Sinter-bonding of Cr3C2 to chromium carbide alloys

Conclusions The sinter-bonding of electrophoretically deposited Cr₃C₂ coatings to KKhN and KKhNF chromium carbide alloys is a result of liquid-phase reaction and of migration of the metallic phase from the basis materials to the carbide layers. The structure and properties of resultant coatings are determined by the sinter-bonding temperature and the composition of the basis material, but are not significantly affected by the latter's condition. Phosphorus-free chromium carbide alloys are preferable to KKhNF alloys as basis materials because they enable optimum properties in coatings to be obtained at a lower temperature.Translated from Poroshkovaya Metallurgiya, No. 9(261), pp. 52–56, September, 1984.     

Deposition of Protective Coatings on Tungsten-Free Hard Alloys

The process of deposition of coatings of titanium carbide, vanadium carbide, and chromium carbide on the surface of the tungsten-free hard alloys TN20, KNT16, and KKhN15 is investigated. The structure and phase composition of specially created layers are explored and the microhardness measured (11.5-24.5 GPa). The optimal temperature-time conditions for deposition of carbide coatings is determined. The ultimate transverse bending strength of hard alloys with and without coatings is determined. From the results of industrial tests, a two- to five-fold increase in the durability of plates in cutting was noted.     

Reaction of tungsten carbide with oxides of refractory metals in a vacuum

Summary An investigation was made into the kinetics of the reaction of tungsten carbide with niobium, tantalum, vanadium, titanium, chromium, and zirconium oxides. Low-carbon alloys of tungsten with niobium, tantalum, chromium, and vanadium were produced. A method of preparing refractory alloys, using an oxide-carbide mixture as an intermediate product, has been proposed.     

Foundations of the Fabrication Technology of Wear-Resistant Coatings Made of Mixtures of Chromium Carbide Powders with a Metallic Binder by Explosive Pressing

Experimental data on the explosive compaction of powder mixtures of chromium carbide (Cr₃C₂) with metals (Ti, Ni, Cu) are presented, their theoretical explanations are given, and scientifically substantiated principles of the composition selection and development of the explosive fabrication of wear-resistant antifriction chromium carbide hard alloys and coatings are formed on this basis. The explosive pressing of powder mixtures was performed according to the scheme with the use of a plane normally incident detonation wave in a broad range of loading parameters (the powder heating temperature in shock waves was varied in experiments from 200 to 1000°C, while the maximal pressure of the shock-wave compression varied from 4 to 16 GPa). To analyze the phase transformations, the numerical thermodynamic simulation of the phase equilibrium was performed applying the Thermo-Calc software complex. The microstructure and the chemical and phase compositions were investigated using an Axiovert 40 MAT optical microscope (Carl Zeiss, Germany), Versa 3d and Quanta 3D FEG scanning electron microscopes (FEI, United States), BS 540 (Tesla, Czech Republic) and Titan 80–300 and Techai G2 20F (FEI, United States) transmission electron microscopes, and a Solver Pro atomic force microscope (OOO NT-MDT, Zelenograd). The temperature stability and oxidation resistance at elevated temperatures of materials formed by the explosion were investigated by thermogravimetric analysis using an STA 449 F3 Jupiter device (NETZSCH, Germany) in synthetic air upon heating to 1500°C. Tribotechnical tests were performed using an MI-1M friction machine (MEZIMiV, Moscow) according to the pin–ring scheme with digging in distilled water. Mechanisms of compaction and formation of strong boundaries between the particles of powder materials during the explosive pressing are described. It is shown that chromium carbide hard alloys with a titanium binder formed by explosion retain their phase composition invariable, do not oxidize to 600°C, and have considerably better antifriction properties and wear resistance when compared with SGP-0.5 and KKhN-20 materials lubricated with water, which have been applied in friction pairs until now.     

