High temperature oxidation of a (Cr2N−Mo2S3)/Cr double-layered coating deposited on steel by D.C. magnetron sputtering

A coating consisting of (Cr₂N−Mo₂S₃) overlay coating and an underlying Cr coating was deposited on a steel substrate by D.C. magnetron sputtering. The oxidation characteristics of the deposited double-layered coating were studied at temperatures ranging from 400 to 900 °C in air. The oxidation product was primarily Cr₂O₃. The unreacted coating beneath the oxide scale had some dissolved oxygen, sulfur, and iron. Oxidation of the coating occurred via complex routes such as the outward diffusion of chromium and nitrogen from Cr₂N and iron from the substrate, and the inward transport of oxygen from air, chromium from Cr₂N, and S from Mo₂S₃. This counter diffusion of various ions occurred easily via fine crystallites that constituted the coating, which had some solubility of S, O, and Fe.     

Effects of Destabilization Temperature on the Microstructure and Mechanical Properties of High Chromium Cast Iron

The effect of destabilization temperature on the microstructure and impact toughness of high chromium cast iron was investigated. The result showed that the microhardness of matrix decreased from 860 to 332 HV with the increase of destabilization temperature from 950 to 1100 °C. The impact toughness of the alloy increased from 5.3 to 8.1 J/cm² with the increase of destabilization temperature from 950 to 1050 °C, while it decreased with further increase of destabilization temperature. The former change of impact toughness was found to be due to the increase in volume fraction of retained austenite from 12.6 to 56.5%, whereas the latter was attributed to the increase of carbon content in retained austenite by analysis of fracture morphologies. The wear resistance decreased with the increase of destabilized temperature from 950 to 1050 °C and increased only slightly for the temperature from 1050 to 1100 °C.     

New Thermodynamic Data for Liquid Aluminum-Magnesium Alloys from emf,Vapor Pressures,and Calorimetric Studies

Experimental thermodynamic studies of liquid Al-Mg alloys have been performed by several methods resulting in: (1) Mg activities from galvanic cells with liquid electrolytes at temperatures from 910 to 1070 K, at X_Mg = 0.1 to 0.7 and for the dilute range when X_Mg = 0.0126 to 0.1430 at 927 K; (2) Mg activities from the emf method with solid CaF2 electrolyte at temperatures 921 to 1093 K, with concentrations XMg = 0.05 to 0.9; (3) Mg activities from vapor pressure measurements (Knudsen effusion method) at temperatures ranging from 722 to 1188 K, at X_Mg = 0.0424 to 0.8885. Vapor pressures of pure solid Mg at temperatures 674 to 851 K. In addition, liquidus temperatures for Mg- and Al-rich alloys were obtained; and (4) Partial and integral enthalpies from reaction calorimetry at 1023 K, starting from pure Mg bath at concentrations, X_Al = 0.066 to 0.499, and starting from pure Al bath at X_Mg = 0.522 to 0.906. The mutual consistency of these four sets of data was analyzed. New results together with the selected thermodynamic information reported in literature were optimized to describe the liquid phase with the Redlich-Kister equation, as a preliminary step for phase diagram calculations of the Al-Mg system.     

The analysis of lateral distribution of barrier height in identically prepared Co/n-Si Schottky diodes

We have studied the experimental linear relationship between ideality factors and barrier heights (BHs) for Co/n-Si metal–semiconductor (MS) structures with a doping density of about 10¹⁵ cm⁻³. The barrier heights for the Co/n-type Si metal–semiconductor structures from the current–voltage (I–V) characteristics varied from 0.64 to 0.70 eV, the ideality factor n varied from 1.18 to 1.26, and from reverse bias capacitance–voltage (C⁻²–V) characteristics the barrier height varied from 0.68 to 0.81 eV. The experimental barrier height distributions obtained from the I–V and C⁻²–V characteristics were fitted by a Gaussian distribution function, and their mean values were found to be 0.67 and 0.75 eV, respectively. Furthermore, the lateral homogeneous BH value of approximately 0.81 eV for Co/n-Si metal–semiconductor structures was obtained from the linear relationship between experimental effective BHs and ideality factors.     

