Cr3C2 Powder Research Articles

Concentrated solar energy for in-situ elaboration of wear-resistant composite layers. Part I: TiC and chromium carbide surface enrichment of common steels

Having already demonstrated the feasibility of using Concentrated Solar Energy (CSE) as a high temperature heat source for the in-situ elaboration of composite surface layers onto steel base metal, the present study focuses on the comparative evaluation of such “solar” titanium and chromium carbide hardfacings with respect to their microstructure characteristics and tribological performance. TiC and Cr3C2 powders were pre-deposited onto common steel base metal and the effects of solar irradiation time and repetition of solar exposure on the obtained microstructure of the surface layer were used as criteria for determining an adequate solar processing path for each specific carbide type. In the case of TiC powder, a single-step solar processing was sufficient to induce homogeneous dispersion of the carbide particles and, hence, surface reinforcement. For the Cr3C2 powder, single-step solar processing above a certain threshold solar processing time period was found to be necessary for the complete incorporation of the chromium carbide within the liquid metal pool, resulting in, however, carbides dissolution and surface alloying rather than carbides dispersion within the ferrous matrix. Thus, a second step of solar exposure of the previously obtained surface alloy above temperatures sufficient to cause re-melting, is necessary to obtain primary chromium carbide precipitates that provide the high wear resistance required. This was, indeed, demonstrated via dry sliding friction tests performed against an Al2O3 ball during which both “solar” surface layers exhibited relatively low specific wear rates. Microscopic observations on the worn surfaces indicated the synergy of distinct wear micro-mechanisms, different for each carbide particle type dispersed in the metallic matrix. These results in combination with the respective ones for WC-based hardfacing layers obtained via the same route and reported in the second part of this study, assist to identify the crucial metallurgical reactions that govern the successful implementation of the proposed “solar” technology.

Microstructure and wear resistance of in situ synthesized particle-reinforced novel stainless steel by laser melting deposition

The in situ synthesized particles-reinforced novel stainless steel was produced via laser melting deposition technology, aiming to fabricate a new wear-resistant material. The Cr3C2 and high vanadium alloy powder were introduced into novel stainless steel and the phase compositions, microstructure, microhardness and wear resistance of the novel wear-resistant material were investigated using XRD, SEM, microhardness tester and friction-wear tester, respectively. The results showed that the V8C7 and Cr23C6 phases were in situ synthesized successfully after the Cr3C2 and high vanadium alloy powder was introduced, and the microstructure of carbides reinforced novel stainless steel was refined significantly. The microhardness of carbides reinforced novel stainless steel was 800HV0.2, which was ~1.2 times that of new stainless steel, and the wear resistance was ~4 times that of the new stainless steel.

Structure, Phase Composition, and Hardness of Coatings Obtained by High-Energy Electron Beam Cladding of a Mixture of Cr3C2 and TiC Powders on Low-Carbon Steel

The methods of optical and scanning electron microscopy, micro-X-ray analysis, and analysis of backscattered electron diffraction are used to study the influence of the input energy on the structure and phase composition of coatings obtained by high-energy electron cladding of a mixture of chromium carbide and titanium carbide powders on low-carbon steel in the open air. A correlation between the structural-phase state of coatings and their microhardness is established. The role of titanium carbide particles in the formation of the structure and changes in the microhardness of coatings is discussed.

Электроискровое осаждение покрытий с использованием порошка Cr3C2 и их характеристика

