Chromium Powder Research Articles

Effects of sintering schedule on the characteristics of Fe-based powder compacts formed through warm compaction route

This paper presents the sintering characteristics of Fe-based powder compacts formed through the warm compaction method. Iron powder ASC100.29 (73 wt%), chromium powder (22 wt%), and aluminium powder (5 wt%) were mixed mechanically for 60 mins in preparing the feedstock. The powder mixture was subsequently compacted at 200ºC through simultaneous loading of 325 MPa from upper and lower punches. The defectfree green compacts were then sintered in an argon gas fired furnace at a rate of 10ºC/min by varying the sintering time (30, 60, and 90 mins) and temperature (600, 750, and 900ºC), respectively. The sintered samples were characterized through physical and mechanical properties and their microstructures were analysed through scanning electron microscopy. The results revealed that sintering at 900ºC for 90 mins contributed to the highest volumetric expansion and relative density change, which are not expected in the powder metallurgy industries. A moderate sintering temperature of 750ºC for a holding time of 60 mins was found to produce a sintered sample with higher bending strength. In these sintering conditions, better dispersion of the alloyed elements is also observed.

Studying High-Temperature Hardness of Powder Cobalt Alloys Strengthened with Niobium or Titanium Carbides

The hardness of cobalt powder alloys in the ‘room temperature–1150°C’ temperature range is investigated. The alloys are prepared by hot pressing of cobalt, chromium, aluminum, and iron powders with titanium or niobium carbides. The hardness of the alloys strengthened with 30 to 50 vol.% carbide at various temperatures show that the amount of the strengthening phase affects the hardness of the alloys investigated. The most significant factor that affects the hardness of the alloys is the temperature factor: with increasing temperature the hardness reduces regardless of the type and content of the carbides. It is shown that the hardness of the alloys with titanium carbide exceeds the hardness of those with niobium carbide. These results could be used to create friction materials for aviation purposes.

Liquid phase surface nitriding of Ti-6Al-4V pre-placed with chromium

In this study, liquid phase surface nitriding of Ti-6Al-4V was carried out by pre-placing of chromium powder on the substrate and subsequent Tungsten Inert Gas (TIG) surface melting. The effect of the application of low and high heat inputs on the microstructure, microhardness and wear resistance of the treated layers were studied. Surface alloying with chromium in a nitrogen containing atmosphere resulted in the formation of hard intermetallic compounds such as TiN, Cr2N and TiCr2. Moreover, the presence of beta stabilizer chromium together with the application of high heat input during surface treatment resulted in the presence of beta phase at room temperature. However, applying low heat input could not prevent transformation of beta to martensite. The hardness of the layers fabricated at high and low heat inputs were respectively 1050 and 1200 HV0.3 compared to average 280 HV0.3 for the as-received material. Liquid phase surface treatment of titanium at the aforementioned conditions improved the wear resistance. The lowest weight loss belonged to the specimen with the beta phase matrix. The formation of the fairly ductile bcc-β phase hindered crack nucleation during wear. The weight loss in this condition was 7 times lower than that of the base material.

Corrosion resistant Cr-coating on mild steel by powder roll bonding

Abstract Chromium powder coating on mild steel was developed by roll-bonding followed by annealing at 1200 °C for different duration in hydrogen atmosphere to promote diffusion bonding and finally furnace cooling. All the coated samples were characterised using scanning electron microscopy, electron probe micro analyser, bend test and potentiodynamic polarisation test in 0.2 N H2SO4 solution. Diffusion layer thickness was in the range of 170–250 μm depending on the annealing time, and the Cr content reached up to 13 wt% in the diffusion layer. Diffusion layer exhibited high ductility and adhesion, since no crack was observed even after 180° bending. The chromium coated mild steels showed comparable stable passivity and corrosion rates in 0.2 N H2SO4 solution as observed in a 304 stainless steel. The corrosion rate decreased from 5.51 mm/y for the uncoated mild steel to 0.2–1.0 mm/y for the coated mild steel sample.

Cr50Cu50 alloys produced from submicrometre structured powders through hot pressing at different pressures

In this study, two different compositions of submicrometre copper and chromium powders were mixed and the Cr50Cu50 alloys were fabricated via the powder metallurgy technique. The research imposed various hot pressing pressures, while the temperature was maintained at 1050°C for 1 h, respectively. The experimental results showed that the Saint Venant's effect obviously appeared in 1050°C, 48 MPa, 1 h hot pressing Cr50Cu50 alloys, which led to differences in the surface and internal hardness of the specimens. As a result, the optimal parameters of hot pressing of Cr50Cu50 alloys were 1050°C, 36 MPa for 1 h possessing the highest transverse rupture strength value (921.69 MPa). Moreover, the surface hardness increased to HV0.2 221.78 (HRB 95.4), the relative density reached 97.15% and apparent porosity decreased to 0.10%, respectively. Furthermore, the resistivity decreased to 5.28 × 10−6 Ω cm, and ICAS was enhanced to 32.65% after the optimal procedure.

