Al含量对Cr1–xAlxN涂层力学、热稳定性、抗氧化性及耐蚀性的影响

目的探讨Al含量对Cr_1–xAl_xN涂层结构和性能的影响。方法在阴极弧蒸发设备中,分别采用Cr、Cr_0.70Al_0.30、Cr_0.50Al_0.50、Cr_0.40Al_0.60和Cr_0.30Al_0.70靶材制备5种不同Al含量的Cr_1–xAl_xN涂层。借助能量色散X射线光谱仪(EDX)、X射线衍射仪(XRD)、纳米压痕仪、扫描电子显微镜(SEM)和电化学工作站对Cr_1–xAl_xN涂层的成分、结构、力学性能、热稳定性、抗氧化性和耐蚀性进行研究。结果5种Cr_1–xAl_xN涂层均呈单相面心立方结构,其硬度随Al含量的增加而提升,由CrN的(16.9±0.8)GPa升至Cr_0.75Al_0.25N的(25.1±0.7)GPa、Cr_0.56Al_0.44N的(27.0±1.1)GPa、Cr_0.46Al_0.54N的(28.5±1.5)GPa和Cr_0.36Al_0.64N的(30.4±0.8)GPa。所有涂层在1000℃退火后,开始出现六方h-Cr2N的衍射峰,其衍射峰强度随Al含量的上升而降低。Cr_0.75Al_0.25N、Cr_0.56Al_0.44N和Cr_0.46Al_0.54N涂层在1100℃退火后,可检测到六方纤锌矿结构w-AlN相,而高Al含量Cr_0.36Al_0.64N涂层在1000℃退火后,便可检测到w-AlN相。在1000℃氧化15 h后,CrN涂层已经完全氧化,Cr_0.75Al_0.25N、Cr_0.56Al_0.44N、Cr_0.46Al_0.54N和Cr_0.36Al_0.64N涂层的氧化层厚度分别约为0.4、0.3、0.3、0.2μm;在1100℃氧化15 h后,CrN、Cr_0.75Al_0.25N和Cr_0.56Al_0.44N涂层已完全氧化,而Cr_0.46Al_0.54N和Cr_0.36Al_0.64N涂层的氧化层厚度分别约为2.5、1.4μm。CrN、Cr_0.75Al_0.25N、Cr_0.56Al_0.44N、Cr_0.46Al_0.54N和Cr_0.36Al_0.64N涂层在3.5%的NaCl溶液中测得的极化电阻分别为567.69、5.34、71.80、160.10、92.56 k?·cm²。结论涂层的硬度和抗氧化性随Al含量的增加而提升。Al的加入在抑制Cr—N分解的同时,促进了涂层中w-AlN的生成。CrN涂层具有最优的耐蚀性,而在含Al涂层中,涂层的耐蚀性随Al含量的增加呈现出先上升、后下降的趋势。     

Effect of partial substitution of Co with Fe on the properties of LaNi3.55Mn0.4Al0.3Co0.75−xFex (x=0, 0.15, 0.55) alloys electrodes

The effect of iron substitution on the electrochemical behaviour of LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x compounds (x=0, 0.15, 0.55) has been studied by chronopotentiometry and cyclic voltammetry techniques. The maximum capacity decreases linearly from 308 to 239 mAhg⁻¹ when the iron content increases from 0 to 7.3 wt.% (x=0.55). This decrease can be explained by the corrosion of the alloy in the aqueous KOH electrolyte. In spite of this decrease and of the long time needed for the activation, a good stability of discharge capacity was observed in LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x compounds. The reversibility of the electrochemical redox reaction of LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x alloy electrodes has been observed in the alloys least rich in iron. The hydrogen diffusivity in LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x alloy electrodes decreases when increasing the iron content. The obtained values of the hydrogen diffusion coefficient D_H, varies between 2.1×10⁻⁷ and 8.2×10⁻⁹ cm² s⁻¹ depending on the iron content of the electrode.     

