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 andCr<sub>2</sub>N phases with compact nano-crystalline structures.The typical hardness values of HV<sub>0.05</sub> increased 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 Cr<sub>2</sub>N phases at the nitrided surfaces.展开更多
The process of the co cementation layers of low temperature powder multicomponent thermochemical treatment with B C N RE and the structure and properties were studied and compared with those of conventional boro carbo...The process of the co cementation layers of low temperature powder multicomponent thermochemical treatment with B C N RE and the structure and properties were studied and compared with those of conventional boro carbo nitriding (B C N) by X ray diffractometer, potentiostat and wear machine. The results show that rare earth elements have significant catalytic effect within proper limits. Both wear resistance and corrosion resistance of the B C N RE co cementation layer are greatly increased in comparison with those of the B C N. The function mechanism of rare earth elements is also discussed.展开更多
β-Sialon was produced by carbon thermal nitriding reaction in N2 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 o...β-Sialon was produced by carbon thermal nitriding reaction in N2 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
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
Nitriding is employed for the hard Fe electrodeposition to produce a hard-facing and antiwear coating. It only takes 1 h for the hard Fe coating, which is much shorter than nitriding the Fe and steel. The results show...Nitriding is employed for the hard Fe electrodeposition to produce a hard-facing and antiwear coating. It only takes 1 h for the hard Fe coating, which is much shorter than nitriding the Fe and steel. The results showed that the nitriding can increase the microhardness, wear resistance of the coating, as well as the bonding strength of the coating with the substrate. Additionally it can eliminate the brittleness, turn the internal stress of the coating from tension to compression. The wear resistance of the nitrided Fe coating is 4.6 times as high as that of Cr coating. It is simple and economic to combine hard be electroplating and nitriding, which is a good technology of the tribological surface modification.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 duplex treatment of plasma Zr-alloying and plasma nitriding was used to improve the tribological properties of Ti-6Al-4V. The microstructure of the Zr-N composite(alloyed) layer formed on Ti-6Al-4V and its hardness,...A duplex treatment of plasma Zr-alloying and plasma nitriding was used to improve the tribological properties of Ti-6Al-4V. The microstructure of the Zr-N composite(alloyed) layer formed on Ti-6Al-4V and its hardness, friction and wear properties were investigated by using OM, SEM, GDOES, EDS, microhardness tester as well as ball-on-disk tribometer. The results of microstructural analysis show that the alloyed layer is compact and uniform and is mainly composed of ZrN, TiN_(0.3) and AlN. A very tiny adhesive and slight oxidation wear is the primary wear mechanism for the modified Ti-6Al-4V. The tribological property is improved significantly after the duplex treatment. The good combination of antifriction and wear resistance for modified Ti-6Al-4V is mainly attributed to the higher surface hardness of metal nitrides formed on the surface and enhanced supporting of the Zr-diffusing layer.展开更多
The plasma electrolytic carbonitriding(PEC/N)process is applied to cast iron using an aqueous solution of acetamide and glycerin as the electrolyte.Mechanical properties of the carbonitriding layers on cast iron are i...The plasma electrolytic carbonitriding(PEC/N)process is applied to cast iron using an aqueous solution of acetamide and glycerin as the electrolyte.Mechanical properties of the carbonitriding layers on cast iron are investigated.After the PEC/N treatment,the microhardness and wear resistance of cast iron are improved significantly compared to the untreated substrate.When the substrate is processed at 350V for 60 s,the coating presents the highest microhardness and it is about 554.14HK0.02,and the coating with the highest hardness has the best wear resistance.展开更多
Titanium(Ti)nitrides were in situ grown on Ti6Al4V alloy(TA)using a glow discharge plasma nitriding(GDPN).The morphology,chemical composition,phase and mechanical property of the obtained nitrided TA were analyzed usi...Titanium(Ti)nitrides were in situ grown on Ti6Al4V alloy(TA)using a glow discharge plasma nitriding(GDPN).The morphology,chemical composition,phase and mechanical property of the obtained nitrided TA were analyzed using a scanning electron microscope(SEM),energy dispersive spectroscope(EDS),X-ray diffraction(XRD),and nanoindentation tester,respectively.The tribological performances of un-nitrided and nitrided TAs were evaluated using a ball-on-plate wear tester,and the wear mechanism was also discussed in detail.The results show that the nitrided layer with the compound and diffusion layers is formed on the nitrided TA,which is composed of δ-TiN and a-Ti phases.The nanohardness and elastic modulus of nitrided TA are 6.05 and 143.13 GPa,respectively,higher than those of un-nitrided TA.The friction reduction and anti-wear performances of nitrided TA are better than those of un-nitrided TA,and the wear mechanism is primary abrasive wear,accompanying with adhesive wear,which is attributed to the formation of Ti nitrides with the high nanohardness and elastic modulus.展开更多
