Using a melt-cooling process with the host glass,Dy_(2)O_(3)(1 wt%,2 wt%,3 wt%,and 4 wt%) doped tellurite glasses were produced.A(65-x)TeO_(2)-20B_(2)O_(3)-10Al_(2)O_(3)-SGeO_(2)-xDy_(2)O_(3) glass system was analyzed...Using a melt-cooling process with the host glass,Dy_(2)O_(3)(1 wt%,2 wt%,3 wt%,and 4 wt%) doped tellurite glasses were produced.A(65-x)TeO_(2)-20B_(2)O_(3)-10Al_(2)O_(3)-SGeO_(2)-xDy_(2)O_(3) glass system was analyzed by Xray diffraction.The patterns have a hump at 2θ=27°-29° and no sharp peaks,indicating that all the glass samples are amorphous.The Vickers microhardness determines how resistant a glass is to persistent deformation produced by a harder substance.Differential scanning calorimetry(DSC) at 300-550℃ was used to evaluate the thermal properties of the Dy_x glass samples.The glass transition temperature T_g(small endothermic peak),start crystallization temperature T_x and crystallization temperature T_c can all be seen on the DSC thermogram(exothermic peaks).The UV-Vis transmittance and absorption spectra were measured.The optical data show that the values of E_d^(ir),E_g^(Ind) and E_U decrease as the amount of Dy_(2)O_(3)increases,indicating a narrowing of the tails due to localized states in the forbidden gap.A concentration quenching event occurs when Dy^(3+) concentrations are above a certain threshold(1%).The addition of Dy_(2)O_(3) increases glass density,while the addition of other Dy(Ⅲ) oxides increases sample density.The radiation shielding values change as a consequence of density fluctuation.The sample with the highest amount of Dy_(2)O_(3)(Dy_(4)) has stronger radiation shielding characteristics;hence,it is superior in terms of shielding outcomes at all energy levels.Such Dy_x samples can be used in various forms of ionizing radiation shielding.展开更多
Silane coupling agent KH560 was used to modify the surface of nano-α-Al<sub>2</sub>O<sub>3</sub> in ethanol-aqueous solution with different proportions. The particle size of nano-α-Al<sub&...Silane coupling agent KH560 was used to modify the surface of nano-α-Al<sub>2</sub>O<sub>3</sub> in ethanol-aqueous solution with different proportions. The particle size of nano-α-Al<sub>2</sub>O<sub>3</sub> was determined by nano-particle size analyzer, and the effects of nano-α-Al<sub>2</sub>O<sub>3</sub> content, ethanol-aqueous solution ratio and KH560 dosage on the dispersion and particle size of nano-α-Al<sub>2</sub>O<sub>3</sub> were investigated. The material structure before and after modification was determined by Fourier transform infrared spectroscopy (FTIR). Aqueous polyurethane resin and inorganic components are combined with modified nano-α-Al<sub>2</sub>O<sub>3</sub> dispersion to form chromium-free passivation solution. The solution is coated on the galvanized sheet, the adhesion and surface hardness are tested, the bonding strength of the coating and the surface hardness of the substrate are discussed. The corrosion resistance and surface morphology of the matrix were investigated by electrochemical test, neutral salt spray test and scanning electron microscope test. The chromium-free passivation film formed after the modification of nano-α-Al<sub>2</sub>O<sub>3</sub> increases the surface hardness of galvanized sheet by about 85%. The corrosion resistance of the film is better than that of a single polyurethane film. The results show that the surface hardness and corrosion resistance of polyurethane resin composite passivation film are significantly improved by the introduction of nano-α-Al<sub>2</sub>O<sub>3</sub>.展开更多
Surface hardness value is a commonly used indicator for describing the mechanical property of stere- olithography parts. In order to investigate colorants how to influence the surface hardness of colorful resin compon...Surface hardness value is a commonly used indicator for describing the mechanical property of stere- olithography parts. In order to investigate colorants how to influence the surface hardness of colorful resin component, a procedure is proposed to fabricate testing specimens based on color stereolithography technology in this study. Liquid photosensitive resin LPR2001 is mixed with two colorants(phthalocyanine blue and eosin powder) respectively before curing. The phthalocyanine blue powder is insoluble and only dispersive in the solid- liquid mixture which results in deposits. Therefore, surface modification is conducted to the phthalocyanine blue powder for improving wettability. By contrast, the eosin powder is dissoluble and does not cause any deposits in the liquid resin. Specimens are produced by laser curing colored resin and tested by MTSRNano Indenter XP system. The change of hardness values is illustrated at certain mass percentages of colorant. Comparisons and discussions are carried out to explain the colorants' efect. It is concluded that incorporating colorant to liquid resin results in decreasing the surface hardness of components. But sensibilization efect of the colorants also influences the curing process. Surface modification to the phthalocyanine blue powder is a feasible method to increase the hardness value of color stereolithography components. Dissolvable eosin has an approximate linear efect on surface hardness.展开更多