A mixture of titanium granules with chromium carbide powder Cr3C2 was employed to prepare Ti-C-Cr coatings on Ti6Al4V titanium alloy using electrospark treatment in granules. Three mixtures of granules with a chromium carbide content of 2.7; 5.1 and 7.4 vol.% were prepared. According to X-ray analysis, it was found that titanium carbide, αTi, chromium and carbide Cr7C3 were observed in the composition of coatings. Titanium carbide was formed as a result of decarburization of Cr3C2 when interacting with molten titanium under the action of electric discharges. The average thickness of the coatings increased from 18 to 34 μm with an increase in the content of Cr3C2 powder in the mixture of granules. Grains of titanium carbide with a dendritic structure, surrounded by a Ti-Cr binder, were observed in the microstructure of the coatings. According to the EDS data, the concentrations of chromium and carbon decreased when scanning from the surface layers of the coating to the substrate. With an increase in the concentration of Cr3C2 powder in the mixture of granules from 2.7 to 5.1 vol.% hardness of coatings increased from 5.2 to 10.6 GPa. This is 1.7 – 3.5 times higher than that of the Ti6Al4V alloy. Dry sliding wear tests showed that the Ti-C-Cr coatings had a wear rate ranging from 0.41 to 2.38 ×10−6 mm3 / Nm. Thus, these can improve the wear resistance of the Ti6Al4V alloy from 18 to 107 times. Testing of the samples for resistance to high-temperature gas corrosion at 900°C for 100 hours showed that the technology of electric spark treatment in a mixture of titanium granules with 7.4 vol.% of chromium carbide powder allows increasing the oxidation resistance of the alloy Ti6Al4V three times.

Preparation and Characterization of Ni60-Cr3C2-WC/TiC Plasma Welding Surfacing Layer

Using plasma build-up welding technology, Ni60, WC, Cr3C2, and TiC composite powders were clad on the surface of the substrate in a certain proportion according to the metallurgical bonding method to increase the bond strength between the coating and the substrate. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microstructure of the surfacing layer and the chemical composition of the sample. The hardness and wear resistance of the surfacing layer were tested and analyzed by the HV-1000 hardness tester and the impact wear device. The results showed that in the microstructure, fishbone, spider-web, and floral-like structures appeared in the surfacing layer. When the micro-hardness was tested, the depth of the indentation reflected the hardness of the surfacing layer. When analyzing wear resistance, the amount of wear increases with time.

Microstructure and tribological behavior of flame sprayed and microwave fused CoMoCrSi/CoMoCrSi–Cr3C2 coatings

This present work deals with the investigation of dry sliding wear behavior of CoMoCrSi and CoMoCrSi–Cr3C2 depositing on titanium substrate through Flame spray process, subsequently fused by the microwave hybrid heating process. Prior to the deposition of the coating, CoMoCrSi powder is milled by using high energy ball milling (HEBM) process and later 30% of Cr3C2 powder is added. Microstructural features and phase analysis of milled powders, as-coated and microwave fused coatings are inspected by using SEM with EDS and XRD process respectively. The coatings before and after fusing are tested for microhardness and bond strength by using a Vickers microhardness and universal tensile machines respectively. Dry sliding wear behavior of coatings before and after fusing is conducted against alumina counter face at ambient and elevated temperatures, also normal load is varied. The wear mechanism of both coatings is examined by employing XRD, SEM-EDS techniques. The fused coatings exhibit lower friction and better wear resistance compared with as-deposited coatings. The detailed results of each test of their coatings are discussed in this paper.

Formation mechanism and phase evolution of in situ synthesizing TiC-reinforced 316L stainless steel matrix composites by laser melting deposition

Different weight ratios of 316L austenitic stainless steel, Cr3C2 and Ti powders were mixed to synthesize TiC-reinforced Fe-based composites by laser melting deposition. Fine TiC-particles were in situ synthesized through the reaction of Ti with Cr3C2 and were found to be uniformly dispersed in the matrix. The α-Fe phase was precipitated out of the γ-Fe matrix with the addition of Cr3C2 and Ti powders. The mechanism of TiC formation and phase evolution was analyzed based on thermodynamics calculations. The volume fraction and the size of the in situ synthesized TiC were found to affect grain texture of the γ-Fe matrix.