Effect of Thermomechanical Processing on the Microstructure and Mechanical Properties of Nb-Ti-V Microalloyed Steel

The paper presents the results of thermomechanical treatment via forging on the microstructure and mechanical properties of newly obtained microalloyed steel containing 0.28% C, 1.41% Mn, 0.027% Nb, 0.028% Ti, and 0.019% V. The investigated steel is assigned to the production of forged elements for the automotive industry. Conditions of forging using the thermomechanical processing method were developed based on plastometric tests. Continuous and double-hit compression tests were conducted using the Gleeble 3800 thermomechanical simulator. The samples were investigated in a temperature range from 900 to 1100 °C and a strain rate of 1 and 10 s^?1. To determine the recrystallization kinetics of plastically deformed austenite, discontinuous compression tests of samples using the applied deformation were conducted in a temperature range from 900 to 1100 °C with isothermal holding of the specimens between successive deformations for 2-100 s. Observations of the microstructures of thin foils were conducted using a TITAN80-300 FEI transmission electron microscope. The applied thermomechanical treatment allows to obtain a fine-grained microstructure of the austenite during hot-working and production of forged parts. These acquire advantageous mechanical properties and guaranteed crack resistance after controlled cooling from the end plastic deformation temperature and successive tempering. Forgings produced using the thermomechanical treatment method, consecutively subjected to tempering in a temperature range from 550 to 650 °C, reveal values of YS_0.2 which equal from 994 to 892 MPa, UTS from 1084 to 958 MPa, KV from 69 to 109 J, KV^?40 from 55 to 83 J, and a hardness ranging from 360 to 300 HBW.     

A comparative study on Ti1 − xAlxN coatings reactively sputtered from compound and from mosaic targets

The aim of this work is to illuminate the influence of two widely applied target types, i.e. TiAl compound targets produced by powder metallurgy and mosaic TiAl targets, on the sputter deposition process as well as on the structure and properties of the obtained coatings. After development of a sputter process for the compound targets by optimization of cathode power and nitrogen partial pressure, this process was compared to the commercially applied mosaic target process by taking into account the sputter yields of Ti and Al and the respective deposition rates. The deposition rate achieved with the compound targets was ~ 44% higher than that obtained for the mosaic targets. The Al content in the coatings deposited from the compound targets was slightly higher and the domain size of the formed cubic Ti_1 − xAl_xN solid solution considerably larger than for the coatings deposited from the mosaic targets. The coatings grown from the compound targets showed, in contrast to those synthesized from the mosaic targets, tensile stresses. While the hardness of the coatings sputtered from the compound targets was slightly below that of the coatings synthesized from the mosaic targets, both their friction and wear behavior were slightly improved. In summary, it could be shown that using compound TiAl targets manufactured by powder metallurgy, Ti_1 − xAl_xN coatings with mechanical and tribological properties comparable to those grown from commercially applied mosaic targets can be deposited at significantly higher growth rates.     

Recovery of magnetite from waste ferrous sulfate using polyethylene glycol (PEG) as a dispersant

The effect of PEG dispersant on the magnetic separation of magnetite (Fe₃O₄) synthesized from ferrous sulfate solution via co-precipitation method with calcium hydroxide as the precipitant was investigated. The results indicated that a PEG dispersant could significantly affect Fe₃O₄ recovery. Adding PEG during the preparation of Fe₃O₄ was unfavorable for Fe₃O₄ recovery. When the PEG-6000 concentration was increased from 0 to 8 g/L, the iron grade and median particle size of the Fe₃O₄ product decreased from 65.58% and 2.35 μm to 57.79% and 1.35 μm, respectively. However, adding PEG during the wet milling of the mixed product promoted the subsequent recovery of Fe₃O₄. When the amount of PEG-200 increased from 0% to 4% of the powder mass, the grade of iron in the Fe₃O₄ product increased from 65.58% to 68.32%. While the relative molecular mass of PEG at an amount of 4% of the powder mass increased from 200 to 20000, the grade of iron was reduced from 68.32% to 66.70%.     

Leaching of heavy metal elements in solder alloys

Leaching behavior of heavy metal elements from Sn–3.5Ag–0.5Cu, Sn–9Zn, and Sn–37Pb solder alloys and their joints was investigated in typical H₂SO₄, NaCl and NaOH solutions. The leaching amount of Sn from solder joints was more than that from solder alloys and the leaching amount of Sn from Sn–3.5Ag–0.5Cu solder joint in the NaCl solution was the most. The surface corrosion products on the solder and their joints were composed of oxide, oxide hydroxide or oxychloride of the component element. Much more surface oxides for the samples treated in the NaCl solution produced than that in the NaOH and H₂SO₄ solutions.     

Centrifugal extraction of rare earths from wet-process phosphoric acid

Phosphorite ore is a potential resource of rare earths (RE) as well as phosphate; therefore, the recovery of RE from wet-process phosphoric acid (WPA) is promising. This study investigated the influence of rotational speed, extractant concentration, flow ratio and phase contact time on the centrifugal extraction of RE from WPA and the separation of RE from impurities. The results indicate that higher rotational speed, higher extractant concentration and larger flow ratio are beneficial to the extraction of RE and impurities from phosphoric acid. It is found that the phase contact time for efficiently extracting RE and that for iron are of great difference, which provides an effective method for separating RE from iron using the non-equilibrium extraction process in centrifugal contactors. Compared with equilibrium extraction, the separation factor βRE/Fe is enhanced from 0.07 to 17.6.     

