NbC Addition Research Articles

Magnetic Flux Penetration into Polycrystalline Superconducting (Bi,Pb)2Sr2Ca2Cu3O10 + xCeramics Containing Additions of Inorganic Compounds

The magnetic flux distribution in superconducting (Bi,Pb)2Sr2Ca2Cu3O10 + x ceramics containing small (0.05–0.3 wt %) additions of ultrafine HfN, Ta3N5, Si3N4, NbC, TaC, and SiC was studied by magneto-optic imaging and scanning Hall magnetometry. The ceramics were prepared by mixing (Bi,Pb)2Sr2Ca2Cu3O10 + x powder with ultrafine additions, followed by pressing and sintering at 840°C for 10 h. The samples were found to differ in magnetic flux penetration and trapping. The critical current density in the samples was determined as a function of temperature and magnetic field.

Effect of Nanocrystalline Powders on the Structure and Properties of Dispersion-Hardened Alloy TiC – 40% KhN70Yu

This article examines aspects of the effect of nanocrystalline powders of ZrO2, Al2O3, W, WC, WC–Co, NbC, and Si3N4 on the combustion, structure, and physical and physico-mechanical properties of new dispersion-hardened electrode alloy TiC – 40%KhN70Yu. This heat-resistant hard alloy, based on titanium carbide and a nickel alloy, was obtained by self-propagating high-temperature synthesis (SHS). It is shown that the addition of a nanocrystalline powder decreases combustion rate, with the magnitude of the reduction depending on the specific surface of the addition. It was determined that the structure of the synthesis products is modified appreciably by introducing a mixture of nanocrystalline powders into the initial charge. Here, additions of ZrO2 and NbC have a positive effect on the main physico-mechanical characteristics of the alloy (strength, hardness, fracture toughness). Nano-powders of Al2O3 and Si3N4 have a negative effect on the alloy's physico-mechanical properties. The addition of WC–Co increases the flexural strength of the material, while the addition of W and WC increases its fracture toughness.

Optimization of NbC Concentration in (Bi,Pb)2Sr2Ca2Cu3O10 + x Superconducting Ceramics Using Multifractal Formalism

The microstructure effect on the superconducting properties of (Bi,Pb)2Sr2Ca2Cu3O10 + x ceramics containing different additions of nanocrystalline NbC powder was analyzed using information interpretation of multifractal formalism. By introducing NbC additions, the midpoint transition temperature Tc of the ceramics can be raised by more than 10 K. The optimal NbC content evaluated with the use of the multifractal parametrization methodology is 0.35 wt %. The corresponding increase in Tc may attain 12–16 K. The crystallite and pore substructures in the ceramics are found to be closely related. The information approaches are shown to have great potential for structural characterization of superconducting materials and optimization analysis of property–structure–composition relationships.

Effect of RSP and NbC addition on microstructural evolution of Fe–40wt.%Ni alloys

Effect of rapid solidification processing (RSP) on Fe–40wt.%Ni alloys with and without NbC addition has been studied using TEM with focuses on the evolution of precipitates, dislocation, cavity, etc. RSP has been found to refine and stabilize the precipitates. Compared to the specimens of ingot metallurgy, the precipitates produced by RSP are found to be very stable up to 1400 °C.

Microstructure of Ti(CN)–WC–NbC–Ni Cermets

An investigation of the microstructural evolution and dissolution phenomena in a Ti(C0.7N0.3)–xWC–yNbC–20Ni system is reported. In Ti(C0.7N0.3)–yNbC–20Ni systems, a phase separation occurs between the Ti(CN) core and the (Ti,Nb)(CN) rim phases when the system contains >15 wt% NbC. This phase separation results from the increased misfit between the cores and the solid‐solution rim phases with the addition of NbC. Based on data obtained from a previous study and compositional analyses of the rim structure of the Ti(C0.7N0.3)–yNbC–20Ni system, the average dissolution rates of WC and NbC appear to be approximately the same with respect to that of Ti(CN), under given sintering conditions (1510°C for 1 h). In addition, compositional changes in the rim structure of the Ti(C0.7N0.3)–xWC–yNbC–20Ni system are compared with those for a Ti(C0.7N0.3)–xWC–20Ni system to explain the effect of NbC on WC dissolution in the Ti(C0.7N0.3)–WC–NbC–Ni system. The presence of NbC in the Ti(C0.7N0.3)–xWC–20Ni system is found to suppress the dissolution of WC.

Effect of fine-particle NbC additions on the structure and superconducting properties of (Bi, Pb)2Sr2Ca2Cu3O10+x ceramics

(Bi,Pb)-2223 superconducting ceramics prepared by heat treatment at 840°C and containing 0.1 to 0.5 wt % fine-particle NbC additions were characterized by microstructural analysis, x-ray diffraction, and magnetic susceptibility measurements. The introduction of 0.1 wt % NbC was found to raise the 77-K zero-field critical current density by a factor of 2 to 3, reduce the superconducting transition width, and slightly increase T c .

Hardmetals star at South Africa's PM symposium

Functionally graded cemented carbides (FGCCs) usually have a coarse-grained surface layer. In order to refine the grain size of WC and to improve the mechanical properties, VC and NbC as grain growth inhibitors, were added to WC–6Co FGCCs. The grain growth kinetics of WC was investigated, and both the room temperature and high temperature mechanical properties were tested. The results show that the additions of NbC and VC reduce the thickness of the gradient layer in FGCCs. The addition of VC reduces the thickness of the gradient layer by half, while that of NbC is less effective. The additions of NbC and VC refine the grain size by suppressing the adsorption/desorption processes of WC grains in Co phase during the pre-sintering and the carburizing processes, and VC is more effective than NbC. The addition of NbC increases the transverse rupture strength of FGCCs, because of the fine microstructure, and the solution strengthening in Co phase. Both the additions of NbC and VC increase the high temperature hardness of FGCCs due to improved oxidation resistance, more homogeneous and finer microstructures.

