Hao Lan

Wear Behavior of a NiCr/AgVO3 Self-Lubricating Composite

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 °C. 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 °C 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 °C. However, the wear rate firstly increases from R.T. to 200 °C, almost remains stable from 200 °C to 600 °C, and then decreases with further increasing the temperature up to 800 °C. 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 °C and forms liquid-film at elevated temperatures above the melting point.

Investigation of Pt-Dy co-doping effects on isothermal oxidation behavior of (Co,Ni)-based alloy

A Co32Ni21Cr8Al0.6Y (wt.%) alloy with and without doping 3 wt.% platinum, or co-doping 3 wt.% platinum and 0.1 wt.% dysprosium was produced by arc melting. The hardness of both base alloy and composition-modified alloy was measured by using a Vickers hardness tester. Isothermal oxidation tests at 1000 degrees C in static air atmosphere were conducted to assess the isothermal oxidation behavior of the alloys. The microstructure and composition of the tested alloys before and after oxidation were investigated by means of X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS) and back scatter detector. Results showed that platinum had significant influence on microstructure of the tested alloy by the formation of beta-(Ni,Pt)Al phase. Addition of 3 wt.% platinum could slightly increase the hardness of the tested alloy. Platinum accelerated phase transformation of alumina from metastable theta-Al2O3 to stable alpha-Al2O3 and suppressed the consumption of beta-phase. Co-doping both 3 wt.% platinum and 0.1 wt.% dysprosium induced the fastest transformation of theta- to alpha-alumina and the formation of a fine-grained oxide scales. The most effective reduction of oxidation rate was achieved by the Pt-Dy co-doping effects.