In this current work,aluminum alloy grade 2024 is adopted as a plate material that is used in the rolling process with three different parameters including thickness reduction,forming temperature,and density of lubric...In this current work,aluminum alloy grade 2024 is adopted as a plate material that is used in the rolling process with three different parameters including thickness reduction,forming temperature,and density of lubrication type.The experimental procedure of the rolling process is performed using the design of the experiment based on the Taguchi technique(L27),then surface roughness,surface hardness,and surface residual stresses are measured.The results showed that the lubrication density has a significant impact on the surface roughness which depends on the lubrication properties(mineral oil type,natural fat,and kinematic viscosity)while surface hardness and surface residual stresses were strongly affected by thickness reduction.On the other side,the augment in forming temperature can decrease the quality of the final surface finish and the surface hardness but reduce the induced residual stresses.The best surface finish is obtained based on the optimum condition of the rolling factors are(R%_(3),T_(1),andρ_(3))while the optimum condition of rolling parameters that generate higher hardness and compressive residual stresses are(R%_(3)T_(1)ρ_(1)).展开更多
The effects of picosecond Nd:YAG laser irradiation on chemical and morphological surface characteristics of the commercially pure titanium and Ti–13Nb–13Zr alloy in air and argon atmospheres were studied under diffe...The effects of picosecond Nd:YAG laser irradiation on chemical and morphological surface characteristics of the commercially pure titanium and Ti–13Nb–13Zr alloy in air and argon atmospheres were studied under different laser output energy values.During the interaction of laser irradiation with the investigated materials,a part of the energy was absorbed on the target surface,influencing surface modifications.Laser beam interaction with the target surface resulted in various morphological alterations,resulting in crater formation and the presence of microcracks and hydrodynamic structures.Moreover,different chemical changes were induced on the target materials’surfaces,resulting in the titanium oxide formation in the irradiation-affected area and consequently increasing the irradiation energy absorption.Given the high energy absorption at the site of interaction,the dimensions of the surface damaged area increased.Consequently,surface roughness increased.The appearance of surface oxides also led to the increased material hardness in the surface-modified area.Observed chemical and morphological changes were pronounced after laser irradiation of the Ti–13Nb–13Zr alloy surface.展开更多
In this paper, we tried to present a qualitative correlation, based on extensive experimental trials between the value and the evolution of the friction coefficient, wear and contact temperature in the case of linear ...In this paper, we tried to present a qualitative correlation, based on extensive experimental trials between the value and the evolution of the friction coefficient, wear and contact temperature in the case of linear dry contact, thermoplastic material reinforced with SGF （short glass fibres） and various steel surfaces. We tried, believing successfully, the graphic illustration of the evolution of the steel surface wear and of the contact temperature, depending on the friction coefficient. It was analyzed in detail the influence of the normal load and sliding speed, but also of the metallic surface roughness on the friction coefficient.展开更多
The present work aims to demonstrate the capabilities of Laser-induced Breakdown Spectroscopy(LIBS)coupled with a multivariate technique for rapid quantification and classification of old Indian coins made of various ...The present work aims to demonstrate the capabilities of Laser-induced Breakdown Spectroscopy(LIBS)coupled with a multivariate technique for rapid quantification and classification of old Indian coins made of various alloys.Thirteen old Indian coins in different years of circulation,(1922–1986)were selected for the study.The concentrations were determined by Calibration free LIBS(CF-LIBS)method.The concentration of cuprum(Cu)is negligible,and aluminum(Al)is maximum in the first five coins,and vice-versa in the remaining eight coins.Two different multivariate methods,Principal Component Analysis(PCA)and Soft Independent Modelling of Class Analogy(SIMCA)have been used to classify and identify the coins.PCA classified all thirteen samples into four main alloy categories.The discernment of unknown samples to their probable class membership of alloy was performed using SIMCA.The surface hardness(Brinell hardness number)is linearly correlated with the plasma temperature and LIBS intensity ratios.The sample surface of the first and fifth coin belongs to Al-alloy,having the least surface hardness,and it became harder for Cu–Ni alloy,Ni-brass alloy,and bronze alloy.The hardness of the surface is more for bronze sample twelve.It is also observed that the plasma temperature increases monotonically with the Brinell hardness number.This analysis provides valuable information on fabrication methodology and explains large diversification in the elementary composition of old coins.展开更多
