Formation Of Carbide Layer Research Articles

Laser-induced carbonization of stainless steel as a corrosion mitigation strategy for high-temperature molten salts applications

New heat transfer fluids are necessary to shift the operation temperature of concentrating solar power plants (CSP) to higher temperatures. Ternary carbonate salts (Li2CO3-K2CO3-Na2CO3) are a promising candidate. However, higher temperature translates to harsher operating conditions for CSP structural components as corrosion is more prevalent. In this work, we explore, for the first time, the use of laser micro-machining technology as a surface modification method to inhibit corrosion of CSP structural materials by molten salts. The corrosion behaviour of SS310 in molten ternary carbonate salt is investigated through static immersion for 600 h. Nanosecond laser treatment results in the adhesion of organic groups in the form of hydrocarbons. These then decompose into carbon and contribute to corrosion inhibition through carbonization and the formation of carbide layers. This is confirmed by the reduced diffusion of Li + ions in the SS310, the formation of denser corrosion products and the protection of chromium oxide layers.

Study of the microstructure and thermomechanical properties of Mo/graphite joint brazed with Ti–Zr–Nb–Be powder filler metal

The aim of this work was to braze molybdenum and graphite with Ti–40Zr–8.5Nb–1.5Be filler metal in order to demonstrate the possibility of its application for X-ray tube target brazing, further to investigate the joint microstructure using energy-dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), X-ray diffraction (XRD), and electron microscopy as well as to conduct shear and unbrazing tests. It is shown that the brazed joint consists of matrix from β-(Ti, Mo) solid solution, mixed ZrC and TiC carbide layers at the braze/graphite interface, and beryllides TiBe2 and MoBe2 located at the grain boundaries of β-(Ti, Mo). The presented data made it possible to propose a brazed joint formation mechanism and explain the concentration of beryllides at the grain boundaries during brazing, as well as the mixed carbide layer formation from the side of the graphite. The mechanical tests showed that Mo/graphite brazed joints have a shear strength of at least 28.0 ± 0.9 MPa. However, sample failure occurred through the graphite due to the graphite surface mechanical treatment and the presence of a ductile β-Ti phase in the joint. The evaluation of joint thermal properties was performed using unbrazing tests. The unbrazing temperature was 1882 °C, which was caused by formation of refractory phases during brazing. The microstructure study shows that unbrazing occurs through the β-(Ti, Mo) phase with grain boundaries and beryllides eutectic melting.

Hard and wear-resistant niobium, molybdenum carbide layered coatings on WC-Co tools produced by ion bombardment and cathodic vacuum arc deposition

Phase and element composition, microhardness, adhesive strength, wear resistance and microstructure of the coatings and underlying layers formed on WC-Co hard alloy using Nb and Mo vacuum-arc sources were studied. It is shown that the influence of ion beams with energy of 1 keV created by Nb and Mo vacuum-arc sources for at least 1–2 min allows the formation of carbide coatings based on embedded metals and alloy elements with (Nb,W)C0.7, Mo2C and Co6W6C2 phases. The synthesis of carbide layers occurred by ion exposure by Nb or Mo at a surface temperature of the hard alloy of at least 1300 °C, controlled by an optical thermograph. Reducing of Nb and Mo ion exposure time down to 30 s does not allow heating of samples surface to temperatures above 700 °C, as a result, the formation of carbide layers on the alloy surface does not occur. The plasma deposition of NbC or MoC coatings on sublayers created by preliminary Nb or Mo ion treatment accompanied by heating of the sample surface up to 1300°С forms carbide layered system with hardness of 60 GPa, adhesive strength of 120–140 N and 2–3-fold lower volume wear compared to NbC and MoC plasma coatings deposited on a hard alloy without preliminary treatment.

Characteristics of Products of Thermo Reactive Deposition Surface Treatment on JIS-SUJ2 Steel using Fe-Cr Coating Powder with Process Temperature Variation

In this study the effect of temperature variation of the thermo-reactive deposition (TRD) process on carbide layer formation on SUJ2 steel substrates by pack cementation using Ferrochromium powder as carbide former was studied. This process was carried out on SUJ2 steel substrates at temperatures of 900, 980 and 1060 °C for 6 hours. The effect of temperature on layer thickness, homogenity and hardness was studied. Results show that the higher the temperature the thicker the layer formed on the substrate surfaces. Furthermore the XRD results show that the layer formed by this process is chromium carbide. The average microhardness of the layer for 3 process temperature variations is around 1750 HV while the wear rate is around 7 x 10−4 mm3/m.

