High Volume Fraction Of Carbides Research Articles

Kinetics and mechanisms of high-temperature oxidation in BCC and FCC high-alloy Fe-based alloys with high volume fraction of carbides

This study conducts a detailed analysis of high-temperature oxidation and microstructural evolution in two high-alloy Fe-based alloys, each characterized by a high-volume fraction of carbides but differentiated by their matrices − body-centered cubic (BCC) and face-centered cubic (FCC), which was achieved by the addition of nickel. By investigating the intricate interplay of factors such as phase composition, nickel content, and the presence of carbides, this research aims to elucidate the diverse oxidation kinetics and underlying mechanisms specific to each alloy type. Results show that the BCC alloy exhibits slower oxidation kinetics compared to its FCC counterpart, suggesting better performance in high-temperature environments. Moreover, while both alloys develop strong adhesive oxide scales primarily composed of Cr2O3, the FCC alloy experiences more pronounced scale spallation and cracking. A faster progression of decarburization was observed in the BCC alloy. This comprehensive comparison highlights how variations in matrix structure, along with nickel content and carbide behavior, critically influence oxidation kinetics, scale adhesion, and the overall integrity of oxide scales. Understanding these nuanced interactions is crucial for designing high-performance alloys tailored for extreme operating conditions.

Abrasive wear behavior of TiC-strengthened eutectic high chromium cast iron composites

The present research on high chromium cast irons (HCCIs) strengthened with TiC particles was motivated by a need to improve the abrasive wear resistance of materials for mining equipment such as board hammers and liners. The effect of TiC content and heat treatment on the wear properties of eutectic HCCIs was investigated by combining the three-body abrasive wear and micro-scratch tests. The experimental results show that the wear rate of the as-cast HCCIs decreases from 8.0 to 5.1 cm3/cm·10−8 as the volume fraction of TiC increases to 9.8%. The superior wear resistance of TiC-reinforced HCCIs was originated from the synergic contributions of ductile austenitic matrix and high volume fraction of carbides. However, the heat treatment reduces the hardness and wear resistance of the HCCIs with high TiC content due to the high volume fraction of brittle carbide phases and the low ductility of martensite matrix.

Wear behavior of HVOF sprayed WC-Co/NiCrAlYSi (35–65%) and WC-Co/NiCrAlYSi (80–20%) coatings on turbine SS316 steel

Abstract The high-Velocity Oxy-Fuel (HVOF) process belongs to the family of thermal spray techniques and are widely used in many industries to protect the components against wear and erosion. HVOF spraying technique is widely used due to its viability to produce low porosity and dense coatings. The wear test will be carried on pin-on-disk for different loading and constant speed conditions on substrate and coated materials. After a thorough review, commercially available powder WC-Co/NiCrAlYSi (80–20%) of nominal composition and blended powder WC-Co/NiCrAlYSi (35–65%), is selected to be coated on the SS316 substrate material for this study. The coefficient of friction and wear rate of both the coatings is lower than that of uncoated samples and the coatings exhibit high hardness with a high volume fraction of carbides being preserved during the HVOF spraying process and have lower sliding wear behavior when compared to uncoated material.

Surface Engineering Analysis of D-Gun Sprayed Cermet Coating in Aggressive Environment

Material degradation due to hot corrosion is a common problem in many engineering system, including coal fired turbines, valves and boiler tubes leading to huge economy losses. Detonation Gun process is a novel coating deposition process among the other thermal spray processes due to its very low porosity, strong adhesion to substrates, high cohesive strength and high hardness. In the present investigation, D-Gun process has been used to deposit Cr3C2–25NiCr coating on 23/8N Nitronic steel. The oxidation behavior of D-Gun sprayed Cr3C2–25NiCr coatings subjected to high temperature (700°C) in actual coal fired boiler for 1000 hours has been carried out in the present work. X-ray diffraction, Field emission–scanning electron microscope technique was used to analyze the scales formed on the surface of the oxidized samples. High volume fraction of carbides contributed for the higher microhardness of the coating (970HV). No microspalling of the scales were showed by the coated specimen. The scale remained intact and adherent to the substrate. The development of protective oxide scale of chromium, nickel and spinel of nickel and chromium have contributed the better oxidation resistance for coated specimen. The Cr3C2-25 NiCr coating imparted better hot corrosion resistance than the uncoated one in the given environment.

