Cr 3C Research Articles

Studies on Formation Mechanism of In Situ Particles During Laser Direct Deposition of Fe-Based Composite Coatings with Valence Electron Structure Parameters

In this study, the formation regularity of C-Cr, C-Fe, and C-Fe-Cr in situ particles during the laser direct deposition of Fe-based composite coatings was theoretically investigated using the phase stability (PS) and phase formation ability (PFA) calculated based on the empirical electron theory of solids and molecules (EET). The calculation results showed that Cr7C3, Cr3C2, and Fe3C are more likely to appear during the laser direct deposition of Fe-based composite coatings because they have ideal PS and PFA values in comparison with Cr3C, Cr23C6, Fe7C3, Fe23C6, and Fe4C compounds. The addition of Cr is beneficial for the formation of (Fe, Cr)3C compounds when the Cr substitution ratio of Fe atoms is within 33.3 pct, whereas it is easier for the (Cr, Fe)7C3 and Cr7C3 compounds to appear in the alloy coatings when the Cr substitution ratio of Fe atoms is greater than 57.1 pct. These investigation results will provide theoretical guidance for the composition design and performance optimization of in situ particle-reinforced Fe-based composite coatings.

Corrosion behavior of porous chromium carbide in supercritical water

The corrosion behavior of highly porous chromium carbide (Cr 3C 2) prepared by a reactive sintering process was characterized at temperatures ranging from 375 °C to 625 °C in a supercritical water environment with a pressure of 25–30 MPa. The test results show that porous chromium carbide is stable in SCW environments at temperatures under 425 °C, above which disintegration occurred. The porous carbide was also tested under hydrothermal conditions of pressures between 12 MPa and 50 MPa at constant temperatures of 400 °C and 415 °C, respectively. The pressure showed little effect on the stability of chromium carbide in the tests at those temperatures. The mechanism of disintegration of chromium carbide in SCW environments is discussed.

Effect of temperature and load on three-body abrasion of cermets and steel

The effect of temperature and load on three-body abrasion resistance has been examined for stainless steel, Cr 3C 2–Ni cermet, plain WC–Co hardmetal and yttria stabilized zirconia doped WC-based composites. Series of tests at various tribo-conditions were performed on a recently developed device. Coefficient of friction and materials response to abrasive actions have been analyzed and positive effect of zirconia addition on materials wear resistance has been shown. The low wear rates of ZrO 2 containing cermets are due to lower susceptibility of zirconia to transgranular crack propagation, smaller mean free path between ceramic grains and formation of lubricating glazed silica-rich layer.

Development and microstructural characterization of microwave cladding on austenitic stainless steel

In the present work microwave cladding was explored as a new processing method for enhancement of surface properties of austenitic stainless steel (SS-316). Cladding of nickel based powder (EWAC) was developed using microwave radiation as the heating source. This paper explains the possible mechanism of clad formation using microwave hybrid heating with the help of a schematic model. The developed clads were characterized using field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD) and measurement of Vicker's microhardness. Typical X-ray diffraction (XRD) pattern of the clad showed the presence of chromium carbide, nickel silicide and nickel iron phases that eventually contribute to enhancement in microhardness of the clads. Clads of approximately 1 mm thickness were developed without any visible interfacial cracking and had significantly less porosity (1.09%). Microstructure of clad transverse section revealed good metallurgical bond with SS-316 substrate by partial mutual diffusion of constituent elements. The microstructure of the clad was found dominantly cellular in nature. Chromium was observed segregated around the cell boundaries while iron and nickel were identified inside the cells. Chromium carbides (Cr 23C 6, Cr 3C 2) were formed during the processing and appeared at the cell boundaries. Vicker's microhardness study revealed that the hardness profile varies within the clad zone and the average microhardness of the developed clad was observed to be 304 ± 48 H v.

