Effect Of NbC Research Articles

Microstructure and tribological properties of in-situ TiC reinforced Ti2AlNb-based coatings by laser cladding

The TiC reinforced Ti2AlNb-based coatings were fabricated on the surface of Ti-6Al-4V using Ti, Al, and Nb powder mixtures with different NbC addition (0, 1.25, 2.5, and 5 wt%) by laser cladding to improve the mechanical behavior of Ti-6Al-4V. The effects of NbC on the morphology, microstructure evolution and mechanical properties of the TiC/Ti2AlNb coatings were studied systematically. Results revealed that the matrix phases of all coatings were mainly composed of lamellar O phase and B2 phase. TiC in situ formed effectively refined grains, in which the length of the B2 grains was reduced from 205.36 μm to 25.31 μm, and the O phase was reduced from 5 μm to <1 μm as the NbC addition increased from 0 wt% to 5 wt%. Mechanical properties illustrated that the coating with the NbC addition of 2.5 wt% had the highest microhardness with 575.6 HV0.2 and the smallest volume loss with 0.66 mm3 due to fine grain strengthening and dispersion strengthening of TiC. Compared to the Ti-6Al-4V substrate, the microhardness was increased by 1.64 times, and the volume loss was reduced to 30 %. Nevertheless, the mechanical properties of the coatings will exhibit a downward trend by adding excessive NbC (5 wt%), and the coarsening of the TiC could be used to explain this slight decrease.

Effect of NbC and VC carbides on microstructure and strength of high-strength low-alloyed steels for oil country tubular goods

High-strength low-alloyed (HSLA) steels for oil country tubular goods (OCTGs) are usually microalloyed with niobium (Nb) and vanadium (V). In this work, the microstructure and strength of HSLA steels with different Nb and V contents were studied with the purpose of investigating the role of NbC and VC carbides. The results showed that NbC carbides were responsible for restraining the growth of prior austenite grains, and when the austenitizing temperature was below 910 °C, it has been found that the prior austenite grain size was similar in steels with 0.02 and 0.006 wt% Nb addition. VC carbides could impede dislocation annihilation and refine Cr-rich carbides and martensitic blocks during tempering. Moreover, VC carbides mainly contributed to the tempering softening resistance so that the V-bearing steels exhibited a higher strength than the V-free steel after tempering at 690 °C–730 °C. To illustrate the high tempering softening resistance of V-bearing steels, the changes in various strengthening contributions induced by V addition were quantitatively evaluated. The calculation results indicated that the main reason for the high tempering softening resistance of V-bearing steels was precipitation strengthening by nanosized VC carbides, in contrast to dislocation strengthening, substructure strengthening, and precipitation strengthening due to the refinement of Cr-rich carbides.

Effect of NbC on the microstructure, mechanical properties, and oxidation resistance of Ti(C,N)-based cermets

Abstract A comprehensive investigation of the effects of NbC on the microstructure and properties of Ti(C,N)-based cermets has been performed. Cermet samples were obtained via liquid-phase sintering under the guidance of thermodynamic calculations, and the amount of NbC was varied. The results showed that when the NbC content exceeded 12 wt.%, a hard phase with an NbC core appeared due to the lattice mismatch between the core and rim. NbC was not completely consumed by dissolution and precipitation, causing it to form a residual NbC core. As the NbC content increased, the grain size was refined, and the hardness of the cermet increased, but the fracture toughness decreased. When NbC was introduced into the cermet, a relatively dense protective layer was formed on the surface during oxidation, which restricted the diffusion of oxygen and improved the oxidation resistance of the cermet.

Effect of NbC on the microstructure, mechanical properties, and oxidation resistance of Ti(C,N)-based cermets

Abstract A comprehensive investigation of the effects of NbC on the microstructure and properties of Ti(C,N)-based cermets has been performed. Cermet samples were obtained via liquid-phase sintering under the guidance of thermodynamic calculations, and the amount of NbC was varied. The results showed that when the NbC content exceeded 12 wt.%, a hard phase with an NbC core appeared due to the lattice mismatch between the core and rim. NbC was not completely consumed by dissolution and precipitation, causing it to form a residual NbC core. As the NbC content increased, the grain size was refined, and the hardness of the cermet increased, but the fracture toughness decreased. When NbC was introduced into the cermet, a relatively dense protective layer was formed on the surface during oxidation, which restricted the diffusion of oxygen and improved the oxidation resistance of the cermet.