Atomistic study on the site preference and thermodynamic properties for Cr23−xFexC6

The site preference of Fe in Cr_23−xFe_xC₆ is investigated based on the interatomic potentials obtained by the lattice inversion method. The calculated results show that Fe atoms preferentially substitute for Cr at 4a sites first and then 8c sites. The structural parameters of Cr_23−xFe_xC₆ with content x are calculated and the results are consistent with experimental results. The calculated cohesive energies indicate that the increase in x value is accompanied by the decrease in the stability of Cr_23−xFe_xC₆. The thermodynamic properties of Cr₂₃C₆, such as the phonon density of states and vibrational entropy, as well as the bulk modulus of Cr_23−xFe_xC₆ are evaluated. The calculated results are in good agreement with experimental results. This work provides a simple and promising method for studying the properties of carbides with complex structures.     

Mechanical properties of nano-structured Ti-Si-N films synthesized by cathodic arc evaporation

Ti_1−xSi_xN coatings were synthesized by cathodic arc evaporation with plasma-enhancing filter duct, using Ti₈₀Si₂₀ alloy target as cathodes. Optical emission study revealed that excitation, ionization and charge transfer reactions of the Ti-Si-N plasma occurred during the Ti_1−xSi_xN deposition process. The chemical content of Si varied from 3.3 to 6.0 at% in Ti_1−xSi_xN depending on the nitrogen partial pressure of the reaction chamber. All the Ti_1−xSi_xN coatings displayed a NaCl structure and a preferred (2 0 0) orientation parallel to the substrate surface. Among the studied Ti_1−xSi_xN coatings, the Ti_1−xSi_xN with 6 at.% Si possessed the highest hardness of 45 GPa and H³/E*² ratio of 0.527 GPa, indicating the best resistance to plastic deformation. We found that the structure and mechanical properties of the Ti_1−xSi_xN films were correlated with the nitrogen pressure and silicon content of the coatings.     

A study on corrosion resistance characteristics of PVD Cr-N coated steels by electrochemical method

The corrosion behavior of Cr-N coated steels with different phases (-Cr, CrN and Cr₂N) deposited by cathodic arc deposition on AISI H13 steel was investigated in a 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization tests than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the Cr₂N coating than in the other Cr-N coated steels. EIS measurements showed, for most of the Cr-N coated steels, that the Bode plot presented two time constants. Also, the Cr₂N coating represented the characteristic of Warburg behavior after 72 h of immersion. The coating morphologies were examined in planar view and cross-section by SEM analysis and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, it is concluded that the CrN coating provided a better corrosion protection than the other Cr-N coated steels.     

Effect of AI content on the phase structure and the hydrogenation characteristic of La（Mg1-xAlx） alloys

La（Mg1-xAlx） （x=0.2, 0.4, 0.6, 0.8） alloys have been prepared using induction melting followed by annealing. It is found that partial substitution of Mg by Al does not lead to a change in crystal structure, and the alloys have a single LaMg phase when x 〈 0.4. The lattice parameter of the LaMg phase decreases obviously after the partial substitution of Mg by Al. However, further substitution of Mg by Al leads to the coexistence of multiple phases when x ≥ 0.6. The alloys consist of the LaMg, LaAl, LaAl2, and La5Al4 phases. The LaMg phase decreases, whereas the La5Al4 phase increases with the increase in x. The Al-substituted La（Mgo.6Al0.4） alloy can be hydrogenated into the tetragonal LaH3, cubic LaH3, MgH2, and LaPd under 5 MPa at 473 K for 5 d.     

Al含量对TiAlN涂层结构及性能的影响

目的 系统研究Al含量对TiAlN涂层结构以及硬度、热稳定性、抗氧化性能和耐腐蚀性能的影响.方法 利用阴极弧蒸发技术,采用Ti、Ti50Al50、Ti40Al60和Ti33Al67靶材制备出4种Ti1–xAlxN涂层.分别利用能量色散X射线光谱仪(EDX)、X射线衍射仪(XRD)、扫描电镜(SEM)、纳米压痕仪、热重分...     

