Titanium nitride films are prepared by plasma enhanced chemical vapor deposition method on titanium foil using N_(2) as precursor. In order to evaluate the effect of oxygen on the growth of titanium nitride films, a s...Titanium nitride films are prepared by plasma enhanced chemical vapor deposition method on titanium foil using N_(2) as precursor. In order to evaluate the effect of oxygen on the growth of titanium nitride films, a small amount of O_(2) is introduced into the preparation process. The study indicates that trace O_(2) addition into the reaction chamber gives rise to significant changes on the color and micro-morphology of the foil, featuring dense and long nano-wires. The as-synthesized nanostructures are characterized by various methods and identified as TiN, Ti_(2) N, and TiO_(2) respectively. Moreover, the experiment results show that oxide nanowire has a high degree of crystallinity and the nitrides present specific orientation relationships with the titanium matrix.展开更多
An integrated low-temperature nitriding process was carried out for Ti6Al4V to investigateitseffect on microstructure and properties.The process was designed to enhance the nitriding kinetics in low-temperature（500℃...An integrated low-temperature nitriding process was carried out for Ti6Al4V to investigateitseffect on microstructure and properties.The process was designed to enhance the nitriding kinetics in low-temperature（500℃） nitriding by deformation, and to strengthen Ti6Al4V alloybydispersionat the same time. Specimens of Ti6Al4V alloyweretreated through the process of solid solutionstrengthening-cold deformation-nitriding at 500℃. The white nitriding layeris formed after some time and then kept stable, changing little withthedeformationdegreeand time. The effect of aging on substrate is significant. Surface hardness and substrate hardnessincrease with deformation increasing. The construction was investigated by XRD.The surface nitridesare TiN, Ti2N, Ti4N3-Xand Ti3N1.29,and thenitridesin cross-section are Ti3N1.29and TiN0.3. The wear tests of specimens after nitriding, aging and deformation were carried out,andthetest data show that the nitrided pieces have the best wear resistance.展开更多
Medical forged CoCrMo alloy was treated by plasma nitriding process.The microstructures were characterized by 3Dprofiler,SEM and XRD.The tribological properties were investigated under lubrication of 25% bovine serum ...Medical forged CoCrMo alloy was treated by plasma nitriding process.The microstructures were characterized by 3Dprofiler,SEM and XRD.The tribological properties were investigated under lubrication of 25% bovine serum solution.Resultsshow that plasma nitriding is a promising process to produce thick,hard,and more wear resistant layers on the surface of CoCrMoalloy.All nitrided samples showed an important increase in the surface hardness due to the formation of harder CrN andCrN phases with compact nano-crystalline structures.The typical hardness values of HVincreased almost two times thanuntreated one.Under bovine serum lubrication,at low nitriding temperature the Coefficient of Friction (COF) of nitrided samplewas lower than that of untreated sample,but at high nitriding temperature the COF was almost the same as the untreated one.Compared with the untreated sample,the nitrided samples showed lower wear rates and higher wear resistance under differentnitriding temperatures.The adhesive wear is the main mechanism for untreated CoCrMo alloy and the wear mechanisms ofnitrided ones are the fatigue wear and slight adhesive wear.It is concluded that the improvement of wear resistance is ascribed tothe hard nitride formation of CrN and CrN phases at the nitrided surfaces.展开更多
The Ti-20Zr-6.5Al-4V(T20Z,wt%)alloy surface was treated by the process of laser surface nitriding.The evolution of microstructures and microhardness has been investigated by changing the laser power parameter from 120...The Ti-20Zr-6.5Al-4V(T20Z,wt%)alloy surface was treated by the process of laser surface nitriding.The evolution of microstructures and microhardness has been investigated by changing the laser power parameter from 120 to 240 W.All laser-treated T20Z samples show two regions with distinctly different microstructural features,as compared with the untreated substrate:dense TiN dendrites and(α+β)-Ti(remelting zone,RMZ),nanoscaleαlaths doped with part of p phase(heat-affected zone,HAZ).The formation of TiN dendrites can be analyzed by a series of complex reactions during the process of melting and solidification.The increase in laser power results in the increase in content of TiN dendrite which is mainly due to the increase in energy input.In HAZ,the self-quenching effect leads to the formation of nanoscale a laths and the residue ofβphase.Microhardness profile of different regions was measured from the surface to the interior,and the highest microhardness was obtained(~HV 916.8)in the RMZ,as the laser power was set to 240 W.In the present study,we explained various microstructural characteristics induced by laser surface nitriding treatment.展开更多
