Many machine components are operated in dry sliding,elevated temperature,and oxidizing environ-ments,leading to material failure or loss of functionality.Despite previous wear studies on conven-tional alloys,wear-rela...Many machine components are operated in dry sliding,elevated temperature,and oxidizing environ-ments,leading to material failure or loss of functionality.Despite previous wear studies on conven-tional alloys,wear-related properties in high-entropy alloys(HEAs)and medium-entropy alloys(MEAs)up to 1000℃ are rarely reported.Here we systematically study the high-temperature hardness,wear be-haviours and mechanisms of two popular MEAs,FeCoNi and CrCoNi,from room temperature to 1000℃.We find that the wear resistance of FeCoNi surpasses that of CrCoNi at room temperature,600℃,and 800℃.Contrarily,the wear resistance of CrCoNi surpasses that of FeCoNi at 400℃ and 1000℃.By characterizing wear tracks,we identify that these wear-mechanism transitions are associated with alloy elements,oxidation rates,and oxide types.At room temperature,FeCoNi forms a spinel oxide layer with a lower wear rate than CrCoNi.At 400℃,the wear rates of FeCoNi and CrCoNi are comparable because of temperature softening.At 600℃ and 800℃,FeCoNi shows Co_(3)O_(4) as the main constituent of the glaze layer,enhancing wear resistance compared to CrCoNi.At 1000℃,such glaze layer in FeCoNi undergoes severe plastic deformation,reducing its wear resistance;the Cr2 O3 oxide layer formed in CrCoNi remains hard and less deformable,contributing to its higher wear resistance.This study provides a fundamental understanding of the effect of principal elements on the wear performance in FeCoNi and CrCoNi-related MEAs and HEAs.展开更多
The present work concerns with correlation between microstructure and wear behavior of AZX915 Mg-alloy reinforced with 12 wt%of TiC particles by stir-casting process.Dry sliding tests were performed under ambient envi...The present work concerns with correlation between microstructure and wear behavior of AZX915 Mg-alloy reinforced with 12 wt%of TiC particles by stir-casting process.Dry sliding tests were performed under ambient environment by using a pin-on-disc(EN8 steel)configuration with a normal load of 50 N at a constant sliding speed of 2.50 ms^(−1).While as-cast composite experienced delamination wear,heat treated composite suffered from delamination and oxidation wear during dry sliding contact.Moreover,the heat treated composite exhibited lower friction and higher wear rate as compared to the as-cast composite.Friction and wear behavior were correlated with microstructures based on the concept of oxidation tendency and crack nucleation/propagation.Further,a schematic model has been proposed illustrating wear mechanisms from the point of view of subsurface microstructural evolution of the AZX915-TiCp composite.展开更多
Braking discs play an important role for the safety of vehicles whereas severe frictional contacts in repeated braking operations result in thermal and tribological failures.This paper reports comprehensive surface an...Braking discs play an important role for the safety of vehicles whereas severe frictional contacts in repeated braking operations result in thermal and tribological failures.This paper reports comprehensive surface and subsurface analyses of a used grey cast iron braking disc to investigate its failure mechanisms as well as related microstructure evolution.Thermal cracking,spalling wear and tribo-oxidation have been found to contribute to the wear failure.The flake-type graphite of the grey cast iron triggered propagation and internal oxidation of the metallic matrix.In a depth of 3 mm beneath the rubbing surface,extensive microstructure evolution occurred by severe plastic deformation of the ferritic matrix,nodularisation and partial dissolution of the lamellar carbides,and internal oxidation.The microstructure evolution resulted in decreased surface hardness to HV0.3247 as compared to HV0.3284 of the bulk cast iron.展开更多
High-temperature tribology,which is often involved during hot metal forming,is controlled via oxidation on a rubbing surface.However,for high chromium stainless steel(ST),where oxidation is strongly inhibited,the effe...High-temperature tribology,which is often involved during hot metal forming,is controlled via oxidation on a rubbing surface.However,for high chromium stainless steel(ST),where oxidation is strongly inhibited,the effect of counterface materials on tribological behavior is yet to be elucidated.In this study,the effects of counterfaces on the tribological behavior of 253MA ST and mild steel(MS)are investigated via a ball-on-disc test at 900°C using a 20 N load.The results reveal that high-speed steel(HSS)experiences severe abrasive wear with MS and causes severe sticking problems with ST.Si3N4 and SiC present substantially stronger abrasive wear resistance than HSS with MS,and the friction coefficients are dependent on the type of ceramic.Both ceramics can facilitate the establishment of a thick tribo-oxide layer(>3μm)on ST to prevent sticking;however,this is accompanied by severe pull-out and fracture wear.The effects of the counterface on the mechanical properties of the tribo-oxide layer,near-surface transformation,and the responses of the tribo-oxide layer to friction and wear are discussed.This study contributes to the understanding of interfacial tribological behaviors when different types of tools are used on MS and ST.展开更多
基金financial support from the Natural Sciences and Engineering Research Council of Canada(NSERC Discovery Grant#RGPIN-2018-05731 and NSERC Alliance Grant-Missions ALLRP 570708-2021)Dean’s Spark As-sistant Professorship in the Faculty of Applied Science&Engi-neering at the University of Toronto+7 种基金supported by the Canada Foundation for Innovation(CFI)the Natural Sciences and Engineer-ing Research Council(NSERC)the National Research Council(NRC)the Canadian Institutes of Health Research(CIHR)the Government of Saskatchewanthe University of SaskatchewanSeed fund from the Low-Carbon Renewable Material Center at the University of Torontofinancial support from the China Scholarship Council(CSC:No.202006230136).