Influence of CH4/N2 ratio on microstructure and mechanical properties of PCVD-Ti (CxN1 − x) coating

A series of samples of hard alloy Ti(C_xN_{1 − x}) coatings were prepared under different CH₄/N₂ ratios by DC plasma chemical vapour deposition (PCVD). The microhardness of the coatings and the adherent strength between the coatings and the substrates were determined. It was found that when the CH₄/N₂ ratio approximately equals 1:1, the coating has the best overall performance. The influence of the CH₄/N₂ ratio on the properties of the coatings was discussed according to the results of XPS, SEM and XRD analyses. The XRD analysis method for the determination of the crystal structures and preferred orientations of the Ti(C_xN_{1 − x}) coatings were elucidated.     

Fatigue behavior of duplex treated TiCxN1−x- and Ti1−xAlxN-hard coating steel compounds

Recently, modified surface treatment methods for cutting tools were developed combining a heat treatment and a subsequent hard coating (duplex treatment). As a consequence, the wear resistance has been improved considerably. As fatigue is an important failure mechanism during application, the present paper focuses on the improvement of the fatigue behavior by an optimization of heat treatment and hard coating. The problem is approached in two steps: first, the fatigue behavior of high-speed tool steel S6-5-2 is investigated, surface-treated with different plasma heat treatments (plasma nitriding and -carbonitriding). The results on bending fatigue testing indicate the superiority of plasma nitriding compared with both plasma carbonitriding and untreated substrate. Hence, in a second step the plasma nitrided tool steel is coated with PACVD hard coatings of the system Ti-Al-C-N and the fatigue behavior of these hard coating steel compounds is investigated. Obviously, the type and stoichiometry of the hard coating influence the fatigue behavior of the compound. For TiC_xN_1−x films, the fatigue strength increases with increasing carbon content, whereas for Ti_1−xAl_xN-films, the fatigue strength decreases with increasing Al content. While for an optimized hard coating the fatigue behavior of the compound is superior to hardened non-nitrided steel, no significant improvement was found as compared with plasma nitrided steel.     

Structural, magnetic and magnetostrictive studies of Tb0.27Dy0.73(Fe1 − xAlx)2

Measurements of magnetic properties, X-ray diffraction and magnetostriction were made on Tb_0.27Dy_0.73(Fe_{1 − x}Al_x)₂ (x = 0.1, 0.2, …, 0.7) compounds. It was found that the system has the cubic MgCu₂ structure over almost the whole (Fe,Al) concentration range investigated, except for a narrow intermediate range (x = 0.4–0.6) where the hexagonal MgZn₂ structure appears. With increasing Al content x, the lattice constant a increases linearly with x. The first replacement of Fe results in a marked decrease in the Curie temperature, which is followed by a slight decrease in T_C with x. A linear decrease in magnetostriction of |λ_| − λ| at room temperature with x was also observed from 1530 × 10⁻⁶ for x=0 to 36×10⁻⁶ for x=0.3. The saturation magnetization σ_s exhibits a complex concentration dependence in the Tb_0.27Dy_0.73(Fe)_{1 − x}Al_x)₂ system: in the range x < 0.5, σ_s increases linearly with x and, for x = 0.5–0.6, σ_s decreases and then increases again. An enhancement of the magnetic ‘hardness’ in this system was also observed at low temperature.     

Physical properties of Mo6−xRuxTe8 and Mo6Te8−xSx

A series of the Chevrel phases, Mo_6−xRu_xTe₈ and Mo₆Te_8−xS_x (x=0, 1, 2), has been prepared and the various physical properties, such as the elastic modulus, Debye temperature, and electrical resistivity, have been evaluated. The relationships between several properties of the compounds have also been studied. Young’s modulus and Debye temperature of Mo_6−xRu_xTe₈ and Mo₆Te_8−xS_x increase with increasing x value. The relationship between the Vickers hardness and Young’s modulus shows ceramic characteristics for Mo_6−xRu_xTe₈, while they show glass-like characteristics for Mo₆Te_8−xS_x. The electrical resistivities of Mo_6−xRu_xTe₈ and Mo₆Te_8−xS_x increase with increasing x value.     

