Metal Carbide Particles Research Articles

Failure analysis of convection section tube in an ethylene cracking furnace due to metal dusting

To study the failure in the convection section tubes of an ethylene cracking furnace, macroscopic inspections, chemical composition analysis, metallographic microscopy, hardness testing, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis are performed. The experiments confirmed the reason for metal dusting occurrence of 304H austenitic stainless steel that the inner wall Cr2O3 protective film was destroyed by overheating. There were dense circular corrosion pits on the fire side inside the furnace tubes, loose metal oxides and carbide particles were filled in the corrosive pits. Severe carburization occurred on the surface of the pits, the furnace tube experienced metal dusting. The metal dusting resulted in the decomposition of the surface layer of the metal alloy into metal particles and graphite to thin the wall thickness. Then the furnace tube cracked because of the stress concentration appeared in the furnace tube with reduced wall thickness. Finally, some suggestions and countermeasures on the failure of metal dusting of the furnace tube were proposed.

Preparation and Characterization of Carbide Particle-Toughened Si-B System of High Thermostability Polycrystalline Diamond by HPHT Sintering.

In this research, we report the synthesis of Si-TmC-B/PCD composites using Si, B, and transition metal carbide particles (TmC) as binders at high pressure and high temperature (HPHT method, 5.5 GPa and 1450 °C). The microstructure, elemental distribution, phase composition, thermal stability, and mechanical properties of PCD composites were systematically investigated. The Si-B/PCD sample is thermally stable in air at 919 °C. The initial oxidation temperature of the PCD sample with ZrC particles is as high as 976 °C, and it also has a maximum flexural strength of 762.2 MPa, and the highest fracture toughness of 8.0 MPa·m1/2.

Effect of heat-treatment on corrosion performance of Ni and Ni-Cr-based alloys

Metal dusting is described as a severe form of corrosion attack in which iron, steels, nickel- and cobalt-based alloys disintegrate into metal or metal carbide particles in a coke deposit when exposed to strongly carburising gases (carbon activity ac>1) at elevated temperatures (300-800°C). Despite intense research efforts, which led to much progress in mitigating metal dusting, particularly in the oil and gas industry, the complete prevention still remains an issue. Current study focuses on measuring corrosion resistance of heat-treated austenitic Ni, Ni-Cr-based complex alloy compositions containing iron and copper as additional alloying elements.

IMPACT OF VARIATION IN SIZES OF BORON CARBIDE ON PROPERTIES OF NOVEL COMPOSITE OF ALUMINIUM ALLOY 6063-T6 AND BORON CARBIDE

Composites are continuously evolving as the most demanding materials among various industries because of their reinforced mechanical properties and lesser weight. The present work aimed to fabricate a novel aluminium matrix composite using Aluminium Alloy 6063 T6 as base metal and ceramic boron carbide particles with three different micro sizes viz.104μm, 74μm, and 53μm as reinforcement. For composite fabrication, stir casting technique has been utilized. Micro-structure and mechanical behavior of base alloy and prepared composites has been analyzed in this work. Observing through optical microscopy reveal a uniform and proper distribution of B4C particle in Al matrix, along with cluster formation at few sites. The results also exhibit that hardness of reinforced composite has been found to be more than that of base alloy by 81.35 %, in which composite with particle size 53μm has shown maximum hardness of 75.77HV. The trend in tensile strength indicates that the ultimate tensile strength of composite with boron carbide of mesh size 53μm is more than the base alloy by 20.79% and is also highest among the rest of composites with a value of 219.196MPa.

Microstructural and compositional effects of transition metal carbide additions on dispersion-strengthened tungsten fabricated via spark plasma sintering

Tungsten is the plasma-facing material of choice for the divertor region in ITER as it has favorable properties under ion irradiation. However, tungsten is a very brittle material whose fabrication is complicated by its high melting point and low recrystallization temperature. Spark plasma sintering is a powder consolidation technique that can rapidly compact tungsten powder to high relative densities while preserving fine grain sizes. Dispersing fine transition metal carbide particles within the tungsten matrix has been proposed to enhance the ductility of tungsten by re-arranging the impurity distribution. Tungsten samples consolidated with 0.5–10 wt% zirconium carbide, titanium carbide, or tantalum carbide have been fabricated via spark plasma sintering to >90% relative density. Consolidated samples have transition metal-rich dispersoids uniformly distributed at grain boundaries and within the micron-sized tungsten grains. The presence of the dispersed second phase particles successfully refined the final grain size, as the average grain size decreased from 11 μm for the pure W samples to ~1 μm for the samples with 10 wt% second phase. Correspondingly, the hardness as measured via Vickers hardness rises as the grain size decreases and volume fraction of the second phase increases. XRD and XPS analyses show that formation of tungsten carbide and transition metal oxide complexes alter the impurity distribution and material performance.