Grain growth and strengthening mechanisms of ultrafine-grained CoCrFeNiMn high entropy alloy matrix nanocomposites fabricated by powder metallurgy

Ultrafine-grained CoCrFeNiMn high entropy alloy matrix nanocomposites reinforced by nanoparticles were fabricated by thermomechanical consolidation of high energy mechanically milled powders. TiO(C) nanoparticles in the CoCrFeNiMnTi0.15 sample make the FCC matrix grains clearly finer than those in the CoCrFeNiMnNb0.1 sample with NbC and (Cr, Mn)3O4 nanoparticles (average grain size: 503 ± 184 vs 778 ± 274 nm). Quantitative analysis reveals that drag force for grain growth during consolidation in the CoCrFeNiMnTi0.15 sample is higher than that in the CoCrFeNiMnNb0.1 sample due to the higher Zener force from the TiO(C) nanoparticles. The microstructural difference renders the yield strength of the CoCrFeNiMnTi0.15 sample to be almost 50% higher than that of CoCrFeNiMnNb0.1 sample (1243 vs. 831 MPa). To elucidate this phenomenon, the strengthening mechanisms are systematically analyzed and a model considering grain boundary dislocation emission is established to account for the interaction between grain boundary strengthening and nanoparticle strengthening. This model explains the different effects of NbC, (Cr, Mn)3O4 and TiO(C) nanoparticles, and estimates the yield strength better than the existing models.

Reactive Fabrication and Effect of NbC on Microstructure and Tribological Properties of CrS Co-Based Self-Lubricating Coatings by Laser Cladding.

The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS2, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS2 and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr23C6, and CoCx. Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS2) were 587.3 HV0.5, 0.426, and 5.61 × 10−5 mm3/N·m, respectively.

The effect of NbC on mechanical properties and fracture behavior of WC–10Co cemented carbides

In an attempt to improve the understanding of fracture behavior of brittle cemented carbides with NbC addition, a detailed study was conducted with the main goal of characterizing the fracture character and crack growth mode. The study showed that NbC had a significant influence on the mechanical properties of WC–10Co alloys. The maximum hardness and transverse rupture strength were observed when the NbC content was 1wt.%. However, with the further addition of NbC, the TRS and fracture toughness degraded. The fracture origin was cleavage fracture from coarse WC when the addition of NbC was 1wt.% and 2wt.%. But in the materials with 3wt.% and 4wt.% NbC addition, the brittle (W,Nb)C solid solution increased considerably, and this leaded to a low stress brittle fracture. In the WC–10Co alloy, intergranular growth was the dominant mode of crack propagation. The ratio of transgranular crack increased because of the grain refinement of WC and solid strengthen effect of binder by NbC, and the transgranular crack in brittle (W,Nb)C solid solution increased when NbC content was increased to 3wt.% and 4wt.%.

The Effect of NbC Precipitates and Nb in Solid-Solution on the Phase Transformation Kinetics in High-Purity Fe-C-Mn-Nb Alloys

The precipitation of NbC in austenite is an important mechanism for improving the strength of steel because NbC-precipitates are known to decrease the ferrite grain size during the subsequent phase transformations upon cooling. The effect of the interaction between niobium (Nb) in solid solution and NbC-precipitates on the austenite-to-ferrite phase-transformation kinetics is not entirely clear. We study a high-purity Fe-C-Mn-Nb alloy cooled at different rates. Different annealing times at 850°C were applied to create different number densities and sizes of the NbC-precipitates in order to study the effect of NbC precipitation on the transformation kinetics. The alloy that is used in this study has an atomic ratio of Nb:C=1.3:1. The fraction of ferrite is measured as a function of temperature during cooling by means of dilatometry. The ferrite grain size is measured by means of optical microscopy. The results are interpreted with thermodynamic and kinetic models.