Plasma nitriding is a widely used technology to enhance the surface performance and extend the service life of alloy parts.The current research mainly focuses on the influences of time,temperature,gas type and pressur...Plasma nitriding is a widely used technology to enhance the surface performance and extend the service life of alloy parts.The current research mainly focuses on the influences of time,temperature,gas type and pressure parameters on nitriding behavior,while fewer studies have been conducted on the electric potential.This paper mainly reports the effect of the electric potential on nitriding behavior.Test conditions were set using cathodic,anodic and floating potentials in a plasma nitriding furnace.2Cr13 stainless steel was nitrided at 450°C for 5h in an NH3 atmosphere.The experimental results show that the nitriding treatment can be well performed under the different electric potentials,but differences exist in microstructures,morphologies and performance results of the modified layers.The thickness and hardness values of the nitrided layer are ranked as follows:cathodic[anodic[floating potential.The anodic nitrided surface has an obvious particle deposition layer composed of nitrides and oxides.Electrochemical and tribological experiments show that the corrosion resistance and wear resistance were significantly improved after a nitriding treatment using the three electric potentials.Moreover,the floating nitriding treatment resulted in the best tribological performance and corrosion resistance.展开更多
The behavior of gaseous nitriding on the surface nanocrystallized (SNCed) steel was investigated. The mild steel discs were SNCed on one side by using the method of ultrasonic shot peening. The opposite side of the di...The behavior of gaseous nitriding on the surface nanocrystallized (SNCed) steel was investigated. The mild steel discs were SNCed on one side by using the method of ultrasonic shot peening. The opposite side of the discs maintained the original coarse-grained condition. The gaseous nitriding was subsequently carried out at three different temperatures: 460, 500 and 560℃. The compound layer growth and diffusion behavior were then studied. It was revealed that SNC pretreatment greatly enhances both diffusion coefficient D and surface reaction rate. As a result, nitriding time could be reduced to the half. It was also found that the growth of compound layer with nitriding time conformed with parabolic relationship from the start of nitriding process in the SNCed samples.展开更多
AISI H13 steel samples were plasma nitrided to improve their surface hardness using a locally developed combined reactor.Pre-ionized RFICP plasma was employed in combination with DC glow discharge and thermal emission...AISI H13 steel samples were plasma nitrided to improve their surface hardness using a locally developed combined reactor.Pre-ionized RFICP plasma was employed in combination with DC glow discharge and thermal emission source to achieve the nitride precipitates in iron-matrix under low sample temperature.Thick nitride layers over 150 microns could be realized with low RF power of 100 W under the processing time between 1-20 h and low sample temperature of 300℃.The gas mixtures of H2 and N2 were utilized while the processing pressure and the DC bias to the sample were maintained at 0.5 torr and 300 V,respectively.Scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),glancing incident angle X-ray diffractometer(GIXD)and Vickers hardness test were employed to characterize the properties of sample surfaces.Significant increases of surface hardness to over 1,000 HV were observed after treatment.展开更多
In this work, the effect of nitriding current density on hardness, crystalline phase composition, layer thickness and corrosion rate of AlSl 4340 steel has been studied. X-ray diffraction analysis shows that thin laye...In this work, the effect of nitriding current density on hardness, crystalline phase composition, layer thickness and corrosion rate of AlSl 4340 steel has been studied. X-ray diffraction analysis shows that thin layers formed during nitriding process are constituted of 7-Fe4N for samples processed between 1 and 2.5 mA/cm2. Thickness of nitrided layer increases proportionally to current density （0 μm for 0.5 mA/cm2 to 15 pm for 2.5 mA/cm2）. Plasma nitriding increased the surface hardness from 300 HV50g for untreated sample, to around 800HV5og for nitrided samples at 1 mA/cm2. While the untreated samples exhibited a corrosion rate of 0.153 mm per year, the corrosion performance was improved up to 0.03 mm per year at current densities above 1 mA/cm2, which is about one fifth of the corrosion rate of the untreated sample.展开更多