Effect of nanophase concentration on the properties of metal-containing silicon–carbon nanocomposites

We have studied the effect of tungsten, molybdenum, and hafnium concentrations on the electrical conductivity, nanohardness, and elastic modulus of metal-containing silicon–carbon nanocomposite films. The results demonstrate that the addition of these metals to the films leads to the formation of metal carbide particles a few nanometers in size. At metal contents from 5 to 35 at %, the conductivity of the films varies over four orders of magnitude (from 10–1 to 103 S/cm). The composition dependences of the mechanical properties of the nanocomposites depend on the nature of the metal. We have analyzed the mechanisms underlying the effect of the metals on these properties.

Tribological properties of Aluminium Metal Matrix Composites (AA7075 Reinforced with Titanium Carbide (TiC) Particles)

In the present work aluminum matrix composites (AMMCs), AA7075 Alloy as the matrix metal and Titanium carbide (TiC) particles (2-10%) with an average particulate size of 2μm as reinforced material were processed by stir casting route. Computerized pin on disc wear tester was used for wear test with counter surface as EN32 steel disc (58-60 HRC) and cylindrical pin as the composite specimens. The wear rate in terms of weight loss per unit sliding distance, coefficient of friction and volume loss were obtained for the matrix metal and composites. The results of composite shows better wear resistance than matrix metal. The microstructural characterization of worn surface was investigated using SEM. Weight loss of samples was calculated and the variation of cumulative wear loss with sliding distance has been found to be uniform for both the matrix metal and the composites. It was also observed that the wear rate is low for composites compared to matrix metal. Further, it was noted from the experimentation that the wear rate decreases with increasing weight fraction of TiC and coefficient of friction decreases with increasing sliding velocity and weight fraction of TiC. SEM-XRD analysis revealed the presence of TiC and other phases. The better wear properties (wear rate, coefficient of friction and wear factor) was observed with 8 wt% TiC composite compared to other composites as well as matrix metal.

Optimization of Machining Parameters for Drilling Al-SiC MMC Using ANOVA and Grey Relational Analysis

Machining of composite materials is an important and current topic in modern researches on manufacturingprocesses. This paper presents the detailed experimental investigation on drilling Aluminium Silicon Carbideparticulate Metal Matrix Composite (Al-SiC –MMC). Experiments were carried out on Radial Drilling Machine.A plan of experiments, based on the techniques of Taguchi, was performed. The objective of this research is tostudy the effect of cutting speed, feed, diameter of cut, machining time on metal removal rate, specific energy,surface roughness, volume fraction and flank wear. The optimum machining parameters were obtained by Greyrelational analysis. Finally, confirmation test was performed to make a comparison between the experimentalresults and developed modelKeywords: Composite materials; drilling processes; Rey relational analysis Optimization

Dissolution of the metal sensitizers Ni, Be, Cr in artificial sweat to improve estimates of dermal bioaccessibility

Dermal exposure to sensitizing metals is a serious occupational and public health problem. The usual approach to dermal exposure assessment is to process samples by chemical methods that use reactants to digest the metal particles and quantify the mass. In the case of dermal exposure assessment, these reactants are not representative of the skin surface film liquids and hence, may overestimate bioaccessibility. We hypothesize that the amount and form of sensitizer on a sample that leaches in a biological fluid, as can be estimated using artificial sweat, may be a more relevant metric for assessing health risks. Beryllium metal (Be), nickel metal (Ni), and chromium carbide (Cr3C2) particles were characterized and masses of sensitizing ions were measured using established reactant-assisted digestion procedures and extraction in artificial sweat under physiologically relevant conditions. Chromium ions released into artificial sweat were speciated to understand valence states. The ratios of the fraction of metal dissolved in artificial sweat relative to that dissolved by chemical-specific reactants were 1/2 (Be), 1/108 (Ni), and 1/2500 (Cr). The divalent Be and Ni cations were stable in artificial sweat over time (did not precipitate) whereas hexavalent chromium [Cr(VI)] ions decayed over time. Further analysis using speciated isotope dilution mass spectrometry revealed that the decay of Cr(VI) was accompanied by the formation of Cr(III) in the sweat model. Use of reactant-assisted analytical chemistry to quantify amounts of metal sensitizers on samples could overestimate biologically relevant exposure. In addition to mass, the valence state also influences penetration through the outer stratum corneum of the skin and is an important consideration when assessing exposure to complex sensitizers such as Cr which have multiple valence states with differing penetration efficiencies.