Nitriding of the surface in martensitic stainless steels is commonly carried out to improve their wear resistance. The process of plasma nitriding in stainless steel is influenced by two mechanisms: physical diffusion...Nitriding of the surface in martensitic stainless steels is commonly carried out to improve their wear resistance. The process of plasma nitriding in stainless steel is influenced by two mechanisms: physical diffusion through the surface and chemical gas-metal reaction. The inner nitriding interaction involves the simultaneous penetration and formation of a solid solution, as well as the interaction of nitrogen with specific alloying elements, resulting in the development of homogeneous and heterogeneous structures. Our study concludes that the observed intergranular hydrogen embrittlement and crack formation during the surface nitridation process of AMS 5719 martensite alloy steel can be attributed to the ammonium concentration of approximately 50% at a temperature of 530˚C.展开更多
Plasma radical nitriding was performed to harden the surface of SCM440 steel for 1-10 h at temperature range of 450-550℃. This process involved the use of NH3 gas instead of N2 gas employed for the well-established p...Plasma radical nitriding was performed to harden the surface of SCM440 steel for 1-10 h at temperature range of 450-550℃. This process involved the use of NH3 gas instead of N2 gas employed for the well-established plasma nitriding method. No compound layer was formed during this process except the experiment carried out at 500℃ for 10 h. The main phase produced in the diffusion zone was identified to be γ＇-Fe4（N, C）. A diffusion depth increased with increasing treatment temperature and time （up to about 250 μm）. The surface hardness of radical nitrided layer was about two times higher than that of the untreated surface. The tensile test was carried out to estimate the mechanical properties of surface-hardened SCM440 steel prepared at various plasma radical nitriding treatment time and temperature. The influence of radical nitriding treatment on the tensile strength of the specimen was found to be insignificant. The highest value of the ultimate tensile strength was obtained in the experiment carried out at 500℃ for 1 h. However, the elongation was greatly affected by the radical nitriding processing parameters. The maximum value of elongation, which is equal to about 18.1%, was also obtained under the condition of 500℃ for 1 h.展开更多
Microstructure evolution and hardening effect of pure tungsten and W-1.5%ZrO_(2) alloy under carbon ion irradiation are investigated by using transmission electron microscopy and nano-indentation.Carbon ion irradiatio...Microstructure evolution and hardening effect of pure tungsten and W-1.5%ZrO_(2) alloy under carbon ion irradiation are investigated by using transmission electron microscopy and nano-indentation.Carbon ion irradiation is performed at 700℃ with irradiation damages ranging from 0.25 dpa to 2.0 dpa.The results show that the irradiation defect clusters are mainly in the form of dislocation loop.The size and density of dislocation loops increase with irradiation damages intensifying.The W-1.5%ZrO_(2) alloy has a smaller dislocation loop size than that of pure tungsten.It is proposed that the phase boundaries have the ability to absorb and annihilate defects and the addition of ZrO_(2) phase improves the sink strength for irradiation defects.It is confirmed that the W-1.5% ZrO_(2) alloy shows a smaller change in hardness than the pure tungsten after being irradiated.From the above results,we conclude that the addition of ZrO_(2) into tungsten can significantly reduce the accumulation of irradiated defects and improve the irradiation resistance behaviors of the tungsten materials.展开更多
Nitriding of aluminium alloy （AlFel.sZn0.8） in nitrogen and nitrogen-helium mixture was carried out by using 100 Hz-pulsed DC glow discharge. Samples are treated for different durations, namely 4 h, 8 h and 12 h, in...Nitriding of aluminium alloy （AlFel.sZn0.8） in nitrogen and nitrogen-helium mixture was carried out by using 100 Hz-pulsed DC glow discharge. Samples are treated for different durations, namely 4 h, 8 h and 12 h, in nitrogen plasma as well as in a mixture of nitrogen- helium plasma for the same processing duration of 4 h. All nitriding treatments are carried out at an input power of 100 W, filling pressure of 1 mbar and substrates temperature of 250~C. X-ray diffraction （XRD） results show an expansion in lattice spacing and consequently shift of diffraction peaks towards lower angle with the addition of helium in nitrogen plasma. Surface morphology of the treated sample is investigated by scanning electron microscopy （SEM） and energy dispersive X-ray analysis （EDX）. Vickers micro-hardness testing results show increases in surface hardness with processing duration as well as with the addition of helium in nitrogen plasmas. This increase of surface hardness may be attributed to the diffusion of nitrogen content in the surface layer generating internal stresses. It is observed that the addition of helium positively affects the nitriding of samples.展开更多