Synthesis of chromium carbide (Cr 3C 2) nanopowders by the carbonization of the precursor

The solution-derived precursor method was used to synthesize chromium carbide (Cr 3C 2) nanopowders, ammonium dichromate ((NH 4) 2Cr 2O 7) and nanometer carbon black were used as raw materials. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the single phase Cr 3C 2 can be synthesized under the conditions of 21 wt.% C, 1100 °C and 30 min, and the average crystallite size is 27.2 nm. The powders show good dispersion and are mainly composed of spherical or near- spherical particles with a mean diameter of ~ 30 nm. The surface of the specimen mainly consists of Cr, C and O three species elements. The XPS spectrum of Cr2p consists of two peaks with the binding energies of 577.5 eV and 575.3 eV, which are assigned to the Cr2p 3/2 species of Cr 2O 3 and Cr 3C 2 − x (0 ≤ x ≤ 0.5), respectively. The XPS spectrum of O1s energy region for chromium carbide contains three peaks (Oa, Oh and Od), which are considered to be due to O −, OH − and Cr 2O 3, respectively.

Ion bombardment-induced nanocrystallization of magnetron-sputtered chromium carbide thin films

Nearly stoichiometric chromium carbide thin films (Cr 3C 2) were deposited by unbalanced r.f. magnetron sputtering of a chromium carbide target in a pure argon discharge. Their microstructure and hardness are shown to be strongly influenced by the working pressure and substrate bias during deposition. Further correlation with the plasma parameters, i.e. the energy and flux of argon ions as well as the flux of film-forming particles, is illustrated, which indicates the momentum transferred by bombarding ions per film-forming particle P dens which creates a densification and simultaneously does not cause a mobility enhancement to be dominant for the film structure. Below a threshold value of P dens of about 0.91 u 0.5eV 0.5, the resulting films exhibited an amorphous structure with a relatively low hardness of 1200 HV0.02. A nanocrystalline structure emerged only for larger values of P dens, and was responsible for a hardness enhancement to 3500 HV0.02.

The wettability and interface thermal resistance of copper/graphite system with an addition of chromium

In the present work, the wettability and interface thermal resistance (ITR) of copper/graphite (Cu/Gr) system with an addition of chromium (Cr) was studied. First, alloy element of Cr (1.0 wt.%) was introduced in copper to improve the wettability of Cu/Gr system. The wetting procedure of liquid Cu–Cr alloy on graphite substrate was studied by sessile drop method. It was found that the contact angle decreased to 43° with addition of Cr. Then, an experimental method was employed to determine the ITR of Cu/Gr system. Results reveal that the ITR decreased significantly with the introducing of Cr. It suggested that the reduction of ITR related to the formation of a continuous carbide layer at the interface zone which consisted of Cr 7C 3 and Cr 3C 2.

The electronic, mechanical properties and theoretical hardness of chromium carbides by first-principles calculations

In the present study, the ground state properties of chromium carbides (h-CrC, c-CrC, Cr 3C, Cr 3C 2, Cr 7C 3, and Cr 23C 6) are calculated by means of the first-principles pseudopotential method using the CASTEP code. The equilibrium crystal structures and thermodynamical stability of the six chromium carbide phases are discussed. Moreover, the chemical bonding in these carbides are interpreted by calculating the density of states, electron density distribution and Mulliken analysis; all the six chromium carbides have a combination of metallic, ionic and covalent bonding characteristic, while Cr 7C 3 exhibits the strongest metallic character. The elastic constants, elastic anisotropies and theoretical hardness of the carbides are also presented, which are important parameters for the structural materials and surface coatings.

Effect of Cr on the wetting in Cu/graphite system

The isotherm wetting and spreading behaviors of the molten Cu–Cr alloys with 0.5, 1.0 and 2.0 at.% Cr on porous graphite substrates were investigated at 1373 K in a flowing Ar atmosphere using a modified sessile drop method. The wettability improves with increasing Cr content in the alloy as a result of phase transition from Cr 3C 2 to more wettable and metallic-like Cr 7C 3 developed at the interface. The spreading kinetics are controlled by the interfacial reaction in the early stage and the diffusion of Cr from the drop bulk to the triple junction in the later stage together with a transition in the intermediate stage.