Selective laser melting of WC reinforced maraging steel 300: Microstructure characterization and tribological performance

Owing to the limited wear resistance, Maraging steels has limited applications in the harsh environments, leading to a shortened service-life or even failure. In this study, WC particles reinforced maraging steel 300 (MS300) composites were produced by selective laser melting (SLM) to enhance the tribological performance. The microstructure and phase analysis of SLM-produced composites were investigated by SEM-EDS. Dry sliding wear test and microhardness were used to investigate the mechanical properties of WC/MS300 composites. As laser energy density increases, the microhardness drops rapidly and the maximum value of 562.2 HV2 was measured at the linear energy density of 110 J/m. Dry sliding tests show that the wear rate was decreased by >1500 times through the WC reinforcement compared with pure MS300 sample, which emphasizes the superior wear-resistance properties of MS300/WC composite. Besides, the best wear-resistance performance at the improved linear energy density of 125 J/m. The study on wear mechanism shows that formation of carbide layer between WC and MS300 matrix significantly prevent the plowing effect. The present work provides an effectively method to improve the tribological performance MS300 through the reinforcement of WC particle by selective laser melting.

Study of temperature effect on carbide layer formation behaviour of dual elements thermal reactive deposition on SUJ2 steel substrate

In this research, the formation of carbide layer coating on SUJ2 steel by pack Thermal Reactive Deposition method was studied. Mixture of 35/65 weight percent of ferrochromium/ferrovanadium (FeCr/FeV) powder was applied as coating elements. The process was carried out at temperatures of 900, 950, and 1000 °C for 6 hours for each temperature. The effects of temperature on layer thickness, microstructures, homogeneity, hardness, and wear resistance were analyzed. The result showed that the higher the temperature, the thicker the layer formed on substrate surface. The higher percentage of vanadium in the coating layer compared to chromium found by EDS Linescan results indicate that vanadium has higher affinity to carbon than chromium. This result also means the possibility of vanadium carbide formation will be higher than chromium carbides, due to the lower Gibbs energy for vanadium carbide formation. XRD results showed that the layer formed in this process consists of vanadium carbide (V8C7 and V6C5), chromium carbide (Cr23C6 and Cr7C3), and complex carbides. The average micro hardness and wear rate of all coatings with three different temperature variations were 2100 HV, and 3 × 10−4 mm3/m respectively. This hardness was close to FeV hardness as single carbide former at approximately 2400 HV.

Interface evolution and superior tensile properties of multi-layer graphene reinforced pure Ti matrix composite

The interfacial structure and mechanical properties of multi-layer graphene (MLG)/pure Ti composites produced by spark plasma sintering (SPS) and subsequent hot-rolling (HR) have been investigated. The hot-rolling temperature has been set at 823K, 1023K and 1223K for composites to obtain various interfacial characteristics and microstructures. (Transmission electron microscopy) TEM observations reveal three types of temperature-dependent interface: Ti carbide nucleation, Ti carbide particles growth and Ti carbide layer formation. Moreover, there exists special crystallographic orientation relation: (1¯01)TiC//(112¯0)Ti and (0001)MLG//(020)TiC. Tensile test shows the MLG/Ti composite owns outstanding mechanical property. Specially, the 0.2wt%MLG/Ti exhibits tensile strength of 1050MPa, nearly two times higher than that of monolithic pure Ti. The relation between interfacial stress and strengthening efficiency has been investigated by using revised shear-lag mode in order to reveal the relation between interfacial microstructure and macro-mechanics. Results show that interfacial Ti carbides on partially reacted MLG led to the great improvement of interfacial strength and consequent enhancement of composites strength. When the HR temperature increased to 1023K and 1223K, the volume fraction of Ti carbides was 2.5 and 12.3 times higher than MLG. Ti carbide layer play a key role in further improvement of the tensile property.