Reactor target from metal chromium for “pure” high-intensive artificial neutrino source

The paper presents the first results of development of manufacturing technology of metallic chromium targets from highly enriched isotope 50Cr for irradiation in a high flux nuclear reactor to obtain a compact high intensity neutrino source with low content of radionuclide impurities and minimum losses of enriched isotope. The main technological stages are the hydrolysis of chromyl fluoride, the electrochemical reduction of metallic chromium, the hot isostatic pressing of chromium powder and the electrical discharge machining of chromium bars. The technological stages of hot isostatic pressing of chromium powder and of electrical discharge machining of Cr rods have been tested.

An investigation into surface roughness of work piece produced by chromium powder suspended dielectric in PMEDM process

In this research article, an investigation of surface roughness (SR) of work surfaces produced by the powder mixed electrical discharge machining of EN-8 steel has been carried out. Response surface methodology has been used to plan and analyse the experiments. Average current, duty cycle, electrode angle and concentration of chromium powder added into the dielectric fluid were selected as process parameters. Experiments have been performed on a newly designed experimental set-up developed in the laboratory. An empirical model has been developed for surface roughness. In addition, the recommended model has been verified by conducting confirmation experiments. [Received 14 May 2015; Revised 14 April 2016; Accepted 8 June 2016]

Simultaneously Recovering High-Purity Chromium and Removing Organic Pollutants from Tannery Effluent

Chromium pollution is a serious issue because of carcinogenic toxicities of the pollutants and low recovery rate of chromium because of the presence of organic, such as protein and fat. In this work, high recovery rate and high purity of the chromium ion were successfully prepared by the way of acid enzyme, flocculant, and Fenton oxidation. The experiments were characterized by TG, TOC, UV-VIS, and SEM. In the work, the tannery waste chrome liquor was used as experimental material. The results showed that the percentage of reduction of TOC in the tannery waste chrome liquor by method of Fenton oxidation, acid enzyme, and the flocculant was 71.15%, 65.26%, and 22.05%, respectively. Therefore, the organism content of chrome tanning waste liquid was greatly reduced through the pretreatment. And the application experiment showed that the properties and grain surface and fibers of the tanned leather with commercial chromium powder and chrome tanning agent prepared from the chromium waste liquid treated with Fenton are nearly the same.

クロム粉末混入放電加工による金型の表面機能向上

クロム粉末混入放電加工による金型の表面機能向上

Improvement in Surface Characteristics by EDM with Chromium Powder Mixed Fluid

Surface finishing technology by EDM has recently progressed, and very small surface roughness can be readily obtained by controlling the electrical discharge conditions, or by using metal powder mixed working fluids. In addition, it was reported that EDMed surface using metal powder mixed fluids sometimes has high surface functions, such as high hardness, high corrosion resistance and so on. Therefore, the high functional EDM finished surface is well expected to be applied as a final metal mold surface. In this study, formation of chromium containing layer on the EDMed surface was tried by using chromium powder mixed fluid. Furthermore, the EDMed surface characteristics with chromium powder mixed fluid were experimentally evaluated.

Fabrication of Photocatalyst Composite Coatings of Cr-TiO2 by Mechanical Coating Technique and Oxidation Process

The photocatalyst composite coatings on alumina (Al2O3) balls had been prepared by mechanical coating technique (MCT) with titanium (Ti) powder, adding a certain content of chromium (Cr) powder and a subsequent oxidation process. The effect of oxidation conditions and adding Cr on the composite coatings of chromium-titanium dioxide (Cr-TiO2) was investigated. The results show Cr-TiO2 coatings are with mixed-phase of anatase and rutile under different oxidation conditions, and the mass fraction of the rutile phase (XR) has been obviously increased when under 973 K. The SEM images indicate that adding Cr could significantly accelerate the growth of surface structures, especially at 1073 K. The photocatalytic activity of Cr-TiO2 coatings firstly increases, then decreases, with the addition of Cr. Compared with that of two other oxidation conditions, the enhancement on photocatalytic activity by adding Cr under visible light is relatively higher, especially at 973 K for 10 h.