Electrochemical properties of LiNi0.8Co0.2?xAlxO2 (0≤x≤0.1) cathode particles prepared by spray pyrolysis from the spray solutions with and without organic additives

Fine-sized LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles were prepared by spray pyrolysis from the spray solutions with and without organic additives. Citric acid, ethylene glycol, and Drying Control Chemical Additive (DCCA) were used as organic additives and improved the morphologies and electrochemical properties of the cathode particles. The LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles obtained from the spray solutions with organic additives were of micro size and had slightly aggregated morphologies. The initial discharge capacities of the LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles obtained from the spray solutions without organic additive changed from 169 mAhg⁻¹ to 190 mAhg⁻¹ when the x changed from 0 to 0.1. However, the initial discharge capacities of the cathode particles obtained from the spray solutions with organic additives changed from 196 mAhg⁻¹ to 218 mAhg⁻¹. The initial discharge capacity of the LiNi_0.8Co_0.15Al_0.05O₂ cathode particles obtained from the spray solution with organic additives was maintained after the 20th cycle at a current density of 0.1 C.     

Release and chemical speciation of copper from anti‐fouling paints with different active copper compounds in artificial seawater

Release rates of total copper in artificial seawater (without organic matter) from anti‐fouling paints of different active copper compounds range from 0.5 to 75 μg cm^?2 day^?1. Approximately 80% of the released total copper was determined to be electrochemically active (labile fraction) for all paints investigated. The remaining fraction is more strongly bonded non‐bioavailable copper complexes with species released from the paints. Model calculations, using MinteqA2, predicted only a small portion (≈ 6%) of the total copper released as free cupric ions (Cu(H₂O)²⁺₆), the most bioavailable form of copper. Similar results were obtained with bioassay testing using bacteria and yeast on released copper from massive copper sheet exposed at identical conditions. The large difference between the total and the bioavailable copper fraction emphasizes the importance of generating chemical speciation data for accurate decisions of potential adverse effects of copper release from anti‐fouling paints. The observed release of other metals and organic substances from the paint matrix, implies the importance to assess an integrated response from released species from paints of anti‐fouling, and not only from single ingredients.     

Quenching of steels from intercritical temperatures

Conclusions Anomalies in the properties of the steels investigated were observed after quenching from temperatures 5–10°C below Ac₃. Quenching from these temperatures results in higher properties than quenching from standard temperatures. With quenching from temperatures near Ac₁ the toughness of the steels is minimal.All-Union Scientific-Research Institute of Compressor Machine Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 57–58, March, 1975.     

论高校管理创新的路径

高校教育教学活动总是在管理过程中进行的，其创新从一定意义上取决于高校管理的创新。就其创新的路径而言，应从管理理念上实现从物本管理向人本管理转变，从管理职能上实现从控制型管理向服务型管理转变，从管理组织上实现从垂直管理向扁平管理转变，从管理方式上实现从经验管理向制度管理转变，从管理机制上实现从维持学校向经营学校转变，这些路径是一个相互联系、相互影响的有机整体。     

Thermal stress induced microcracking in alumina–20% SiCp composites

Spontaneous microcracking caused by interphase thermal expansion mismatch stresses has been investigated in alumina–20% SiC_p composites. Specimens containing SiC particles with mean sizes ranging from 3 to 23 μm were fabricated and examined using SEM. The microstresses arising from the thermal expansion mismatch between the alumina and the SiC were measured by neutron diffraction. An abrupt transition from negligible microcracking to general cracking of the alumina matrix occurred when a critical SiC particle size of 10 ± 3 μm was exceeded. Above the critical size, approximately radial microcracks extended from every particle, and propagated fully from each particle to the next without terminating in the matrix. Neutron diffraction measurements of the thermal microstresses showed that microcracking reduced the mean stress level in the particles from −1275 MPa in the uncracked material to −800 MPa in the microcracked specimens. A model for matrix microcracking that accounts for SiC particle size and volume fraction has been developed. The model correctly predicts the critical particle size and explains the abrupt nature of the transition from little microcracking to general microcracking of the matrix.     

Density, stress, hardness and reduced Young's modulus of W-C:H coatings

Density, hardness and compressive stress of tungsten contained in an amorphous-hydrogenated-carbon matrix (W-C:H) have been studied as a function of composition and bias voltage. W-C:H coatings were deposited by reactive sputter deposition from a tungsten-carbide (WC) target on silicon substrate in an argon-acetylene plasma. W-C:H coatings obtained at different acetylene flow rates and substrate bias voltages, were characterized by scanning electron microscopy, X-ray diffraction, nanoindentation and substrate curvature method. It has been observed that compressive stress, hardness and reduced Young's modulus decrease when the acetylene flow is increased from 0 to 10 sccm. Also, compressive stress and hardness increases with the substrate bias voltage. In particular, for W-C:H coatings obtained at 5 sccm of acetylene flow, the compressive stress and hardness increase from − 1.6 GPa to − 3.2 GPa and from 19 GPa to 24 GPa, respectively, when increasing the substrate bias from 0 to 200 V. The variation of the internal stress, hardness and density of the coatings is discussed in terms of composition and structure of the W-C:H coatings.     

