Cr 3C Research Articles

Influence of CO 2 laser heat treatment on surface properties, electrochemical and tribological performance of HVOF sprayed WC–24%Cr 3C 2–6%Ni coating

In this investigation, the tribological and electrochemical performances of HVOF sprayed WC–24%Cr 3C 2–6%Ni coatings before and after laser heat (LH) treatment were investigated. In the wear test, the friction and wear resistance of the coatings were improved significantly with an optimized LH process. The improvement can be attributed to the improved roughness and hardness, as well as the formation of oxide tribofilms. With LH treatment, the local corrosion of the coating had a decrease and the pit corrosion resistance of the WC–24%Cr 3C 2–6%Ni coating was improved as a result of the decreasing the size and number of the porosities, especially compact interface achieved by LH treatment.

Chromium carbide thin films deposited by ultra-short pulse laser deposition

Pulsed laser deposition performed by a laser with a pulse duration of 250 fs has been used to deposit films from a Cr 3C 2 target. Due to the different processes involved in the laser ablation when it is performed by an ultra-short pulse source instead of a conventional short pulse one, it has been possible to obtain in vacuum films containing only one type of carbide, Cr 3C 2, as shown by X-ray photoelectron spectroscopy. On the other hand, Cr 3C 2 is not the only component of the films, since a large amount of amorphous carbon is also present. The films, deposited at room temperature, are amorphous and seem to be formed by the coalescence of a large number of particles with nanometric size. The film composition can be explained in terms of thermal evaporation from particles ejected from the target.

Investigation on microstructure, surface properties and anti-wear performance of HVOF sprayed WC–CrC–Ni coatings modified by laser heat treatment

Laser heat (LH) treatment was found to be an effective method to alter the microstructure and mechanical properties of conventional coatings. In this investigation, the effects of laser scanning velocity on microstructure, microhardness and wear performance of high velocity oxygen fuel sprayed (HVOF) WC–CrC–Ni coatings during laser heating treatment were investigated. The results showed that the microstructure of the HVOF coatings changed greatly after the LH treatment. X-ray diffraction (XRD) patterns indicated that WC and Cr 3C 2, as primary phases, were present in both the HVOF- and LH-treated coatings, while only a small amount of Ni phase existed in the LH-treated coatings. With the post-treatment process of laser heating, a compact interface was found between the coating and substrate. When the laser scanning velocity decreased, the porosity and thickness of the LH-treated coatings decreased, leading to a gradual increase of microhardness. In the wear test, the friction and wear resistance of the coating were improved significantly with an optimal laser heating process (600 W power, 300 mm/min scanning velocity). The improvement can be attributed to the improved porosity and hardness, as well as the formation of oxide tribofilms.

The direct laser deposition of AISI316 stainless steel and Cr 3C 2 powder

The laser deposition of AISI316 powder blended with Cr 3C 2 over austenitic stainless steel plate was carried out as part of an investigation aimed at determining the feasibility of applying localized reinforcement to stainless steel components. The chromium carbide powder dissolved in the process to produce a range of carbides which reinforced and increased the hardness of the material. The results of optical microscope metallography and SEM/EDX and XRD analysis as well as microhardness measurements are reported. Surfaces produced by deposition of the powder blend were machine-ground and subjected to pin-on-disc and corrosion tests. The tests indicated an improvement to sliding wear resistance and a good resistance to salt spray and pitting corrosion conditions.

Direct laser cladding of SiC dispersed AISI 316L stainless steel

The present study concerns development of SiC dispersed (5 and 20 wt%) AISI 316L stainless steel metal–matrix composites by direct laser cladding with a high power diode laser and evaluation of its mechanical properties (microhardness and wear resistance). A defect free and homogeneous composite layer is formed under optimum processing condition. The microstructure consists of partially dissociated SiC, Cr 3C 2 and Fe 2Si in grain refined stainless steel matrix. The microhardness of the clad layer increases to a maximum of 340 VHN (for 5% SiC dispersed) and 800 VHN (for 20% SiC dispersed) as compared to 150 VHN of commercially available AISI 316L stainless steel. Direct laser clad SiC dispersed AISI 316L stainless steel has shown an improved wear resistance against diamond surface with a maximum improvement in 20% SiC dispersed AISI 316L stainless steel. The mechanism of wear was predominantly abrasive in nature.