Comparing metabolic effects of six different commercial trivalent chromium compounds

Recent reports provide cogent evidence that the average individual becomes chromium deficient with age. Unfortunately, chromium deficiency is strongly associated with many aspects of the Metabolic Syndrome, including insulin resistance and type 2 diabetes. Since replacement of chromium, per os, often ameliorates many deleterious manifestations associated with insulin resistance and diabetes, it is not surprising that many different, commercial trivalent chromium compounds are available on the market. However, previous reports have shown that the form of trivalent chromium (negative charges) can influence effectiveness markedly. We compared various commercial forms of trivalent chromium commonly used alone or in formulations, to examine whether they are equally effective and non-toxic. In the first study, five different chromium products were examined – citrate, amino acid chelate (AAC), chelavite, polynicotinate (NBC), and nicotinate. In the second study, effects of NBC and picolinate were assessed. Results demonstrated that only chelavite and NBC improved insulin sensitivity, and only NBC decreased systolic blood pressure (SBP) significantly. In the second study, both picolinate and NBC significantly decreased SBP compared to control. NBC and picolinate decreased malonyldialdehyde concentrations (free radical formation) and DNA fragmentation in hepatic and renal tissues. No evidence of adverse effects was noted with any of the compounds tested. In conclusion, while all the trivalent chromium compounds tested seem safe, only three enhanced insulin sensitivity (NBC, chelavite, and picolinate) and only two decreased SBP significantly (NBC and picolinate). Furthermore, both NBC and picolinate were protective in lessening free radical formation and DNA damage in the liver and kidneys.

Model Alloys to Study the Solute Drag and Precipitation Effect on the Recrystallization Kinetics of Nb-Microalloyed Steels

A good combination of strength and toughness in HSLA steels can be achieved by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at low temperatures by either a solute drag or by a precipitation pinning (when bonded to C or N) effect. Both mechanisms result in improved mechanical properties due to grain size refinement of the transformed ferrite. In this study, 3 Nb-microalloyed model alloys were designed to investigate the solute drag and the precipitation effect separately. The first alloy, containing a stoechiometric ratio of Nb and C, was designed to study the retarding effect of NbC on the recrystallization behavior. A second alloy, containing Nb and only few ppm C, was casted in order to study the effect of Nb in solid solution. The two alloys were compared with a C-Mn reference alloy. The recrystallization behavior of the three alloys were compared by multi-hit torsion tests and double hit compression tests. The Nb-C and the Nb-very low C showed small differences in recrystallization behavior. These results show that Nb delays the recrystallization by a solute drag effect or by the formation of a very small amount of precipitates.

Effect of Mn on strain accumulation in Nb microalloying steels

High Mn is added in line pipe steels to strengthen them. Also, Mn lowers the phase transformation temperature, which is an advantage because it lowers the rolling temperature for grain size control. However, Mn retards the kinetics of precipitation of NbC in thermo-mechanical processing in Nb microalloying steels. In high-grade line pipe steels, the control of strain accumulation behavior is the key to the control of grain size. Strain accumulation can only be obtained when static recrystallization between passes could be suppressed. The effect of NbC precipitates on suppressing recrystallization has been widely investigated, mostly focusing on the Zener pinning of NbC on grain boundaries. However, it is applicable in large strain and long inter-pass time. In short inter-pass time, such as strip mill rolling, recrystallization behavior is controlled by the complicated interaction of precipitation with recovery and recrystallization. In this paper, the effect of Mn on strain accumulation during multi-pass strip mill rolling based on the interaction of precipitates with the activation energy of grain boundary migration and recovery, and the thermodynamics and kinetics of recrystallization are discussed systematically.

Effect of NbC and TiC precipitation on shape memory in an iron-based alloy

This paper examines the effects of TiC and NbC precipitation and prior cold rolling on the shape memory behaviour of an iron-based alloy. A precipitate-free alloy was used as a reference to investigate the relative contributions of prior-deformation and precipitation on shape memory. Heat treatment of the Nb- and Ti-containing alloys at 700 °C and 800 °C resulted in carbide precipitates between 120 nm and 220 nm in diameter. Bend testing of these samples showed a marginal increase in shape memory compared to the precipitate-free alloy. Under these conditions TiC precipitation exhibited slightly better shape memory than for NbC. However, this small increase was over-shadowed by the marked increase in shape memory that can be produced by subjecting the alloys to cold rolling followed by recovery annealing. When processed in this way, fine carbides are formed in the Ti- and Nb-containing alloys during the heat treatment. For particles >25 nm in diameter the shape memory is unaffected, but, it was found that small <5 nm particles have a detrimental effect on shape memory due to pinning of the martensite plates, thereby inhibiting their reversion to austenite. The optimum shape memory was observed in the precipitate-free alloy after cold rolling and recovery annealing.

