VC Particles Research Articles

<i>In situ</i> Synthesis of Ceramic Phase Reinforced Fe-Based Alloy Surface Coating by PTA

The in-situ ceramic phases reinforced Fe-based surface coating had been produced by prepared high-carbon ferrochromium, ferrovanadium and graphite power on 20g steel through plasma transferred arc weld-surfacing process(PTA). The microstructure and properties were investigated by means of optical microscopy(op), scanning electron microscopy(SEM), X-ray diffraction(XRD) and microhardness meter. The results showed that the substrate and the coating formed good metallurgical bonding.The microstructure of coating consists of primary M7C3 carbide and eutectic structures[M+γ′+M7C3+VC]. The primary hexagonal (Fe,Cr,V)7C3 with larger size evenly distributed in coating and the fine VC particles were globular shape. The microhardness appeared reasonable distribution from substrate to the top ,which ensured that the materials had good abrasive wear resistance.

Characterization of nano-structured W-, Ti-, V-, and Zr-doped carbon films

Bonding structure of carbon and metal as well as nanostructural changes of metal-doped amorphous carbon films (a-C:Me) were investigated depending on metal type (W, Ti, V, and Zr), concentration (<25 at.%) and annealing temperature (< 1300 K, except W: < 2800 K). Pure C films exhibit ~ 2 nm distorted aromatic and graphene-like regions. Both increase in size with annealing. After deposition the metals have carbide-like bonding and are mainly distributed atomically disperse in an amorphous environment. Annealing leads to the formation of carbide crystallites (TiC, VC, ZrC, WC, W 2C, and WC 1 − x ) of several nanometers. The VC particles reach the largest size up to 1300 K. All metal dopings reduce the erosion rate against oxidation (expect V) and hydrogen impact.

Reactive sintering mechanism of Ti + Mo2C and Ti + VC powder compacts

TiC reinforced Ti-matrix composites have been synthesized successfully by reactive sintering of Ti-1.5%Fe-2.25%Mo (wt%) powder compacts with addition of Mo2C and VC particles. The reactions for the formation of TiC particles start at 600 °C, but the distribution of TiC particles and the densification behavior in the two compacts are significantly influenced by the metal carbides (Mo2C or VC). The compact with addition of Mo2C has a relative density of 98% after sintering at 1300 °C for 1.5 h, but TiC particles are agglomerated in the Ti matrix. The compact with addition of VC has a relative density of about 91% after sintering at 1300 °C for 1.5 h, but TiC particles distribute more homogenously in the Ti matrix. Different TiC particle distribution and densification behaviors are attributed to the reaction rates between Ti and metal carbides and the subsequent diffusion process.

Correlation of Microstructure, Hardness, and Fracture Toughness of Fe-Based Surface Composites Fabricated by High-Energy Electron Beam Irradiation with Fe-Based Metamorphic Alloy Powders and VC Powders

Iron-based surface composites were fabricated with Fe-based metamorphic alloy powders and VC powders by high-energy electron beam irradiation, and the correlation of their microstructure with hardness and fracture toughness was investigated. Mixtures of metamorphic powders and VC powders were deposited on a plain carbon steel substrate, and then the electron beam was irradiated on these powders without flux, to fabricate surface composites. The composite layers 1.3 to 1.8 mm in thickness contained a large amount (up to 47 vol pct) of hard Cr2B and V8C7 particles formed in eutectic colony regions and inside colonies, respectively. The hardness of the surface composites was approximately 2 to 4 times greater than that of the substrate because of Cr2B and V8C7 particles. According to the microfracture observation of the composite fabricated with mixing 30 wt pct VC powders, microcracks initiated at coarse V8C7 particles ins inside colonies as well as at Cr2B particles in colony regions, and were connected with other microcracks in a zigzag shape. Thus, it showed a higher fracture toughness and hardness twice as high as the composite fabricated without mixing VC powders.

Microstructure and Wear Properties of In Situ Synthesized VC Carbide Reinforced Fe-based Surface Composite Coating Produced by Laser Cladding

In situ synthesized VC carbide particles reinforced Fe-based composite coating was fabricated by laser cladding on steel substrate using ferrovanadium (Fe–V) alloy and graphite as the precursor powders. The phase structure and microstructure of the clad layer were investigated by means of X-ray diffraction analysis, scanning electron microscopy, and electron probe microanalysis. Results showed that uniformly distributed VC particles with the radial dendrites shape could be synthesized by the in situ reaction. The hardness and wear properties of the clad coatings were greatly improved due to the presence of VC particles in comparison with the substrate.