The effect of TiO2nanoparticles on fluid quenching characteristics

AbstractNanofluids are colloidal suspensions of nanoparticles in base fluids. Some of the particles used in recent research are metal oxide and carbide particles, such as SiC, CuO, Al2O3 and TiO2, graphite and carbon nanotubes and particles. Quenching in such colloids results in better cooling abilities, higher impact toughness and smaller dimension changes of steels, compared with pure quenching media. In this investigation, nanofluids with TiO2 powders of 50 nm average particle size were investigated. Base fluids of primary interest were deionised (DI) water, some commercial quenching oils and polyalkylene glycol water solution of various polymer concentrations, 5–30 vol.-%. The investigated fluids were prepared with the addition of the same TiO2 powder with different concentrations, from extremely low, 10 mg nanopowder per litre to 1 g L−1. The cooling characteristics of these colloids were compared with the results of base fluids, but also with the results of previous measurements carried out on the f...

Sedimentation casting of wear resistant metal matrix composites

A new sand casting technique to produce particle reinforced composites has been developed. It is called “the drawer casting technique”. The technique is based on sedimentation casting and gives a high concentration of particulates at and below the working surface of the component. Two models that assisted the development of the drawer casting technique are described. It is shown that WC reinforcing particles settle in the bottom of the mould quickly to form a sediment bed. The critical flow velocity required to avoid sediment bed particle motion as the mould is filled is calculated. The use of the technique for the production of materials with a flat wear resistant working surface consisting of a white cast iron matrix reinforced with ex situ (WC) and in situ formed transition and refractory metal carbide particles is described.

Synthesis of single-and multi-component carbides utilizing exfoliated graphite

Different metal alkoxides were impregnated into exfoliated graphite (EG) by sorption and hydrolyzed with steam. Thus formed precursors were pyrolyzed at 1500-1700°C for 1-10h in argon to form single- and multi-component carbides, such as ZrC, TiC, (Ti, Zr) C solid solutions, TiC-ZrC composites, and TiC-Fe composites. In this process, hydrolyzed metal alkoxides were converted mainly to oxides and/or oxyhydroxides on the surface of graphite sheet composing EG, and eventually they are reduced to carbide or metal by graphite carbon at elevated temperatures. The small reaction spaces in EG produce fine metal carbide particles only by the pyrolysis. The process is simple and low cost, and possible to be developed to synthesize other carbides and composites.

Titanium carbide particles as pre-solar grains

Focusing on the growth of metal carbide particles and the formation of pre-solar grains, a new attempt has been made for titanium carbide (TiC) systems. Using the noble gas evaporation method, we succeeded in producing TiC core (50-nm) carbon mantle (2-nm) grains of the same core size as pre-solar grains. The infrared spectrum has broad absorption features at 9.5 and 12.5 µm. It was also found that these absorption peaks became weaker by an increase to 15 nm of carbon mantle layer. The determination method of the contact angle of carbon on the TiC grain has been developed using a high-resolution electron microscopic technique. The contact angles between TiC and carbon were 22. ◦ 8 ± 0. ◦ 7 and 24. ◦ 0 ± 0. ◦ 4 on the (111) and (100) TiC

In vitro genotoxic effects of different combinations of cobalt and metallic carbide particles.