Thermodynamic analysis of carbide-layer formation in steel with microarc saturation by molybdenum

Existing systems for diffusional saturation with molybdenum have numerous problems. The use of microarc treatment for this purpose is investigated. A steel sample is immersed in coal powder and heated by current transmission. Ammonium molybdate is the source of the molybdenum. The pyrolysis of coal is accompanied by the emission of hydrogen, methane, carbon dioxide, and carbon monoxide, which form a protective atmosphere and may reduce molybdenum to the atomic state. To identify the most likely chemical reactions, we calculate the standard change in Gibbs energy. The temperature ranges in which molybdenum trioxide is reduced to obtain molybdenum dioxide and atomic molybdenum are determined. The calculation results are verified experimentally. Simultaneous diffusion of carbon and molybdenum leads to the formation of a carbide coating (thickness 80–150 μm), with microhardness 13.5–15.0 GPa.

Structural investigations of diamond composites prepared by the infiltration of the diamond compact near the line of thermodynamic equilibrium of graphite with diamond

The structural order of diamond polycrystalline composite materials obtained by the infiltration of the diamond compact by nickel-silicon alloys at pressures up to 5.0 GPa and temperatures reaching 1800 K is investigated. It is established that they consist of a diamond skeleton and intercrystallite metal-ceramic binder. The diamond skeleton is formed from diamond grains of the starting size with weak diamond-diamond bonds, while the intergrain space is filled by diamond fragments and an intermetallic binder. The formation of carbide layers from silicon carbide on the surface of diamond grains determines the strength properties of diamond composites in general.

Fabrication of (Ti,Hf)-rich NiTiHf Alloy Using Graphitic Mold and Crucible

In this research, fabrication of a (Ti,Hf)-rich NiTiHf alloy by using vacuum induction melting (VIM) process and a graphitic crucible was investigated. For this purpose, casts with the nominal composition of Ni 49 Ti 36 Hf 15 were prepared in graphitic crucible and mold. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) tests were employed to characterize the samples. Results demonstrated that microstructure of the first cast was composted of a B2 austenite phase as well as a great amount of two differently formed (Ti,Hf)C carbides. Moreover, no austenite ↔ martensite transformation peak was detected in the DSC curve of this sample, indicating a drastic decline in the transformation temperatures. In the succeeding cast, however, owing to the formation of carbide layers on the inner surfaces of the graphitic crucible and mold during the initial casting process, the amounts of carbides decreased remarkably. This cast exhibited transformation temperatures above 100 °C, while XRD pattern denoted the presence of B19′ monoclinic martensite phase at room temperature. All in all, results confirmed that VIM process using graphitic mold and crucible can be considered as an appropriate method for the fabrication of (Ti,Hf)-rich NiTiHf high temperature shape memory alloys.

Synthesis and Characterization of Particulate SiC<sub>p</sub> Reinforced Al-Si-Mg Alloy Composite with Varying Si Content

Amongst the Metal Matrix Composites (MMCs), Al-Si-Mg alloy/ SiCp MMCs are very attractive for their properties. But, the formation of brittle interfacial reaction product, Aluminium carbide has been one of the major concerns when these materials are processed by liquid phase methods. The extent of Aluminium carbide formation depends on various processing parameters such as temperature, wt% of SiCp, particle size of SiCp and chemical composition of the matrix alloy especially Silicon (Si) content. According to recent studies, various difficulties in finding the process parameters to get desirable properties of Al alloy/ SiCp MMCs as desired by the industries. Thus, in the present study thermodynamic & structural estimates in Al alloy/ SiCp MMCs under various process conditions, composition, microstructures were performed. The relatively low cost liquid stir casting technique is used in the production of Al alloy/ SiCp MMCs with varying Silicon content (0–7%) in the alloy matrix using process temperature 710°C. Aluminium carbide layer formation on SiCp surface, Critical Si content for Aluminium carbide separation from SiCp surface, eutectic Si formation, existence of near-dislocation segregation regions after formation of Aluminium carbide on SiCp surface and the equilibrium amount of Si to suppress Aluminium carbide formation were investigated using Transmission electron microscopy (TEM). The separation of Aluminium carbide from SiCp surface was observed after 3% Si. The equilibrium Si content of 7% was found to suppress the formation of Aluminium carbide with thermodynamic model and its significance has been assessed.

