Carbide Size Research Articles

Effect of Cerium on the Behavior of Primary Carbides in Cast H13 Steels

Different amounts of elemental cerium were added into H13 ingots to investigate the effect of cerium content on primary carbides’ behavior. The enrichment of the elemental Cr, Mo, V, and C in the last-to-solidify region was identified by EPMA. The enrichment of alloy elements is the main reason for the precipitation of primary carbides during solidification. As the increase of cerium content, the size of the last-to-solidify region decreases first and then increases. We found a huge difference between the 2D and the 3D observations of primary carbides. The number density of the primary carbides appeared higher, while their size was smaller in the 2D observation. In the 3D observation, as the cerium content increases, the primary carbides’ size also decreases first and then increases, while the morphology of the primary carbides changes from dendritic structure to sheet structure and then to dendritic structure again. The cerium content has little influence on the thermodynamic precipitation process of primary carbides. The enrichment of the elemental cerium in the last-to-solidify region observed by TOF-SIMS accelerates the nucleation of the austenite, further leading to smaller last-to-solidify region size. The smaller last-to-solidify region size provides less space for the further growth of the primary carbide, resulting in the smaller primary carbide size.

The Σ = 2 and Σ = 13a grain boundary distributions in cemented tungsten carbides with/without metallic binders

Cemented tungsten carbides with/without metallic binders were prepared through spark plasma sintering (SPS). The coincidence site lattice grain boundaries of the materials were characterized by electron backscattered diffraction (EBSD) technology. Misorientation angle distribution and grain boundary plane orientation distributions of Σ = 2 and Σ = 13a boundaries in the above WC materials are demonstrated. The reasons for the high fraction of Σ = 2 boundaries and the weaker misorientation texture at 30° in cemented tungsten carbides without metallic binders were discussed. It was found that the binder types have little effect on the high population of Σ = 2 boundaries in spark plasma sintered pure WC, WC-Co and WC with various ceramic binders such as Al2O3, ZrO2, Al2O3-ZrO2 and Al2O3-ZrO2-B2O3. In contrast, the mean grain size of WC carbides exhibits direct relation with the population of Σ = 2 boundaries. The coalescence mechanism during solid-state sintering are confirmed for eliminating the 90° boundaries and decreasing the intensity for habit planes distribution for Σ = 2 boundaries. The result support the theory that the preference of Σ = 2 low-energy boundaries in cemented carbides is rather dependent on the anisotropic surface energy of different planes than the cobalt content. This discovery facilitates to a better understanding of the origin of Σ = 2 boundaries in WC based materials.

Effect of Aging Process on the Strain Rate Sensitivity in V-Containing TWIP Steel

The dynamic tensile behavior of the twinning-induced plasticity (TWIP) steel with the vanadium carbide is investigated at different strain rates of 10−4, 10−3, 10−2 and 0.05 s−1. Microstructure characterization, carried out using back scatter electron diffraction (EBSD) and transmission electron microscopy (TEM), shows a homogeneous face center cubic structured matrix with uniformly dispersed vanadium carbide. The vanadium carbide is controlled by the aging temperature and time. The best comprehensive mechanical properties are achieved when the tested steel is aged at 550 °C for 5 h. With the increase of strain rate, the tensile strength and work hardening rate decrease, and the tested material shows negative strain rate sensitivity. This would be due to an increase in stacking fault energy caused by temperature rise by adiabatic heating, which must suppress the formation of twinning. On the other hand, the strain rate sensitivity is affected by dynamic strain aging (DSA). With the increase of strain rate, the DSA weakens, which causes negative strain rate sensitivity. The tensile strength and strain rate sensitivity value both increase first and then decrease with the increase of vanadium carbide size. This is because the tensile strength is mainly affected by the vanadium carbide. In addition to the vanadium carbide, the strain rate sensitivity is also affected by the amount of solute atom (V and C) during the dynamic strain aging process.

Effect of the Morphology, Size, Distribution and Homogeneity of Carbides and Matrix on Wear Resistance in High Cr-Alloys White Cast Iron

The aim of this work was to study the wear behavior of high-chromium white cast iron of families ASTM A-532 II (B, D) and III A, used in mining equipment, in order to establish relationships between the wear resistance, hardness and microstructure of the alloys, with the ultimate purpose of predicting their resistance to abrasion. Samples from these cast irons were subjected to mechanical wear tests by rotating drum, then their micro/macro hardness was measured and microstructure analyzed by optical and scanning electron microscopy .It was found that when the macroscopic hardness differences were significant there was a strong correlation between the hardness and the loss of mass due to abrasion-impact wear. By contrast, when the alloys had similar hardness, the wear resistance was determined by morphology, size, and the distribution and connectivity of carbides and matrix and therefore was not predictable by an only simple hardness test.