Estimation of the mechanical properties of concrete in an existing structure is possible with the results of surface hardness and ultrasound tests (nondestructive tests (NDTs)). For both the use of correlation curves ...Estimation of the mechanical properties of concrete in an existing structure is possible with the results of surface hardness and ultrasound tests (nondestructive tests (NDTs)). For both the use of correlation curves is necessary, it is established between NDT and the results of the compressive strength of test specimens or extracted from structure. The objective of this study is to produce correlations between the results of surface hardness and ultrasound NDTs and the compressive strength of the structural concrete in the bleachers of a soccer stadium in the city of Cianorte, which is located in the northwest part of the state of Paraná, Brazil. This concrete structure, which is approximately 26 years old, has some defects, such as corrosion, concrete segregation and cracks. Concrete spalling in one of the slabs has recently raised some concern. Another significant issue is the absence of records regarding concreting of the bleachers’ structure. Therefore, mapping the reinforcement was initially performed according to the results of a surface hardness test, as recommended by standard [1]. An ultrasound test was simultaneously performed according to standard [2] for the same points employed in the surface hardness test. The concrete specimens were extracted according to the recommendations of standard [1] to determine compressive strength, perform the NDT and construct the correlation curves for the results. A total of 26 concrete specimens were obtained from all structures of the bleachers. From the methodology and the results of the study, highly reliable equations were obtained from the correlation curves among the compressive strength of the concrete specimens and the values of the surface hardness index and the ultrasound wave propagation velocity.展开更多
Copper-nickel nanoparticle was directly prepared by flow-levitation method （FL） and sintered by vacuum sintering of powder （VSP） method. Several characterizations, such as transmission electron microscopy （TEM）,...Copper-nickel nanoparticle was directly prepared by flow-levitation method （FL） and sintered by vacuum sintering of powder （VSP） method. Several characterizations, such as transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, differential thermal analysis （DTA）, and energy-dispersive X-ray spectroscopy （EDX） were used to investigate the prepared nanostructures. The results of the study show that FL method could prepare high purity Cu-Ni nanocrystals of uniform spheres with size distribution between 20 and 90 nm. After sintering the bulk nanocrystalline copper-nickel has obvious thermal stability and the surface Webster hardness increases with the rising sintering temperature. At the temperature of 900 ℃, the specimen shows higher surface Webster hardness, which is about two times of traditional materials. When the sintering temperature arrives at 1 000 ℃ the relative density of bulk nanocrystals can reach 97.86 percent. In this paper, the variation tendency of porosity, phase and particles size of bulk along with the changing of sintering temperature have been studied.展开更多
In this paper we tried to present a qualitative correlation,based on extensive experimental determinations between the value and the evolution of the friction coefficient,wear,and contact temperature,in the case of li...In this paper we tried to present a qualitative correlation,based on extensive experimental determinations between the value and the evolution of the friction coefficient,wear,and contact temperature,in the case of linear dry contact,for thermoplastic material reinforced with short glass fibers(SGF)and various steel surfaces.The aim was to highlight the evolution of the wear process depending on the evolution of the friction coefficient.As a result,it was possible to graphically illustrate the evolution of the friction coefficient and the change of the wear process,emphasizing the abrasive,adhesive and corrosive wear.The evolution of the plastic material transfer function of the contact temperature,namely of the power lost by friction(product between the contact pressure and sliding speed,p and v)was aimed and it was highlighted.It has been demonstrated that in the case of a 30%SGF content it can reach and even exceed contact temperatures very close to the flow limit of the plastic material.We tried,believing successfully,the graphic illustration of the evolution of the steel surface wear and of the contact temperature,depending on the friction coefficient.The influence of the normal load and sliding speed was evaluated in detail,but also the influence of the metallic surface roughness on the friction coefficient was discussed.展开更多