Структурно-фазовое состояние и твердость покрытий, полученных при наплавке порошков Cr3C2 и TiC на низкоуглеродистую сталь высокоэнергетическим электронным пучком

Структурно-фазовое состояние и твердость покрытий, полученных при наплавке порошков Cr3C2 и TiC на низкоуглеродистую сталь высокоэнергетическим электронным пучком

Study on the properties of WC-10Co alloys adding Cr3C2 powder via various vacuum sintering temperatures

The aim of the present research is to determine the optimal process of WC-10Co and WC(90 wt%)-Co(10-X wt%)-Cr3C2(X wt%)-cemented alloys, especially as related to their microstructural, magnetic and mechanical properties. In this work, different temperatures (1280 °C, 1320 °C, 1360 °C and 1400 °C) are explored in order to investigate the optimal parameters of the WC-10Co alloys. The influence on the WC-Co-cemented alloys of adding Cr3C2 powder is also evaluated. The experimental results show the optimal sintering temperature of the WC-10Co-cemented alloys as 1360 °C, with the WC-9.25Co-0.75Cr3C2-cemented alloys possessing the smallest grain size (480 nm) and a relatively higher hardness (93.23 HRA) after 1360 °C sintering for 1 h. It is also shown that the increase in the Cr3C2 content into the cemented alloys is effective in refining the WC grains and obtaining higher coercive force values.

Improvement of Wear Resistance of Stainless Steel AISI 304L by Diode Laser Surface Alloying with Chromium Carbide

Metal matrix composite layers were fabricated on AISI 304L substrate by diode laser surface alloying with direct injection of chromium carbide Cr3C2 powder into the molten-pool. The influence of laser alloying parameters on the quality of the alloyed layers were investigated. The alloyed layers were examined by optical metallography and scanning electron microscopy. Comparative erosion tests between the AISI 304L substrate and the alloyed layers have been performed following the ASTM G 76 standard test method. The uniform laser beam intensity profile of the laser used ensures to produce fully dense alloying layers with homogenous distribution of Cr3C2 particle throughout the matrix alloy. Distribution and dissolution of Cr3C2 particles are strongly dependent on the laser power level. The alloyed layers exhited noticeable increased erosion resistance in comparison to AISI 304L substrate for both 30° and 90° impact angles.

Powder metallurgy of high speed-steel produced by solid state sintering and heat treatment

Abstract High-speed steel is successfully fabricated by solid state sintering of Fe, Co, WC, Mo2C, Cr3C2 and VC powders under vacuum. The sintering density, microstructure, phase structure, hardness, and transverse rupture strength of the specimens are examined. Results show that the density increases with increasing sintering temperature. Nearly full density is obtained without microstructural coarsening in the sintering temperature range of 1190–1210°C. The optimum sintering temperature for the steel is 1200°C. The suitable quenching temperatures range from 1200 to 1240°C. After heat treatments, the microstructure consists of a martensitic matrix (grain size ≈5 μm) with a homogeneous distribution of MC and M 6C carbides (average size lower than 1 μm). The highest hardness of 68.5 ± 0.3 HRC and the maximum transverse rupture strength of 3.58 ± 0.12 GPa is obtained for the specimen tempered at 560°C.

High-temperature oxidation of HVOF thermally sprayed NiCr–Cr3C2 coatings: microstructure and kinetics

In this study, 25 wt% Ni(Cr)–75 wt% Cr3C2 powder was thermally sprayed onto 304 stainless steel substrate to produce coatings of ~400-µm thick and the oxidation behaviour of the coatings was investigated. The kinetic behaviour of oxidation of freestanding coatings was investigated over short times at 650, 700 and 800 °C using the thermogravimetric analysis technique. The oxidation rate for all samples was parabolic in nature and the parabolic rate constant (k) increased with increasing temperature. The activation energy (Q) for oxidation was found to be around 226 kJ mol−1. Furnace oxidation tests were also carried out on the as-sprayed samples at 700 and 800 °C in laboratory air for times ranging from 1 h up to 16 days (384 h). The oxide scale growth, morphology and phase formation were investigated using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. An oxide scale covered the surface of the cermet coating following oxidation at both 700 and 800 °C; the scale was significantly thicker at the higher temperature. It was found to be Cr2O3 and it covered both the metal matrix and the Cr3C2 particles present in the coating. The oxide grains had an angular shape after 16 days of exposure at both temperatures but the grain size was significantly larger after exposure at 800 °C.