Performance of a Matrix Type High Speed Steel after Deep Cryogenic and Low Tempering Temperature

A matrix type high speed steel YXR3 designed for a combination of wear resistance and toughness is investigated for its mechanical properties after hardening by deep cryogenic treatment follow by tempering. The deep cryogenic quenching carried out at -200 °C for 36 hours and the single step tempering results in an obvious improvement in wear resistance while balancing the toughness, comparing with the conventional quenching followed by a double tempering treatment. The quantitative image analysis reveals little difference in the MC carbide size distribution between tempering at different temperatures. The synchrotron high energy XRD confirms the MC type carbide with some evolution in its orientation together with tempered martensite approaching the BCC structure at higher temperatures. In contrary to the conventional quenching and tempering, the lowest tempering temperature at 200 °C yields a moderate drop in hardness with increase in surface toughness proportionally while exhibiting exceptional wear resistance. Such thermal cycle can be recommended for the industry both for the practicality and improved tool life.

A simplified hardness model for WC-Co-Cubic cemented carbides

Hardness is an essential mechanical indication of cemented carbides. The current work presents an approach to predict the hardness of three-phase WC?Co?Cubic cemented carbides, which establishes a relationship among composition, structure and mechanical performance. With the input of initial composition and grain sizes of carbides, structural parameters needed to predict the hardness can be calculated by thermodynamic calculations and diffusion simulations. The calculated hardness of a series of WC?Co?Cubic cemented carbides agrees reasonably with the experimental data. The present model is of reference to predict the hardness for multi-phase composites and design the new type of WC?Co-based cemented carbides.

The effect of solid solution treatment parameters on the microstructure and mechanical properties of A286 superalloy

In this investigation, the effects of solution parameters on the microstructure and hardness of a Fe-Ni superalloy were studied. Samples were solutionized in temperature ranges of 900 °C to 1060 °C for the times of 0.5 h to 2.5 h, water quenched and aged at 720 °C for 16 h. for more structural examinations, some solutionized samples were aged at 800 °C and 860 °C for 8 h. The microstructure of the alloy was investigated using optical and scanning electron microscopes and the volume fraction of phases was measured by image analyzer software. The hardness of solutionized and aged specimens and tensile strength of aged samples at room temperature were also assessed. The results showed that hardness and ultimate tensile strength decrease with increasing solution temperature. It was found that increase in the solution temperature led to a decrease in volume fraction of η and carbide phases and an increase in the carbide sizes. It was also found that solution annealing time had no significant effect on the properties of the alloy.

Взаимодействие карбидов WС и Cr3С2 при термообработке сплавов WС – Cr3С2 – Сu

Composite alloys WC – Cr3C2 – Cu were obtained by infiltration of copper melt into uncompacted powders WC and Cr3C2 (reference alloys) and their mixtures with a weight ratio WC: Cr3C2 = 1:1. Impregnation of uncompacted carbide powders with copper melt was carried out at low frequency (~ 80 Hz) vertical vibration (LFV) of the crucible with alloy components for 10 min in a resistance furnace in an atmosphere of flowing argon. The effect of heat treatment of the obtained model composites on the interaction of carbides WC and Cr3C2 under isothermal and dynamic action of temperature, as well as during high-speed cyclic heating of the alloy surface by an electric arc (120 A, 45 V, 2 Hz, 10000 arc interruption cycles) has been studied. The evolution of the structure of alloys has been investigated by means of electron microscopy, X-ray spectral microanalysis, X-ray phase and differential thermal analysis. It is shown that the action on the sample surface of the temperature field created by an electric arc leads to an intense interaction of carbides. In this case, matrix copper, periodically transforming into a melt, plays the role of a transfer medium (diffusion medium). As a result of such heat treatment in the upper layers of the alloys, finely dispersed compositions of complex carbide phases with sizes of ≤ 1 – 2 μm were formed, i.e. 1 – 2 orders of magnitude smaller than the size of the initial carbides.