文摘Many machine components are operated in dry sliding,elevated temperature,and oxidizing environ-ments,leading to material failure or loss of functionality.Despite previous wear studies on conven-tional alloys,wear-related properties in high-entropy alloys(HEAs)and medium-entropy alloys(MEAs)up to 1000℃ are rarely reported.Here we systematically study the high-temperature hardness,wear be-haviours and mechanisms of two popular MEAs,FeCoNi and CrCoNi,from room temperature to 1000℃.We find that the wear resistance of FeCoNi surpasses that of CrCoNi at room temperature,600℃,and 800℃.Contrarily,the wear resistance of CrCoNi surpasses that of FeCoNi at 400℃ and 1000℃.By characterizing wear tracks,we identify that these wear-mechanism transitions are associated with alloy elements,oxidation rates,and oxide types.At room temperature,FeCoNi forms a spinel oxide layer with a lower wear rate than CrCoNi.At 400℃,the wear rates of FeCoNi and CrCoNi are comparable because of temperature softening.At 600℃ and 800℃,FeCoNi shows Co_(3)O_(4) as the main constituent of the glaze layer,enhancing wear resistance compared to CrCoNi.At 1000℃,such glaze layer in FeCoNi undergoes severe plastic deformation,reducing its wear resistance;the Cr2 O3 oxide layer formed in CrCoNi remains hard and less deformable,contributing to its higher wear resistance.This study provides a fundamental understanding of the effect of principal elements on the wear performance in FeCoNi and CrCoNi-related MEAs and HEAs.
文摘The present work concerns with correlation between microstructure and wear behavior of AZX915 Mg-alloy reinforced with 12 wt%of TiC particles by stir-casting process.Dry sliding tests were performed under ambient environment by using a pin-on-disc(EN8 steel)configuration with a normal load of 50 N at a constant sliding speed of 2.50 ms^(−1).While as-cast composite experienced delamination wear,heat treated composite suffered from delamination and oxidation wear during dry sliding contact.Moreover,the heat treated composite exhibited lower friction and higher wear rate as compared to the as-cast composite.Friction and wear behavior were correlated with microstructures based on the concept of oxidation tendency and crack nucleation/propagation.Further,a schematic model has been proposed illustrating wear mechanisms from the point of view of subsurface microstructural evolution of the AZX915-TiCp composite.
基金partially funded by in the European Regional Development Fund of European Union in the title‘Sheffield Innovation Programme’with the series number 28R18P02582.
文摘Braking discs play an important role for the safety of vehicles whereas severe frictional contacts in repeated braking operations result in thermal and tribological failures.This paper reports comprehensive surface and subsurface analyses of a used grey cast iron braking disc to investigate its failure mechanisms as well as related microstructure evolution.Thermal cracking,spalling wear and tribo-oxidation have been found to contribute to the wear failure.The flake-type graphite of the grey cast iron triggered propagation and internal oxidation of the metallic matrix.In a depth of 3 mm beneath the rubbing surface,extensive microstructure evolution occurred by severe plastic deformation of the ferritic matrix,nodularisation and partial dissolution of the lamellar carbides,and internal oxidation.The microstructure evolution resulted in decreased surface hardness to HV0.3247 as compared to HV0.3284 of the bulk cast iron.
基金This work is financially supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.51905213)the Natural Science Foundation of Guangdong(906055014066)the Fundamental Research Funds for the Central Universities(No.21619337).
文摘High-temperature tribology,which is often involved during hot metal forming,is controlled via oxidation on a rubbing surface.However,for high chromium stainless steel(ST),where oxidation is strongly inhibited,the effect of counterface materials on tribological behavior is yet to be elucidated.In this study,the effects of counterfaces on the tribological behavior of 253MA ST and mild steel(MS)are investigated via a ball-on-disc test at 900°C using a 20 N load.The results reveal that high-speed steel(HSS)experiences severe abrasive wear with MS and causes severe sticking problems with ST.Si3N4 and SiC present substantially stronger abrasive wear resistance than HSS with MS,and the friction coefficients are dependent on the type of ceramic.Both ceramics can facilitate the establishment of a thick tribo-oxide layer(>3μm)on ST to prevent sticking;however,this is accompanied by severe pull-out and fracture wear.The effects of the counterface on the mechanical properties of the tribo-oxide layer,near-surface transformation,and the responses of the tribo-oxide layer to friction and wear are discussed.This study contributes to the understanding of interfacial tribological behaviors when different types of tools are used on MS and ST.