Prior studies have noted that gas nitriding has a considerable effect for wear resistance. The aim of this paper is to study the influence of gas nitriding time (12, 24, 36 and 48 h) in the wear behaviour of 42CrMo4 s...Prior studies have noted that gas nitriding has a considerable effect for wear resistance. The aim of this paper is to study the influence of gas nitriding time (12, 24, 36 and 48 h) in the wear behaviour of 42CrMo4 steel. It has been assessed by micro hardness, pin-on-disc tribosystem, and SEM through the nitrided layer for each nitriding time. The study relates to the performance of the compound layer and the diffusion layer with respect to adhesive wear. The results were analyzed in terms of the weight lost during wear, for nitrided steel with and without the compound layer, and for untreated steel. It has been observed that wear rate varies as a function of the tests conditions due to the presence of different wear mechanisms. Thus, for short tests conditions wear rate depends on two mechanisms: plastic deformation and adhesive wear, whereas for large tests conditions the mechanisms controlling wear rate are abrasive and oxidative wear. Furthermore, this study contains an analysis of the wear mechanisms of a nitrided part, founded on scanning electron microscopy (SEM) observations of the wear traces at various stages of the evolution of wear. The SEM examination of worn surfaces revealed signatures for the adhesion, abrasion, delamination and tribochemical (oxidative) modes of wear. This is an important issue for future research.展开更多
In this paper,Si3N4 fiber materials were fabricated by nitridation of porous Si green bodies,which were prepared by the foaming method combined with gel-casting.The effect of the nitriding process(the heating rate and...In this paper,Si3N4 fiber materials were fabricated by nitridation of porous Si green bodies,which were prepared by the foaming method combined with gel-casting.The effect of the nitriding process(the heating rate and the nitrogen flow rate)on the phase and the microstructure was studied.The results show that decreasing the heating rate and the nitrogen flow rate is both beneficial to the growth of Si3N4 nanofibers and promoting the disintegration of the pore wall structure of the porous green bodies.The optimized nitrogen flow rate and the heating rate for the growth of silicon nitride fibers are 150 mL/min and 0.5℃/min,respectively.展开更多
The present work is to characterize both processes of thermochemical treatments: plasma nitriding and gas. The tests were carried out in collaboration with the Franco-Tunisian heat treatment (F3T) applied to a widely ...The present work is to characterize both processes of thermochemical treatments: plasma nitriding and gas. The tests were carried out in collaboration with the Franco-Tunisian heat treatment (F3T) applied to a widely used steel in industrial production as a tool for hot work on X38CrMoV5 (AISI H13). The material underwent a first cycle of hardening heat treatment at 1030℃ followed by two successive incomes at 550℃ and 590℃. After nitriding (ion and gas), the quantification of wear was performed in the laboratory of tribology at SUPMECA (St. Ouen). After defining the test conditions on the alternative tribometer ensuring on one hand a quantitatively sufficient wear and avoiding on the other hand, the phenomenon of jamming. The conditions chosen are: 58.8 N load, frequency 0.5 Hz, friction coefficient μ = 0.5. The wear tracks were scanned using the profilometer Talysurf 5 M type, which allowed us to assess the volume used and the wear rate. Moreover, these tracks were characterized by metallography. What emerges from this work is that the control parameters of ion nitriding ensures a better depth of treatment for the same holding time with a total absence of the white layer known for chipping and fragility.展开更多
The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excel...The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excellent properties such as improved hardness and wear resistance along with sustained corrosion resistance. The concentrated nitrogen via SPN process was injected to form S-phase with time at 713 K. This study was carried out under the conditions of 44 at% of nitrogen injection, which was higher than 25 at% known as the condition of no precipitation of S-phase formed by the SPN process, and 20 K higher than the maximum temperature without precipitation phase. The hardness analysis of stainless steel sample treated by the SPN process at 713 K showed a much higher value than the typical nitriding hardness at a depth of lower nitrogen than the maximum nitrogen concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated nitrogen formed in the SPN process reacting with the alloying elements contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme hardening effect;that is, the movement of precipitates and dislocations due to the GP-zone (Guinier-Preston zone).展开更多