Synthesis and Characterization of Nanostructured Tungsten-30 Atomic % Chromium Produced by Mechanical Attrition and Hydrogen Sintering

Nanostructured W70Cr30 powders were produced by mechanical alloying (MA) of elemental tungsten (W), Chromium (Cr) powders in a high energy planetary ball-mill using tungsten carbide as grinding media and toluene as a process control agent. The crystallite size and lattice strain of the nanostructured powders at different milling time (0 h to 10 h) was calculated from X-ray diffraction patterns (XRD). The crystallite size of W in W70Cr30 powder reduced from 100 μm at 0 h to 32.8 nm at 10 h of milling with increase in lattice strain of 0.43% at 10 h of milling. The lattice parameter of tungsten shows initial expansion of lattice upto 0.56% at 5 h of milling and contraction of lattice upto 0.93% at 10 h of milling. The scanning electron microscopy (SEM) micrograph also revealed mixed morphology of elemental W and Cr powders consist of spherical and elongated particles during mechanical alloying (0 h to 10 h). The dark-field transmission electron microscopy (TEM) observations indicated that the crystallite size (~30 nm) of W in W-Cr alloy in the as-milled powder is in good agreement with calculated crystallite size from XRD. Maximum solid solubility of 4.4 at.% Cr in W was found at 10 h of milling. The dislocation density increases from 6.75 (1016/m2) to 17.56 (1016/m2) with increase in the milling time from 0 h to 20 h. No cracks in the sintered pellets were visible under scanning electron microscope (SEM). Hardness and Elastic Modulus of sintered W70Cr30 alloy determined by nanoindentation test are less compared to pure W.

Multi-attribute optimization of machining process parameters in powder mixed electro-discharge machining using TOPSIS and grey relational analysis

Powder Mixed Electro-Discharge Machining (PMEDM) is a hybrid machining process where a conductive powder is mixed to the dielectric fluid to facilitate effective machining of advanced material. In the present work application of Taguchi method in combination with Technique for order of preference by similarity to ideal solution (TOPSIS) and Grey Relational Analysis (GRA) have been adopted to evaluate the effectiveness of optimizing multiple performance characteristics for PMEDM of H-11 die steel using copper electrode. The effect of process variables such as powder concentration (Cp), peak current (Ip), pulse on time (Ton), duty cycle (DC) and gap voltage (Vg) on response parameters such as Material Removal Rate (MRR), Tool Wear Rate (TWR), Electrode Wear Ratio (EWR) and Surface Roughness (SR) have been investigated using chromium powder mixed to the dielectric fluid. Analysis of variance (ANOVA) and F-test were performed to determine the significant parameters at a 95% confidence interval. Predicted results have been verified by confirmatory tests which show an improvement of 0.161689 and 0.2593 in the preference values using TOPSIS and GRA respectively. The recommended settings of process parameters is found to be Cp = 6 g/l, Ip = 6Amp, Ton = 100 µs, DC = 90% and Vg = 50 V from TOPSIS and Cp = 6 g/l, Ip = 3Amp, Ton = 150 µs, DC = 70% and Vg = 30 V from GRA. The microstructure analysis has been done for the optimal sample using Scanning Electron Microscope (SEM).

Effect of pulsed Nd:YAG laser re-melting on chromium surface alloyed AA6061-T6 aluminum

In this work, in situ formation of Al–Cr intermetallic compound on the surface of AA6061-T6 aluminum pre-placed chromium powder via pulsed Nd:YAG laser surface alloying was investigated. The effect of laser re-melting on microstructure and hardness of the treated layers was examined. Laser re-melting resulted in a significant reduction in the presence of cracks, pores, and undissolved Cr-rich particles along with a more uniform distribution of intermetallic compounds. The results showed that the alloyed layers mainly consisted of fine Al7Cr and Al4Cr intermetallic compounds in an α-Al solid solution matrix with cellular and dendritic morphologies. Hardness profiles along cross section and top surface of the alloyed layers indicated that laser re-melting enhanced homogeneity and increased the hardness value to more than six times of that of the base material.