Improvements in thermo reactive deposition of carbide layers

This paper presents developments contributing to the improvement of the process of producing hard carbide layers, with special attention to the application on tools and dies. The quantitative impact of the chemical composition of the steel and the process temperature on the kinetics of the carbide layer formation has been determined. In conventional processes of diffusion formation of carbide layers the phenomenon of partial decarburisation of steel occurring beneath the carbide layer during the process of its formation has been dealt with by the introduction of controlled precarburisation. Diffusion formation of carbide layers has been improved by the development of duplex processes that enable the formation of a case hardened layer which is harder than the core. Thus, the substrate for the hard and brittle carbide layer is improved. This development should contribute to the improvement of properties of the surface layers produced by the diffusion formation of carbide layers. In this way this process can be applied to the manufacturing of tools and dies.

Improvements in thermoreactive deposition of carbide layers

The paper presents developments contributing to the process of producing hard carbide layers, with special attention to the application on tools and dies. The quantitative impact of the steel composition and the process temperature on the kinetics of the carbide layer formation has been determined. In conventional processes of diffusion formation the phenomenon of partial decarburization of the steel has been dealt with by the introduction of controlled precarburization. Diffusion formation of carbide layers has been improved by duplex processes, which enable the formation of a case hardened layer which is harder than the core. Thus, the substrate for the hard and brittle carbide layer is improved. The development should contribute to the improvement of properties of the surface layers. The process can be applied to the manufacturing of tools and dies.

Formation of carbide layers on AISI H13 and D2 steels by treatment in molten borax containing dissolved both Fe–Nb and Fe–Ti powders

In this work, AISI H13 and D2 tool steels were treated in molten borax, containing dissolved ferro-niobium, ferro-titanium and aluminum, at 1020 °C for 4 h. Samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and Vickers microhardness. Well defined layers were obtained with excellent thickness regularity. For the AISI H13 steel the layer measured 9 μm and for the AISI D2 steel the layer thickness was 18 μm. Their microhardness values were at about 2600 HV 0.050. The layers consisted of niobium carbide according to XRD analysis. EDS results showed the predominance of niobium and absence of iron in the layers on both steels. The presence of titanium was detected, just in small amounts, in the region of the layer next to substrate.

The interface diffusion and reaction between Cr layer and diamond particle during metallization

A Cr layer with a thickness of 150 nm was successfully deposited on the surface of diamond particles using the dc magnetron sputtering technique. AES analysis indicated that the Cr layer reacted with diamond particle to form Cr 2C 3 carbide species on the interface during the deposition. With the rising of deposition power, the interface diffusion between Cr layer and diamond substrate increased. The interface diffusion and reaction between the Cr layer and diamond substrate were promoted significantly by an annealing treatment at a temperature range from 300 to 600°C in a ultrahigh vacuum (UHV). When the annealing temperature was below 500°C and annealing time was less than 4 h, CrC carbide species were formed on the interface. Higher temperature and longer time resulted in a Cr 2C carbide interlayer. The carbide species of Cr 2C was resulted from the interface diffusion and reaction which can be intensified significantly with raising the annealing temperature and time. The depletion of carbon atoms from diamond substrate and the diffusion of carbon controlled the formation of carbide layer. The apparent activation energy of interface diffusion and reaction was about 38.41 kJ/mol. The interface diffusion and reaction can be impeded by low vacuum.