Interfacial microstructure and performance of brazed diamond grits with Ni–Cr–P alloy

The reaction mechanism of the interface among diamond, commercial Ni–Cr–P alloy and steel substrate has been studied by optical microscopy, scanning electron microscope, X-ray diffraction and Raman spectroscopy. The reaction layers formed among diamond, brazing alloy and steel substrate produced good wettability of diamond grits for achieving better quality tools. The reaction layer between diamond and brazing alloy comprised a reaction layer of brazing alloy and a reaction layer of diamond. Cr 7C 3 and Cr 3C 2 formed in the reaction layer of brazing alloy was the main reason for improving the bonding strength of Ni–Cr alloy to the diamond grits. A reaction layer of diamond may be a graphitization layer formed on the surface of diamond under high temperature brazing. The reaction layer of brazing alloy and steel substrate was the co-diffusion of Ni, Cr and Fe between the brazing alloy and the steel substrate. The life and sharpness of brazed diamond boring drill bits fabricated in this study were superior to the electroplated one in the market owing to its high protrusion and bonding strength.

On the hardness and the inherent ductility of chromium carbide nanostructured coatings prepared by RF sputtering

Homogenous and nanostructured chromium carbide thin coatings are prepared by RF sputtering. The nanoindentation tests are used to investigate the evolution of plastic deformation and hardness as a function of the grain size. The Cr 3C 2 films have been deposited on magnesium oxide substrates from a Cr 3C 2 target in pure argon atmosphere. Based on the effect of the deposition temperature, we have generated nanostructured Cr 3C 2 coatings with different mechanical properties. We have found that both crystalline texture and grain size increased with increasing the deposition temperature. The nanostructured chromiumcarbide film with grain size in the order of 5 nm, prepared at a deposition temperature of 600 °C, showed a higher hardness as well as a good ductility compared to the samples prepared at 850 °C or at room temperature. The cyclic nanoindentation measurements at constant loading rate allowed qualitative characterization of the change in the irreversible plastic work for the samples considered in this report.

Evaluation of cyclic hot corrosion behaviour of detonation gun sprayed Cr 3C 2–25%NiCr coatings on nickel- and iron-based superalloys

In the present investigation, Cr 3C 2–NiCr cermet coatings were deposited on two Ni-based superalloys, namely superni 75, superni 718 and one Fe-based superalloy superfer 800H by detonation-gun thermal spray process. The cyclic hot-corrosion studies were conducted on uncoated as well as D-gun coated superalloys in the presence of mixture of 75 wt.% Na 2SO 4 + 25 wt.% K 2SO 4 film at 900 °C for 100 cycles. Thermogravimetric technique was used to establish the kinetics of hot corrosion of uncoated and coated superalloys. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyze the corrosion products for rendering an insight into the corrosion mechanisms. It was observed that Cr 3C 2–NiCr-coated superalloys showed better hot-corrosion resistance than the uncoated superalloys in the presence of 75 wt.% Na 2SO 4 + 25 wt.% K 2SO 4 film as a result of the formation of continuous and protective oxides of chromium, nickel and their spinel, as evident from the XRD analysis.

Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr) 2C-7%Ni, Cr 3C 2-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10 −6 mm 3/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.