In this paper,the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.The hardness and fracture toughness...In this paper,the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.The hardness and fracture toughness was tested by using a Vickers hardness tester and a universal testing machine.The cutting test was carried out at different feed velocities（250 r/min and 320 r/min）,and the contact pairs are cutting tools and 45# steel bars.Results showed that the hardness and fracture toughness of WC-Co cemented carbides with nano-additives are higher than that of WC-Co cemented carbides without nano-additives,and they are increased 10.21% and 19.69%,respectively.The flank worn width and crater width of cutting tools decrease greatly with the addition of nano-additives.For the nano-modified specimen with WC grain size of 7 μm,both the flank worn width and crater width are the minimum after the cutting process.And there are little built-up layers and some pile-up regions on the flank face leading to high cutting performance for the nano-modified cemented carbides.There are some melted regions on the flank face of cutting tools without nano-additives,and the WC grains on the cross section of alloys without nano-additives show severe fragmentation.The wear type of WC-Co is flank wear,and the wear mechanism is abrasive,adhesion and oxidation wear.展开更多
文摘Using a melt-cooling process with the host glass,Dy_(2)O_(3)(1 wt%,2 wt%,3 wt%,and 4 wt%) doped tellurite glasses were produced.A(65-x)TeO_(2)-20B_(2)O_(3)-10Al_(2)O_(3)-SGeO_(2)-xDy_(2)O_(3) glass system was analyzed by Xray diffraction.The patterns have a hump at 2θ=27°-29° and no sharp peaks,indicating that all the glass samples are amorphous.The Vickers microhardness determines how resistant a glass is to persistent deformation produced by a harder substance.Differential scanning calorimetry(DSC) at 300-550℃ was used to evaluate the thermal properties of the Dy_x glass samples.The glass transition temperature T_g(small endothermic peak),start crystallization temperature T_x and crystallization temperature T_c can all be seen on the DSC thermogram(exothermic peaks).The UV-Vis transmittance and absorption spectra were measured.The optical data show that the values of E_d^(ir),E_g^(Ind) and E_U decrease as the amount of Dy_(2)O_(3)increases,indicating a narrowing of the tails due to localized states in the forbidden gap.A concentration quenching event occurs when Dy^(3+) concentrations are above a certain threshold(1%).The addition of Dy_(2)O_(3) increases glass density,while the addition of other Dy(Ⅲ) oxides increases sample density.The radiation shielding values change as a consequence of density fluctuation.The sample with the highest amount of Dy_(2)O_(3)(Dy_(4)) has stronger radiation shielding characteristics;hence,it is superior in terms of shielding outcomes at all energy levels.Such Dy_x samples can be used in various forms of ionizing radiation shielding.
文摘Silane coupling agent KH560 was used to modify the surface of nano-α-Al<sub>2</sub>O<sub>3</sub> in ethanol-aqueous solution with different proportions. The particle size of nano-α-Al<sub>2</sub>O<sub>3</sub> was determined by nano-particle size analyzer, and the effects of nano-α-Al<sub>2</sub>O<sub>3</sub> content, ethanol-aqueous solution ratio and KH560 dosage on the dispersion and particle size of nano-α-Al<sub>2</sub>O<sub>3</sub> were investigated. The material structure before and after modification was determined by Fourier transform infrared spectroscopy (FTIR). Aqueous polyurethane resin and inorganic components are combined with modified nano-α-Al<sub>2</sub>O<sub>3</sub> dispersion to form chromium-free passivation solution. The solution is coated on the galvanized sheet, the adhesion and surface hardness are tested, the bonding strength of the coating and the surface hardness of the substrate are discussed. The corrosion resistance and surface morphology of the matrix were investigated by electrochemical test, neutral salt spray test and scanning electron microscope test. The chromium-free passivation film formed after the modification of nano-α-Al<sub>2</sub>O<sub>3</sub> increases the surface hardness of galvanized sheet by about 85%. The corrosion resistance of the film is better than that of a single polyurethane film. The results show that the surface hardness and corrosion resistance of polyurethane resin composite passivation film are significantly improved by the introduction of nano-α-Al<sub>2</sub>O<sub>3</sub>.
