Study On Fabrication,Interface Microstructure And Properties Of Al₂O₃@Ni/HCS Composites

The failure of friction and wear is one of the three major failure modes of materials.It caused economic losses for 6%of GDP per year in the past,A conservative estimate,over 3million tons of steel were consumed each year.The friction and wear caused much economic loss and resources waste,therefore,it`s necessary to improve the wear resistance of materials.While Metal is still the main wear-resistant material in industrial production by mow.In fact Ceramic is an ideal wear-resistant material because of its high hardness and excellent wear resistance,but the ceramic is too brittle to application as a large size workpiece entirety,so it`s usually used as a reinforcement element in metal to make ceramic reinforce steel matrix composites,which has advantages of good toughness of metal and high wear resistance of ceramic simultaneously.In this study,High Chromium Alloy Steel(HCS)was been used as metal matrix,and Al₂O₃particle was been applied as a reinforcement element to fabricate Al₂O₃reinforced HCS matrix composites.To improve the poor interface bonding between Al₂O₃and HCS,Al₂O₃was coated with a layer of Ni by means of electroless plating;The finite element simulation platform ANSYS was been used to simulate the process of sintering,the mechanism of particle`s interface bonding was explored,which is of reference significance to the fabrication of Al<sub>2</sub>O<sub>3</sub>@Ni/HCS composites by SPS;The microstructure of Al<sub>2</sub>O<sub>3</sub>@Ni/HCS composites obtained was observed,and the interface behavior was investigated.Finally,the wear resistance property of Al<sub>2</sub>O<sub>3</sub>@Ni/HCS composites obtained was evaluated,the wear resistance mechanism was analyzed,and the mechanism of Ni coating on improving wear performance was analyzed.The research results are as follows:The Ni coating was successfully coated on the surface of Al<sub>2</sub>O<sub>3</sub>by electroless plating.The structure of Ni coating is about 2?3.5?m spore,they deposited in pits and holes of Al<sub>2</sub>O<sub>3</sub>`s surface first,then grew up and extended outward gradually,the cell body gathered together as a co MPact arrangement of sediments,covered on the surface of Al₂O₃completely,the thickness of Ni coating is about 100 microns.And the process showed that the deposition rate of Ni decreased with the increase of sodium citrate(C₆H₅Na₃O₇)in solution,and accelerated with the increase of solution`s p H and temperature.The Optimized solution formula is:nickel chloride(Ni Cl<sub>2</sub>)40 g/L,sodium citrate(C<sub>6</sub>H<sub>5</sub>Na<sub>3</sub>O<sub>7</sub>)48 g/L,sodium potassium tartrate(Na KC<sub>4</sub>H<sub>4</sub>O<sub>6</sub>)144 g/L,sodium hyposp Hite(Na H<sub>2</sub>PO<sub>2</sub>)60 g/L,p H 5.7 and 65 ?.From the result of temperature distribution,current density distribution and equivalent stress distribution during sintering process calculated by ANSYS,we know that:At the beginning,the current flowed through the surface of Fe particle,and the current density of particle`s joint was 9.45×10⁵A/m²,and the temperature in the joint reached to 1707?,which removed the oxide layer of Fe`s surface and cause partial melting in particle`s joint,the melting area was called sintering neck,at this time,melting was main connection mechanism,then sintering neck grow up,main connection mechanism changed to joule heat.as the sintering goes on,the pressure is applied,the particles were connected by joule heat and plastic deformation.Al₂O_3p@Ni/HCS composites were prepared at different pressure by SPS,the density is better as the pressure increased,it reached 97.48%when the pressure is 40 MPa,After that,the density remained almost unchanged when the pressure increased.The interface behavior of Al₂O_3p@Ni/HCS composites was analyzed.The interface bonding mechanism is mainly diffusion bonding,accompanied by mechanical bonding and metallurgical bonding.The experiment results showed that the Ni coating can improve the interface connection of Al₂O_3p@Ni/HCS composites,which is because:(1)The Ni coating improved the wettability of molten iron on Al₂O₃surface,and the wettability Angle of iron drops on Al₂O₃surface decreases from 140°to 76°.(2)Ni plating layer promotes the element diffusion and reaction between the Al₂O₃and iron matrix,the interface products are NiAl₂O₄,(Al_0.8Cr_0.2)₂O₃and FeNi₃.The wear resistance of Al₂O_3p@Ni/HCS composites was evaluated,the stable friction coefficient is 0.41,frictional weight loss is 3 mg,the wear resistance performance increased by 46.4%compared with Al₂O₃/Fe composite materials,which is because that the Ni coating enhanced the interface bonding force between Al₂O₃and iron matrix,made Al₂O₃hard to fall off,thus the wear resistance was improved.