Medium-carbon alloy steel was plasma nitrided with rare earths La, Ce and Nd into the nitriding chamber respectively. The nitriding layer microstructures with and without rare earths were compared using optical micros...Medium-carbon alloy steel was plasma nitrided with rare earths La, Ce and Nd into the nitriding chamber respectively. The nitriding layer microstructures with and without rare earths were compared using optical microscope,normal SEM and high resolution SEM, as well as TEM. It was found that the extent of the influence on plasma nitriding varies with different contents of rare earth. The effect of plasma nitriding is benefit from adding of Ce or Nd. The formation of hard and brittle phase Fe_(2-3)N can be prevented and the butterfly-like structure can be improved by adding Ce or Nd. However, pure La may prevent the diffusion of nitrogen and the formation of iron nitride, and reduce the depth of diffusion layer.展开更多
This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions.The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless ...This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions.The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations.Results reveal that nitriding depth increased as process temperature and duration increase.The nitriding depth remarkably increased at 475℃for 8 h and at 550℃for 4 h.An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite(S-phase)during low-temperature plasma nitriding.The S-phase was converted to CrN precipitation at 475℃for 8 h and at 550℃for 4 h.Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions.The best surface hardness and fatigue limit were obtained at 550℃for 4 h because of the occurrence of CrN precipitation.展开更多
A composite layer was prepared on the surface of Ti-6Al-4V alloy by nitriding-sulfurizing composite treatment,and its microstructure and phase structure were examined by scanning electron microscopy（SEM） and X-ray d...A composite layer was prepared on the surface of Ti-6Al-4V alloy by nitriding-sulfurizing composite treatment,and its microstructure and phase structure were examined by scanning electron microscopy（SEM） and X-ray diffraction（XRD）,respectively.The tribological performance was measured to investigate its dependence on the nitriding-sulfurizing composite treatment process.The results indicated that the composite layer was mainly comprised of Ti2N,TiN,and TiS2.It was found that the composite layer exhibited superior tribological properties under dry friction and absolute sliding conditions due to the formation of sulfides with self-lubricating function.展开更多
Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys(HEAs)with finelydivided Al content(i.e.,x values in molar ratio,x=0.1-0.8)to develop wear-resistant structural materials.Nitridatio...Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys(HEAs)with finelydivided Al content(i.e.,x values in molar ratio,x=0.1-0.8)to develop wear-resistant structural materials.Nitridation greatly removes the Al from the matrix that completely deplete the Ni-Al enriched phase,forming nanoscaled nitrides(AIN and CrN)precipitations near the surface.Nitriding promotes the hardness of present alloys with values widely ranging from 276 HV to 722 HV.Interestingly,the higher content the Al,the smaller thickness the nitrides layer,but the higher hardness due to the increased amount of hard nitrides phases and volume fraction of BCC phase.Significantly,plasma nitriding considerably improves the wear re sistance of AlxCoCrFeNi HEAs by 4-18 times.展开更多
Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent ap...Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent application. This magnetic behavior in high nitrogen stainless steel was investigated by optical microscopy, X-ray diffraction （XRD）, electron probe microanalysis （EPMA） and superconducting quantum interference device （SQUID）. The results showed that the magnetism came from the composition segregation of ferrite formation elements such as Cr and Mo in the steel and some 6-ferrites were locally formed during the pressurized electroslag remelting process. The magnetism of high nitrogen stainless steel could be eliminated by a proper high temperature gas nitriding （HTGN）.展开更多
An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nit...An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400℃, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti3N（2-X）. The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.展开更多
A cathodic plasma electrolytic nitriding(CPEN)treatment with a urea aqueous solution was performed on 316L stainless steel to rapidly improve its surface properties in this work.Test results show that the PEG2000 macr...A cathodic plasma electrolytic nitriding(CPEN)treatment with a urea aqueous solution was performed on 316L stainless steel to rapidly improve its surface properties in this work.Test results show that the PEG2000 macromolecules increased the nitriding energy via enhancing the ability to bond the produced gas film to the metal/electrolyte interface.The cross-sectional morphologies indicate that a thick nitrided layer was obtained when the urea concentration was 543 g I^-1,corresponding to a Vickers hardness 450 HV(0.1),which was 3.5 times larger than that of the substrate.The nitrided layer mainly contained expanded austenite(γN),oxides and iron nitrides(e.g.,Fe3O4 and FeN(0.076)).In terms of its performance,coefficient of friction(COF)of the nitride layer decreased to nearly two-thirds that of the untreated layer,and the passivation current densities of the nitrided sample in a 3.5%NaCl solution decreased by an order of magnitude compared to that of the substrate.Therefore,the approach presented herein provides an attractive way to modify the effect of CPEN in a urea aqueous solution.展开更多