Mechanical Behavior of the Cr<sub>3</sub>C<sub>2</sub> Compound at High Pressure and High Temperature

In the present study, we present a novel method to sinter Cr3C2 powders under high pressure without any addittives. The sintering Cr3C2 samples were charaterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), relative density measurements, Vicker’s hardness tests and Fracture toughness tests. The reasults show that Cr3C2 powders could be sintered to be bulk under the conditions of 3-5 GPa, 800-1200 °C and the heat preservation for 15 min. Moreover, the sintering body of Cr3C2 compound with the relative density of 99.84% by simultaneously tuning the pressure-temperature conditions exhibited excellent mechanical properties: a Vickers hardness of 20.3 GPa and a fracture toughness of ~8.9 MPam1/2. These properties were much higher than that by using the previous methods. The temperature condition obtained good mechanical properties in the experiment was about 1/3 lower than that using any other methods owing to the high pressure.

Microstructures and properties of in-situ TiC particles reinforced Ni-based composite coatings prepared by plasma spray welding

In this investigation, the in-situ TiC particles reinforced Ni-based composite coatings were produced by plasma spray welding with mixed powders (NiCrBSi+Ti+NiCr–Cr3C2). Their microstructures and properties were studied. The experimental results showed that the composite coatings consisted mainly of γ-Ni, Cr23C6, Cr7C3, Ni3Si, Cr5B3, CrB, FeNi3 and TiC phases. TiC particles were in-situ synthesized during plasma spray welding. The content of TiC particles and chromium carbides in the coatings increased with the mass fractions of Ti and NiCr–Cr3C2 powders increasing in the mixed powders, which resulted in enhancing the composite coatings hardness. The composite coating prepared with the mixed powder (70wt%NiCrBSi+30wt% (Ti+NiCr–Cr3C2)) showed a higher hardness 1142HV0.5. The wear resistance of the composite coatings were greatly improved due to the presence of in-situ TiC particles in comparison with the substrate. When the mixed powder (75wt%NiCrBSi+25wt% (Ti+NiCr–Cr3C2)) was used, the composite coating had better wear resistance, and the coating wear volume loss after wear tests was 6mm3, which was only 5% of that for the low carbon steel substrate (125mm3).

In-situ synthesis of chromium carbide (Cr3C2) nanopowders by chemical-reduction route

Chromium carbide nanopowder (Cr3C2) has been synthesized from chromium oxide (Cr2O3) by chemical-reduction route under autogenic pressure of hydrogen and CO gases at 87MPa. The reduction of Cr2O3 to Cr3C2 has taken place at a relatively low temperature (700°C) in the presence of Mg in an autoclave. The increased pressure of hydrogen and CO gases facilitates the reduction and carburization simultaneously which helps in reducing the reaction temperature. The nanopowder shows faceted morphology as observed in TEM. High resolution transmission electron micrographs reveal that the size of Cr3C2 powders varies in the range of 30–40nm and is coated by 12–13 layers of carbon with average thickness of 3.5–4nm. Thermal stability of the as-obtained product was investigated by TGA/DTA analysis. Based on the experimental results, possible reaction mechanism for the transformation and formation of nanopowder is discussed in the light of the obtained structure.

Effect of re-melting on the cladding coating of Fe-based composite powder

The aim of this paper is to investigate the influence of laser re-melting on the geometry and overlapping pores of cladding coating. In this study, Fe-based alloy mixed with 5wt.% Cr3C2 powder was used as cladding material to obtain high hardness and strength coating. However, this coating has overlapping pores and a rough surface. Therefore, re-melting process is explored systematically. The geometry, microhardness and microstructure of the coatings have been analyzed and compared subsequently. Besides, a 3D finite element model has been built to provide a thermal field analysis for laser re-melting. Finally, it is found that re-melting process is an effective method to improve the surface smoothness of cladding layer, which could reduce the process cycle and cost of secondary operations. More importantly, it could remove the overlapping pores easily.