The effects of the nitrided case produced by gas nitriding processes on the mechanical and corrosion resistance properties of the JIS SACM 645 steel were studied in this paper. JIS SACM 645 steel specimens with differ...The effects of the nitrided case produced by gas nitriding processes on the mechanical and corrosion resistance properties of the JIS SACM 645 steel were studied in this paper. JIS SACM 645 steel specimens with different substrate hardness were gas nitrided at 530?C for various nitriding durations. Nitrided specimens were characterized by means of optical and scanning electron microscopy, X-ray diffraction, glow discharge optical spectrometry, microhardness profiling, wear test, torsion mode fatigue test as well as electrochemical corrosion test in an aerated 3.5% NaCl solution. The surface hardness values of the nitrided specimens with Fe3N and Fe4N phases precipitated in the case layer were observed higher than 1000 HV0.1. Mass loss measurement of the wear test showed increases of wear resistance of the nitrided specimens, and the mass losses of the specimens were strongly influenced by nitriding durations. Electrochemical measurements showed that corrosion current density of the specimens was significantly decreased after nitriding and the corrosion potential was shifted to the noble direction as the increase of the nitriding durations. The fatigue limit of the specimen nitrided for 96 h rose 44% to 600 MPa in exceeding the untreated specimen in this study.展开更多
A series of experiments were carried out to investigate the influence of pure rare earth addition on the plasma nitriding response of low alloy steel. For this purpose, pure rare earth metals (La, Ce and Nd) were put ...A series of experiments were carried out to investigate the influence of pure rare earth addition on the plasma nitriding response of low alloy steel. For this purpose, pure rare earth metals (La, Ce and Nd) were put into the plasma nitriding furnace as sputter sources during nitriding of 722M24 steel. A variety of experimental and analytical techniques were employed to evaluate the structures and hardening response of the nitrided layers which included metallography for structural examination, glow discharge spectrometry and secondary ion mass spectrometry for chemical composition profile analysis, X ray diffraction for phase identification and microhardness testing for hardness profile measurements. The results show that the incorporation of rare earth metals in the glow discharge during plasma nitriding not only influences the discharge characteristics but also results in the deposition of rare earth atoms and their compounds onto the specimen surface. These significantly affect the response of the investigated steel to plasma nitriding. The extent of the influence on plasma nitriding varies with different rare earth metals.展开更多
The cross-sectional microstructure of an ion-nitrided layer on a No.45 steel was studied by transmission electron microscopy (TEM). The results show that the columnar crystals constitute the compound layer. Most of th...The cross-sectional microstructure of an ion-nitrided layer on a No.45 steel was studied by transmission electron microscopy (TEM). The results show that the columnar crystals constitute the compound layer. Most of them have the microstructure of alternating ε-Fe2-3N and γ-Fe4N and others are single ε-Fe2-3N phase. There are abnormal strip ferrites between the columnar crystals. The transition layer mainly consists of spherical γ-Fe4N and cementite (Fe3C) particles in the pearlite are dissolved in this layer. In diffusion layer, besides the equilibrium phase γ-Fe4N, there are α -Fe16N2 and the satellite spots around main spots of α-Fe16N2 demonstrate its modulation structure. A metastable ordered cluster zone of the nitropen atoms was found in the division layer.展开更多
The sliding wear and impact wear resistances of D2 steel with nitriding layer, PVD titanium nitride coating and their duplex treatment were investigated. The experimental results suggest that the duplex treatment has ...The sliding wear and impact wear resistances of D2 steel with nitriding layer, PVD titanium nitride coating and their duplex treatment were investigated. The experimental results suggest that the duplex treatment has the best sliding and impact wear resistances under experimental conditions. And the wear resistance of PVD titanium nitride is better than that of nitriding. The impact wear resistance and wear mechanism of all three surface layers remain unchanged under impact load of 0.2 J or 1 J. All samples end with the same symptom of flaking.展开更多
