NiCr/AgVO3 self-lubricating composite was prepared by powder cold-pressed method with the NiCr alloy as the matrix and 10 wt.% additive of AgVO3 as solid lubricant.The AgVO3 additive powder was synthesized by the precipitation method which exhibits a melting point of 460℃.Microstructure,phase composition and thermal properties of the AgVO3 powder,as well as the composite of NiCr/AgVO3 were analyzed using scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD) and differential scanning calorimeter(DSC).The friction and wear behavior of the specimens from room temperature(R.T.) to 800℃ was evaluated using a ball-on-disk tribometer and 3D white light interference(WLI).The results showed that the friction coefficient of this material under atmosphere decreases with temperature increasing from R.T.to 800℃.However,the wear rate firstly increases from R.T.to 200℃,almost remains stable from 200℃ to 600℃,and then decreases with further increasing the temperature up to 800℃.It is also found that the prepared composite materials show a better frictional behavior than NiCr alloy over the whole range of temperatures,which is mainly attributed to solid lubrication of AgVO3 exhibiting a lamella-slip structure at temperatures below 460℃ and forms liquid-film at elevated temperatures above the melting point.
Novel Co0.3Cr0.7Ox(x=2-3)particles with spinel structure were synthesized via precipitation method through the reactions among CoSO4,Cr(NO3)3 and NaOH solutions,followed by spray-drying and sintering at 1200 ℃for 4h in the air.The particles were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The XRD results revealed that the particles are composed of Co0.3Cr0.7Ox phase without the presence of other phases.The SEM observation showed that the particles are in the shape of sphere with well flowability.Infrared radiation test indicated that the total infrared normal emissivity of the coating made of Co0.3Cr0.7Ox can be up to 0.92 at 800℃.And the normal emissivities of the prepared Co0.3Cr0.7Ox particles are always slightly larger than those of CoCr2O4 particles prepared by solid-state reaction method in the test temperature range of 50-300℃.The relatively high thermal emissivity of Co0.3Cr0.7Ox is assumed to be mainly attributed to the spinel structure.These results indicated that Co0.3Cr0.7Ox particles are a good thermal radiation material,which can be used as infrared radiation layer in thermal protection system.
Luo Lijie1,2,Huang Chuanbing1,Zhu Yongping1,Zhang Weigang1 1 State Key Laboratory of Multi-phase Complex Systems,Institute of Process Engineering,Chinese Academy of Sciences,Beijing 100190,China 2 Graduate University of Chinese Academy of Sciences,Beijing 100049,China
