| Aiming at the problem of wetting mismatch between components of high temperature self-lubricating composite,based on the idea of generating lubricating phase by solid-state reaction,Fe-Al based high temperature self-lubricating composites containing SrSO4,SrSO4/Al2O3 and SrSO4 Al2O3/NiCr were prepared by vacuum hot pressing sintering.The effects of SrSO4 content,Al2O3 and Al2O3/NiCr on the phase composition,microstructure,hardness and tribological properties of the composites over a wide temperature range were investigated.The internal relations between the composition,structure,phase transformation evolution and tribological properties of the composites at different temperatures were clarified in order to reveal the lubrication mechanism.The main results were as follows:1.The new phases of SrAl2O4,FeA12O4,FeO,NiCr2O4 and Sr3Al2O6 were generated in the composite due to the weak oxygen environment derived by the decomposition of SrSO4 during the vacuum hot pressing sintering process.2.The tribological properties of Fe-Al-SrSo4 composites over a wide temperature range were improved due to the formation of SrAl2O4,FeAl2O4 and FeO during the sintering process Below 200℃,the tribolayer consisting of SrAl2O4,FeAl2O4 and FeO endowed the sintered specimens with the improved friction and wear rate.However,the appearance of Fe2O3 and Fe3O4 on the worn surface led to a distinct increase in the wear rate for the sintered composites containing 15 wt.%SrSO4.At 400℃,the interaction of SrAl2O4,FeAl2O4,Fe2O3 and Fe3O4 exhibited low friction coefficient and wear rate.When the temperature was up to 600℃,the formation of SrAl12O19 and orthorhombic-SrA1407 respectively due to the transformation of SrAl2O4 with strontium sulfate content is 15wt.%and below 10wt.%.The phase transitionon of the worn surface brought about the increase in the friction coefficient.Above 800℃,the tribofilm containing orthorhombic-SrAl407,SrAl2O4 and iron oxides(orthorhombic-SrA1407 and iron oxides)on the rubbing surface played a dominate role in the decrease in the friction coefficient and wear rate,as compared to the synergistic action of SrAl12O19,SrAl2O4 and iron oxides(Fe2O3 and Fe3O4).3.bove 600℃,the wear resistance of Fe-Al-10SrSO4 composite material was improved due to the addition of Al2O3.The addition of NiCr and Al2O3 lead to the formation of NiCr2O4 and Sr3Al2O6,the bad wear resistance of the sintered composite was owing to the existence of NiCr2O4,as compared to FA-10SA composite. |