Low-temperature nitriding of steel or iron can produce an expanded austenite phase,which is a solid solution of a large amount of nitrogen dissolved interstitially in fcc lattice.It is characteristic that the nitogen ...Low-temperature nitriding of steel or iron can produce an expanded austenite phase,which is a solid solution of a large amount of nitrogen dissolved interstitially in fcc lattice.It is characteristic that the nitogen depth profiles in expanded austenite exhibit plateau-type shapes.Such behavior cannot be considered with a standard analytic solution for diffusion in a semi-infinite solid and a new approach is necessary.We formulate a model of interdiffusion in viscoelastic solid(Maxwellmodel)during the nitriding process.It combines themass conservation and Vegard’s rule with the Darken bi-velocity method.The model is formulated in any dimension,i.e.,a mixture is included in R^(n),n=1,2,3.For the system in one dimension,n=1,we transform a differential-algebraic system of 5 equations to a differential system of 2 equations only,which is better to study numerically and analytically.Such modification allows the formulation of effective mixed-type boundary conditions.The resulting nonlinear strongly coupled parabolic-elliptic differential initial-boundary Stefan type problem is solved numerically and a series of simulations is made.展开更多
Ti-N graded ceramic layer was formed on titanium by using DC hollow-cathode plasma nitriding technique. The structure of Ti-N layer was analyzed using X-ray diffractometry(XRD) with Cu Kα radiation, and the microhard...Ti-N graded ceramic layer was formed on titanium by using DC hollow-cathode plasma nitriding technique. The structure of Ti-N layer was analyzed using X-ray diffractometry(XRD) with Cu Kα radiation, and the microhardness( HV0.1) was measured from the surface to inner along the cross section of Ti-N layer. The results indicate that the Ti-N graded layer is composed of ε-Ti2 N, δ-TiN and α-Ti(N) phases. Mechanism discussion shows that hollow-cathode discharge can intensify gas ionization, increase current density and enhance the nitriding potential, which directly increases the thickness of the diffusion coatings compared with traditional nitriding methods.展开更多
A niobium microalloyed nitriding steel has been introduced to meet the high demand in modern engine applications,based on compositions of traditional nitriding steels,and on phase calculation and prediction with JmatP...A niobium microalloyed nitriding steel has been introduced to meet the high demand in modern engine applications,based on compositions of traditional nitriding steels,and on phase calculation and prediction with JmatPro software.The new nitriding steel BTHJ-1 shows a better nitriding tendency,as well as a good combination of strength and toughness,while compared with 38CrMoAl and H13 steels.BTHJ-1 steel also shows a better thermal stability when being held at 620℃.Investigations with OM,TEM,XRD have been made so as to get a better understand on the characteristics of BTHJ-1 steel.The quantities optimization of alloy elements and the grain refinement of niobium seem to be reasons for the improved properties of the nitriding steel.展开更多
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 andCr<sub>2</sub>N phases with compact nano-crystalline structures.The typical hardness values of HV<sub>0.05</sub> increased 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 Cr<sub>2</sub>N phases at the nitrided surfaces.
文摘The process of the co cementation layers of low temperature powder multicomponent thermochemical treatment with B C N RE and the structure and properties were studied and compared with those of conventional boro carbo nitriding (B C N) by X ray diffractometer, potentiostat and wear machine. The results show that rare earth elements have significant catalytic effect within proper limits. Both wear resistance and corrosion resistance of the B C N RE co cementation layer are greatly increased in comparison with those of the B C N. The function mechanism of rare earth elements is also discussed.
文摘β-Sialon was produced by carbon thermal nitriding reaction in N2 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.
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.
文摘Nitriding is employed for the hard Fe electrodeposition to produce a hard-facing and antiwear coating. It only takes 1 h for the hard Fe coating, which is much shorter than nitriding the Fe and steel. The results showed that the nitriding can increase the microhardness, wear resistance of the coating, as well as the bonding strength of the coating with the substrate. Additionally it can eliminate the brittleness, turn the internal stress of the coating from tension to compression. The wear resistance of the nitrided Fe coating is 4.6 times as high as that of Cr coating. It is simple and economic to combine hard be electroplating and nitriding, which is a good technology of the tribological surface modification.