Effect of PCBN tool grade and cutting type on hard turning of high-chromium white cast iron

The turning of mechanical construction and bearing steels is widely carried out using PCBN and oxide ceramic tools, even when materials have high hardness (40 to 60 HRC), reached after quenching and tempering heat treatment. However, mechanical components submitted to severe abrasive loads show, in addition to matrix hardness, the presence of a high-volume fraction of hard particles in the microstructure. Turning materials with a high content of hard particles in the microstructure will result in high rates of abrasive wear or damage to the cutting edges of the tool. Information regarding the turning of materials characterized by a high-volume fraction of carbides in the microstructure is limited in literature. The objective of this study was to determine the performance of two grades of PCBN tools (high CBN and low CBN content with an added ceramic phase) in the turning of high-chromium white cast iron applying continuous and interrupted cutting. Evaluations of tools’ life, wear mechanisms at the tool cutting edges, roughness, and microstructure remaining on the turned surface were carried out. The results show that the grades with low CBN content and the addition of a ceramic phase, the tool life was three times longer than that of the grades with high CBN content. The most interesting result obtained concerns the microstructural modifications in a narrow subsurface layer of the turned material. Carbide fragmentation and alignment in the direction of the cutting shear plane were identified, which may potentiate the use of the material.

The Characterization Of Cast Fe-Cr-C Alloy

AbstractThe paper presents the results of the characterization of alloy from Fe-Cr-C (carbon content 0.79 wt.%) system including the microstructure, phase analysis, morphology and hardness in as cast state. The chemical composition was designed to create chromium-rich ferritic matrix with high volume fraction of carbides in form of interdendritic eutectics. The research was carried out on the cross section of the ingot, synthesized in an arc furnace under high purity argon atmosphere and crystallized on water-cooled copper mould. Microstructural characterization was carried out by light microscopy and scanning electron microscopy (SEM). Phase identification was performed by X-Ray diffraction (XRD). The microstructure of the investigated alloy is composed of primary and secondary dendrites Fe-Cr solid solution and complex M23C6and M7C3carbides in interdendritic areas. Segregation of Cr and C during crystallization causes precipitation of M7C3carbides. The average hardness of the alloy is 205±12 HV10.

Microstructure refinement of hypereutectic high Cr cast irons using hard carbide-forming elements for improved wear resistance

Hypereutectic high Cr cast irons (HCCIs) possess high resistance to wear, benefiting from their high volume fraction of hard carbides. However, the primary carbides are usually coarse, rendering the materials less tough and thus negatively influencing their resistance to wear, especially when impact force is involved. Refining the microstructure of hypereutectic HCCIs has been demonstrated an effective approach to improve the performance of HCCIs during wear processes. Previously we demonstrated that adding Ti to a hypereutectic HCCI resulted in the formation of fine TiC, which consumed carbon and thus shifted the carbon concentration in the remaining liquid to one corresponding to the eutectic state. As a result, microstructure of the HCCI was refined without the formation of primary carbides while still retaining high volume fraction of carbides. The wear resistance of the modified HCCI was markedly improved. In the present work, we added several other carbide-forming elements, V, Nb, B, and Mo, to a hypereutectic HCCI, respectively, and evaluated the effectiveness of each element in improving the wear resistance of the HCCI. The amount of each added element was adjusted in order to have the HCCI in slightly hypereutectic, eutectic, and hypoeutectic states, respectively. Optimal ranges of the added elements were thus determined based on the degree of microstructure refinement and corresponding wear resistance. Microstructure characterization was carried out using scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffraction technique. Micromechanical properties and wear resistance were evaluated using micro-indenter and pin-on-disc tester, respectively.

Microstructure and wear properties of Fe-Cr-C and Fe-Cr-Nb-C clads on carbon steel by TIG surfacing process

In the present study, the surface of St52 steel was alloyed with preplaced Fe-Cr-C and Fe-Cr-Nb-C powders by using a tungsten-inert gas (TIG) heat source. The microstructure and phase composition of the alloyed surfaces were investigated using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction. Microhardness measurements were performed across the alloyed zone. The tribological behaviour of the coatings was evaluated using dry sliding wear tests at room temperature. It was found that the as-deposited coatings consisted of high volume fraction of carbides (Cr7C3, NbC). The Nb free and Nb-contained clad coatings both exhibited an excellent wear resistance compared to 0.22% C carbon steel under dry sliding wear tests. The wear resistance of Nb-contained clad coating was higher than that of the Nb-free clad coating because the hard carbide NbC was distributed in clad coating which increased the wear resistance of clad coating under dry sliding wear test. No cracks were found in the coatings.