β-Sialon was produced by carbon thermal nitriding reaction in N_2 gas atmosphere when the mixtures of bauxite and anthracite were put into vertical furnace. According to the mass loss of raw materials and the result ...β-Sialon was produced by carbon thermal nitriding reaction in N_2 gas atmosphere when the mixtures of bauxite and anthracite were put into vertical furnace. According to the mass loss of raw materials and the result of X-ray diffration (XRD) of products, the influences of the process parameters on the compositions and relative contents of products, such as the fixed carbon content, the flow of N2, the soaking time and the temperature, were researched.展开更多
CW-CO2 laser nitriding technique was applied to improve the properties （such as aging property and the core loss） of grain oriented silicon steel. The samples were nitrided with regular space. Laser power density an...CW-CO2 laser nitriding technique was applied to improve the properties （such as aging property and the core loss） of grain oriented silicon steel. The samples were nitrided with regular space. Laser power density and scanning speed were chosen as 7.8×10^5W·cm^-2 and 100mm·min^-1. By some laser irradiation, Fe4N and Fe3N were formed in the nitrided zone. The nitrided samples were annealed at the temperatures ranged from 100 to 90℃. The core loss of some interested samples was tested. The results show that the core loss of the nitrided samples with different thickness of 0.23 and 0.30mm decreased by 14.9% and 9.4% respectively, and the aging property were improved up to 800℃. The mechanism of laser nitriding to improve the properties of grain oriented silicon steel is discussed.展开更多
Plasma rare earth nitriding of nanocrystallized surface layer of 3J33B steel at 350 and 410℃ for different time was studied. The microstructure observation and X-ray diffraction（XRD） analysis show that the nitrid...Plasma rare earth nitriding of nanocrystallized surface layer of 3J33B steel at 350 and 410℃ for different time was studied. The microstructure observation and X-ray diffraction（XRD） analysis show that the nitriding layer consists of compound layer （γ′-Fe4N） and diffusion layer （α-Fe）. Lanthanum content profiles in nanocrystallized surface layer were measured using glow discharge spectometry（GDS）. The results show that lanthanum can diffuse into the surface layer of the steel to a large depth. Based on the experimental results mentioned above, the diffusion coefficients and activation energy of lanthanum in γ′ phase are calculated to be 1.03×10 -15 cm2/s （350℃）, 1.75×10 -15 cm2/s （410℃） and 31.313kJ/mol, respectively.展开更多
基金Project supported by the Innovation Funding of Beijing Institute of Aeronautical Materials。
文摘Titanium nitride films are prepared by plasma enhanced chemical vapor deposition method on titanium foil using N_(2) as precursor. In order to evaluate the effect of oxygen on the growth of titanium nitride films, a small amount of O_(2) is introduced into the preparation process. The study indicates that trace O_(2) addition into the reaction chamber gives rise to significant changes on the color and micro-morphology of the foil, featuring dense and long nano-wires. The as-synthesized nanostructures are characterized by various methods and identified as TiN, Ti_(2) N, and TiO_(2) respectively. Moreover, the experiment results show that oxide nanowire has a high degree of crystallinity and the nitrides present specific orientation relationships with the titanium matrix.
基金Projects(51275105,51375106)supported by the National Natural Science Foundation of China
文摘An integrated low-temperature nitriding process was carried out for Ti6Al4V to investigateitseffect on microstructure and properties.The process was designed to enhance the nitriding kinetics in low-temperature（500℃） nitriding by deformation, and to strengthen Ti6Al4V alloybydispersionat the same time. Specimens of Ti6Al4V alloyweretreated through the process of solid solutionstrengthening-cold deformation-nitriding at 500℃. The white nitriding layeris formed after some time and then kept stable, changing little withthedeformationdegreeand time. The effect of aging on substrate is significant. Surface hardness and substrate hardnessincrease with deformation increasing. The construction was investigated by XRD.The surface nitridesare TiN, Ti2N, Ti4N3-Xand Ti3N1.29,and thenitridesin cross-section are Ti3N1.29and TiN0.3. The wear tests of specimens after nitriding, aging and deformation were carried out,andthetest data show that the nitrided pieces have the best wear resistance.
