Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was appli...Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.展开更多
An aluminide（AlFe and α-（FeAl）） surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment（SMAT） combined with a duplex aluminization proce...An aluminide（AlFe and α-（FeAl）） surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment（SMAT） combined with a duplex aluminization process at lower temperatures,i.e.a packed aluminization followed by a diffusion annealing treatment below its tempering temperature.Indentation tests indicated that the lower-Al surface layer formed on the SMAT sample is more resistant to cracking and has better adhesion to the substrate in comparison with the Al 5Fe 2 layer formed on the as-received sample after the duplex aluminization process.Isothermal steam oxidation measurements showed that the oxidation resistance is increased significantly by the lower-Al surface layer due to the formation of a protective（Fe,Cr）Al 2O 4 layer.The rate constant of oxidation was estimated to decrease from-0.849 mg^2 cm^-4h^-1 of the as-received material to^0.011 mg^2 cm^-4 h^-1 of the AlFe layer at 700 ℃.展开更多
The correlation between depassivation and repassivation processes,which is significant in erosioncorrosion,was quantitatively investigated by single particle impingement tests at various flow velocities and impact ang...The correlation between depassivation and repassivation processes,which is significant in erosioncorrosion,was quantitatively investigated by single particle impingement tests at various flow velocities and impact angles.The results show that both repassivation and depassivation processes are associated with the kinetic energy of solid particle,and demonstrate that the repassivation is retarded by depassivation.This phenomenon probably results from the depassivation-induced microstructure evolution.On this basis,the dependence of critical flow velocity(CFV)for erosion-corrosion on the solid particle concentration and diameter is further theoretically predicted and experimentally verified.Accordingly,the crucial role of depassivation-repassivation in CFV phenomenon is further highlighted.展开更多
Nanolaminated structures composed of low-angle grain boundaries(LAGBs) possess high thermal stability. In this paper, a gradient nanolaminated(GNL) surface layer with smooth finish was fabricated on an interstitial-fr...Nanolaminated structures composed of low-angle grain boundaries(LAGBs) possess high thermal stability. In this paper, a gradient nanolaminated(GNL) surface layer with smooth finish was fabricated on an interstitial-free steel by means of surface mechanical rolling treatment. Microstructural observations demonstrated that the average lamellar thickness is about 80 nm in the topmost surface layer and increases with increasing depth. High thermal stability was confirmed in the GNL surface layer after annealing at 500℃. Diffusion measurements showed that effective diffusivity of Cr in GNL layer is 4–6 orders of magnitude higher than lattice diffusivity within the temperature range from 400 to 500℃. This might be attributed to numerous LAGBs or dislocation structures with a higher energy state in the GNL surface layer. This work demonstrates the possibility to advanced chromizing(or other surface alloying)processes of steels with formation of GNL surface layer, so that a thicker alloyed surface layer with a stable nanostructure is achieved.展开更多
In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twi...In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.展开更多
The microstructure in the surface layer of iron and steel samples can be refined at the nanometer scale by means of a surface mechanical attrition treatment (SMAT) that generates repetitive severe plastic deformation ...The microstructure in the surface layer of iron and steel samples can be refined at the nanometer scale by means of a surface mechanical attrition treatment (SMAT) that generates repetitive severe plastic deformation to the surface layer. The subsequent nitriding kinetics of the as-treated samples with the nanostructured surface layer is greatly enhanced so that the nitriding temperatures can be reduce to 300 - 400 °C regions. This enhanced processing method demonstrates both the technological significance of nanomaterials in advancing the traditional processing techniques, and provides a new approach for selective surface reactions in solids. This article reviews the present state of the art in this field. The microstructure and properties of SMAT samples nitrided will be summarized. Further considerations of the development and applications of this new technique will also be presented.展开更多