Occupational exposure to hard metal dust, consisting of tungsten carbide (WC) and metallic cobalt particles (Co), is associated with an increased risk of lung cancer, while no increased risk was observed in workers exposed to Co alone. In vitro, in human peripheral blood mononucleated cells (PBMC), we previously demonstrated that WC-Co is more genotoxic than Co and WC alone. A possible mechanism underlying this higher genotoxicity is a specific physicochemical interaction between Co and WC particles leading to the enhanced short-term formation of active oxygen species. The aim of this study was to evaluate the in vitro genotoxicity of other combinations of Co with metal carbide particles in comparison with WC-Co. The ability of Cr(3)C(2), Mo(2)C and NbC and of their powder mixtures with Co to induce DNA strand breaks and alkali-labile sites was assessed by the alkaline Comet assay and their potential to induce chromosome(/genome) mutations by the cytokinesis-block micronucleus test on human PBMC from two donors. PBMC were treated in vitro for 15 min, 24 h after the onset of PHA stimulation. In the micronucleus test, while the metal carbides alone did not increase the micronucleus frequency, Co alone and the four tested carbide-Co mixtures induced a statistically significant concentration-dependent increase in micronucleated binucleates. In addition to WC, NbC and Cr(3)C(2) particles were able to interact with Co, producing a higher mutagenic effect than the individual metal particles. Mo(2)C particles did not display interactive mutagenicity with Co in the micronucleus test, possibly related to their small specific surface area, compactness and/or spherical shape. With the Comet assay, applied directly at the end of the treatment, less clear results, due to inter-experimental and inter-donor variation, were obtained. These data indicate that particular interaction of a metal carbide with Co leading to enhanced mutagenicity is not specific for WC.

Carbide precipitation and high-temperature strength of hot-rolled high-strength, low-alloy steels containing Nb and Mo

The effects of a Mo addition on both the precipitation kinetics and high-temperature strength of a Nb carbide have been investigated in the hot-rolled high-strength, low-alloy (HSLA) steels containing both Nb and Mo. These steels were fabricated by four-pass hot rolling and coiling at 650°C, 600°C, and 550°C. Microstructural analysis of the carbides has been performed using field-emission gun transmission electron microscopy (TEM) employing energy-dispersive X-ray spectroscopy (EDS). The steels containing both Nb and Mo exhibited a higher strength at high temperatures (∼600 °C) in comparison to the steel containing only Nb. The addition of Mo increased the hardenability and led to the refinement of the bainitic microstructure. The proportion of the bainitic phase increased with the increase of Mo content. The TEM observations revealed that the steels containing both Nb and Mo exhibited fine (<10 nm) and uniformly distributed metal carbide (MC)-type carbides, while the carbides were coarse and sparsely distributed in the steels containing Nb only. The EDS analysis also indicated that the fine MC carbides contain both Nb and Mo, and the ratio of Mo/Nb was higher in the finer carbides. In addition, electron diffraction analysis revealed that most of the MC carbides had one variant of the B-N relationship ((100)MC//(100)ferrite, [011]MC//[010]ferrite) with the matrix, suggesting that they were formed in the ferrite region. That is, the addition of Mo increased the nucleation sites of MC carbides in addition to the bainitic transformation, which resulted in finer and denser MC carbides. It is, thus, believed that the enhanced high-temperature strength of the steels containing both Nb and Mo was attributed to both bainitic transformation hardening and the precipitation hardening caused by uniform distribution of fine MC particles.

Absence of significant genotoxicity in lymphocytes and urine from workers exposed to moderate levels of cobalt-containing dust: A cross-sectional study

Mortality studies have shown that, in the past, lung cancer occurred after exposure to mixtures of cobalt metal and metallic carbide particles, the main constituents of hard metals, but apparently not when exposure was to cobalt alone. The major objective of this biomonitoring study was to assess genotoxic effects as a measure for carcinogenic risk in workers from cobalt refineries and hard metal plants currently exposed to the threshold limit value/time-weighted average (TLV-TWA) for cobalt-containing dust. The study comprised three groups of workers: 35 workers exposed to cobalt dust from three refineries, 29 workers exposed to hard metal dust from two producing plants, and 35 matched control subjects recruited from the respective plants. The study design integrated complementary methodologies to assess biomarkers of effects that represent both initial DNA damage (8-hydroxydeoxyguanosine [8-OHdG] in urine and comet assay on lymphocytes) and definitive chromosome breakage/loss (micronuclei in lymphocytes). Cobalt and cotinine were determined in urine as a measure for cobalt exposure and recent smoking, respectively. No significant increase of genotoxic effects was detected in workers exposed to cobalt-containing dust as compared to controls. No difference in any genotoxicity biomarker was found between workers exposed to cobalt and hard metal dusts. Multiple regression analysis indicated that workers who smoked and were exposed to hard metal dusts had elevated 8-OHdG and micronuclei values. Because this observation is in line with a previous epidemiological study of an increased risk of dying from lung cancer in workers from the hard metal industry who smoked, it is concluded that this specific occupational group needs closer medical surveillance.