基金the supports by Tribology Science Fund State Key Laboratory of Tribology (SKLT) at Tsinghua University(SKLTKF08A01)Fundamental Research Funds for the Central UniversitiesNational Natural Science Foundation of China (No.51005234)
文摘Medical forged CoCrMo alloy was treated by plasma nitriding process.The microstructures were characterized by 3Dprofiler,SEM and XRD.The tribological properties were investigated under lubrication of 25% bovine serum solution.Resultsshow that plasma nitriding is a promising process to produce thick,hard,and more wear resistant layers on the surface of CoCrMoalloy.All nitrided samples showed an important increase in the surface hardness due to the formation of harder CrN andCrN phases with compact nano-crystalline structures.The typical hardness values of HVincreased almost two times thanuntreated one.Under bovine serum lubrication,at low nitriding temperature the Coefficient of Friction (COF) of nitrided samplewas lower than that of untreated sample,but at high nitriding temperature the COF was almost the same as the untreated one.Compared with the untreated sample,the nitrided samples showed lower wear rates and higher wear resistance under differentnitriding temperatures.The adhesive wear is the main mechanism for untreated CoCrMo alloy and the wear mechanisms ofnitrided ones are the fatigue wear and slight adhesive wear.It is concluded that the improvement of wear resistance is ascribed tothe hard nitride formation of CrN and CrN phases at the nitrided surfaces.
基金financially supported by the Youth Top Talents Research Project of Hebei Provincial Education Department China(No.BJ2018052)the Natural Science Foundation of Hebei Province of China(Nos.E2019208205 and E2018208126)+3 种基金the National Natural Science Foundation of China(No.51701064)the Science and Technology on Plasma Dynamics Laboratory Fund Project(No.614220206021806)the Key Research and Development Program of Hebei Province(No.19211016D)the Open Foundation of State Key Laboratory of Metastable Materials Science and Technology(Nos.201804 and 201812).
文摘The Ti-20Zr-6.5Al-4V(T20Z,wt%)alloy surface was treated by the process of laser surface nitriding.The evolution of microstructures and microhardness has been investigated by changing the laser power parameter from 120 to 240 W.All laser-treated T20Z samples show two regions with distinctly different microstructural features,as compared with the untreated substrate:dense TiN dendrites and(α+β)-Ti(remelting zone,RMZ),nanoscaleαlaths doped with part of p phase(heat-affected zone,HAZ).The formation of TiN dendrites can be analyzed by a series of complex reactions during the process of melting and solidification.The increase in laser power results in the increase in content of TiN dendrite which is mainly due to the increase in energy input.In HAZ,the self-quenching effect leads to the formation of nanoscale a laths and the residue ofβphase.Microhardness profile of different regions was measured from the surface to the interior,and the highest microhardness was obtained(~HV 916.8)in the RMZ,as the laser power was set to 240 W.In the present study,we explained various microstructural characteristics induced by laser surface nitriding treatment.
基金supported by the National Key Basic Research Program of China (No.2014CB046404)the Shandong Provincial Natural Science Foundation, China (No.ZR2018MEE016)+1 种基金the Shandong Provincial Key Research and Development Plan, China (No.2017GGX20140)the National Natural Science Foundation of China (No.51301149)
文摘Plasma nitriding is a widely used technology to enhance the surface performance and extend the service life of alloy parts.The current research mainly focuses on the influences of time,temperature,gas type and pressure parameters on nitriding behavior,while fewer studies have been conducted on the electric potential.This paper mainly reports the effect of the electric potential on nitriding behavior.Test conditions were set using cathodic,anodic and floating potentials in a plasma nitriding furnace.2Cr13 stainless steel was nitrided at 450°C for 5h in an NH3 atmosphere.The experimental results show that the nitriding treatment can be well performed under the different electric potentials,but differences exist in microstructures,morphologies and performance results of the modified layers.The thickness and hardness values of the nitrided layer are ranked as follows:cathodic[anodic[floating potential.The anodic nitrided surface has an obvious particle deposition layer composed of nitrides and oxides.Electrochemical and tribological experiments show that the corrosion resistance and wear resistance were significantly improved after a nitriding treatment using the three electric potentials.Moreover,the floating nitriding treatment resulted in the best tribological performance and corrosion resistance.
文摘The behavior of gaseous nitriding on the surface nanocrystallized (SNCed) steel was investigated. The mild steel discs were SNCed on one side by using the method of ultrasonic shot peening. The opposite side of the discs maintained the original coarse-grained condition. The gaseous nitriding was subsequently carried out at three different temperatures: 460, 500 and 560℃. The compound layer growth and diffusion behavior were then studied. It was revealed that SNC pretreatment greatly enhances both diffusion coefficient D and surface reaction rate. As a result, nitriding time could be reduced to the half. It was also found that the growth of compound layer with nitriding time conformed with parabolic relationship from the start of nitriding process in the SNCed samples.