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.
基金Funded by the National Natural Science Foundation of China(Nos.51474154,51401141,51501125)the Provincial Natural Science Foundation of Shanxi(Nos.2014011015-7,2014021017-3)
文摘A duplex treatment of plasma Zr-alloying and plasma nitriding was used to improve the tribological properties of Ti-6Al-4V. The microstructure of the Zr-N composite(alloyed) layer formed on Ti-6Al-4V and its hardness, friction and wear properties were investigated by using OM, SEM, GDOES, EDS, microhardness tester as well as ball-on-disk tribometer. The results of microstructural analysis show that the alloyed layer is compact and uniform and is mainly composed of ZrN, TiN_(0.3) and AlN. A very tiny adhesive and slight oxidation wear is the primary wear mechanism for the modified Ti-6Al-4V. The tribological property is improved significantly after the duplex treatment. The good combination of antifriction and wear resistance for modified Ti-6Al-4V is mainly attributed to the higher surface hardness of metal nitrides formed on the surface and enhanced supporting of the Zr-diffusing layer.
基金by the National Natural Science Foundation of China under Grant Nos 10735090 and 11005151(Young Scientists Fund).
文摘The plasma electrolytic carbonitriding(PEC/N)process is applied to cast iron using an aqueous solution of acetamide and glycerin as the electrolyte.Mechanical properties of the carbonitriding layers on cast iron are investigated.After the PEC/N treatment,the microhardness and wear resistance of cast iron are improved significantly compared to the untreated substrate.When the substrate is processed at 350V for 60 s,the coating presents the highest microhardness and it is about 554.14HK0.02,and the coating with the highest hardness has the best wear resistance.
基金Funded by the Fundamental Research Funds for the Central Universities(Nos.2232018A3-08,2232018D3-04)
文摘Titanium(Ti)nitrides were in situ grown on Ti6Al4V alloy(TA)using a glow discharge plasma nitriding(GDPN).The morphology,chemical composition,phase and mechanical property of the obtained nitrided TA were analyzed using a scanning electron microscope(SEM),energy dispersive spectroscope(EDS),X-ray diffraction(XRD),and nanoindentation tester,respectively.The tribological performances of un-nitrided and nitrided TAs were evaluated using a ball-on-plate wear tester,and the wear mechanism was also discussed in detail.The results show that the nitrided layer with the compound and diffusion layers is formed on the nitrided TA,which is composed of δ-TiN and a-Ti phases.The nanohardness and elastic modulus of nitrided TA are 6.05 and 143.13 GPa,respectively,higher than those of un-nitrided TA.The friction reduction and anti-wear performances of nitrided TA are better than those of un-nitrided TA,and the wear mechanism is primary abrasive wear,accompanying with adhesive wear,which is attributed to the formation of Ti nitrides with the high nanohardness and elastic modulus.
文摘Prior studies have noted that gas nitriding has a considerable effect for wear resistance. The aim of this paper is to study the influence of gas nitriding time (12, 24, 36 and 48 h) in the wear behaviour of 42CrMo4 steel. It has been assessed by micro hardness, pin-on-disc tribosystem, and SEM through the nitrided layer for each nitriding time. The study relates to the performance of the compound layer and the diffusion layer with respect to adhesive wear. The results were analyzed in terms of the weight lost during wear, for nitrided steel with and without the compound layer, and for untreated steel. It has been observed that wear rate varies as a function of the tests conditions due to the presence of different wear mechanisms. Thus, for short tests conditions wear rate depends on two mechanisms: plastic deformation and adhesive wear, whereas for large tests conditions the mechanisms controlling wear rate are abrasive and oxidative wear. Furthermore, this study contains an analysis of the wear mechanisms of a nitrided part, founded on scanning electron microscopy (SEM) observations of the wear traces at various stages of the evolution of wear. The SEM examination of worn surfaces revealed signatures for the adhesion, abrasion, delamination and tribochemical (oxidative) modes of wear. This is an important issue for future research.