Effects of cooling rate on the mechanical properties and precipitation behavior of carbides in H13 steel during quenching process

The effects of cooling rate (CR) on the mechanical properties and precipitation behavior of carbides in H13 steel during quenching process were investigated. The retained austenite tends to be more unstable with increasing CRs, while the martensite increases gradually, based on XRD analyses and EBSD results. The values of hardness are increased, and the elongation along with impact energy is decreased, respectively, at higher CRs. Tensile strength remains above 2.0 GPa. Work hardening rates increase considerably in three samples, suggesting that transformation-induced plasticity effect may take place during the tensile test. Moreover, an increase in yield strength is observed when CR exceeds 15 K s−1, possibly due to a high volume fraction of martensite, decline in average grain size and precipitation of fine carbides. Types of the precipitates acquired were identified by electrolysis and XRD analyses. The results indicate the predominant existence of MC, M6C and M7C3, which are confirmed by SEM-EDS analyses and FactSage thermodynamic calculations. The size, volume and distribution of the carbides were also scrutinized under SEM. It is found that the volume fraction and size of the precipitates both decrease with increasing CRs. Based on these experimental data, an optimum CR for the quenching process could be determined to achieve the desired distribution of carbides, which in turn leads to the enhanced mechanical behaviors.

Effect of Alloying on the Nucleation and Growth of Laves Phase in the 9–10%Cr-3%Co Martensitic Steels during Creep

Five Co-modified P92-type steels with different contents of Cr, W, Mo, B, N, and Re have been examined to evaluate the effect of the chemical composition on the evolution of Laves phase during creep at 650 °C. The creep tests have been carried out at 650 °C under various applied initial stresses ranging from 80 to 200 MPa until rupture. An increase in the B and Cr contents leads to a decrease in the size and volume fraction of M23C6 carbides precipitated during tempering and an increase in their number particle density along the boundaries. In turns, this affects the amount of the nucleation sites for Laves phase during creep. The (W+Mo) content determines the diffusion growth and coarsening of Laves phase during creep. Susceptibility of Laves phase to coarsening with a high rate is caused by the large difference in Gibbs energy between fine and large particles located at the low-angle and high-angle boundaries, respectively, and can cause the creep strength breakdown. The addition of Re to the 10%Cr steel with low N and high B contents provides the slowest coarsening of Laves phase among the steels studied.

Effect of Titanium and Boron Microalloying on Sulfide Stress Cracking in C110 Casing Steel.

The effect of Ti and B microalloying on the hardenability, prior austenite grain size (PAGS), mechanical properties, and sulfide stress cracking (SSC) of C110 grade steel was studied by Jominy testing, static tensile testing, an optical microscope (OM), scanning electron microscopy (SEM) and double cantilever beam (DCB) testing. The results show that the addition of 0.015% Ti and 0.002% B into a medium-carbon Fe-Cr-Mo-Nb-V steel increased the hardenability and refined the PAGS and quenched martensite packets, and the size of carbides was reduced. It is believed that these behaviors are responsible for the improvement in the threshold stress intensity factor KISSC.

Solidification Structure of Superalloy René 80 and Variation of Tensile Properties after Heat-Treatment

Microstructural characteristics of directionally solidified Rene 80 superalloy are investigated with optical microscope and scanning electron microscope; solidification velocity is found to change from 25 to 200 μm/s under the condition of constant thermal gradient (G) and constant alloy composition (Co). Based on differential scanning calorimetry (DSC) measurement, γ phase (1,322 oC), MC carbide (1,278 oC), γ/γ' eutectic phase (1,202 oC), and γ' precipitate (1,136 oC) are formed sequentially during cooling process. The size of the MC carbide and γ/γ' eutectic phases gradually decrease with increasing solidification velocity, whereas the area fractions of MC carbide and γ/γ' eutectic phase are nearly constant as a function of solidification velocity. It is estimated that the area fractions of MC carbide and γ/γ' eutectic phase are determined not by the solidification velocity but by the alloy composition. Microstructural characteristics of Rene 80 superalloy after solid solution heat-treatment and primary aging heat-treatment are such that the size and the area fraction of γ' precipitate are nearly constant with solidification velocity and the area fraction of γ/γ' eutectic phase decreases from 1.7 % to 0.955 %, which is also constant regardless of the solidification velocity. However, the size of carbide solely decreases with increasing solidification velocity, which influences the tensile properties at room temperature.