基金the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20112302120054)the Fundamental Research Funds for Central Universities(No.HIT.NSRIF.201169)
文摘Surface hardness value is a commonly used indicator for describing the mechanical property of stere- olithography parts. In order to investigate colorants how to influence the surface hardness of colorful resin component, a procedure is proposed to fabricate testing specimens based on color stereolithography technology in this study. Liquid photosensitive resin LPR2001 is mixed with two colorants(phthalocyanine blue and eosin powder) respectively before curing. The phthalocyanine blue powder is insoluble and only dispersive in the solid- liquid mixture which results in deposits. Therefore, surface modification is conducted to the phthalocyanine blue powder for improving wettability. By contrast, the eosin powder is dissoluble and does not cause any deposits in the liquid resin. Specimens are produced by laser curing colored resin and tested by MTSRNano Indenter XP system. The change of hardness values is illustrated at certain mass percentages of colorant. Comparisons and discussions are carried out to explain the colorants' efect. It is concluded that incorporating colorant to liquid resin results in decreasing the surface hardness of components. But sensibilization efect of the colorants also influences the curing process. Surface modification to the phthalocyanine blue powder is a feasible method to increase the hardness value of color stereolithography components. Dissolvable eosin has an approximate linear efect on surface hardness.
文摘In this current work,aluminum alloy grade 2024 is adopted as a plate material that is used in the rolling process with three different parameters including thickness reduction,forming temperature,and density of lubrication type.The experimental procedure of the rolling process is performed using the design of the experiment based on the Taguchi technique(L27),then surface roughness,surface hardness,and surface residual stresses are measured.The results showed that the lubrication density has a significant impact on the surface roughness which depends on the lubrication properties(mineral oil type,natural fat,and kinematic viscosity)while surface hardness and surface residual stresses were strongly affected by thickness reduction.On the other side,the augment in forming temperature can decrease the quality of the final surface finish and the surface hardness but reduce the induced residual stresses.The best surface finish is obtained based on the optimum condition of the rolling factors are(R%_(3),T_(1),andρ_(3))while the optimum condition of rolling parameters that generate higher hardness and compressive residual stresses are(R%_(3)T_(1)ρ_(1)).
基金This work was financially supported by the Ministry of Education,Science and Technological Development of the Republic of Serbia through Project Nos.ON174004 and ON172019the PhD fellowship of Slađana Laketić.
文摘The effects of picosecond Nd:YAG laser irradiation on chemical and morphological surface characteristics of the commercially pure titanium and Ti–13Nb–13Zr alloy in air and argon atmospheres were studied under different laser output energy values.During the interaction of laser irradiation with the investigated materials,a part of the energy was absorbed on the target surface,influencing surface modifications.Laser beam interaction with the target surface resulted in various morphological alterations,resulting in crater formation and the presence of microcracks and hydrodynamic structures.Moreover,different chemical changes were induced on the target materials’surfaces,resulting in the titanium oxide formation in the irradiation-affected area and consequently increasing the irradiation energy absorption.Given the high energy absorption at the site of interaction,the dimensions of the surface damaged area increased.Consequently,surface roughness increased.The appearance of surface oxides also led to the increased material hardness in the surface-modified area.Observed chemical and morphological changes were pronounced after laser irradiation of the Ti–13Nb–13Zr alloy surface.
文摘In this paper, we tried to present a qualitative correlation, based on extensive experimental trials between the value and the evolution of the friction coefficient, wear and contact temperature in the case of linear dry contact, thermoplastic material reinforced with SGF （short glass fibres） and various steel surfaces. We tried, believing successfully, the graphic illustration of the evolution of the steel surface wear and of the contact temperature, depending on the friction coefficient. It was analyzed in detail the influence of the normal load and sliding speed, but also of the metallic surface roughness on the friction coefficient.
文摘The present work aims to demonstrate the capabilities of Laser-induced Breakdown Spectroscopy(LIBS)coupled with a multivariate technique for rapid quantification and classification of old Indian coins made of various alloys.Thirteen old Indian coins in different years of circulation,(1922–1986)were selected for the study.The concentrations were determined by Calibration free LIBS(CF-LIBS)method.The concentration of cuprum(Cu)is negligible,and aluminum(Al)is maximum in the first five coins,and vice-versa in the remaining eight coins.Two different multivariate methods,Principal Component Analysis(PCA)and Soft Independent Modelling of Class Analogy(SIMCA)have been used to classify and identify the coins.PCA classified all thirteen samples into four main alloy categories.The discernment of unknown samples to their probable class membership of alloy was performed using SIMCA.The surface hardness(Brinell hardness number)is linearly correlated with the plasma temperature and LIBS intensity ratios.The sample surface of the first and fifth coin belongs to Al-alloy,having the least surface hardness,and it became harder for Cu–Ni alloy,Ni-brass alloy,and bronze alloy.The hardness of the surface is more for bronze sample twelve.It is also observed that the plasma temperature increases monotonically with the Brinell hardness number.This analysis provides valuable information on fabrication methodology and explains large diversification in the elementary composition of old coins.