Temperature dependence of silicon carbide interface formation: A photoelectron spectroscopy study

The formation of a carbide interface layer between the Si(100) surface and hydrogen-free ${\mathrm{sp}}^{2}$ amorphous carbon films is investigated at different substrate temperatures in the range from ambient to 1040 \ifmmode^\circ\else\textdegree\fi{}C. The analysis of the interface and film is performed with photoelectron spectroscopy in the ultraviolet and x-ray regime. A carbon beam is created by electron-beam evaporation of graphite and the stepwise in situ deposition of carbon (0.3 monolayer/min) allows to follow the evolution of the carbide surface layer and interface. At temperatures at and below 750 \ifmmode^\circ\else\textdegree\fi{}C a thin carbide layer (\ensuremath{\leqslant}0.4 nm) is rapidly formed, followed by the growth of a pure carbon overlayer. The valence band (VB) as well as the core-level spectra reflect the rapid formation of a SiC interface and subsequent carbon overlayer growth. If a substrate temperature above 900 \ifmmode^\circ\else\textdegree\fi{}C is chosen, the carbon overlayer growth is completely suppressed, and a pure carbide layer is present. The VB spectra of the carbide layer are identical to those of the bulk SiC phases. The continued carbide layer formation and absence of a carbon overlayer is attributable to the enhanced outdiffusion of silicon, which leads at the same time to the formation of a Si-rich surface. For temperatures below 900 \ifmmode^\circ\else\textdegree\fi{}C the carbidic interface is carbon-rich, which is attributed to carbon enrichment at the carbon-overlayer--carbide contact area. A comparison with experiments described in the literature allows to evaluate the influence of processing parameters such as ion irradiation on the interface formation.

Carburization of high temperature PM-materials

Carburization of powder metallurgically processed materials for high temperature use is interesting for several reasons: Production of carbide powders e.g. for hard metals, formation of carbide layers on bulk materials to improve corrosion and/or wear resistance and degradation of material properties like strength and ductility by metal-carbon reactions. Molybdenum, TZM (Mo-0.5Ti-0.07Zr-0.05C) and tungsten are finding wide application as construction material in high temperature furnaces which are operated under high vacuum or inert/protective gas conditions. If grafite is used in the same system reactions of the refractory metal components with carbon containing species have to be considered. Therefore a variety of examinations was performed on the carburization characteristics of molybdenum and tungsten (and alloys), especially at temperatures above 1200°C where carburization rates become technically relevant. High temperature oxidation resistant alloys like steels or Ni- and Co-based superalloys can withstand severe carburization as long as their surfaces are covered with tight, protective chromia scales. In case of porous or cracked scales or conditions where chromia is not stable anymore a front of carburization proceeds through the materials - frequently along the grain boundaries. The PM-materials Ducropur (pure chromium) and PM 2000 (Fe-19Cr-5.5Al -0.5Ti-0.5Y 2 O 3 ) show distinctly lower carburization rates: Ducropur forms tight chromium carbide layers, whereas PM 2000 is nearly unaffected up to 1100°C because of its tight and stable alumina scale.

Thermal reactive deposition coating of chromium carbide on die steel in a fluidized bed furnace

The application of thermal reactive deposition (TRD) and diffusion technique to form a carbide layer for enhancing the tool life is of increasing importance in surface modification of steel. This study focused on investigating the influences of the amount of addition on the formation rate of the chromium carbide layers by three different alloy powders, namely, pure chromium, 71Cr-29Fe-0.03C, and 66Cr-26Fe7.7C containing carbide-forming elements. Three kinds of tool steel (AISI M2, H13 and modified D2) were treated between the temperature of 950–1050 °C in a fluidized bed furnace where a special feeder was designed and used for continuous feeding of the activator. The carbide layers were evaluated based on microstructure, thickness, hardness, X-ray diffraction and chemical composition distribution analysis. The results indicated that the formation of carbide layers was not only influenced by the purity of chromium powder but also by the amount of the carbon dissolved in the matrix of the steels at the TRD processing temperature, rather than the nominal carbon content of the steels.

Observation of c(4 × 4) LEED pattern induced by reaction of Si(100) surface with C 2H 4

The initial stage of carbide layer formation on a Si(100) surface by reaction with C 2H 4 gas was studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). A c(4 × 4) LEED pattern was clearly observed after an exposure of C 2H 4 of 5 × 10 −6 Torr for 5 min at a sample temperature of 600°C to the Si(100) surface. Some factors which induce the c(4 × 4) pattern are discussed.

Formation of carbide layer on carbon materials by silicon and chromium impregnation (part 1: Effect of impurity and porosity on the formation)

Formation of carbide layer on carbon materials by silicon and chromium impregnation (part 1: Effect of impurity and porosity on the formation)