Characterization and corrosion behavior of high-chromium white cast irons

Erosion-resistant high-chromium white cast irons (CWIs) are widely used in hydrotransport components, particularly in oil-sand operations. Due to the acceptance that corrosion processes can accentuate material degradation by erosion processes andvice versa, it is important to understand the corrosion resistance of these materials in the environments in which they are used. Three CWI alloys with different chemical compositions—chromium (26 to 40 wt pct) and carbon (2.5 to 4.3 wt pct)—were investigated in this study. Electrochemical DC potentiodynamic polarization and potentiostatic tests were carried out in a solution of 1000 ppm Cl⁻ at a pH of 8.5 (obtained by adding NaOH) that simulates a recycle cooling water. A detailed characterization of the microstructures was also performed. There are significant effects of microstructural features and alloy composition on the corrosion behavior of CWIs. Two key factors have been shown to determine the corrosion behavior: the primary carbide area fraction and the amount of chromium as well as other elements in the matrix. The corrosion resistance of the CWI alloys strongly depends on the ratio of chromium content in the M₇C₃ carbide to that in the matrix (Cr_M7C3/Cr_matrix).     

Reaction layer formation at the graphite/copper-chromium alloy interface

Sessile drop tests were used to obtain information about copper-chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Auger electron spectroscopy (AES), and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 °C for 1 hour, copper alloys containing greater than 0.98 at. pct chromium form continuous reaction layers of approximately 10-μm thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 deg or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modeled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of the Cu alloy and later by the diffusion of C through chromium carbide. This article is based on a presentation made in the symposium “High Performance Copper-Base Materials” as part of the 1991 TMS Annual Meeting, February 17–21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee.     

碳化铬/Ni_3Al复合材料的室温微动磨损性能

对比研究了碳化铬/Ni3Al复合材料和传统高温耐磨材料Stellite 6合金和T800合金的室温耐微动磨损性能。结果表明,碳化铬/Ni3Al复合材料具有优异的耐微动磨损性能,与GCr15对磨时,其室温相对耐磨性分别是Stellite 6和T800合金的5.5倍和2.6倍。通过分析微动磨损机制认为,碳化铬/Ni3Al复...     

Chromium depletion in the vicinity of carbides in sensitized austenitic stainless steels

The analytical electron microscope (AEM) was used to examine the microstructure of type 316LN stainless steel alloys which had been annealed for 50 to 300 hours in the temperature range 600 to 700 °C. The M₂₃C₆ carbide chemistry and distribution are described as a function of heat treatment.X-ray spectroscopy in the AEM revealed significant chromium depletion at grain boundaries in the vicinity of carbides for samples aged at 50 and 100 hours at 650 °C and 100 and 300 hours at 700 °C, with lower grain boundary chromium values observed at 650 °C than at 700 °C. The width of the chromium depleted zone normal to the grain boundaries increased with increasing annealing time and/or temperature. Measurements of chromium concentration along the grain boundaries away from a carbide were made after aging at 700 °C for 100 hours, and the chromium level rose steadily until the bulk value was reached at a distance of ~3μm from the carbide. The width of the chromium depleted zone normal to the boundaries in the same sample was an order of magnitude less. Some molybdenum depletion was also found at the grain boundaries, and the Mo-depletion profiles were in form and extent similar to the chromium results. Simple thermodynamic models were used to calculate the equilibrium value of chromium at the carbide-matrix interface, and the chromium distribution along and normal to the grain boundaries. The results of these models agreed well with the AEM results, and the agreement can be improved by considering the effect of electron probe configuration on the AEM measurements. The calculated thermodynamic data and the AEM results were related to the corrosion behavior of the alloys. The occurrence of severe asymmetries in some concentration profiles normal to the grain boundaries, which increased with increasing annealing temperature or time, was shown to be due to boundary movement during the discontinuous precipitation of M₂₃C₆ carbides.     

Mechanical properties of heterogeneous-structure wear-resistant high-chromium powder materials

Studies have been made on the effects of the production technology and composition of the initial material on the microstructure and some properties of powder materials having high chromium contents, which have heterogeneous structures. The materials were prepared from mixtures of iron powder and finely divided chromium and chromium carbide Cr₃C₂. The materials have a high wear resistance and also good mechanical characteristics and high resistance to corrosion in fresh water and sea water.     