Effect of partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)–Ni-based cermets

Four cermets of composition TiC–10TiN–16Mo–6.5WC–0.8C–0.6Cr 3C 2–(32 − x)Ni– xCr ( x = 0, 3.2, 6.4 and 9.6 wt%) were prepared, to investigate the effect of the partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)–Ni-based cermets. The partial substitution of Cr for Ni decreased full densification temperature, and the higher the content of Cr additive was, the lower full densification temperature was. The partial substitution of Cr for Ni had no significant effect of the formation of Mo 2C and Ti(C,N) and the dissolution of WC, and however, it had a significant effect on the dissolution of Mo 2C. Cr in Ni-based binder phase diffused into undissolved Mo 2C to form (Mo,Cr) 2C above 1000 °C at 6.4–9.6 wt% Cr additive, and a small amount of (Mo,Cr) 2C did not dissolve after sintering at 1410 °C for 1 h at 9.6 wt% Cr additive. In the final microstructure, Cr content in Ni-based binder phase increased with increasing the content of Cr additive, and however, regardless of the content of Cr additive, coarse Ti(C,N) grains generally consisted of black core, white inner rim and grey outer rim, and fine Ti(C,N) grains generally consisted of white core and grey rim. The partial substitution of Cr for Ni increased hardness and decreased transverse rupture strength (TRS). Ni-based binder phase became hard with increasing the content of Cr additive, therefore resulting in the increase of hardness and the decrease of TRS. TRS was fairly low at 9.6 wt% Cr additive, which was mainly attributed hardening of Ni-based binder phase and undissolved (Mo,Cr) 2C.

TEM and ToF-SIMS studies on the corrosion behavior of vanadium and chromium containing WC–Co hard metals in alkaline solutions

The corrosion behavior of hard metals with VC and Cr 3C 2 grain growth inhibitors was investigated in alkaline solutions by electrochemical methods. The two inhibitors have opposite effects on the corrosion behavior: Cr 3C 2 significantly improves the corrosion behavior, whereas VC-containing alloys show a poor resistance. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and analytical transmission electron microscopy (TEM) analyses of the distributions of Cr and V in the composite material, as well as in the surface layers formed during corrosion were employed to clarify the influence of these elements on the corrosion behavior. The measurements showed that VC is precipitated mostly along the WC/binder interface after the liquid-phase sintering process, while Cr 3C 2 is almost homogeneously dissolved in the binder. As VC is chemically instable in alkaline solutions, it completely dissolves out of the binder. In accordance with this observation no V was found in the corrosion product layer on the surface. As WC is more noble than Co, galvanic coupling between the two phases reinforces the Co dissolution, while the WC-phase is protected cathodically. Contrary to VC, chromium is stable in alkaline environments and forms a passivating Cr 2O 3 layer. Enrichment of Cr in the corrosion product layers was detected by TEM and ToF-SIMS. Due to surface passivation by Cr 2O 3, galvanic coupling effects between Co and WC play a much less important role in the corrosion process of the composite material.

Fabrication and mechanical properties of ultrafine grained WC–10Co–0.45Cr 3C 2–0.25VC alloys

The ultrafine grained WC–10Co–0.45Cr 3C 2–0.25VC alloys were fabricated through planetary ball milling and low pressure sintering. The effects of the cobalt particle size, milling speed and sintering temperature on the microstructure, hardness and fracture toughness of the ultrafine grained alloys were investigated using optical microscopy, scanning electron microscopy and mechanical testing. The results showed that the mechanical properties of the low pressure-sintered alloys substantially depend on the milling speed and sintering temperature. At the same time, the hardness and fracture toughness of the samples can be increased from 1703 MPa and 8.90 MN m −3/2 to 1789 MPa and 11.21 MN m −3/2, respectively, when the cobalt particle size is reduced from 17 μm to 1.4 μm.