Morphology of Sintered Cr-Mo Porous Materials

Chromium and molybdenum exhibit continuous solubility in the solid phase region at temperatures of 908°C and above [1]. At lower temperatures, the system exhibits a miscibility gap. Furthermore a congruent minimum in the liquidus boundary exists at 1854°C. Chromium and molybdenum powders with different particle morphologies were mixed and porous green parts were produced by pressing. Sintering experiments were performed at different temperatures and for different chromium to molybdenum ratios. To investigate the evolution of the microstructure, sintering was interrupted at different temperatures and points in time. The microstructure and morphology of the sintered parts was investigated by scanning electron microscopy as well as light optical microscopy. It was found that during sintering, a Cr-Mo solid solution is formed. Depending on the molybdenum content, this induces either shrinking or swelling of the porous parts. Samples exhibited a linear expansion of up to 10% and final porosities of up to 65%.

Nitridation of chromium powder in ammonia atmosphere

CrN powder was synthesized by nitriding Cr metal in ammonia gas flow, and its chemical reaction mechanism and nitridation process were studied. Through thermodynamic calculations, the Cr-N-O predominance diagrams were constructed for different temperatures. Chromium nitride formed at 7002-1200°C under relatively higher nitrogen and lower oxygen partial pressures. Phases in the products were then investigated using X-ray diffraction (XRD), and the Cr2N content varied with reaction temperature and holding time. The results indicate that the Cr metal powder nitridation process can be explained by a diffusion model. Further, Cr2N formed as an intermediate product because of an incomplete reaction, which was observed by high-resolution transmission electron microscopy (HRTEM). After nitriding at 1000°C for 20 h, CrN powder with an average grain size of 63 nm was obtained, and the obtained sample was analyzed by using a scanning electron microscope (SEM).

Amorphous-silicon@silicon oxide/chromium/carbon as an anode for lithium-ion batteries with excellent cyclic stability

A new amorphous-Si@SiOx/Cr/carbon (a-Si@SiOx/Cr/C) anode composite for lithium-ion batteries is synthesized, using SiO, chromium powder and graphite as starting materials. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) are employed to characterize the composition, morphology and microstructure of the composite. Coin-type cells are assembled to investigate the electrochemical behaviors of the as-prepared composites by constant current charge–discharge technique, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that chromium facilitates the crush of Si@SiOx and graphite during milling, and thus improves their mutual dispersion in the composite. When cycled at 100mAg−1, the a-Si@SiOx/Cr/C exhibits a stable discharge capacity of about 810mAhg−1 (calculated on the mass of a-Si@SiOx/Cr/C) with good capacity retention up to 200 cycles. The improved electrochemicalperformance is attributed to the reduced particle size of a-Si@SiOx and the synergistic effect of carbon and chromium.

EFFECT OF CHROMIUM POWDER MIXED DIELECTRIC ON PERFORMANCE CHARACTERISTIC OF AISI D2 DIE STEEL USING EDM

In this paper, the effect of chromium powder mixed dielectric fluid on machining characteristics of AISI D2 die steel has been studied. Peak current, pulse on time, pulse off time, concentration of powder are the process parameters. The process performance is measured in terms of material removal rate (MRR), tool wear rate (TWR) and surface roughness (SR). The research outcome will identify the important process parameters that maximize MRR, minimize TWR and SR. The design of experiment has been undertaken using Taguchi method. ANOVA analysis has been used to investigate the percentage contribution of each process parameter for optimizing the performance. The study indicates that all the selected parameters except pulse off time have a significant effect on MRR. Current is found to be the most significant factor for MRR and TWR. With increase in current, TWR increases. Also, surface roughness increases with increase in pulse off time.

405 クロム粉末混入放電加工によるクロム含有層の形成(生産加工・工作機械+材料加工I)

405 クロム粉末混入放電加工によるクロム含有層の形成(生産加工・工作機械+材料加工I)

Photon emission produced by Kr+ ions bombardment of Cr and Cr2O3 targets

The sputter induced photon spectroscopy technique was used to study the luminescence spectra of the species sputtered from chromium powder and its oxide Cr2O3, during 5keV Kr+ ions bombardment in vacuum better than 10−7torr. The optical spectra recorded between 350 and 470nm exhibit discrete lines which are attributed to neutral excited atoms of chromium (Cr I lines). The experiments are also performed under 10−5torr ultra pure oxygen partial pressure. The results demonstrate that the measured intensities of the emitted photons are always higher in the presence of oxygen and even higher than those obtained for Cr2O3 target. In the presence of oxygen vapor we assume that an oxide film is formed on the chromium surface which is responsible of the increase of photon emission. This variation in the intensities is correctly explained in the model of electron transfer processes between the excited sputtered atom and the bombarded surface. This model suggests that the structure formed on the Cr surface in the case of oxygenated chromium is closer to that of Cr2O3 oxide.