文摘AISI H13 steel samples were plasma nitrided to improve their surface hardness using a locally developed combined reactor.Pre-ionized RFICP plasma was employed in combination with DC glow discharge and thermal emission source to achieve the nitride precipitates in iron-matrix under low sample temperature.Thick nitride layers over 150 microns could be realized with low RF power of 100 W under the processing time between 1-20 h and low sample temperature of 300℃.The gas mixtures of H2 and N2 were utilized while the processing pressure and the DC bias to the sample were maintained at 0.5 torr and 300 V,respectively.Scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),glancing incident angle X-ray diffractometer(GIXD)and Vickers hardness test were employed to characterize the properties of sample surfaces.Significant increases of surface hardness to over 1,000 HV were observed after treatment.
文摘In this work, the effect of nitriding current density on hardness, crystalline phase composition, layer thickness and corrosion rate of AlSl 4340 steel has been studied. X-ray diffraction analysis shows that thin layers formed during nitriding process are constituted of 7-Fe4N for samples processed between 1 and 2.5 mA/cm2. Thickness of nitrided layer increases proportionally to current density （0 μm for 0.5 mA/cm2 to 15 pm for 2.5 mA/cm2）. Plasma nitriding increased the surface hardness from 300 HV50g for untreated sample, to around 800HV5og for nitrided samples at 1 mA/cm2. While the untreated samples exhibited a corrosion rate of 0.153 mm per year, the corrosion performance was improved up to 0.03 mm per year at current densities above 1 mA/cm2, which is about one fifth of the corrosion rate of the untreated sample.
文摘Medium-carbon alloy steel was plasma nitrided with rare earths La, Ce and Nd into the nitriding chamber respectively. The nitriding layer microstructures with and without rare earths were compared using optical microscope,normal SEM and high resolution SEM, as well as TEM. It was found that the extent of the influence on plasma nitriding varies with different contents of rare earth. The effect of plasma nitriding is benefit from adding of Ce or Nd. The formation of hard and brittle phase Fe_(2-3)N can be prevented and the butterfly-like structure can be improved by adding Ce or Nd. However, pure La may prevent the diffusion of nitrogen and the formation of iron nitride, and reduce the depth of diffusion layer.
基金the Scientific and Technological Research Council of Turkey(TUBITAK)for the support of this study(Grant No:215M134)。
文摘This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions.The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations.Results reveal that nitriding depth increased as process temperature and duration increase.The nitriding depth remarkably increased at 475℃for 8 h and at 550℃for 4 h.An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite(S-phase)during low-temperature plasma nitriding.The S-phase was converted to CrN precipitation at 475℃for 8 h and at 550℃for 4 h.Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions.The best surface hardness and fatigue limit were obtained at 550℃for 4 h because of the occurrence of CrN precipitation.
文摘A composite layer was prepared on the surface of Ti-6Al-4V alloy by nitriding-sulfurizing composite treatment,and its microstructure and phase structure were examined by scanning electron microscopy（SEM） and X-ray diffraction（XRD）,respectively.The tribological performance was measured to investigate its dependence on the nitriding-sulfurizing composite treatment process.The results indicated that the composite layer was mainly comprised of Ti2N,TiN,and TiS2.It was found that the composite layer exhibited superior tribological properties under dry friction and absolute sliding conditions due to the formation of sulfides with self-lubricating function.
基金supported financially by the opening project from the National Key Laboratory for Remanufacturing(No.61420050204)Transformation of Scientific and Technological Achievements Programs of Higher Education Institutions in Shanxi(2019)the financial support from the China Scholarship Council(CSC)。
文摘Plasma nitriding is successfully employed in treating AlxCoCrFeNi high-entropy alloys(HEAs)with finelydivided Al content(i.e.,x values in molar ratio,x=0.1-0.8)to develop wear-resistant structural materials.Nitridation greatly removes the Al from the matrix that completely deplete the Ni-Al enriched phase,forming nanoscaled nitrides(AIN and CrN)precipitations near the surface.Nitriding promotes the hardness of present alloys with values widely ranging from 276 HV to 722 HV.Interestingly,the higher content the Al,the smaller thickness the nitrides layer,but the higher hardness due to the increased amount of hard nitrides phases and volume fraction of BCC phase.Significantly,plasma nitriding considerably improves the wear re sistance of AlxCoCrFeNi HEAs by 4-18 times.