High temperature oxidation studies of detonation-gun-sprayed Cr 3C 2–NiCr coating on Fe- and Ni-based superalloys in air under cyclic condition at 900 °C

The cyclic oxidation behavior of detonation-gun-sprayed Cr 3C 2–NiCr coating on three different superalloys namely Superni 75, Superni 718 and Superfer 800H at 900 °C for 100 cycles in air under cyclic heating and cooling conditions has been investigated in the present work. The kinetics of oxidation of coated and bare superalloys was analysed, using thermogravimetric technique. It was observed that all the coated and bare superalloys obey a parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of coated and bare superalloys. The results on the Cr 3C 2–NiCr-coated superalloys showed better oxidation resistance due to the formation of a compact and adhesive thin Cr 2O 3 scale on the surface of the coating during oxidation. The scale remained intact and adherent to the partially oxidised coating during cyclic oxidation due to its good compatibility and similar thermal expansion coefficient between Cr 3C 2–NiCr coating and the superalloy substrates. In all the coated superalloys, the chromium, iron, silicon and titanium were oxidised in the inter-splat region, whereas splats which consisted mainly of Ni remained unoxidised. The parabolic rate constants of Cr 3C 2–NiCr-coated alloys were lower than that of the bare superalloys as observed in the present work.

Consolidation and properties of ultrafine binderless cemented carbide by spark plasma sintering

Owing to the absence of metal binder, binderless cemented carbides have higher wear, corrosion, and oxidation resistance. WC-0.3VC- 0.5Cr 3C 2 powders with an average particle size of 200 nm and a little amount of active element were consolidated by spark plasma sintering. The sintered microstructure revealed that the average WC grain size was 0.24 μm, which was almost consistent with the initial fine powder. The results of XRD showed that W 2C phase was formed. Nearly complete densification of ultrafine binderless cemented carbide was achieved by sintering at 1400°C for 120 s under 50 MPa. The resulting hardness and the fracture toughness were 28.18 GPa and 6.05 MPa·m ½, respectively.

Scuffing resistance of plasma and HVOF sprayed WC12Co and Cr 3C 2-25(Ni20Cr) coatings

The objective of this study is to characterize the tribological properties of plasma and HVOF sprayed WC12 Co and Cr 3C 2 25(Ni20Cr) coatings. The coefficient of friction and scuffing resistance of coatings were found using the tests of ball-on-disc and Falex routines. The chemical composition of coatings was characterized using energy dispersive spectrometry (EDS) performed on the cross-sections of the coatings. The surface of deposits after measuring of friction coefficient was observed using scanning electron microscope (SEM). It was found out that the following properties of the coatings influence the scuffing process: (i) hardness; (ii) friction coefficient; (iii) method of spraying; and (iv) coatings' morphology. The WC12Co coating sprayed using HVOF method showed the best scuffing resistance and the most homogeneous structure.

Field electron emission experiments with plasma sprayed layers

The paper summarizes the investigation of field electron emission properties of plasma sprayed layers. The tested layers were Cr 2O 3 + SiO 2, Al 2O 3 + TiO 2, TiO 2, Cr 3C 2 + NiCr and Cr 3C 2 + NiCrAlY. The deposition methods were APS and SPS. The Cr 2O 3 + SiO 2, Al 2O 3 + TiO 2 and TiO 2 layers were laser engraved after deposition. Structure investigations of the deposited layers revealed them as composite. The obtained results show, that field electron emission from plasma sprayed layers is comparable with emission from DLC and other carbon-based layers. The best turn-on field was 12 V/μm and has been obtained for laser engraved Al 2O 3 + 13 wt.% TiO 2 layers. Investigation of temperature dependence of emission showed a remarkable influence of hot (Schottky) emission. The emission of Al 2O 3 + TiO 2 layers decreased in elevated temperatures. This has been attributed to the temperature dependence of TiO 2 permittivity, which increases with temperature. Computer calculations supported this explanation. The emission parameters suggested very high local electric fields. This probably was the result of field enhancement due to presence of dielectric–conductor–vacuum junction points in addition to that caused by the surface topography.