Contribution of Soft Copper Particle on Work Hardening Behavior in Ferritic Iron

Tensile tests were performed for two kinds of model alloys containing soft Cu particles or hard VC particles. Work hardening rate was obviously smaller in the Cu particle dispersion steel than in the VC particle dispersion steel. TEM observation for the cold-rolled specimens revealed the different dislocation arrangement; high density dislocations are introduced around the carbide particles in the VC steel, while dislocations are less accumulated in the Cu steel because dislocations can pass through Cu particles during plastic deformation.

Effect of initial particulate and sintering temperature on mechanical properties and microstructure of WC–ZrO 2–VC ceramic composites

Owing to improving the mechanical properties of cemented carbides in high speed machining fields, a new composite tool material WC–ZrO 2–VC (WZV) is prepared from a mixture of yttria stabilized zirconia (YSZ) and micrometer VC particles by hot-press-sintering in nitrogenous atmosphere. Commercial WC, of which the initial particle sizes are 0.2 μm, 0.4 μm, 0.6 μm and 0.8 μm, is mixed with zirconia and VC powder in aqueous medium by following a ball mill process. The sintering behavior is investigated by isostatic pressing under different sintering temperature. The relative density and bending strength are measured by Archimedes methods and three-point bending mode, respectively. Hardness and fracture toughness are performed by Vickers indentation method. Microstructure of the composite is characterized by scanning electron microscopy (SEM). The correlations between initial particles, densification mechanism, sintering temperature, microstructure and mechanical properties are studied. Experimental results show that maximum densification 99.5% is achieved at 1650 °C and the initial particle size is 0.8 μm. When temperature is 1550 °C and particle size is 0.4 μm, the optimized bending strength (943 MPa) is obtained. The best hardness record is 19.2 GPa when sintering temperature is 1650 and particle size is 0.8 μm. The indention cracks propagate around the grain boundaries and the WC particles fracture, which is associated with particle and microcrack toughening mechanism.

Investigation of surfacing electrode with high hardness based on lath martensite

Based on lath martensite and carbides, the surfacing electrode with high hardness was developed owing to adding graphite, ferrotitanium (Fe–Ti), ferrovanadium (Fe–V), etc., in electrode coating. Although the content of carbon element in deposited metal is very high, the lath martensite is generated in welded metal because TiC–VC particles formed by means of high temperature arc metallurgic reaction. The mechanism of crack resistance and wearability were systemically studied by cracking test and wear test. The results show that the hardness of surfacing metal is above 60 HRC. Surfacing layers have fine crack resistence and high wearability. The mass loss of surfacing metal in unit area is only one-eighth comparing to EDZCr-C-15 electrode. It also greatly excels EDZCr-C-15 in crack resistence. Carbide particles formed by arc metallurgic reaction are dispersedly distributed in matrix structure. In the course of wear, carbides embedded in lath martensite provide a composite effect of hardness and toughness.

Effect of addition of V and C on strain recovery characteristics in Fe–Mn–Si alloy

Shape recoverable strain, recovery stress and low-temperature stress relaxation characteristics in an Fe–17Mn–5Si–10Cr–4Ni (0.08C) alloy and an Fe–17Mn–2Cr–5Si–2Ni–1V (0.23C) alloy have been studied by means of X-ray diffraction, transmission electron microscopy and measurement of recoverable strain and recovery stress. The amount of stress-induced ɛ martensite under tensile deformation at room temperature, recoverable strain and recovery stress are increased obviously with addition V and C in Fe–Mn–Si alloy, which is owing to the influence of addition V and C on strengthening austenitic matrix. Addition of V and C in Fe–Mn–Si alloy is evidently effective to reduce the degree of low-temperature stress relaxation, for the dispersed VC particles 50–180 nm in size precipitated during annealing restrain the stress induced martensitic transformation.

A comparative study of precipitation effects in Ti only and Ti–V Ultra Low Carbon (ULC) strip steels

Two ULC steel grades were investigated, one based on combined vanadium and titanium additions and the other based on titanium only additions. It has been established that TiC formation during interphase precipitation retards grain growth of the {111} texture grains during continuous annealing and hence positively affects the r value of the Ti only steel. The formation of newly formed TiC precipitates on dislocations during continuous annealing has been found to result in an increase of the yield strength in both steel grades, as the annealing temperature is increased. It is also confirmed that VC particles formed during the coiling process dissolve during the continuous annealing cycles. Suitable continuous annealing cycles can be adopted to produce high formable steels with a bake hardening potential using the beneficial effects of combined Ti–V additions.