文摘Nitriding of the surface in martensitic stainless steels is commonly carried out to improve their wear resistance. The process of plasma nitriding in stainless steel is influenced by two mechanisms: physical diffusion through the surface and chemical gas-metal reaction. The inner nitriding interaction involves the simultaneous penetration and formation of a solid solution, as well as the interaction of nitrogen with specific alloying elements, resulting in the development of homogeneous and heterogeneous structures. Our study concludes that the observed intergranular hydrogen embrittlement and crack formation during the surface nitridation process of AMS 5719 martensite alloy steel can be attributed to the ammonium concentration of approximately 50% at a temperature of 530˚C.
文摘Plasma radical nitriding was performed to harden the surface of SCM440 steel for 1-10 h at temperature range of 450-550℃. This process involved the use of NH3 gas instead of N2 gas employed for the well-established plasma nitriding method. No compound layer was formed during this process except the experiment carried out at 500℃ for 10 h. The main phase produced in the diffusion zone was identified to be γ＇-Fe4（N, C）. A diffusion depth increased with increasing treatment temperature and time （up to about 250 μm）. The surface hardness of radical nitrided layer was about two times higher than that of the untreated surface. The tensile test was carried out to estimate the mechanical properties of surface-hardened SCM440 steel prepared at various plasma radical nitriding treatment time and temperature. The influence of radical nitriding treatment on the tensile strength of the specimen was found to be insignificant. The highest value of the ultimate tensile strength was obtained in the experiment carried out at 500℃ for 1 h. However, the elongation was greatly affected by the radical nitriding processing parameters. The maximum value of elongation, which is equal to about 18.1%, was also obtained under the condition of 500℃ for 1 h.
基金Project supported by the President's Foundation of the ChinaAcademy of Engineering Physics(Grant No.YZJJLX2018003)the National Natural Science Foundation of China(Grant Nos.U2004180 and 12105261)the Program for Changjiang Scholars and Innovative Research Team in Universities,China(Grant No.IRT1234).
文摘Microstructure evolution and hardening effect of pure tungsten and W-1.5%ZrO_(2) alloy under carbon ion irradiation are investigated by using transmission electron microscopy and nano-indentation.Carbon ion irradiation is performed at 700℃ with irradiation damages ranging from 0.25 dpa to 2.0 dpa.The results show that the irradiation defect clusters are mainly in the form of dislocation loop.The size and density of dislocation loops increase with irradiation damages intensifying.The W-1.5%ZrO_(2) alloy has a smaller dislocation loop size than that of pure tungsten.It is proposed that the phase boundaries have the ability to absorb and annihilate defects and the addition of ZrO_(2) phase improves the sink strength for irradiation defects.It is confirmed that the W-1.5% ZrO_(2) alloy shows a smaller change in hardness than the pure tungsten after being irradiated.From the above results,we conclude that the addition of ZrO_(2) into tungsten can significantly reduce the accumulation of irradiated defects and improve the irradiation resistance behaviors of the tungsten materials.
文摘Nitriding of aluminium alloy （AlFel.sZn0.8） in nitrogen and nitrogen-helium mixture was carried out by using 100 Hz-pulsed DC glow discharge. Samples are treated for different durations, namely 4 h, 8 h and 12 h, in nitrogen plasma as well as in a mixture of nitrogen- helium plasma for the same processing duration of 4 h. All nitriding treatments are carried out at an input power of 100 W, filling pressure of 1 mbar and substrates temperature of 250~C. X-ray diffraction （XRD） results show an expansion in lattice spacing and consequently shift of diffraction peaks towards lower angle with the addition of helium in nitrogen plasma. Surface morphology of the treated sample is investigated by scanning electron microscopy （SEM） and energy dispersive X-ray analysis （EDX）. Vickers micro-hardness testing results show increases in surface hardness with processing duration as well as with the addition of helium in nitrogen plasmas. This increase of surface hardness may be attributed to the diffusion of nitrogen content in the surface layer generating internal stresses. It is observed that the addition of helium positively affects the nitriding of samples.