Wear and corrosion behavior of Mg-based alloy reinforced with TiC and ZrC particles

Abstract In this contribution, particle sizes of TiC (13 and 93 μm) and volume fractions of ZrC (5 and 10 vol.-%) with respect to reinforcement particles were varied to investigate the effects on the microstructure, hardness, density, wear and corrosion properties of AZ91 Mg matrix alloy. Experimental results revealed that the hardness, density and sliding wear performance of AZ91 alloy were markedly improved by the addition of carbide particles. Predominant wear and corrosion mechanisms were identified considering the size and volume fraction of the carbides. The composite sample comprising fine TiC particles (13 μm) exhibited the highest wear resistance at the same volume fraction as the coarse particles. Moreover, coarse ZrC particles with a low volume fraction (5 vol.-%) provided an enhanced wear resistance beyond that of the 10 vol.-% ZrC particles. Considering all the investigated composites, the corrosion resistance of the composites deteriorated with the increasing volume fraction and size of the carbide particles. Electrochemical measurements of the 0,5M NaCl solution revealed that increasing carbide particle size and volume fraction leads to lower corrosion resistance due to the formation of more cathodic areas which are preferred sites for the initiation of pitting corrosion.

Effect of direct quenched and tempering temperature on the mechanical properties and microstructure of high strength steel

The effect of direct quenched (DQ) and tempering temperature on the microstructure and mechanical properties of high strength steel were studied by means of SEM, EBSD, TEM and mechanical properties test. The results showed that in DQ state, the tensile strength could reach 1420 Mpa, the yield strength could be 1050 Mpa, and the elongation was about 9.0%, impact energy at −20 °C was 59 J. High density entangled dislocation was distributed inside the lath and at the boundary. A small amount of Nb and Ti carbide was precipitated at the dislocation and lath boundary, and a small amount (about 2.15%) of residual austenite distributed between the lath. With the tempering temperature rising from 500 °C to 720 °C, the tensile strength of the experimental steel decreased from 1220 MPa to 840 MPa, the yield strength decreased from 1190 MPa to 780 MPa, the elongation increased from 10% to 13%, and the impact energy at −20 °C increased from 84 J to 153 J. When the tempering temperature rised from 500 °C to 640 °C, the structure was mainly composed of lath martensite and a large number of dislocations were still distributed inside the lath. The size of carbides precipitated inside and on the boundary of the lath was about 20–30 nm. When tempered at 680 °C, the structure was mainly composed of martensite and a small amount of polygonal ferrite. There were still a large number of entangled dislocations inside and on the boundary of martensite. The carbide precipitate at the matrix boundary and dislocation line was obviously coarsening (70–80 nm). When tempered at 720 °C, the microstructure was mainly polygonal ferrite, the dislocation density in the matrix significantly decreased, and the carbide precipitated at the matrix boundary and dislocation line significantly coarsened (about 100 nm). With the tempering temperature rising from 500 °C to 720 °C, the proportion of small-angle grain boundary was gradually decreased from 88.64% to 70.50%.

Controlling centre segregation and shrinkage cavities without internal crack in as-cast bloom of steel GCr15 induced by soft reduction technologies

ABSTRACT To investigate the alleviation technology of internal cracks, center shrinkage cavities and center segregation of as-cast bloom simultaneously, a three-dimensional finite element model was developed to calculate and analyze the strain fields and deformation behavior of as-cast bloom induced by soft reduction process. In the present work, a multi-stage mechanical soft reduction (MSR) has been developed to simultaneously alleviate center segregation and shrinkage cavities without internal cracks, which aims to provide theoretical basis for improving the internal quality of high carbon as-cast blooms induced by soft reduction technologies. According to the experimental results, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments, the homogeneity and compactness of as-cast bloom can been remarkably improved in comparison with that induced by the conventional soft reduction process. The carbide size and bandwidth of the carbides in the hot-rolled wire were both decreased.

Nonstoichiometry, structure and properties of nanocrystalline oxides, carbides and sulfides

The results of recent experimental studies of the influence of the size of oxide, carbide and sulfide nanoparticles on changes in their nonstoichiometry are analyzed and generalized. In relation to intrinsically nonstoichiometric titanium oxides and niobium and vanadium carbides, on the one hand, and stoichiometric silver sulfides, on the other hand, it is shown that a decrease in the particle size to the nano scale has a strong impact on the chemical composition of nanocrystalline compounds, viz., it leads to the occurrence of or increase in nonstoichiometry. A conclusion is drawn that interplay between the particle size and nonstoichiometry is common to all solid nanocrystalline substances and should be taken into account in studies on the synthesis, structure and properties of these systems.The bibliography includes 260 references.

