Preparation And Properties Of SHS Coatings On Cu Matrix And Al Matrix Synthesized By V-EPC

The traditional heat treatment methods and multi-alloying for copper and aluminum alloys are more and more difficult to meet the requirements of high temperature,high speed and high loading working condition.Traditional coating preparation methods like surfacing and laser cladding are no longer applicable for copper and aluminum alloys because of high thermal conductivity.It is urgent to develop copper and aluminum alloy products prepared by short process and with high performance and long life.This paper aims at preparing composite coating on copper and aluminum alloy with high degree of freedom,good bonding strength,and high performance in short process,combining SHS and Vacuum-Expendable Pattern Casting(V-EPC).The molten metal ignites the SHS and infiltrates into the pores of SHS products.The in-situ particle surface composite coating is synthesized with the cast-copper simultaneously.Using phase analysis,performance test and other comprehensive test methods,this paper has studied the preparation technology of SHS coating on copper and aluminum matrix.The research results are supposed to provide theoretical basis and technical support for the application of SHS coating technology in the preparation of nonferrous metal matrix.The paper has chosen Ti-C system and Ti-C-B4C system as main reaction system and prepared two kinds of coatings with TiC and TiC-TiB2 as the hard phase in coatings on copper,pure aluminum and ZL205A aluminum alloy respectively.Addition with Cu content in Ti-C system,Cu-Ti liquids has been formed between Cu and Ti particles,and quenching effect of copper matrix can be alleviated.The most uniform distribution of TiC particles,higher hardness(165HB),better bonding strength and less weight loss of coating was observed at adding 5 wt.%of Cu.Introducing CuO-Al reaction system into Ti-C system,the temperature compensation effect can be achieved because of the heat release from CuO-Al reaction.The quenching effect of copper matrix can be eliminated and the final product in coatings are TiC and α-Al2O3.The TiC particles are close to spherical with particle size distribution from 1 to 10μm.The α-Al2O3 particles with bigger size are surrounded by TiC,and the interface between TiC and α-Al2O3 is smooth.The most appropriate addition of CuO-Al system is 9.09 mol.%,in which case the coating shows higher hardness(197HB),better bonding strength and wear resistance is about 10 times more than copper matrix under different loads.PTFE(polytetrafluoroethylene)can react with Ti under 470-550℃,and the heat released can ignite the reaction of Ti-C system and Ti-C-B4C system in the condition of casting pure aluminum and ZL205A aluminum alloy.The coatings contain TiC(hard phase)+ Al(binding phase)and TiC-TiB2(hard phase)+ Al(binding phase)respectively.The TiC with fine particles has appeared aggregation to some extent.The finer TiB2 particles embedded on large TiC region.The TiC reinforced coatings on pure aluminum matrix has higher hardness(115HB),better shear bond strength(193MPa)and less weight loss during wear test with adding 5.8wt.%PTFE in Ti-C system.The TiC-TiB2 reinforced coatings on ZL205A aluminum alloy matrix shows better properties(295HB,160MPa)and good wear resistance with adding 3.8wt.%PTFE in Ti-C-B4C system.Besides,TiC-TiB2 reinforced coatings on ZL205A aluminum alloy matrix has exhibited thermostability during heat treatment.The reaction velocity is inversely proportional to the quadratic particle size of high melting point powder in raw materials.Referring to the Fourier heat transfer model,the thermal equilibrium equation of SHS coating forming process has been constructed.With combustion wave moving forward,the exothermic process is the dominant process.The heat would ensure the SHS reaction go completely and the expected product could be generated.The heat dissipation process is dominant after combustion wave going to end.The relationship between infiltration length of Al melt into TiC porous area and time has been calculated.Under the same porosity,the coarser the product TiC particles,the faster the metal infiltration rate.