Under-deposit corrosion(UDC)due to the presence of deposits has become a major concern threatening the safe service of pipelines in oil and gas fields,causing economic loss and even irreversible damage to life and env...Under-deposit corrosion(UDC)due to the presence of deposits has become a major concern threatening the safe service of pipelines in oil and gas fields,causing economic loss and even irreversible damage to life and environment.Herein,we provide a critical review of UDC in terms of testing methods,corrosion mechanisms and mitigation strategies,so as to better understand and prevent UDC.Two deposit simulation methods and three UDC testing systems are summarized.Two popular UDC mechanisms are discussed based on the coverage and protectiveness of deposits,and the galvanic couple caused by the uneven distribution of deposits is found to be the root cause for the prevailed localized corrosion under deposits.The mitigation strategies for UDC are reviewed from the aspects of scale controlling and corrosion inhibition.In the last,the demands for developing accurate deposit simulation methods,effective UDC inhibitors and advanced on-site scale monitoring technologies are proposed.展开更多
Future sediment transport from the North Sea coasts to the Dutch Wadden Sea for various future sea level scenarios has been studied because it influences the future sand nourishment demand for the maintenance of the c...Future sediment transport from the North Sea coasts to the Dutch Wadden Sea for various future sea level scenarios has been studied because it influences the future sand nourishment demand for the maintenance of the coastline and because it determines bio-geomorphological development of the Wadden Sea.The present study focuses on two questions which have not yet been considered in the previous modelling studies using ASMITA:How will the transport develop around drowning of the intertidal flats in the Wadden Sea?How will tidal range change influ-ence the future sediment exchange?By using SLR scenarios with faster acceleration and running the simulations for longer periods of time some inlets exhibited drowning,i.e.,where the tidal flat volume vanishes.When drowning occurs,the sediment import rate approaches a maximum or a minimum,depending on the initial morphological state of the tidal inlet system.This maximum or minimum rate for a certain tidal inlet system depends on the SLR scenario.Theoretical analysis as well as modelling results show that tidal range change will influence the sediment import to the Wadden Sea.A tidal range increase will cause a decrease of the sediment demand in the Wadden Sea resulting into less sediment import to the Wadden Sea.It is thus important to study the tidal range development in the Wadden Sea by considering the interaction between SLR,tidal range change and morphological development in the system.It is further concluded that the empirical relation used in the previous studies is not representative of conditions in a tidal basin with fixed basin area,even though this relation has been derived from field observations in many tidal inlet systems worldwide.The equilibrium channel volume should be proportional to the tidal prism instead of to its 1.5^(th) power.展开更多
基金The financial supports by the Chinese Academy of Sciences(Nos.XDC04030300 and XDB0510303)CAS-HK Joint Laboratory of Nanomaterials and MechanicsShenyang National Laboratory for Materials Science are acknowledged.
文摘Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.
基金Financial supports from the Ministry of Science and Technology of the People’s Republic of China (No.2012CB932201)the National Natural Science Foundation of China (No.91226204)the Key Research Program of Chinese Academy of Sciences (No.KGZD-EW-T06)
文摘An aluminide（AlFe and α-（FeAl）） surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment（SMAT） combined with a duplex aluminization process at lower temperatures,i.e.a packed aluminization followed by a diffusion annealing treatment below its tempering temperature.Indentation tests indicated that the lower-Al surface layer formed on the SMAT sample is more resistant to cracking and has better adhesion to the substrate in comparison with the Al 5Fe 2 layer formed on the as-received sample after the duplex aluminization process.Isothermal steam oxidation measurements showed that the oxidation resistance is increased significantly by the lower-Al surface layer due to the formation of a protective（Fe,Cr）Al 2O 4 layer.The rate constant of oxidation was estimated to decrease from-0.849 mg^2 cm^-4h^-1 of the as-received material to^0.011 mg^2 cm^-4 h^-1 of the AlFe layer at 700 ℃.
基金the financial support from the National Natural Science Foundation of China(grant numbers:51801218,51571200)。
文摘The correlation between depassivation and repassivation processes,which is significant in erosioncorrosion,was quantitatively investigated by single particle impingement tests at various flow velocities and impact angles.The results show that both repassivation and depassivation processes are associated with the kinetic energy of solid particle,and demonstrate that the repassivation is retarded by depassivation.This phenomenon probably results from the depassivation-induced microstructure evolution.On this basis,the dependence of critical flow velocity(CFV)for erosion-corrosion on the solid particle concentration and diameter is further theoretically predicted and experimentally verified.Accordingly,the crucial role of depassivation-repassivation in CFV phenomenon is further highlighted.