Multiscale characterization of the 3D network structure of metal carbides in a Ni superalloy by synchrotron X-ray microtomography and ptychography

Synchrotron X-ray microtomography and ptychography were used to characterize the 3D network structure, morphology and distribution of metal carbides in an as-cast IN713LC Ni superalloy. MC typed carbides were found to distribute mainly on the grain boundary between the matrix γ and γ' phase. The differences in solidification cooling rate had a minor influence on the volume fraction of the MC type carbides, but significantly affected the carbide size, distribution and network morphology. Depending on the local composition of the remaining liquid phase and geometric constraints, the carbides can form either spherical or strip or network morphologies. The research demonstrated clearly the advantage and technical potential of using the two complementary tomography techniques synergistically to characterize non-destructively complex multiple-phase structures in three dimensional space with a spatial resolution of ~30 nm.

Improvement of wear resistance of aluminum alloy by HVOF method

This work is devoted to establishing the effect of High Velocity Oxygen-Fuel (HVOF) method for spraying coatings with vanadium carbide (VC) (as an alternative to galvanic chromium plating) on the wear resistance of obtained coatings in friction conditions with a rigidly fixed and non-fixed abrasive. The initial components for spraying coatings were powders of VC, ferrochrome (FeCr) and cobalt (Co). The powder compositions of the two (FeCr – VC) and (FeCr – VC – Co) systems were deposited on to a substrate of an aluminum alloy 7075. Each of compositions was mixed in a planetary mill for the mechanical alloying. A thickness of obtained coatings was 200 μm. It was discovered that (FeCr – VC) and (FeCr – VC – Co) coatings, obtained by the HVOF method with using of both gaseous (propane - oxygen) and liquid (kerosene – oxygen) fuels, have high wear resistance. The wear resistance of the coatings with using of friction method with rigidly bonded abrasive increases with the size of the VC carbide inclusions. In the presence of cobalt in the coating, the trend is similar, but its wear is bigger. Since cobalt does not form carbides, in the structure of such coating forms ductile inclusions based on it. As a result of the friction test using non-fixed abrasive, the wear resistance of coatings increased with decreasing VC carbide size in their structure and increased at addition of cobalt powder to powder composition for spraying.

As-Built and Post-treated Microstructures of an Electron Beam Melting (EBM) Produced Nickel-Based Superalloy

The microstructures of an electron beam melted (EBM) nickel-based superalloy (Alloy 718) were comprehensively investigated in as-built and post-treated conditions, with particular focus individually on the contour (outer periphery) and hatch (core) regions of the build. The hatch region exhibited columnar grains with strong 〈001〉 texture in the build direction, while the contour region had a mix of columnar and equiaxed grains, with no preferred crystallographic texture. Both regions exhibited nearly identical hardness and carbide content. However, the contour region showed a higher number density of fine carbides compared to the hatch. The as-built material was subjected to two distinct post-treatments: (1) hot isostatic pressing (HIP) and (2) HIP plus heat treatment (HIP + HT), with the latter carried out as a single cycle inside the HIP vessel. Both post-treatments resulted in nearly an order of magnitude decrease in defect content in hatch and contour regions. HIP + HT led to grain coarsening in the contour, but did not alter the microstructure in the hatch region. Different factors that may be responsible for grain growth, such as grain size, grain orientation, grain boundary curvature and secondary phase particles, are discussed. The differences in carbide sizes in the hatch and contour regions appeared to decrease after post-treatment. After HIP + HT, similar higher hardness was observed in both the hatch and contour regions compared to the as-built material.

Effect of carbides on the wear resistance of white cast iron alloyed with 12.7 wt.-% Cr and nickel

Abstract White cast iron with about 12.7 wt.-% chromium was alloyed with Ni, W and Mo for heat treatment applications. Heat treatments were performed at a range of 850-1050 °C for 1 h in order to distribute M7C3 carbides homogeneously in an environment of high wear resistance. The contents of the C, Cr, Ni, Mo, Mn and Si elements selected for the alloys were similar, though a 6 wt.-% nickel concentration was chosen. Microstructural changes in the specimens were examined by scanning electron microscopy (SEM) and optical microscopy (OM). Macro-hardness, average carbide size and volume fraction were analyzed. Wear tests were carried out under different loads of 10, 20 and 30 N. It was seen that heat treatment changed the carbide size and homogeneous distribution of the carbides. Moreover, the addition of nickel to HCrWCI increased fracture toughness and reduced the wear rate.