基金This work was supported by the National Natural Science Foundation of China(NSFC-No.51672256)National Natural Science Foundation of China-Key Projects of Henan United Fund(NSFC-No.U1904217).
文摘In this paper,Si3N4 fiber materials were fabricated by nitridation of porous Si green bodies,which were prepared by the foaming method combined with gel-casting.The effect of the nitriding process(the heating rate and the nitrogen flow rate)on the phase and the microstructure was studied.The results show that decreasing the heating rate and the nitrogen flow rate is both beneficial to the growth of Si3N4 nanofibers and promoting the disintegration of the pore wall structure of the porous green bodies.The optimized nitrogen flow rate and the heating rate for the growth of silicon nitride fibers are 150 mL/min and 0.5℃/min,respectively.
文摘The present work is to characterize both processes of thermochemical treatments: plasma nitriding and gas. The tests were carried out in collaboration with the Franco-Tunisian heat treatment (F3T) applied to a widely used steel in industrial production as a tool for hot work on X38CrMoV5 (AISI H13). The material underwent a first cycle of hardening heat treatment at 1030℃ followed by two successive incomes at 550℃ and 590℃. After nitriding (ion and gas), the quantification of wear was performed in the laboratory of tribology at SUPMECA (St. Ouen). After defining the test conditions on the alternative tribometer ensuring on one hand a quantitatively sufficient wear and avoiding on the other hand, the phenomenon of jamming. The conditions chosen are: 58.8 N load, frequency 0.5 Hz, friction coefficient μ = 0.5. The wear tracks were scanned using the profilometer Talysurf 5 M type, which allowed us to assess the volume used and the wear rate. Moreover, these tracks were characterized by metallography. What emerges from this work is that the control parameters of ion nitriding ensures a better depth of treatment for the same holding time with a total absence of the white layer known for chipping and fragility.
文摘The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excellent properties such as improved hardness and wear resistance along with sustained corrosion resistance. The concentrated nitrogen via SPN process was injected to form S-phase with time at 713 K. This study was carried out under the conditions of 44 at% of nitrogen injection, which was higher than 25 at% known as the condition of no precipitation of S-phase formed by the SPN process, and 20 K higher than the maximum temperature without precipitation phase. The hardness analysis of stainless steel sample treated by the SPN process at 713 K showed a much higher value than the typical nitriding hardness at a depth of lower nitrogen than the maximum nitrogen concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated nitrogen formed in the SPN process reacting with the alloying elements contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme hardening effect;that is, the movement of precipitates and dislocations due to the GP-zone (Guinier-Preston zone).
文摘The effects of the nitrided case produced by gas nitriding processes on the mechanical and corrosion resistance properties of the JIS SACM 645 steel were studied in this paper. JIS SACM 645 steel specimens with different substrate hardness were gas nitrided at 530?C for various nitriding durations. Nitrided specimens were characterized by means of optical and scanning electron microscopy, X-ray diffraction, glow discharge optical spectrometry, microhardness profiling, wear test, torsion mode fatigue test as well as electrochemical corrosion test in an aerated 3.5% NaCl solution. The surface hardness values of the nitrided specimens with Fe3N and Fe4N phases precipitated in the case layer were observed higher than 1000 HV0.1. Mass loss measurement of the wear test showed increases of wear resistance of the nitrided specimens, and the mass losses of the specimens were strongly influenced by nitriding durations. Electrochemical measurements showed that corrosion current density of the specimens was significantly decreased after nitriding and the corrosion potential was shifted to the noble direction as the increase of the nitriding durations. The fatigue limit of the specimen nitrided for 96 h rose 44% to 600 MPa in exceeding the untreated specimen in this study.
文摘A series of experiments were carried out to investigate the influence of pure rare earth addition on the plasma nitriding response of low alloy steel. For this purpose, pure rare earth metals (La, Ce and Nd) were put into the plasma nitriding furnace as sputter sources during nitriding of 722M24 steel. A variety of experimental and analytical techniques were employed to evaluate the structures and hardening response of the nitrided layers which included metallography for structural examination, glow discharge spectrometry and secondary ion mass spectrometry for chemical composition profile analysis, X ray diffraction for phase identification and microhardness testing for hardness profile measurements. The results show that the incorporation of rare earth metals in the glow discharge during plasma nitriding not only influences the discharge characteristics but also results in the deposition of rare earth atoms and their compounds onto the specimen surface. These significantly affect the response of the investigated steel to plasma nitriding. The extent of the influence on plasma nitriding varies with different rare earth metals.
