Preparation And Tribological Properties Of Metal/Nanometer Alumina Composite Coatings

Friction is everywhere in social production and living life,the friction of machine parts always cause the loss of material,and the reducing of equipment life.Spraying wear-resistant coatings on metal matrix is one of the most frequently used surface engineering technology,it doesn’t change texture of material in the while can increase wear-resistance.Ceramic material is always used as wear-resistant coating because of their high hardness and stability,cheap and with high performance alumina is the most widely used.As one of thermal spraying technology,plasma spraying has high temperature and fast flame flow,is very suitable for spraying ceramic material.Nanostructured coatings demonstrate different characteristics compared with conventional micron coatings because of their unique organization structure,meanwhile,adding metal elements can improve the toughness and bonding strength of coatings too.In this paper,nanometer Al₂O₃ feed was prepared using spray drying technology,Al₂O₃、nano Al₂O₃、Ni-Al₂O₃、Ni-nano Al₂O₃、Cu-Al₂O₃and Cu-nano Al₂O₃coatings were prepared by plasma spraying equipment.Phase composition and cross-section morphologies were observed by using XRD and scanning electron microscope.Microhardness and bonding strength of coatings were tested,friction and wear tests were carried out on friction and wear testing machine,mechanical properties and tribological properties were contrasted,the results are as follows:1.Obtained nanometer Al₂O₃ feed was spherical,particle size range was between dozens micron,was basically suitable for plasma spraying.2.The phase composition of nanometer coatings and micron coatings was basically the same,Ni and Cu were uniform distributed in coatings,part of Ni and Cu was oxidized to Ni O and Cu₂O.All six kinds of coatings were lamella structure,combination modes between layers are all mechanical combination,and there were pores and other microdefects in coatings.There were partial melting zones in nanometer coatings,nanometer particles were retained.Cu-nano Al₂O₃ coating was not well deposited because of the dispersal of feed and bad mobility.3.The hardness of nano Al₂O₃ coating was higher than Al₂O₃coating,the microhardness of Ni-nano Al₂O₃coating was about the same with Ni-Al₂O₃coating,the hardness of nanometer coatings was a little higher than micron coatings’.Owing to the low hardness of metal elements,the microhardness of coatings adding metal have reduced.The bonding strength of nano Al₂O₃coating has increased 30%than Al₂O₃coating,the bonding strength of Ni-nano Al₂O₃ coating has increased 13% than Ni-Al₂O₃ coating,the bonding strength of Ni-Al₂O₃coating has increased 30%than Al₂O₃coating,the bonding strength of Ni-nano Al₂O₃coating has increased 14%than nano Al₂O₃coating,using nanometer material or adding metal elements can both increase the bonding strength of coatings.4.Excepting the friction coefficient of Cu-nano Al₂O₃coating was increased all the time,the other five kinds of coatings have experienced running in stage and stable friction and wear stage,the friction coefficient of Ni-nano Al₂O₃coating was the least,is only 0.38,the friction coefficient of Al₂O₃coating was the maximal,is about 0.48.The wear rates of all six kinds of coatings were small,the wear rate of Ni-nano Al₂O₃ coating is the least,is 2.27×10^-4mm³/m,the wear rate of Cu-nano Al₂O₃coating is the maximal.Using nanometer material or adding meatal elements can both improve the tribological property.5.The wear modes of all six kinds of coatings were mainly layer strip,there were furrows on the wear scars of Ni-nano Al₂O₃coating.The production of micro flaws was difficult in nanometer coatings and the spreading resistance of micro flaws was also bigger than micron coatings,adding metal elements can be used for lubrication in the friction and wear processing,both of the two reasons can improve the strip of coating,increased the wear resistance of coatings.