Absence of significant genotoxicity in lymphocytes and urine from workers exposed to moderate levels of cobalt-containing dust: a cross-sectional study.

Mortality studies have shown that, in the past, lung cancer occurred after exposure to mixtures of cobalt metal and metallic carbide particles, the main constituents of hard metals, but apparently not when exposure was to cobalt alone. The major objective of this biomonitoring study was to assess genotoxic effects as a measure for carcinogenic risk in workers from cobalt refineries and hard metal plants currently exposed to the threshold limit value/time-weighted average (TLV-TWA) for cobalt-containing dust. The study comprised three groups of workers: 35 workers exposed to cobalt dust from three refineries, 29 workers exposed to hard metal dust from two producing plants, and 35 matched control subjects recruited from the respective plants. The study design integrated complementary methodologies to assess biomarkers of effects that represent both initial DNA damage (8-hydroxydeoxyguanosine [8-OHdG] in urine and comet assay on lymphocytes) and definitive chromosome breakage/loss (micronuclei in lymphocytes). Cobalt and cotinine were determined in urine as a measure for cobalt exposure and recent smoking, respectively. No significant increase of genotoxic effects was detected in workers exposed to cobalt-containing dust as compared to controls. No difference in any genotoxicity biomarker was found between workers exposed to cobalt and hard metal dusts. Multiple regression analysis indicated that workers who smoked and were exposed to hard metal dusts had elevated 8-OHdG and micronuclei values. Because this observation is in line with a previous epidemiological study of an increased risk of dying from lung cancer in workers from the hard metal industry who smoked, it is concluded that this specific occupational group needs closer medical surveillance.

Processing, microstructure and properties of in-situ reinforced SiC matrix composites

Abstract SiC matrix composites were fabricated by in-situ formation of transition metal boride and carbide particles from oxide powders by carbothermal reactions. Dense composites with various microstructures were produced by pressureless sintering and additional hot-isostatic pressing. The microstructures and mechanical properties of the composites were dependent upon the pressureless-sintering temperature. The use of submicron-sized TiO 2 lead to fine and equiaxial TiB 2 particulates. The composites exhibited high flexural strengths (>700 MPa). At higher sintering temperatures, the grain growth of SiC swept the boride into clusters with larger sizes and anisotropic shapes, which improved the fracture toughness of the composite at the expense of strength.

Microstructural inhomogeneities and sea water corrosion in laser-deposited Ti–6Al–4V alloy matrix/carbide particulate composite surfaces

Metal matrix/carbide particulate composite surface layers were produced on Ti–6Al–4V alloy samples by injecting metal carbide particles into laser-melted surfaces followed by rapid solidification. Hard, wear-resistant surfaces were produced on a strong alloy which normally has poor wear resistance. The corrosion behaviour of the composite surface was evaluated after a month's exposure to flowing sea water. A variety of solidification products was found in the laser-deposited surface layers, but corrosion was observed only in the carbide particulate phase in the WC-injected sample. No corrosion was observed in the TiC-injected sample nor in the Ti–6Al–4V base alloy. Corrosion in the WC-injected sample was related to the formation of a narrow interphase zone surrounding the particulate phase and a thin reaction zone on the surface of the particulate phase during solidification. The titanium-rich interphase zone formed a galvanic couple with the WC particulate. Crevice-type corrosion initiated at the interface between the two phases and proceeded into the particulate phase assisted by the reaction zone. Electrochemical test results revealed a high corrosion rate for the WC-injected sample and almost none for both the TiC-injected sample and the Ti–6A1–4V base alloy, confirming the microstructural observations.

Kinetics of metal-catalyzed growth of single-walled carbon nanotubes

Molecular-dynamics and total-energy calculations using a realistic three-body potential for carbon reveal the basic atomic processes by which single-shelled nanotubes can grow out of metal-carbide particles by the root growth mechanism. We find that nanometer-sized protrusions on the metal-particle surface lead to the nucleation of very narrow tubes. Wide bumps lead to a strained graphene sheet and no nanotube growth. The results also explain the absence of multishelled tubes in metal-catalyzed growth.