Nanocrystalline LaNi4−xMn0.75Al0.25Cox electrode materials prepared by mechanical alloying (0≤x≤1.0)

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH_x) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi_4−xMn_0.75Al_0.25Co_x (x=0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu₅-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH_x battery. Cobalt substituting nickel in LaNi₄Mn_0.75Al_0.25 greatly improved the discharge capacity and cycle life of the LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacities up to 258 mA h g⁻¹ (at 40 mA g⁻¹ discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi₅-type alloy powders for electrochemical energy storage.     

等离子喷涂WC-20Cr3C2-7Ni/8YSZ复合涂层的组织及摩擦学性能

为提高连铸机拉矫辊的服役寿命,通过等离子喷涂技术在模具钢H13表面制备不同质量比的WC-20Cr₃C₂-7Ni+8YSZ复合涂层,分析各涂层的微区组织、显微硬度、抗划伤性、耐磨性和磨损形式。结果表明,在WC-20Cr₃C₂-7Ni粉末中分别加入30wt%、50wt%的8YSZ,其复合涂层的致密性明显提高,且涂层晶粒明显得到细化;WC-20Cr₃C₂-7Ni涂层中出现WC_1-x与W相,且随着8YSZ的添加WC相的结晶强度变弱;WC-20Cr₃C₂-7Ni+30wt%8YSZ涂层平均硬度(1172 HV0.2)相对于WC-20Cr₃C₂-7Ni涂层(1152 HV0.2)并没有明显变化,WC-20Cr₃C₂-7Ni+50wt%8YSZ涂层硬度(1052 HV0.2)相对于WC-20Cr₃...     

Mechanical and tribological properties of TiCxN1−x wear resistant coatings

The aim of this work is to investigate the mechanical and tribological properties of TiC_xN_1−x wear resistant coatings grown on a Ti–0.2 Pd alloy substrate. Films were deposited by dual ion beam sputtering (DIBS) system with different proportions of N₂ and Ar in the assisting beam. The friction tests have been carried out with a pin-on-disc tribometer with different applied loads. The films present high hardness and elastic properties whose values depend upon preparation conditions. The mechanical properties and the tribological behaviour of the coatings seem to depend on their stoichiometry and microstructure. The coating TiC_0.5N_0.5 shows less hardness and better wear resistance than the coating with stoichiometry TiC_0.15N_0.85. The influence of the stoichiometry and the local structure of the films on its mechanical properties have been ruled out.     

X-ray diffraction and Mössbauer study of (Fe1−xNix)4N (0.2 ≤ x ≤ 0.6) films

Single phase (Fe_1−xNi_x)₄N compounds (0.2 ≤ x ≤ 0.6) have been synthesized by reactive evaporation and investigated by X-ray diffraction and Mössbauer spectrometry. The lattice parameters of the nitrides decrease from 3.796 to 3.774 Å with increasing Ni concentration. The fitting results of Mössbauer spectra indicate that the average hyperfine field have the same changing tendency with lattice parameter and the nickel atoms have a tendency to be located at the corner site.     

Electrochemical properties of the MmNi3.55Mn0.4Al0.3Co0.75−xFex (x = 0.55 and 0.75) compounds

The hydrogen storage alloys MmNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x (x = 0.55 and 0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. For the MmNi_3.55Mn_0.4Al_0.3Co_0.2Fe_0.55 compound, the discharge capacity reaches its maximum of 210 mAh/g after 12 cycles and then decreases to 190 mAh/g after 30 charge–discharge cycles. However, for the MmNi_3.55Mn_0.4Al_0.3Fe_0.75 compound, the discharge capacity reaches its maximum of 200 mAh/g after 10 cycles and then decreases to 160 mAh/g after 30 cycles.

