Ni - Cr / 20 Hbn High-temperature Self-lubricating Composite Material Preparation Process And The High Temperature Oxidation Behavior Research

In the research of Ni-20Cr/hBN self-lubricating composites, the main problems are that, the adding of hexagonal boron nitride(hBN) powder makes the sintering difficult, and the composites with high hBN content perform low density, poor mechanical properties, and poor tribological properties. In order to improve the properties of Ni-20Cr/hBN composites, hBN powder is plated with nickel layer by the precipitation method, and repressing/re-sintering process is used in the preparation of Ni-20Cr/hBN composites as well. The effects of new processes on the Ni-20Cr/hBN composites are studied. The mechanics of new processes are analyzed. The high temperature anti-oxidation properties are tested. The thermodynamics and kinetics of high temperate oxidation are studied. The results that are as follows:(1)The hBN powder coated with Ni could be prepared by the precipitation method with NiCl2and Na2CO3(The CO32-and Ni2+ratio is1.2:1, Concentration of NiCl2is0.05mol/L, the static time is2h.). As the Ni layer provides extra sintering driving force, and changes the contact state of the Ni-20Cr powder and hBN powder, and increases the contact responsibility of Ni-20Cr powder. The Ni-20Cr/hBN composites with hBN coated with Ni have better combined tribological properties and show good anti-friction self-lubricating performance in a wide temperature range.(2)The Ni-20Cr/hBN composites with different hBN content perform higher density, mechanical properties after repressing and re-sintering. The effect of repressing and re-sintering for2h is the most apparent when the hBN content is10%(mass fraction). The effect of repressing and re-sintering more than once can be ignored. The Ni-20Cr/hBN composites have better tribology properties after repressing and re-sintering at room temperature,400℃and600℃. The process of repressing and re-sintering can decrease the possibily of occlusal at high temperature. (3)The oxidation of Ni-20Cr/hBN composites is not obvious at600℃. The oxide scales consist of Cr2O3, NiCr2O4and CrBO3at700℃and800℃. The kinetic curves of the composites oxidized obey the parabolic rate law at the beginning of100h, and exhibits higher resistance to oxidation at700℃than at800℃. Meanwhile, the masses of Ni-20Cr/hBN composites become stable or even decrease after100h. The microstructures show that the oxide scales are complete and do well in protection at700℃, but are corroded at800℃.