文摘Estimation of the mechanical properties of concrete in an existing structure is possible with the results of surface hardness and ultrasound tests (nondestructive tests (NDTs)). For both the use of correlation curves is necessary, it is established between NDT and the results of the compressive strength of test specimens or extracted from structure. The objective of this study is to produce correlations between the results of surface hardness and ultrasound NDTs and the compressive strength of the structural concrete in the bleachers of a soccer stadium in the city of Cianorte, which is located in the northwest part of the state of Paraná, Brazil. This concrete structure, which is approximately 26 years old, has some defects, such as corrosion, concrete segregation and cracks. Concrete spalling in one of the slabs has recently raised some concern. Another significant issue is the absence of records regarding concreting of the bleachers’ structure. Therefore, mapping the reinforcement was initially performed according to the results of a surface hardness test, as recommended by standard [1]. An ultrasound test was simultaneously performed according to standard [2] for the same points employed in the surface hardness test. The concrete specimens were extracted according to the recommendations of standard [1] to determine compressive strength, perform the NDT and construct the correlation curves for the results. A total of 26 concrete specimens were obtained from all structures of the bleachers. From the methodology and the results of the study, highly reliable equations were obtained from the correlation curves among the compressive strength of the concrete specimens and the values of the surface hardness index and the ultrasound wave propagation velocity.
基金Supported by the National Natural Science Foundation of China(No.10804101)
文摘Copper-nickel nanoparticle was directly prepared by flow-levitation method （FL） and sintered by vacuum sintering of powder （VSP） method. Several characterizations, such as transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, differential thermal analysis （DTA）, and energy-dispersive X-ray spectroscopy （EDX） were used to investigate the prepared nanostructures. The results of the study show that FL method could prepare high purity Cu-Ni nanocrystals of uniform spheres with size distribution between 20 and 90 nm. After sintering the bulk nanocrystalline copper-nickel has obvious thermal stability and the surface Webster hardness increases with the rising sintering temperature. At the temperature of 900 ℃, the specimen shows higher surface Webster hardness, which is about two times of traditional materials. When the sintering temperature arrives at 1 000 ℃ the relative density of bulk nanocrystals can reach 97.86 percent. In this paper, the variation tendency of porosity, phase and particles size of bulk along with the changing of sintering temperature have been studied.
基金the Romanian Acad-emy and University of Civil Engineering Bucharest,for its material and technical support offered in order to achieve these researches.
文摘In this paper we tried to present a qualitative correlation,based on extensive experimental determinations between the value and the evolution of the friction coefficient,wear,and contact temperature,in the case of linear dry contact,for thermoplastic material reinforced with short glass fibers(SGF)and various steel surfaces.The aim was to highlight the evolution of the wear process depending on the evolution of the friction coefficient.As a result,it was possible to graphically illustrate the evolution of the friction coefficient and the change of the wear process,emphasizing the abrasive,adhesive and corrosive wear.The evolution of the plastic material transfer function of the contact temperature,namely of the power lost by friction(product between the contact pressure and sliding speed,p and v)was aimed and it was highlighted.It has been demonstrated that in the case of a 30%SGF content it can reach and even exceed contact temperatures very close to the flow limit of the plastic material.We tried,believing successfully,the graphic illustration of the evolution of the steel surface wear and of the contact temperature,depending on the friction coefficient.The influence of the normal load and sliding speed was evaluated in detail,but also the influence of the metallic surface roughness on the friction coefficient was discussed.
基金supported by the Program of Excellent Team at Harbin Institute of Technology
文摘In this paper,the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.The hardness and fracture toughness was tested by using a Vickers hardness tester and a universal testing machine.The cutting test was carried out at different feed velocities（250 r/min and 320 r/min）,and the contact pairs are cutting tools and 45# steel bars.Results showed that the hardness and fracture toughness of WC-Co cemented carbides with nano-additives are higher than that of WC-Co cemented carbides without nano-additives,and they are increased 10.21% and 19.69%,respectively.The flank worn width and crater width of cutting tools decrease greatly with the addition of nano-additives.For the nano-modified specimen with WC grain size of 7 μm,both the flank worn width and crater width are the minimum after the cutting process.And there are little built-up layers and some pile-up regions on the flank face leading to high cutting performance for the nano-modified cemented carbides.There are some melted regions on the flank face of cutting tools without nano-additives,and the WC grains on the cross section of alloys without nano-additives show severe fragmentation.The wear type of WC-Co is flank wear,and the wear mechanism is abrasive,adhesion and oxidation wear.