The diffusion behavior of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi_3.55Mn_0.4Al_0.3Co_0.2Fe_0.55 and MmNi_3.55Mn_0.4Al_0.3Fe_0.75 are, respectively, equal to 2.96 × 10⁻⁹ and 4.98 × 10⁻¹⁰ cm² s⁻¹. However, the values of the charge transfer coefficients are, respectively, equal to 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.     

Power factor of La1−xSrxFeO3 and LaFe1−yNiyO3

The electrical conductivity (σ), Seebeck coefficient (S), and power factor (σS²) of perovskite-type LaFeO₃, La_1−xSr_xFeO₃ [0.1 ≤ x ≤ 0.4] and LaFe_1−yNi_yO₃ [0.1 ≤ y ≤ 0.6] were investigated in the temperature range of 300–1100 K to explore their possibility as thermoelectric materials. The electrical conductivity of LaFeO₃ showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO₃ increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La_1−xSr_xFeO₃ was positive, whereas that of LaFe_1−yNi_yO₃ changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO₃; 0.0053 × 10⁻⁴ Wm⁻¹ K⁻² for LaFeO₃ (1050 K), 1.1 × 10⁻⁴ Wm⁻¹ K⁻² for La_1−xSr_xFeO₃ (x = 0.1 at 1100 K) and 0.63 × 10⁻⁴ Wm⁻¹ K⁻² for LaFe_1−yNi_yO₃ (y = 0.1 at 1100 K).     

Tailoring of misfit along interfaces between ZnxMn3−xO4 and Ag

This work is aimed at examining how the tetragonality of Zn_xMn_3−xO₄ spinel structures depends on the chemical composition when Zn_xMn_3−xO₄ is embedded in a metal matrix. The paper focuses on a wide range of Zn_xMn_3−xO₄ precipitates in a Ag matrix with x varying between 0 and 1.5. This variation of x has been obtained by internal oxidation of Ag–2at.%Mn–4at.%Zn in air followed by annealing in vacuo at different temperatures. It will be demonstrated that the Zn concentration x in Zn_xMn_3−xO₄ has a major influence on the interfacial misfit and orientation relation between Ag/Zn_xMn_3−xO₄. The degree of mismatch of 10.4% of 1 1 1 Ag–Mn₃O₄ and 2.4% of Ag–Zn_1.5Mn_1.5O₄ was visualized using the Bragg filtering technique on HRTEM micrographs of those interfaces. It was possible to identify misfit dislocations qualitatively with this technique at 1 1 1 Ag–Zn_xMn_3−xO₄ interfaces with different degree of mismatch.     

Solid solution Pb1−xSrxTiO3 and its thermal expansion

The solid solution limit of Pb_1−xSr_xTiO₃ was determined in the composition range of 0≤x≤1.0 at room temperature (RT). The phases were isolated and indexed in a tetragonal system with x<0.5 and in a cubic one with x≥0.5. The cell parameters of Pb_1−xSr_xTiO₃ continuously, but nonlinearly, change with solubility x. The intrinsic thermal expansions of the solid solution compounds Pb_1−xSr_xTiO₃ (x=0, 0.15, 0.20, 0.50, 0.90, 1.0) were obtained in the temperature range from RT to 1173 K with high-temperature X-ray powder diffraction. Negative thermal expansion coefficients of Pb_1−xSr_xTiO₃ (x=0, 0.15, 0.20) were found below the Curie points. The thermal expansions of these titanate ceramics were highly correlated with the solubility in the solid solution Pb_1−xSr_xTiO₃.     

封孔处理等离子喷涂Cr2O3涂层耐蚀性的电化学表征

用等离子喷涂工艺在Q235钢基体上制备Cr₂O₃陶瓷涂层,并采用磷酸铝和环氧树脂对其进行封孔处理。利用图像分析法和电化学方法对封孔前后涂层的孔隙率进行了测试,采用弱极化技术和电化学阻抗谱技术对封孔前后涂层的耐蚀性能进行了研究。结果表明,封孔处理提高了涂层的耐蚀性能,环氧树脂封孔涂层的耐蚀性能更优异;陶瓷涂层在腐蚀介质中耐蚀性能主要取决于涂层的孔隙率。