Iron-chromium-carbon system at 870°C

A series of 13 Fe-Cr-C alloys was studied to determine the phases present after the alloys were equilibrated for 1000 h at 870°C (1600°F). The alloys had a nominal composition of 1 pct carbon and 0 to 29 pct chromium. The experimental program employed: a) selective etching plus X-ray diffraction studies of extracted carbides to identify the carbides, b) quantitative metallography plus electrolytic carbide extraction to determine the quantity of carbides, and c) electron microprobe analyses plus chemical analyses of extracted carbides to determine the carbide compositions. Microprobe traverses through the carbide particles and the adjoining matrices showed that equilibrium had been established. The In and In₆ carbides were all stoichiometric with respect to car bon—in contrast to most prior diagrams which show the M₃C and M₇C₃ forming a pseudobinary system.     

Behavior of grain boundary chemistry and precipitates upon thermal treatment of controlled purity alloy 690

Grain boundary composition and carbide composition and structure were characterized for various microstructures of controlled purity alloy 690. Heat treatments produced varying degrees of grain boundary chromium depletion and precipitate distributions which were characterizedvia scanning transmission electron microscopy (STEM). Convergent beam electron diffraction revealed that the dominant carbide is M₂₃C₆, and energy dispersive X-ray analysis (EDAX) determined that the metallic content was about 90 at. pct chromium. A discontinuous precipitation reaction was observed and is attributed to a high degree of carbon supersaturation. Grain boundary composition measurements confirm that chromium depletion is controlled by volume diffusion of chromium to chromium-rich grain boundary carbides in the temperature range of 873 to 1073 K. Grain boundary chromium levels as low as 18.8 at. pct were obtained by thermal treatment at 873 K for 250 hours and 973 K for 1 hour. A thermodynamic and kinetic model developed for alloy 600 was modified to describe the development of the chromium depletion profile in alloy 690 during thermal treatment. Experimentally measured chromium profiles agree well with the model results for the dependence of the chromium depletion zone width and depth on various input parameters. The establishment of the model for alloy 690 allows the chromium depletion zone width and depth to be computed as a function of alloy composition, grain size, and temperature. The chromium depletion profiles and the precipitate structure and composition of controlled purity 690 are compared to those of controlled purity 600. A thermodynamic analysis of the carbide stability indicates that other factors, such as favorable orientation relationships, play an important role in controlling the precipitation of Cr₂₃C₆ in nickel-base alloys.     

Thermodynamics of carbon in nickel,iron-nickel and iron-chromium-nickel alloys

Iron-nickel alloys with 8 and 16 wt pct nickel and iron-chromium-nickel alloys with 8 pct nickel and chromium contents in the range of 2 to 22 pct were equilibrated with iron and nickel in flowing CH₄-H₂ gas mixtures and in sealed capsules under partial vacuum at temperatures between 700 and 1060°C. Carbon activities in these alloys were established from the carbon concentrations in the nickel by applying Henry’s law to the solubility of carbon in nickel that was determined in the temperature range of 500 to 1000°C. First-order free-energy interaction parameters were used to relate the carbon activities to composition and temperature in the single-phase austenitic Fe-Ni and Fe-Cr-Ni alloys. An expression was also developed to evaluate carbon activities in Fe-Cr-Ni alloys in the region of higher chromium contents (〉4 wt pct) that result in a two-phase austenite plus carbide mixture at these temperatures.     

碳化铬基自润滑耐磨涂层材料的制备及表征

采用碳化铬、镍铬合金、氟化物共晶体和银的复合粉末为原料,通过等离子体喷涂方法制备高温耐磨自润滑涂层。利用扫描电子显微镜对粉末材料和涂层的微观组织结构进行分析,并对其摩擦性能分析、研究。结果表明:分别采用镍铬合金润湿碳化铬、银包覆氟化物共晶体的方法有效的降低了等离子体喷涂过程中的脱碳、烧损问题。与国外相同材料组分的碳化铬基自润滑涂层相比,涂层具有孔隙率低、自润滑组分(氟化物、银)分布均匀、摩擦系数为0.18~0.20等特点。     