Effect of nitrogen content on the properties of CrN xO yC z coating prepared by DC reactive magnetron sputtering

The CrN x O y C z coatings were deposited by planar DC reactive magnetron sputtering onto AZ31 Mg alloy and high speed tool steel (HSTS) substrates at a substrate temperature of 200 °C. The effect of N 2 content on composition and structure of the CrN x O y C z coatings was investigated. The structure of the CrN x O y C z coatings was analyzed by a glancing angle X-ray diffraction (GXRD). The cross-section morphology and thickness of the CrN x O y C z coatings were checked by a field emission scanning electron microscope (FESEM), and the composition profile and chemical state were carried out by an X-ray photoelectron spectroscopy (XPS). The experimental results showed that the structure and phase composition of the CrN x O y C z coatings depended on N 2 content. The evolution of the structure of CrN x O y C z coatings was consistent with CrN x -based coatings, and the CrN x O y C z coatings contained Cr 2O 3, CrO 2, CrO, Cr 3C 2, CrN x (Cr, CrN, Cr 2N), as well as different chromium oxynitride. However, the carbide and oxynitride were oxidized after annealing.

Tribological behavior of Cu–Cr–SiC p in situ composite

In situ composites based on copper chromium alloys have important application in resistance welding electrodes and improvement of their mechanical and wear properties may offer better materials for similar applications. In the present investigation, mechanical and tribological properties of Cu–Cr–SiC p composites have been investigated and compared with as-received wrought copper and cast copper. The cast in situ Cu–4%Cr–4%SiC composite has a matrix of solid solution of chromium in copper, containing grayish phases of carbides such as Cr–C, Cr 23C 6, Cr 3C 7, and Cr–Si–C, as determined by X-ray diffraction analysis and optical microscopy. The cumulative volume loss of the cast composite as determined by pin-on-disk tests for dry sliding wear against hardened steel counterface is observed to decrease to about 65% and 72%, respectively, as compared to those observed in as-received copper and cast copper at 40 N loads. The surface profile of the samples after wear test, show a significantly lower R t and R z in all the three materials at 20 N load. Bearing ratio curve shows that Mr1, the extent of surface which will wear out faster, has a higher value for the composites compared to that in as-received copper although the composites wear out much less because of reinforcement. Mr2, oil retaining property from the bearing ratio curves, has a fairly steady value of about 10% in cast composite after dry sliding under increasing load.

Analytical modeling to calculate the hardness of ultra-fine WC–Co cemented carbides

An analytical model to calculate the hardness of ultra-fine WC–10Co cemented carbides was investigated. The nanocrystalline WC–10Co powders were manufactured using a spray conversion process and sintered at 1375 °C in a vacuum. Varying amounts of TaC, Cr 3C 2, and VC were added to nanocrystalline WC–10Co cemented carbides as grain growth inhibitors. The hardness of WC–10Co cemented carbides increased with a decreasing WC grain size from 5 μm to 300 nm. An analytical model to calculate the hardness of WC–10Co cemented carbides was proposed under the assumption that the applied load is transferred from the WC to the Co binder phase. The analytically calculated hardness showed good agreement with the experimentally measured hardness of WC–10Co cemented carbides. In the proposed analytical model, the hardness of WC–10Co cemented carbides is similar to that predicted by the Hall–Petch relationship when the WC grain size is large. However, when the grain size is finer than a critical value, the predicted hardness of the WC–10Co cemented carbide becomes saturated.

Properties and microstructure of VC/Cr 3C 2-doped WC/Co cemented carbides

This paper deals with the effects of codoped VC/Cr 3C 2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr 3C 2 in optimal proportion enhances both the hardness and transverse rupture strength (TRS) of the alloys, with more homogeneous microstructure. When the alloy is sintered at 1430†C and with 0.5% Cr 3C 2/0.2% VC, the TRS reaches 3786 MPa, the hardness is 91.7 HRA and the grain size smaller than 0.6 μm. The numerical analyses on grain growth during the sintering process show that both VC precipitating on the WC grain boundary and Cr 3C 2 dissolving in the Co phase decrease the solid/liquid interfacial energy γ, the process of dissolution and reprecipitation is greatly retarded and the coarsening of WC grains is inhibited.

