructure on wear properties were determined.The main conclusions are as follows:（1）Synthesis ofβ-Sialon powder by reduction reaction of aluminum dross metal.When the synthesis temperature is 1450℃,the holding time is 4h,and the Si-Al ratio is 2.5,the purity ofβ-Sialon is the highest.With the increase of Si/Al ratio,the length-diameter ratio ofβ-Sialon grains increases rapidly,and the whisker structure is formed when the Si/Al ratio is 2.5.There were two kinds of whiskers,rods and villous whiskers,which followed the mechanism of VS and VLS,respectively.The product is divided into two layers,the lower layer is fibrous,the main phase isβ-Sialon,the upper layer is layered structure and whisker interlaced,mainly composed ofβ-Sialon,Al₂O₃and spinel.The main cause of phase stratification is the separation of metal oxides from liquid silicon under the action of gravity.（2）Study onβ-Sialon densification and sintering and its friction and wear properties.The phase of the sintered body isβ-Sialon,the average density is 3.12 g/cm³,the relative density is 0.975,the microhardness is 1252 HV₁,and the compressive strength is 2869MPa.The longitudinal fracture form ofβ-Sialon ceramics is layered fracture,and the fracture mechanism is a composite mode of transgranular fracture and intergranular fracture.The grains exist in columnar form,interweave with each other to form interlocking structure,and grow directionally.The friction coefficient ofβ-Sialon ceramics is in the range of 0.45～0.65,and the wear amount is in the range of 0.0008～0.0072mm³.The wear mechanism is mainly spalling,bonding wear and abrasive wear.（3）Study on the Tribological and Wear Properties of Ni-basedβ-Si Alon Composite Coating Prepared by Laser Cladding.The ratio ofβ-Si Alon ceramic powder was determined as 10%β-Si Alon+90%Ni62 alloy powder.The technological parameters are as follows:laser power is 3 k W,square laser spot is used,spot width is 5 mm,cladding speed is 6～10 mm/s,and lap rate is 30%.The coating is mainly divided into substrate,bonding zone and cladding layer.Due to the fact that the cladding material cannot shrink freely and evaporate at high temperature,there are obvious cracks and pores in the coating and pits on the surface.β-Si Alon heterogeneous particles change the grain growth morphology from planar grain to equiaxed grain,and the surface morphology is continuous network structure and snowflake shape.Cr-Fe-Ni,Al-B-Ni,Al-Fe-Si and Al-Ni strengthening phases are formed to strengthen the coating.The microhardness of the cladding layer is significantly increased,which is about 4 times that of the base metal,the average friction coefficient is reduced by about 1/4,and the wear amount is reduced by more than 50%.The wear mechanism is mainly abrasive wear and adhesive wear,and the cladding layer has good wear resistance.The research results will provide theoretical and experimental basis for the low cost and high efficiency application of Sialon in agricultural machinery.