Quantitative evaluation of general corrosion of Type 304 stainless steel in subcritical and supercritical aqueous solutions via electrochemical noise analysis

Electrochemical noise (EN) sensors have been developed to measure the corrosion rate of Type 304 stainless steel (SS) in subcritical and supercritical environments. The EN sensors were tested in flowing aqueous solutions containing NaCl and HCl at temperatures from 150°C to 390°C, a pressure of 25 MPa, and flow rates from 0.375 to 1.00 ml/min. The potential and coupling current noise were recorded simultaneously and the noise resistance (R_n) was calculated from the standard deviations in the potential and current records. We found that the inverse noise resistance correlated very well with the corrosion rate evaluated from separate mass loss experiments, and that both the inverse noise resistance and the average corrosion rate were functions of temperature and flow rate. In the temperature range from 200°C to 390°C, the corrosion rate was found to be proportional to the inverse noise resistance and hence the Stern-Geary relationship can be used to evaluate the corrosion rate. However, at 150°C, the relation between inverse noise resistance and corrosion rate significantly deviated from the Stern-Geary relationship. It was found that the deviation was related to the low corrosion rate of Type 304 SS and 150°C.     

Characteristics of Fe powders prepared by spray pyrolysis from various types of Fe precursors as a heat pellet material

Aggregated Fe powders comprising elongated and aggregated particles used in the production of heat pellets for application in thermal batteries were prepared by spray pyrolysis. Iron oxide powders comprising dense and hollow particles were prepared by spray pyrolysis from spray solutions containing various types of Fe precursors. Iron oxide powders prepared from iron chloride and iron nitrate precursors were comprised of spherical and micron-sized particles. On the other hand, iron oxide powders prepared from iron oxalate were comprised of large, hollow, and thin-walled particles. The Brunauer-Emmett-Teller (BET) surface areas of iron oxide powders prepared from iron chloride, iron nitrate, and iron oxalate precursors were 17.5, 71.9, and 78.5 m² g⁻¹, respectively. At a low reduction temperature of 550 °C, iron oxide powders prepared from iron oxalate afforded loosely aggregated Fe powders comprised of elongated and loosely aggregated particles, with a BET surface area of 5.9 m² g⁻¹. The heat pellets prepared from Fe powders reduced at 550 °C and composed of fine primary powders had an ignition sensitivity of 0.9 W and a burn rate of 10 cm s⁻¹.     

Diffusion parameters of grain-growth inhibitors in WC based hardmetals with Co,Fe/Ni and Fe/Co/Ni binder alloys

The diffusion behaviour of the grain-growth inhibitors (GGI) Cr and V during early sintering stages from 950 to 1150 °C was investigated by means of diffusion couples of the type WC-GGI-binder/WC-binder. Besides Co, also alternative Fe/Ni and Fe/Co/Ni binder alloys were investigated. It was found that the diffusion in green bodies differs significantly from sintered hardmetals. Diffusivities in the binder phase were determined from diffusion couples prepared from model alloys and were found to be almost equal for Co and alternative binder alloys. The diffusion parameters determined from green bodies allowed to estimate the GGI distribution in a hardmetal during heat up. This was subsequently used to estimate an appropriate grain size of VC and Cr₃C₂ in hardmetals, which is required to ensure a sufficient GGI distribution during sintering before WC grain-growth initiates.     

Microstructure and mechanical properties of a spray-formed Ti-based metallic glass former alloy

A Ti_45.8Zr_6.2Cu_39.9Ni_5.1Sn₂Si₁ composite plate was spray deposited on a copper substrate. From the bottom substrate-contact surface to the upper free surface of the deposit, a layered microstructure evolution in the order of fully amorphous (for the region 1-2 mm perpendicularly away from the substrate), amorphous/nanocrystalline (3-4 mm from the substrate), ultrafine-grained crystalline (5-6 mm from the substrate) and micron-sized crystalline phases (7-8 mm from the substrate) was observed. The oversprayed powders bellow 50 μm exhibit fully amorphous structure, while the ones above 50 μm show certain crystallization behavior. The fracture strength of 1.58-1.85 GPa with obvious plastic strain can be achieved under compressive tests for the spray-formed deposit. Spray forming can therefore produce bulk-sized high strength Ti-based alloy which evolves gradually from certain non-equilibrium towards equilibrium during deposition, which were considered to be attributable to the chill effect at the bottom substrate-contact surface and the following heat entrapment from the successively deposited droplets or powders.