Study of Surface Alloying of TiC, TiB2 and VC with Carbon Steel Using High Energy Electron Beam Irradiation

Surface alloying using TiC, and VC ceramic particles on carbon steel has been performed using high voltage electron beam. Each type of ceramic particles was mixed with flux of Al and in 1 to 4 ratio. The microstructures of the surface alloyed layers consisted of melted region, interface region. heat affected region and the unaffected matrix. The surface layer of the TiC surface alloyed had a cubed primary and a eutectic type of TiC. in surface layer of surface alloyed were incompletely melted with particles as observed before the alloying. On the surface layer of the VC surface alloyed, very well defined cell structure was observed with VC on the cell boundary. In addition, ~50 nm in diameter VC particles in high density were ubiquitous in the matrix. Those fine VC particles prominently improved the hardness and wear resistance of the surface layer of the VC surface alloyed.

In situ production of Fe–VC and Fe–TiC surface composites by cast-sintering

Abstract Using a new cast-sintering technique, iron-base surface composites reinforced by VC and TiC particles which were produced in situ and consisting of self-lubricant graphite and chromium-carbide, were sintered on the surface of cast steel during casting. The structure and composition of the surface composites were studied with the help of a SEM, an electron probe and XRD. From the outside in of the iron-based surface composites, the concentration of V and Ti was relatively stable and consistently retained a high level, while the concentration of Cr and Ni took on a gradient distribution and decreased gradually. The fine particles of VC and TiC measuring between 1 and 3 μm in diameter were uniformly dispersed in their matrices, and there was a perfect metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping with a heavy load, the Fe–VC and Fe–TiC surface composites offer virtually unique wear-resistance.

Use of phosphide additions to promote liquid phase sintering of stainless steel: H.Preusse, J.D.Bolton. (University of Bradford, Bradford, UK.) Powder Metall., vol 42, no 1, 1999, 51–62

Composite precursor powders for liquid phase sintering were obtained by coating WC and VC particles. The Ni–B coating was deposited onto the carbide nucleus by electroless processes in alkaline and acid bath, both based on nickel chloride. In order to observe structural modifications, the composite powders were heated in an argon atmosphere, during 5 min, at different temperatures in the range 400–1200°C. When heating, Ni and Ni3B phases progressively formed within the amorphous Ni–B layer; then, Ni was retained as a unique crystalline phase. Sintering was performed in a temperature range of 1035–1200°C where a eutectic liquid phase is expected in the Ni–B system. The wetting behavior of the molten coating depended on the characteristics of the carbide skeleton. Thus, the segregation of the matrix toward the outer surfaces occurred when sintering VC and it adversely affected densification. In the case of WC sinters, the same effect was found at relatively high temperatures (1150–1200°C) while at lower temperatures (1035–1100°C) the metal matrix was uniformly distributed and the densification degree were between 91 and 93%.

Electroless Ni–B coated WC and VC powders as precursors for liquid phase sintering

Composite precursor powders for liquid phase sintering were obtained by coating WC and VC particles. The Ni–B coating was deposited onto the carbide nucleus by electroless processes in alkaline and acid bath, both based on nickel chloride. In order to observe structural modifications, the composite powders were heated in an argon atmosphere, during 5 min, at different temperatures in the range 400–1200°C. When heating, Ni and Ni 3B phases progressively formed within the amorphous Ni–B layer; then, Ni was retained as a unique crystalline phase. Sintering was performed in a temperature range of 1035–1200°C where a eutectic liquid phase is expected in the Ni–B system. The wetting behavior of the molten coating depended on the characteristics of the carbide skeleton. Thus, the segregation of the matrix toward the outer surfaces occurred when sintering VC and it adversely affected densification. In the case of WC sinters, the same effect was found at relatively high temperatures (1150–1200°C) while at lower temperatures (1035–1100°C) the metal matrix was uniformly distributed and the densification degree were between 91 and 93%.

Structure and wear-resistance of an Fe-VC surface composite produced in situ

An iron base surface composite, reinforced with VC particles, with a thickness of 3–4 mm, consisting of (Fe,Cr) 7C 3 and graphites on a Martensite matrix, was produced in situ on a surface of cast steel by means of metal-coated casting. The structure and wear-resistance of the Fe-VC surface composite were studied with the help of a SEM, electron probe and XRD. From the outside in, the quantity of VC particles and the concentration of alloy elements took on a gradient distribution and decreased gradually. In the subsurface layer of the surface composite, the volume fraction of VC particles was up to 39.5% with particle sizes in the range 1–3 μm. The Fe-VC surface composite possesses great wear-resistance under the condition of dry slipping with a heavy load.