A mathematical model describing carburization in multielement alloy systems

Previously, a finite difference model was set up describing the diffusion of carbon in high-temperature model alloys and its chemical reaction with one of the alloy components. The model described the formation of up to three different chromium carbides, two of which could coexist. This paper describes the further development of the model for application to commercial alloys. The model was extended to enable treatment of an arbitrary number of (a) metallic carbide-forming components in the alloys, (b) carbides which may form, (c) components out of which each carbide may be composed, and (d) carbides which may coexist. With this model, carbon concentration profiles and distribution profiles of precipitated carbides occurring during carburization of binary, ternary, and quaternary Ni-based alloys were calculated. Kinetic and thermodynamic data needed for the calculations were obtained by combining literacture data with experimental results and by fitting measured with calculated concentration profiles. The resulting calculated carbon profiles and carbide distributions were in good agreement with the experimental results. R. Supchulten, formerly with Kernforschungsanlage Jülich     

A model to predict carburization profiles in high temperature alloys

A mathematical model has been developed which, by means of finite difference computation techniques, permits the prediction of carbon concentration profiles in carburized high temperature alloys. It is assumed that a proportion of the carbon which diffuses into the alloy reacts with elements such as chromium to form carbide precipitates. The amount of carbon remaining in solution is determined from the solubility product of the carbide. Only this carbon in solution is able to diffuse through the alloy matrix, and thus the carbide precipitation process reduces the rate of carburization. Applying the model, the diffusion coefficient of carbon in Alloy 800 H at 900 °C has been determined as (3.3 ± 0.5) × 10⁻⁸ cm²/s. The model can also treat the carburization of an alloy containing two carbide-forming elements, but application to alloys containing both chromium and niobium (columbium) was successful only to a limited extent, probably as a result of the slow, complex kinetics of carbide precipitation. The model can be used to adapt carbon concentration profiles from one geometrical configuration to another. On the basis of profiles determined experimentally on small, cylindrical test specimens, carbon concenration profiles have been predicted for thick section tubes of Alloy 800 H exposed to a carburizing environment for up to 100,000 h. Formerly of the Institute of Reactor Materials, Nuclear Research Centre (KFA), Jülich     

Structures and Properties of Iron Matrix Composites with Tungsten Carbide Particle by EPC-V Process

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Synthesis of cast graphite-containing Cu–Cr–C composites

Casting with the use of low-frequency vibrations is applied to fabricate copper-based materials containing graphite and chromium. The conditions of formation of core (graphite)–shell (chromium carbide) complexes and the influence of low-frequency mechanical activation of molten copper on them are studied.     

直流电弧原子发射光谱法测定超细碳化钨中痕量元素

超细碳化钨(WC)主要用于生产棒材硬质合金,一般含有0.1％～1.0％的碳化钒(VC)或碳化铬(Cr3 C2),具有细化晶粒作用,提高棒材合金强度.超细碳化钨中痕量元素对合金性能具有重要的影响.因此建立一种快速测量超细碳化钨中痕量元素检测方法具有重要的生产指导意义.实验采用直流电弧原子发射光谱仪,建立了快速测量超细碳化...     

Structures and tempering behavior of rapidly solidified high-carbon iron alloys

High-carbon iron alloys containing carbide formers of chromium and molybdenum were rapidly solidified by means of a single roller method. In the alloy containing a high level of both chromium and molybdenum (10Cr-5Mo) and a critical carbon content of about 4 pct, the metastable phases,ε phase and austenite, are retained after solidification. Theε phase could contain a large amount of carbon in solid solution so that during tempering at about 900 K, it decomposes to very fine ferrite and carbide, which bring about an enhanced hardness of 1300 DPN. Even after tempering at a high temperature around 1100 K, the hardness hardly deteriorates due to a remarkable dispersion of fine M₃C and M₇C₃ carbides. Thus, coaddition of chromium and molybdenum is effective in obtaining high hardness. Formerly Graduate Student, Kyushu Institute of Technology