文摘The cross-sectional microstructure of an ion-nitrided layer on a No.45 steel was studied by transmission electron microscopy (TEM). The results show that the columnar crystals constitute the compound layer. Most of them have the microstructure of alternating ε-Fe2-3N and γ-Fe4N and others are single ε-Fe2-3N phase. There are abnormal strip ferrites between the columnar crystals. The transition layer mainly consists of spherical γ-Fe4N and cementite (Fe3C) particles in the pearlite are dissolved in this layer. In diffusion layer, besides the equilibrium phase γ-Fe4N, there are α -Fe16N2 and the satellite spots around main spots of α-Fe16N2 demonstrate its modulation structure. A metastable ordered cluster zone of the nitropen atoms was found in the division layer.
文摘The sliding wear and impact wear resistances of D2 steel with nitriding layer, PVD titanium nitride coating and their duplex treatment were investigated. The experimental results suggest that the duplex treatment has the best sliding and impact wear resistances under experimental conditions. And the wear resistance of PVD titanium nitride is better than that of nitriding. The impact wear resistance and wear mechanism of all three surface layers remain unchanged under impact load of 0.2 J or 1 J. All samples end with the same symptom of flaking.
基金the National Science Center(Poland)Decision No.UMO-2013/11/B/ST8/03758the Faculty of Applied Mathematics AGH UST statutory tasks within subsidy of Ministry of Science and Higher Education(Grant No.16.16.420.054).
文摘Low-temperature nitriding of steel or iron can produce an expanded austenite phase,which is a solid solution of a large amount of nitrogen dissolved interstitially in fcc lattice.It is characteristic that the nitogen depth profiles in expanded austenite exhibit plateau-type shapes.Such behavior cannot be considered with a standard analytic solution for diffusion in a semi-infinite solid and a new approach is necessary.We formulate a model of interdiffusion in viscoelastic solid(Maxwellmodel)during the nitriding process.It combines themass conservation and Vegard’s rule with the Darken bi-velocity method.The model is formulated in any dimension,i.e.,a mixture is included in R^(n),n=1,2,3.For the system in one dimension,n=1,we transform a differential-algebraic system of 5 equations to a differential system of 2 equations only,which is better to study numerically and analytically.Such modification allows the formulation of effective mixed-type boundary conditions.The resulting nonlinear strongly coupled parabolic-elliptic differential initial-boundary Stefan type problem is solved numerically and a series of simulations is made.
基金Project(50271045) supported by the National Natural Science Foundation of China Project supported by the Talent Foundation of Beijing Jiaotong University, China
文摘Ti-N graded ceramic layer was formed on titanium by using DC hollow-cathode plasma nitriding technique. The structure of Ti-N layer was analyzed using X-ray diffractometry(XRD) with Cu Kα radiation, and the microhardness( HV0.1) was measured from the surface to inner along the cross section of Ti-N layer. The results indicate that the Ti-N graded layer is composed of ε-Ti2 N, δ-TiN and α-Ti(N) phases. Mechanism discussion shows that hollow-cathode discharge can intensify gas ionization, increase current density and enhance the nitriding potential, which directly increases the thickness of the diffusion coatings compared with traditional nitriding methods.
文摘A niobium microalloyed nitriding steel has been introduced to meet the high demand in modern engine applications,based on compositions of traditional nitriding steels,and on phase calculation and prediction with JmatPro software.The new nitriding steel BTHJ-1 shows a better nitriding tendency,as well as a good combination of strength and toughness,while compared with 38CrMoAl and H13 steels.BTHJ-1 steel also shows a better thermal stability when being held at 620℃.Investigations with OM,TEM,XRD have been made so as to get a better understand on the characteristics of BTHJ-1 steel.The quantities optimization of alloy elements and the grain refinement of niobium seem to be reasons for the improved properties of the nitriding steel.