Corrosion behavior of Ni-Cr weld overlay alloys with dispersed carbide particles in sodium chloride solution

Ni-Cr weld overlay alloys with dispersed carbide particles were prepared by a plasma transferred arc welding process. The corrosion behavior of the 40 vol% carbide/Ni-Cr materials was studied in sodium chloride solution by electrochemical techniques, scanning electron microscopy, x-ray diffraction, and electron dispersive spectroscopy. The materials under investigation were powder blends of Ni-50 mass % Cr powder mixed with NbC, TaC, TiC, WC, O3C2, or VC. The NbC, TaC, TiC, and WC particles partially dissolved in the molten alloy, causing the crystallization of M23C6. Blends with Cr3C2 and VC particles produced the crystallization of M7C3, VxCryCz and M23C6. The VC/Ni-Cr alloy combination caused preferential localized corrosion and the carbide remained as VxCryCz. The Cr3C2/Ni-Cr alloy combination became studded with the Cr-Cl corrosion product compound. With the WC/Ni-Cr alloy combination, the WC particles became oxidized and corrosion product spread over the matrix. Other carbides were not oxidized, but the matrix of the alloys with these dispersed particles did become covered with Cr-rich corrosion products. The NbC/Ni-Cr material exhibited the best corrosion resistance.

各種金属炭化物の溶融アルミニウムへの分散挙動およびＴｉＣ粒子強化アルミニウム複合材料の機械的性質

The dispersion behavior and the interfacial reaction of various carbide particles in pure aluminum matrix composites made by a melt stirring method were observed and mechanical properties of TiC particulate aluminum matrix composites were also measured. WC particles decompose completely in molten pure aluminum during the stirring. Although NbC and VC particles can be incorporated into molten Al-1mass%Mg alloy, most of them decompose. Among various carbide particles, TaC, ZrC and TiC particles show high stability and uniform distribution, even though minute amounts of Al3Zr and Al3Ti are observed in the ZrC/Al and TiC/Al systems, respectively. The effect of processing temperature on mechanical properties of TiC/Al composites was evaluated. The properties are rarely affected by the processing temperature when the temperature is ranging from 1073K to 1273K. The strength of TiC/Al-Mg (Mg: 1-5mass%) composites is higher than that of a TiC/pure Al composite. The increment in strength by dispersing TiC particles becomes smaller with an increase in the strength of the matrix alloy for TiC/Al- (Cu, 5mass%Cu-Mg) composites. The strength increases and the elongation decreases with increasing volume fraction of TiC particles up to 17vol%.

Effects of magnesium and long-term ageing on intragranular precipitation in Fe-Cr-Ni-Mn-Mo-V-Nb superalloy

Adding a suitable amount of magnesium to Fe-Cr-Ni-Mn-Mo-V-Nb alloy decreases largesized intragranular lamellae and dentritic lamellae of M23C6, promotes the loss of the coherent relationship between intragranular small M23C6 block and mother phase and causes M23C6 lamellae to become spherical. During long-term ageing, intragranular fine VC precipitate as well as VC particles conglomerate. A mechanism by which some dislocations can cut across the VC particles is suggested. Increase in misfit between VC and austenite is about 1% at 160 p.p.m. magnesium content or after long-term ageing for 1000 h at 650°C. The misfit between VC ribbon precipitated along dislocations and matrix is smaller than that between the VC particles near the ribbons and matrix.

Elevated-temperature heavy-ion damage in (Co 0.78Fe 0.22) 3V ordered alloy

Irradiation-induced changes in microstructure were studied in a (Co 0.78Fe 0.22) 3V long-range-ordered alloy after bombardment with 4 MeV nickel ions at temperatures from 843 to 1023 K and damage levels from 10 to 70 dpa. Small cavities and Frank loops were developed, and particles of pre-existing VC phase were redistributed by the irradiation. Long-range order was retained under all irradiation conditions, but domain size was effectively reduced by the Frank loops that served as antiphase boundaries. Simultaneous injection of helium at a rate of 3 at.ppm/dpa and deuterium at a rate of 12 at.ppm/dpa during irradiation produced gas bubbles in the grain boundaries, increased the dislocation and cavity densities, reduced the mean cavity size, but had little effect on the ordered domain size or the redistribution of VC particles. Even with injected gases, swelling remained below 0.25%. It is deduced that swelling did not reach the rapid bias-driven state because the critical cavity size was large.

Weld microstructure of (Ni, Fe)3(V,Ti) long-range-ordered alloy

The microstructure of gas tungsten arc (GTA) welds of a (Ni, Fe)3 (V, Ti) long-range-ordered alloy has been investigated. Crack-free welds were produced in which the heat affected zone (HAZ) and fusion zone were disordered and softened. A post-weld heat treatment increased the hardness of both zones by reordering the structure. The reordering treatment produced additional hardening in the fusion zone due to precipitation of small VC particles on grain boundaries and matrix dislocations.