Effect of the Cr content on the sintering behaviour of TiCN–WC–Ni–Cr3C2 powder mixtures

In TiCN–W–Cr–Ni cermets produced by liquid phase sintering melting occurs at lower temperatures as their Cr content increases. For low Cr additions (up to 4wt.%) eutectic temperatures are close to those found in the TiC–WC–Ni system. For 8wt.% Cr and above, temperatures are similar to those found in the Cr–Ni–C system. The precipitation of M7C3 carbides is observed to start at 8wt.% Cr in samples sintered at 1425°C for 1h. This sets a limit for the Cr solubility in the binder phase of these cermets around 18wt.%. The dissolution of WC and Cr3C2 particles starts at temperatures as low as 1150°C, but that the homogenization of the binder phase is only achieved after melting. The carbonitride phase exhibits the typical precipitation of inner and outer rims onto Ti(C,N) cores. However, a fine precipitation of Ni-rich particles is found inside Ti(C,N) cores, likely related to coalescence phenomena.

Microstructure and Mechanical Properties of HVOF Sprayed WC-Co/NiCrBSi, Cr3C2 Coatings on Al Alloys

Abstract In this study, WC-Co/NiCrBSi and Cr3C2 powders were coated on surface of Al alloys (AA7075-T651, AA5083, AA2024-T4) by using HVOF (High Velocity Oxy Fuel) process. The coated samples were characterized by means of a scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX, XRD), hardness and bonding strength. These results showed that the maximum hardness and minimum surface roughness have been obtained at specimens coated with WC-Co. The bonding strengths of specimens used AA2024-T4 substrates were maximum. XRD study revealed that WC, W2C, C, Co, Cr3Ni2SiC, W5Si3, Cr7C3, Cr3C2, Cr, and Ni phases are present in the coatings.

Microstructure and Dry Sliding Wear Behavior of Fe-Based (Cr, Fe)7C3 Composite Coating Fabricated by PTA Welding Process

Using Cr3C2 and Fe-CrNiBSi powder blends as raw materials, an α-Fe matrix composite coating reinforced by in situ (Cr, Fe)7C3 rods, with a thickness of about 3.6 mm, was fabricated on the surface of AISI A36 low carbon steel by means of plasma-transferred arc welding. The results of microstructural analysis show that in the coating, a large number of carbides, (Cr, Fe)7C3, in rod shape grow, and radiate around some half-dissolved Cr3C2 particles. The results of dry sliding wear tests at loads 100, 200, and 300 N show that the wear resistances of (Cr, Fe)7C3-reinforced coating, respectively, are about 6.9, 14.9, and 17 times higher than that of nonreinforced pure Fe-CrNiBSi alloy coating; the average value and fluctuation range of friction coefficient (FC) of (Cr, Fe)7C3-reinforced coating are less than those of pure Fe-CrNiBSi alloy coating; the main wear mechanisms of pure Fe-CrNiBSi alloy coating are ploughing, deformation, and adhesive wear, whereas those of (Cr, Fe)7C3-reinforced coating are microcutting, abrasive, and oxidation wear; the cracks on surfaces of (Cr, Fe)7C3 rods increased with the increasing loads; and the matrix α-Fe can prevent them from extending further in the composite coating.

Microstructure and Microhardness Characterization of Cr3 C2 -SiC Coatings Produced by the Plasma Transferred Arc Method

Abstract The purpose of this work was to investigate the coatings made of Cr3 C2 and SiC powder manufactured on AISI 304 stainless steel applied by the plasma transferred arc (PTA) welding process. SiC content in the produced coated layer was varied between 0–100 wt.% and the effect of SiC concentration on the microstructure and hardness of the coating was measured experimentally. SEM analyses revealed that the composite coatings had a homogeneous, nonporous, and crack-free microstructure. Dendrites and interdendrite eutectics formed on the coating layer, subject to the temperature gradient and the solidification ratio. There was a significant increase in the hardness of coating layers with the effect of the γ -(Fe,Ni), Cr7 C3, Cr23 C6, Fe5 C2, Cr3 Si, CrSi2, Fe>0.64 Ni0.36, CFe15.1, C-(Fe,Cr)-Si phases formed in the microstructure. In comparison to the substrate, the microhardness of the coatings produced by PTA were 2.5–3.5 times harder.