Microchemical and microstructural studies in a PTA weld overlay of Ni–Cr–Si–B alloy on AISI 304L stainless steel

Ni–Cr–Si–B alloy coatings deposited on AISI 304L stainless steel substrate using plasma transferred arc welding process were studied with respect to the microchemical and microstructural modifications that take place during the process. The coating was characterized for (1) interface integrity and dilution (2) type, morphology and distribution of secondary phases in the coating (3) elemental redistribution between substrate and coating and (4) different phases that form during the deposition process. Formation of a transition zone of only 760 μm width was understood in terms of interdiffusion of Fe and Ni across the interface. Preferential redistribution of carbon to the surface of the coating was observed. It was explained on the basis of difference in thermodynamic activity. Apart from γ-Ni solid solution, the other primary phases identified in Ni–Cr–Si–B alloy were Cr 2B, Cr 7C 3 and Cr 3C 2. The observed changes in microstructure, microchemistry and hardness have been understood based on the phase transitions of the Ni rich alloy during solidification and cooling on the substrate.

Cr 3C 2–NiCr and WC–Ni thermal spray coatings as alternatives to hard chromium for erosion–corrosion resistance

Cr 3C 2–NiCr and WC–Ni coatings are widely used for wear applications at high and room temperature, respectively. Due to the high corrosion resistance of NiCr binder, Cr 3C 2–NiCr coatings are also used in corrosive environments. The application of WC–Ni coatings in corrosive media is not recommended due to the poor corrosion resistance of the (pure Ni) metallic matrix. It is well known that the addition of Cr to the metallic binder improves the corrosion properties. Erosion–corrosion performance of thermal spray coatings is widely influenced by ceramic phase composition, the size of ceramic particles and also the composition of the metallic binder. In the present work, two types of HVOF thermal spray coatings (Cr 3C 2–NiCr and WC–Ni) obtained with different spray conditions were studied and compared with conventional micro-cracked hard chromium coatings. Both as-sprayed and polished samples were tested under two erosion–corrosion conditions with different erosivity. Tungsten carbide coatings showed better performance under the most erosive condition, while chromium carbide coatings were superior under less erosive conditions. Some of the tungsten carbide coatings and hard chromium showed similar erosion–corrosion behaviour under more and less erosive conditions. The erosion–corrosion and electrochemical results showed that surface polishing improved the erosion–corrosion properties of the thermally sprayed coatings. The corrosion behaviour of the different coatings has been compared using Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Total material loss due to erosion–corrosion was determined by weight loss measurements. An estimation of the corrosion contribution to the total weight loss was also given.

Nanomechanical and nanowear properties of Cr 3C 2 thin films deposited by rf sputtering

In this investigation, nanoindentation, nanoscratch and nanowear tests were done in order to study the nanomechanical and nanotribological properties of the chromium carbide nanostructured thin films. Chromium carbide films were synthesized by rf sputtering from a Cr 3C 2 target on magnesium oxide substrate. The samples were characterized by X-ray diffraction and grazing X-ray reflectivity. All the films have a thickness of 300 nm. A pyramidal Berkovich indenter diamond tip was used for nanomechanical testing. The residual wear depth of the samples was examined using an atomic force microscope (AFM). In this study, an experimental method adapted to the nanowear properties was explored. We have studied the influence of the substrate temperature on the structural, mechanical and tribological properties of chromium carbide films. We have shown that Cr 3C 2 films deposited at a substrate temperature up to 600 °C exhibit a better wear resistance and a hardness value higher than what is measured in the case of the films deposited at room temperature.