Mesoporous carbide-derived carbons prepared from different chromium carbides

Mesoporous carbide-derived carbons were synthesised from different chromium carbides (Cr 3C 2, Cr 7C 3, Cr 23C 6) powder via gas phase chlorination within the temperature range from 800 to 1100 °C. Analysis of XRD results show that chromium carbide-derived carbons (C(Cr x C y )) consist mainly on graphitic crystallites and the apparent crystallite size along the a- and c-directions of graphite structure L a ≈ 9 nm and L c ≈ 6 nm were calculated, respectively. The first-order Raman spectra showed the graphite-like absorption peak at ∼1586 cm −1 and the disorder-induced peak at ∼1355 cm −1. The low-temperature N 2 sorption experiments were performed and a specific surface area up to 285 m 2 g −1 and total pore volume up to 0.796 cm 3 g −1 were obtained for C(Cr 7C 3) synthesised at T = 1100 °C. For materials prepared at T > 800 °C the sorption measurements determined only the presence of mesopores at/inside of the porous carbon powders. Differently from other carbide-derived carbon powders studied previously the bimodal pore size distribution function has been established with the first maxima in the region from 2.5 to 3.5 nm and the second maximum from 6 to 8 nm, respectively. Taking into account the high mesoporosity values in the mesoporous region these C(Cr x C y ) materials can be attractive for the development of the high power density non-aqueous tetraalkylammonium cation salt based supercapacitors.

Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr 3C 2 addition and consolidation by SPS and HIP technologies

The aim of present work is to study the effect of VC and/or Cr 3C 2 in densification, microstructural development and mechanical behavior of nanocrystalline WC-12wt.%Co powders when they are sintered by spark plasma sintering (SPS) and hot isostatic pressing (HIP). The results were compared to those corresponding to conventional sintering in vacuum. The density, microstructure, X-ray diffraction, hardness and fracture toughness of the sintered materials were evaluated. Materials prepared by SPS exhibits full densification at lower temperature (1100 °C) and a shorter stay time (5 min), allowing the grain growth control. However, the effect of the inhibitors during SPS process is considerably lower than in conventional sintering. Materials prepared by HIP at 1100 °C and 30 min present full densification and a better control of microstructure in the presence of VC. The added amount of VC allows obtaining homogeneous microstructures with an average grain size of 120 nm. The hardness and fracture toughness values obtained were about 2100 HV 30 and close to 10 MPa m 1/2, respectively.

Experiment and modeling of mechanical properties on iron matrix composites reinforced by different types of ceramic particles

The strength, Young's modulus and hardness properties of iron matrix composites reinforced by different types of ceramic particles (SiC, Cr 3C 2, TiC and Ti(C, N)) prepared by the dynamic temperature control direct current heating technology were investigated experimentally. The stress–strain curves of the different composites and stress in reinforcing particles were simulated by Eshelby approach modeling in order to interpret the experiments and to reveal the strengthening mechanisms. It was found that SiC reinforcing particles show the strongest effect on improving the strength of the composite among the four types of reinforcements experimentally. The theoretical analysis exposes the reason as its higher fracture toughness and hardness as well as a limited decomposition to increase matrix strength. The strength of the four composites all presents a maximum value at 10% volume fraction and the reason can be interpreted by that glomeration of particulate reinforcements happens remarkably only when the fraction is over 10%. The stress–strain curves by the modeling agree well with those of the experiments on TiC/Fe and Ti(C, N)/Fe composites but not on SiC/Fe and Cr 3C 2/Fe composites. This suggests that the strengthening mechanisms of the composites rely not only on load sharing of the reinforcements but also on increasing matrix strength.

Influence of alloy chemistry on microstructure and properties in NiCrBSi overlay coatings deposited by plasma transferred arc welding (PTAW)

The microstructures and performance of two NiCrBSi alloy overlays deposited by plasma transferred arc welding are studied. The coatings consist of a γ-Ni primary dendritic phase with harder Ni + Ni 3B or Ni + Ni 3Si eutectics and Cr-based particles (CrB, Cr 3C 2, and Cr 7C 3) situated at the interdendritic regions. It was found that the volume fraction of the soft primary dendritic phase drastically decreased and the proportion of chromium borides and carbides increased with an increase of C, B, Si, and Cr content. Microhardness testing revealed that the primary Ni dendrite, interdendritic, and Cr-particle phases had average hardness values of 405, 860, and 1200 HV respectively. An increase in the volume fraction of hard eutectics and Cr-particles lead to a substantial increase in hardness and wear resistance.