Effect of high temperature and sub-ambient treatments on the matrix structure and abrasion resistance of a high-chromium white iron

The addition of NbC to high chromium white cast irons (WCIs) has potential to improve component wear lives in mining and ore beneficiation environments, due to the combined presence of Cr-rich and niobium carbides. While the effect of chromium carbide volume fraction (Cr-CVF) on abrasion performance of plain-Cr WCIs is well understood, its effect on NbC-bearing WCIs is unknown. This work studies the effect of Cr-CVF on high-stress abrasion of this newer class of dual-reinforced high-Cr WCIs, using the ball mill abrasion test with quartzite and basalt. The alloys cover a wide range of Cr-CVF, from M7C3-free NbC-reinforced steel to hyper-eutectic WCI. Bulk hardness increased linearly with Cr-CVF, at a rate of 3.9 HV per 1% Cr-CVF. In basalt, abrasion resistance increased linearly with Cr-CVF, at an average life improvement rate of 24% per 1% Cr-CVF. This confirms that performance is maximized by increasing Cr-CVF even in the presence of substantial volumes of cubic carbides. In quartzite the trend is again linear up to 30 vol% M7C3 (3.7% life increase per 1% Cr-CVF), but the hyper-eutectic alloy shows poorer resistance than slightly hypo-eutectic alloy. SEM studies of the worn surfaces demonstrate that micro-fracture of the hard carbides was the controlling damage mechanism. Primary M7C3 was observed to suffer fragmentation in high-stress abrasion in quartzite, confirming the expectation from the quantitative trend.

Microstructural Development and Sintering Kinetics in Ceramic Reinforced High Speed Steel Metal Matrix Composites

Studies were made of sintering kinetics and micro-structural development when additions of either TiC or NbC were made to a sintered M3/2 high speed steel. Sintering occurred by a supersolidus liquid phase mechanism with diffusion controlled solution-reprecipitation as the predominant sintering mechanism, except in the case of TiC based composites where a much slower, unidentified, liquid phase sintering reaction occurred. Both ceramic carbide additions were found to raise the temperature required to sinter to full density but they also increased the width of the ‘sintering window’ and restricted the formation of the coarse carbide grain boundary films and eutectics normally produced by oversintering in M3/2 high speed steel. These effects were related to changes in the alloy composition and phase equilibria caused by interaction between the steel and carbide additive. In the case of the TiC composite, some TiC particles were retained but their solution into the steel caused the M6C matrix carbides to be replaced by a titanium/vanadium containing MC carbide. Conversion of NbC into a more complex alloyed MC carbide containing both vanadium and molybdenum took place in the NbC based composite. PM/0747

Heat Treatment Response of Sintered M3/2 High Speed Steel Composites Containing Additions of Manganese Sulphide, Niobium Carbide, and Titanium Carbide

Abstract Metal matrix composites based on a sintered M3/2 high speed steel (HSS) and containing either single additions of TiC, NbC, or MnS particles or combined additions of MnS + TiC or MnS + NbC were sintered to full density and subjected to a conventional hardening heat treatment cycle of austenitisation, quenching, and double tempering. Relatively poor hardnesses and strengths were obtained in any composites that contained MnS particles, principally because of the weakening effects of MnS particles in the structure but also as a result of decarburisation of the steel matrix when oxygen introduced by the MnS particles reacted with carbon. Composites that contained TiC were changed in structure so that matrix M6C carbides were replaced by the less soluble MC carbide. They consequently showed slightly reduced hardening response compared to the baseline M3/2 HSS after heat treatment. Ball milling was necessary in powder mixtures that contained NbC to break up particle agglomerates. The resultant fine gra...

NbC粒子を分散させたNi-Cr-Fe肉盛合金の時効析出

Isothermal aging at 773∼1023 K has been carried out to investigate precipitation in low Fe, high Cr, Ni-base overlay weld alloys which were formed on a mild steel by plasma powder welding process. In this work, effects of NbC addition on precipitation process were studied by hardness measurements, X-ray diffraction and metallographic methods.It was found that the NbC dispersed alloy was higher in age-hradenability than the NbC-free alloy in the as-welded condition and both alloys had a peak hardness followed by slowly softening during aging. In the NbC-free alloy, nodular precipitates appeared at grain boundaries and then continuous precipitation of α′-phase occurred within the matrix (γ-phase). However, in the NbC dispersed alloy, any precipitaion has not occurred except for continuous precipitation of α′ in the matrix. It was considered that such different precipitation phenomena have been caused by niobium atoms dissolved in the matrix. Age hardening observed is due to the continuous precipitation of α′ particles and the softening is caused by their coarsening.

超硬合金に対する添加炭化物としてのＴａＣとＮｂＣの役割の差

The effect of TaG or NbC addition on some mechanical properties of WC-β-Co and WC-β(N)-Co alloys (β, WC-TiC solid solution; variable β(N), WC-TiC-TiN s.s.) was investigated to make clear the difference between TaC and NbC as the additional carbides.It was found that the effect of TaC or NbC addition was nearly in the same way, so far as transverse-rupture strength, hardness and high temperature deformation were concerned. However, it was emphasized that the TaC addition was more effective than the NbC addition to improve the oxidation resistance of the alloys.