Self-lubricating composites(SLCs)are widely used in the fields of aerospace and marine,but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures.I...Self-lubricating composites(SLCs)are widely used in the fields of aerospace and marine,but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures.In view of its high affinity with oxygen and also the high oxidation rate,appropriate amount of nano Ti was added to NiCr-WS_(2)composites prepared by spark plasma sintering(SPS)to adjust the oxidation behavior and surface texture.When exposed to high temperature,Ti was preferentially oxidized in comparison to Ni and Cr,resulting in abundant TiO_(2)protrusions and microdimples on the surface,i.e.in situ surface texturing.Besides,TiO_(2)was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO_(3)and CrTi_(2)O_(5).The high chemical activity of oxide debris that was conducive to sintering,combining with the special surface texture that stores as many wear debris as possible,promoted the rapid formation of a protective glaze layer on the sliding surface.The NiCr-WS_(2)-Ti composite exhibited low friction coefficient but high wear resistance at elevated temperatures.Especially at 800℃,it presented a wear rate of as low as(2.1±0.3)×10^(-5)mm^3N-1m^(-1),accounting for only 2.7%of that of NiCr-WS_(2)composite.展开更多
The aim of this study was to compare the effects of different porcelain polishing techniques on the color change and surface roughness of feldspathic porcelains and lithium disilicate glass-ceramic system. 80 porcelai...The aim of this study was to compare the effects of different porcelain polishing techniques on the color change and surface roughness of feldspathic porcelains and lithium disilicate glass-ceramic system. 80 porcelain specimens were divided into two subgroups, each subgroup was divided into 4 groups of 10 specimens. Surfaces were polished with different ceramic polishers. VITA Easyshade spectrophotometer was used to measure color differences. Surface roughness was evaluated using a profilometer. The color change and surface roughness of porcelains were statistically analyzed by Two-way ANOVA followed by a Tukey HSD test (α = 05). There were relationships between the porcelain systems and polishing techniques (p 0.05). For △E values, there was relationship between the porcelain systems and polishing techniques (p 0.05). Chairside porcelain polishing systems were not able to provide a porcelain surface as smooth as the glazed surface for the IPS empress and Ceramco 3 porcelains.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51871051)。
文摘Self-lubricating composites(SLCs)are widely used in the fields of aerospace and marine,but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures.In view of its high affinity with oxygen and also the high oxidation rate,appropriate amount of nano Ti was added to NiCr-WS_(2)composites prepared by spark plasma sintering(SPS)to adjust the oxidation behavior and surface texture.When exposed to high temperature,Ti was preferentially oxidized in comparison to Ni and Cr,resulting in abundant TiO_(2)protrusions and microdimples on the surface,i.e.in situ surface texturing.Besides,TiO_(2)was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO_(3)and CrTi_(2)O_(5).The high chemical activity of oxide debris that was conducive to sintering,combining with the special surface texture that stores as many wear debris as possible,promoted the rapid formation of a protective glaze layer on the sliding surface.The NiCr-WS_(2)-Ti composite exhibited low friction coefficient but high wear resistance at elevated temperatures.Especially at 800℃,it presented a wear rate of as low as(2.1±0.3)×10^(-5)mm^3N-1m^(-1),accounting for only 2.7%of that of NiCr-WS_(2)composite.
基金This study was supported by the Mustafa Kemal Univer-sity Scientific Research Section
文摘The aim of this study was to compare the effects of different porcelain polishing techniques on the color change and surface roughness of feldspathic porcelains and lithium disilicate glass-ceramic system. 80 porcelain specimens were divided into two subgroups, each subgroup was divided into 4 groups of 10 specimens. Surfaces were polished with different ceramic polishers. VITA Easyshade spectrophotometer was used to measure color differences. Surface roughness was evaluated using a profilometer. The color change and surface roughness of porcelains were statistically analyzed by Two-way ANOVA followed by a Tukey HSD test (α = 05). There were relationships between the porcelain systems and polishing techniques (p 0.05). For △E values, there was relationship between the porcelain systems and polishing techniques (p 0.05). Chairside porcelain polishing systems were not able to provide a porcelain surface as smooth as the glazed surface for the IPS empress and Ceramco 3 porcelains.