Early high temperature oxidation behaviour of Ti(C,N)-based cermets in air

Isothermal oxidation behaviour of two Ti(C,N)-based cermets (TiC–10TiN–16Mo–6.5WC–0.8C–0.6Cr 3C 2–(32–x)Ni–xCr, x = 0 and 6.4 wt%) was investigated in air at 800–1100 °C up to 2 h. Mass gains exhibited neither linear nor parabolic law during isothermal oxidation. The oxide scales formed at 800–1100 °C were multi-layered, consisting of NiO outerlayer, NiTiO 3 interlayer and TiO 2-based innerlayer. The internal oxidation zones formed at 1000–1100 °C consisted of Ti-based, Ni-based and Mo-based complex oxides. Cermet with 6.4 wt% Cr exhibited superior oxidation resistance, due to the presences of Cr 0.17Mo 0.83O 2 in TiO 2-based innerlayer of the oxide scale and Cr-rich Ti-based complex oxide in the internal oxidation zone.

Theoretical study on the stability, elasticity, hardness and electronic structures of W–C binary compounds

The ground state properties of W–C binary compounds (h-WC, c-WC, α-W 2C, β-W 2C, γ-W 2C, ɛ-W 2C) are studied in this paper by using first-principles calculations. Formation enthalpy and cohesive energy for each phase are calculated. The calculated elastic constants satisfy the Born–Huang's stability criterion, indicating all studied compounds are mechanically stable. All W–C compounds studied in this paper exhibit larger bulk modulus values than many other binary types of carbide such as Fe 3C, Cr 7C 3, Cr 3C, and TiC. Using a theoretical method based on the works of Šimůnek, the hardness of the crystal is estimated. The electronic structures of these compounds are calculated and discussed. Stoner's polarization theory for itinerant magnetism is applied to explain the observed paramagnetic behavior of the compounds. Moreover, the heat capacity is also calculated for each compound based on the knowledge of the elasticity and Debye temperature.

Polarity of prismatic facets delimiting WC grains in WC–Co alloys

This study reports a determination of the polarity of WC facets in WC–Co alloys sintered at the liquid state. In these alloys, WC grains are delimited by basal facets and two sets of { 1 0 1 ¯ 0 } prismatic facets, one set of facets being much more developed than the other. A variation of the shape is observed as a function of the composition of the alloy. High resolution transmission electron microscopy is used to investigate the polarity of the prismatic facets owing to the typical triangular patterns appearing on the images. The effect of the composition is investigated using two alloys with different carbon potentials and one containing VC and Cr 3C 2 as grain growth inhibitors. The interpretation of the images shows that in all cases, the same set of prismatic planes is favoured.

Cermets surface transformation under erosive and abrasive wear

The subsurface developed in ceramic–metal composites WC–Co, TiC–NiMo and Cr 3C 2–Ni during tribological testing (abrasion, sliding, erosion) under different conditions (impact angle, velocity, pressure, temperature) is the primary concern of the study. Mechanisms responsible for mechanically mixed layer (MML) development and wear resistance of materials are discussed in details. Instrumented indentation combined with consecutive polishing-testing procedure was used for mechanical characterisation. Microstructural features of the worn surface and subsurface region were studied with the help of optical microscope and scanning electron microscope equipped with energy dispersive spectroscopy analyser to evaluate difference between properties of the bulk and modified subsurface layers of materials. Formation of subsurface layer is found to be an essential feature of materials response to applied loading. Modified layer consists of highly deformed binder metal; cracked and decohesed large grains of carbides; embedded and/or fused debris of erosive/abrasive particles; and products of oxidation.