基金supported by National Natural Science Foundation of China(No.31000428)National Basic Research Program of China(973Program)(No.2012CB619101)
文摘Stable austenitic structure in medical stainless steels is basically required for surgical implantation. A weak magnetism was found in a high nitrogen nickel-free austenitic stainless steel for cardiovascular stent application. This magnetic behavior in high nitrogen stainless steel was investigated by optical microscopy, X-ray diffraction （XRD）, electron probe microanalysis （EPMA） and superconducting quantum interference device （SQUID）. The results showed that the magnetism came from the composition segregation of ferrite formation elements such as Cr and Mo in the steel and some 6-ferrites were locally formed during the pressurized electroslag remelting process. The magnetism of high nitrogen stainless steel could be eliminated by a proper high temperature gas nitriding （HTGN）.
基金Projects(51275105,51375106)supported by the National Natural Science Foundation of China
文摘An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400℃, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti3N（2-X）. The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.
基金supported financially by the National Natural Science Foundation of China (No.51771027)the Fundamental Research Funds for the Central Universities (No.FRF-BD-18-019A)+1 种基金the National Key Research and Development Program of China (No. 2017YFB0702100)the National Environmental Corrosion Platform
文摘A cathodic plasma electrolytic nitriding(CPEN)treatment with a urea aqueous solution was performed on 316L stainless steel to rapidly improve its surface properties in this work.Test results show that the PEG2000 macromolecules increased the nitriding energy via enhancing the ability to bond the produced gas film to the metal/electrolyte interface.The cross-sectional morphologies indicate that a thick nitrided layer was obtained when the urea concentration was 543 g I^-1,corresponding to a Vickers hardness 450 HV(0.1),which was 3.5 times larger than that of the substrate.The nitrided layer mainly contained expanded austenite(γN),oxides and iron nitrides(e.g.,Fe3O4 and FeN(0.076)).In terms of its performance,coefficient of friction(COF)of the nitride layer decreased to nearly two-thirds that of the untreated layer,and the passivation current densities of the nitrided sample in a 3.5%NaCl solution decreased by an order of magnitude compared to that of the substrate.Therefore,the approach presented herein provides an attractive way to modify the effect of CPEN in a urea aqueous solution.
文摘β-Sialon was produced by carbon thermal nitriding reaction in N_2 gas atmosphere when the mixtures of bauxite and anthracite were put into vertical furnace. According to the mass loss of raw materials and the result of X-ray diffration (XRD) of products, the influences of the process parameters on the compositions and relative contents of products, such as the fixed carbon content, the flow of N2, the soaking time and the temperature, were researched.
基金supported by the National Natural Science Foundation of China(No.50174020).
文摘CW-CO2 laser nitriding technique was applied to improve the properties （such as aging property and the core loss） of grain oriented silicon steel. The samples were nitrided with regular space. Laser power density and scanning speed were chosen as 7.8×10^5W·cm^-2 and 100mm·min^-1. By some laser irradiation, Fe4N and Fe3N were formed in the nitrided zone. The nitrided samples were annealed at the temperatures ranged from 100 to 90℃. The core loss of some interested samples was tested. The results show that the core loss of the nitrided samples with different thickness of 0.23 and 0.30mm decreased by 14.9% and 9.4% respectively, and the aging property were improved up to 800℃. The mechanism of laser nitriding to improve the properties of grain oriented silicon steel is discussed.
文摘Plasma rare earth nitriding of nanocrystallized surface layer of 3J33B steel at 350 and 410℃ for different time was studied. The microstructure observation and X-ray diffraction（XRD） analysis show that the nitriding layer consists of compound layer （γ′-Fe4N） and diffusion layer （α-Fe）. Lanthanum content profiles in nanocrystallized surface layer were measured using glow discharge spectometry（GDS）. The results show that lanthanum can diffuse into the surface layer of the steel to a large depth. Based on the experimental results mentioned above, the diffusion coefficients and activation energy of lanthanum in γ′ phase are calculated to be 1.03×10 -15 cm2/s （350℃）, 1.75×10 -15 cm2/s （410℃） and 31.313kJ/mol, respectively.