Effects of TiC, TaC, WC, TaC-WC, NbC, and VC on grain refining of pure aluminum and its alloys

In order to investigate the effects of the grain refining of pure aluminum (99.99%) and its alloys (with copper, magnesium, zine, silicon, manganese, and nickel), powder of a carbide such as TiC, TaC, WC, TaC-WC, NbC and VC was added to the former metal or alloys. Chiolite was also added as a flux to prevent the oxidation of the carbide. The molten alloys containing the carbide and chiolite were thoroughly stirred in a crucible and slowly allowed to cool. The influences of remelting and holding of the alloys at a high temperature were investigated. The average diameters of the grains were measured in macro-and micro-structures of the specimens. Some of the specimens were investigated with X-ray micro-analyzer.The results obtained were as follows.(1) Powders of TiC, TaC, TaC-WC, NbC and VC were very effective in grain refining of pure aluminum and its alloys. The effects of TiC, TaC and TaC-WC were almost kept constant at a high temperature, and the growth of grains in size was not seen after holding at that temperature.(2) The effects of TiC, TaC, and TaC-WC were very remarkable as compared with other carbides. The effects of NbC and VC came second, and that of WC was the least.(3) Very effective agents for grain refining were obtained when the carbides were under the following conditions at the same time:(a) Large free energy for formation(b) Small density(c) Crystal structure of NaCl type and small size factor for aluminum.

Protection of Natural Rubber against Atmospheric Agents. I. The Effects of Nickel Dibutyldithiocarbamate Alone and in Combination with Protective Agents

Abstract Latex-rubber mixtures vulcanized with zinc diethyldithiocarbamate as accelerator show excellent resistance to sunlight if they contain 1.5–5 per cent of NBC. Combinations of protective agents which were tested contributed nothing to the protective effect of NBC alone as far as resistance to cracking is concerned; in fact, under some conditions they had an unfavorable influence. Only with respect to the maintenance of mechanical properties do these combinations have any noticeable protective effect, as do combinations of NBC with DNPD and with methyl di (tert.-butyl)phenol. However, such combinations should not be disregarded a priori, for it is possible that some of them would impart an appreciable increase of resistance to heat. In the present investigation, natural aging in darkness at ordinary temperature for twenty-four months was excellent, and this is at variance with the accelerated aging tests, except for the oxidizability measurements. The behavior of dry-rubber vulcanizates accelerated by mercaptobenzothiazole differs greatly from that of corresponding latex-rubber vulcanizates. Only NBC showed any protective effect against cracking; on the contrary, it promoted a rapid loss of the mechanical properties of vulcanizates when they were exposed to light or were stored in darkness. The action of heat or oxygen under pressure is still more striking from this viewpoint. By the concurrent action of structurizing agents, among which DPPD has been found to be the most effective, it is possible to attain a final protective effect which is manifest by a notable retardation of the appearance of cracks on exposure to light and by outdoor weathering, and at the same time, by a satisfactory retention of good mechanical properties during aging. Aging at ordinary temperature in darkness is likewise good, since the loss of tensile strength in two years was only 2–3 per cent. By way of comparison, a control vulcanizate, protected by PBN and stored under the same conditions, lost approximately 1 per cent of its tensile strength. Recent experiments indicate that some carbon blacks have a very favorable effect. This should make it possible to utilize simultaneously effective protection against cracking, maintenance of good mechanical properties during exposure to light and during aging in darkness, and increased resistance to heat. This remarkable resistance to exposure cracking and to cracking by light of rubber-carbon black vulcanizates indicates the possibilities in the practical application of combinations of NBC and DPPD. In the case of reinforced mixtures, the combined effect of a complex nickel compound, a structurizing agent, and a deactivating agent seems to be the most effective system. The choice of the structurizing agent is very important, as are also the proportions of all the agents. A later study will be concerned with establishing the best proportions from the viewpoint of obtaining satisfactory protection with the minimum quantities of these agents. Finally, it must always be kept in mind that there may be other protective agents which would make superior combinations with NBC or with other organic nickel complexes.