Characterisation of detonation gun sprayed Cr3C2–25NiCr coatings on Ni and Fe based superalloys

Cr3C2–25NiCr coatings are essential to provide protection against both wear and corrosion of superalloys particularly in the temperature range up to 900–1000°C. The Cr3C2–25NiCr coatings were deposited on the Fe and Ni based superalloys by D gun spray technique and subsequently investigated for their microstructural characteristics such as coating thickness, porosity, phase formation, microhardness, surface and cross-sectional morphologies. The coatings showed a dense microstructure with porosity contents less than 0·69%. The carbide grains of different size are uniformly cladded with the metallic binder and located around the splat boundaries as observed in the coatings. Lower carbide dissolution and its uniform distribution ensured a better binder protection in the coatings. High cohesive strength of the individual splats and high volume fraction of carbides contributed for the higher microhardness values of the coatings (775–1200 HV).

Structure and wear behaviour of HVOF sprayed Cr3C2–NiCr and WC–Co coatings

Hard chrome plating is used to restore the original dimensions to worn surfaces of gas turbine shafts. However, its use is about to decrease due to some intrinsic limitations of its deposits and the toxic and carcinogenic characteristics of the hexavalent chromium. During the last decade high velocity oxy-fuel (HVOF) thermal sprayed cermet coatings play an important role in industrial applications where exceptional friction and wear resistance are required. The purpose of this study is to investigate and to compare the microstructure, wear resistance and potentials of HVOF sprayed Cr3C2–NiCr and WC–Co coatings for a possible replacement of hard chromium plating in gas turbine components repair. It has been shown that coatings exhibit high hardness with a high volume fraction of carbides being preserved during the spraying, and have different wear behaviour.

Wear of hardfacing white cast irons by solid particle erosion

The response of three commercial weld-hardfacing alloys to erosive wear has been studied. These were high chromium white cast irons, deposited by an open-arc welding process, widely used in the mineral processing and steelmaking industries for wear protection. Erosion tests were carried out with quartz sand, silicon carbide grit and blast furnace sinter of two different sizes, at a velocity of 40 m s −1 and at impact angles in the range 20° to 90°. A monolithic white cast iron and mild steel were also tested for comparison. Little differences were found in the wear rates when silica sand or silicon carbide grit was used as the erodent. Significant differences were found, however, in the rankings of the materials. Susceptibility to fracture of the carbide particles in the white cast irons played an important role in the behaviour of the white cast irons. Sinter particles were unable to cause gross fracture of the carbides and so those materials with a high volume fraction of carbides showed the greatest resistance to erosive wear. Silica and silicon carbide were capable of causing fracture of the primary carbides. Concentration of plastic strain in the matrix then led to a high wear rate for the matrix. At normal impact with silica or silicon carbide erodents mild steel showed a greater resistance to erosive wear than these alloys.

Properties of sintered wear-resistant alloys having high volume fraction of carbides

The authors tried to develop a new ferrous alloy with high volume fraction of carbides under the concept that such alloys should reduce metallic adhesion between contacting parts, resulting in improved scuffing wear resistance. The alloy obtained using a co-reduced powder had volume fraction of carbides of about 72%, relative density of over 99%, hardness of about 69Rc and transverse-rupture strength of about lOOOMPa. According to a block-on-ring test, the alloy showed superior adhesion resistance to conventional one. In a firing engine test, the alloy presented improved wear resistance of both rocker arms and mating cams with no signs of scuffing wear.

焼結高速度鋼の破壊じん性評価

Fracture toughness tests of high speed steels were carried out to develop a method for evaluating fracture toughness. A precrack introduced by the BC (Bridge Compression) method, at the front of which the damage region with microcracks was formed, could not be assumed as an ideal crack. On the other hand, a precrack introduced by the FP (Fatigue Precracking) method, where the precrack was introduced under a sufficiently low level of Kfmax, could be assumed as an ideal crack. The KIC-values evaluated by the BC method were lower than those by the FP method. Therefore, it is necessary to introduce a fatigue precrack, which can be assumed an ideal crack, by the FP method for evaluating fracture toughness.The size and volume fraction of carbides in the sintered high speed steel were smaller and higher than those in the melted high speed steel. The high volume fraction of carbides gave low fracture toughness, while the small size of carbides improved fracture toughness. Since in the present sintered high speed steel these effects by the size and volume fraction of carbides compensated each other, the fracture toughness of the sintered high speed steel was almost equal to that of the melted high speed steel.

On the thermal Cyclic Loading Behaviour of a directional eutectic superalloy based on the CoCrC system

AbstractVarious modifications of the eutectic, directionally solidified superalloy 73 C were investigated with respect to creep fatigue effects. This was carried out using a thermal cycling apparatus where a mechanical uniaxial load could be applied. A high volume fraction of carbides had an impairing effect on fatigue life. An improvement, however, could be obtained using low concentrations of refractory elements which form monocarbides.