基金Financial supports from the National Key Research and Development Program of China (No. 2017YFA0204401)Shenyang National Laboratory for Materials Science (No. 2015RP04)
文摘Nanolaminated structures composed of low-angle grain boundaries(LAGBs) possess high thermal stability. In this paper, a gradient nanolaminated(GNL) surface layer with smooth finish was fabricated on an interstitial-free steel by means of surface mechanical rolling treatment. Microstructural observations demonstrated that the average lamellar thickness is about 80 nm in the topmost surface layer and increases with increasing depth. High thermal stability was confirmed in the GNL surface layer after annealing at 500℃. Diffusion measurements showed that effective diffusivity of Cr in GNL layer is 4–6 orders of magnitude higher than lattice diffusivity within the temperature range from 400 to 500℃. This might be attributed to numerous LAGBs or dislocation structures with a higher energy state in the GNL surface layer. This work demonstrates the possibility to advanced chromizing(or other surface alloying)processes of steels with formation of GNL surface layer, so that a thicker alloyed surface layer with a stable nanostructure is achieved.
基金supported financially by the National Key Research and Development Program of China (No.2017YFA0204400)Shenyang National Laboratory for Materials Science(No. 2015RP04)
文摘In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.
基金supported by NSF of China(Grants No.50021101)Ministry of Science&Technology of China(G1999064505).
文摘The microstructure in the surface layer of iron and steel samples can be refined at the nanometer scale by means of a surface mechanical attrition treatment (SMAT) that generates repetitive severe plastic deformation to the surface layer. The subsequent nitriding kinetics of the as-treated samples with the nanostructured surface layer is greatly enhanced so that the nitriding temperatures can be reduce to 300 - 400 °C regions. This enhanced processing method demonstrates both the technological significance of nanomaterials in advancing the traditional processing techniques, and provides a new approach for selective surface reactions in solids. This article reviews the present state of the art in this field. The microstructure and properties of SMAT samples nitrided will be summarized. Further considerations of the development and applications of this new technique will also be presented.
基金financially supported by the Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan Province(No.2017CL18)
文摘Under-deposit corrosion(UDC)due to the presence of deposits has become a major concern threatening the safe service of pipelines in oil and gas fields,causing economic loss and even irreversible damage to life and environment.Herein,we provide a critical review of UDC in terms of testing methods,corrosion mechanisms and mitigation strategies,so as to better understand and prevent UDC.Two deposit simulation methods and three UDC testing systems are summarized.Two popular UDC mechanisms are discussed based on the coverage and protectiveness of deposits,and the galvanic couple caused by the uneven distribution of deposits is found to be the root cause for the prevailed localized corrosion under deposits.The mitigation strategies for UDC are reviewed from the aspects of scale controlling and corrosion inhibition.In the last,the demands for developing accurate deposit simulation methods,effective UDC inhibitors and advanced on-site scale monitoring technologies are proposed.
基金supported by the Dutch national research programme Sea level rise,theme Sandy coastsby the Dutch Ministry of Economic Affars and Climate via Programme subsidy Deltares.
文摘Future sediment transport from the North Sea coasts to the Dutch Wadden Sea for various future sea level scenarios has been studied because it influences the future sand nourishment demand for the maintenance of the coastline and because it determines bio-geomorphological development of the Wadden Sea.The present study focuses on two questions which have not yet been considered in the previous modelling studies using ASMITA:How will the transport develop around drowning of the intertidal flats in the Wadden Sea?How will tidal range change influ-ence the future sediment exchange?By using SLR scenarios with faster acceleration and running the simulations for longer periods of time some inlets exhibited drowning,i.e.,where the tidal flat volume vanishes.When drowning occurs,the sediment import rate approaches a maximum or a minimum,depending on the initial morphological state of the tidal inlet system.This maximum or minimum rate for a certain tidal inlet system depends on the SLR scenario.Theoretical analysis as well as modelling results show that tidal range change will influence the sediment import to the Wadden Sea.A tidal range increase will cause a decrease of the sediment demand in the Wadden Sea resulting into less sediment import to the Wadden Sea.It is thus important to study the tidal range development in the Wadden Sea by considering the interaction between SLR,tidal range change and morphological development in the system.It is further concluded that the empirical relation used in the previous studies is not representative of conditions in a tidal basin with fixed basin area,even though this relation has been derived from field observations in many tidal inlet systems worldwide.The equilibrium channel volume should be proportional to the tidal prism instead of to its 1.5^(th) power.
