NbC Alloy Research Articles

Numerical Simulation Analysis of Temperature Distribution of NbC-Reinforced Ti-Based Composite Coating by Laser Cladding

In this article, three-dimensional numerical modeling of the laser cladding process by Ansys was proposed. The three-dimensional Gaussian heat source model was used to simulate the actual laser heat source to analyze the temperature distribution of the molten pool. The temperature distribution of the molten pool of TiAlSi + NbC coatings within different process parameters was obtained by simulation. To obtain finer simulation results, the thermophysical properties of TiAlSi + NbC powder and TiAlSi + NbC alloy were investigated, respectively. The temperature selection judgment mechanism, which is used to distinguish the powder and alloy elements, was built. The results showed that the laser power and laser scanning speed play a vital role in the temperature distribution along with the track width and the depth of the molten pool. The simulation values of the width and depth of the cladding layer under different processing parameters were obtained by using the temperature selection judgment mechanism and fitting. The results showed that the track width and depth had a positive correlation with the laser power, whereas they had a negative correlation with the laser scanning speed.

Thermodynamic modeling and computational predictions of NbC precipitation in Fe–Mn–Si-based shape memory alloys by the classical nucleation and growth theories

NbC precipitation in Fe–Mn–Si-based alloys is an effective method to improve the shape memory effect. In this study, the precipitation behavior was investigated using a thermodynamical model to understand the mechanism and optimize the precipitates for a better performance of Fe–Mn–Si-based shape memory alloys. The influence of alloying elements can be considered in the model by introducing interaction parameters. The precipitate size distribution, mean size, precipitate volume faction, and number density of three typical Fe–Mn–Si-based alloys with different NbC addition amounts were calculated. The results indicated that the mean size could be decreased significantly as the NbC addition increased from 0.5% to 1.0%, while the precipitate volume fraction and number density showed obvious increments. The Fe–28Mn–6Si–5Cr alloys exhibited smaller mean sizes and higher number densities than the Fe–14Mn–6Si–9Cr–5Ni and Fe–21Mn–6Si–9Cr–5Ni alloys. It was also found that the precipitate size distribution showed no evident change as the aging time increased from 0.5 h to 2 h except for the Fe–28Mn–6Si–5Cr–0.5NbC alloy in which the precipitates began to coarsen after about 1.25 h.

Effects of rolling conditions on recrystallization microstructure and texture in magnetostrictive Fe-Ga-Al rolled sheets

The effects of different rolling conditions on the microstructure and texture of primary and secondary recrystallization in magnetostrictive Fe82Ga9Al9+0.1at%NbC alloy sheets were investigated. After the primary recrystallization annealing at 850 °C for 5 min, the as-rolled sheets prepared by warm-cold rolling with an intermediate annealing, can be fully recrystallized, and obtain the homogeneous matrix in which the fine dispersed NbC precipitate particles are distributed. The primary recrystallization textures of sheets with different rolling conditions consist mostly of strong {1 0 0} textures, γ-fiber textures, {4 1 1}〈1 4 8〉 texture and weak Goss texture. In the primary recrystallized sheets prepared by warm-cold rolling with an intermediate annealing, the high energy grain boundaries and ∑9 boundaries have the highest proportion. After high temperature annealing, the secondary recrystallizations of Goss grains in these sheets are more complete, and the size of abnormal grown Goss grain is up to several centimeters, which results in the strongest Goss texture. Correspondingly, the largest magnetostriction of 183 ppm is observed. The sample prepared by warm-cold rolling with an intermediate annealing, has homogeneous primary matrix, special texture components and grain boundary distribution, all of which provide a better surrounding for the abnormal growth of Goss grains. This work indicates that the control of rolling conditions of Fe-Ga-Al alloy sheets is necessary to achieve the strong Goss texture and obtain a possible high magnetostriction if other appropriate conditions (stress, domain structure) are achieved.

Inhibition force of precipitates for promoting abnormal grain growth in magnetostrictive Fe83Ga17-(B,NbC) alloy sheets

Inhibition force of precipitate particles for promoting abnormal grain growth in magnetostrictive Fe83Ga17-(B,NbC) alloy sheets was investigated in this study. After a continuous heating and a high-temperature annealing, the Fe83Ga17 + 0.5 at% B alloy sheets do not occur significant abnormal grain growth. Correspondingly, textures of {111} and {100} in addition to the Goss texture are obtained in the final annealed alloy sheets. By contrast, after the same annealing processes, the size of {110} textured grains is very large in the final annealed Fe83Ga17 + 0.5 at% NbC alloy sheets due to the abnormal grain growth, which results in a sharp Goss texture. BN precipitates were introduced into Fe83Ga17 + 0.2 at% B alloy sheets by nitriding annealing at 800 °C for 2 min under NH3 atmosphere. The abnormal grain growth of Goss grains is achieved in 0.2 at% B-doped Fe83Ga17 alloy sheets after a high-temperature annealing, which is attributed to the enhanced inhibition force by introducing BN precipitates. During the recrystallization annealing process, Fe2B precipitates is easy to coarsen and decompose at high temperature due to the low thermal stability, resulting in a decrease or even disappearance of the inhibition force. For NbC and BN precipitates, the thermal stability and hardness of particles are both better than those of Fe2B precipitates, leading to strong inhibition force. Because of the preferred Goss texture, the magnetostriction of 2.05 × 10−4 and 1.81 × 10−4 is obtained in the secondary recrystallized Fe83Ga17 + 0.5 at% NbC and Fe83Ga17 + 0.2 at% B alloy sheets, respectively.

Fatigue properties of Fe-28Mn-6Si-5Cr-0.5NbC alloy

In this study, we conducted a low-cycle fatigue testing in a Fe-28Mn-6Si-5Cr-0.5NbC (FMS) alloy and a SUS304 steel. The fatigue tests were made using a servo hydraulic fatigue testing machine of capacity 50kN, at maximum total strain amplitudes (εta) of 2.0%, 1.4%, 0.9%, 0.6%. In the SUS304 steel, with decrease in applied strain amplitude, stress-strain hysteresis loop is reduced. On the other hand, the stress response of the FMS alloy is almost unchanged, irrespective of the applied strain amplitude. The life to failure of the FMS alloy is 4 times higher at εta=0.6%, and twice at εta=0.9% and at εta=1.4% than the SUS304 steel. In addition, the stress amplitude of the FMS alloy is 2 times higher at εta =0.6 %, and 1.5 times higher at εta =0.6% than the SUS304 steel. The prolonged fatigue life of the FMS alloy is attributable to the reversible deformation associated with the transformation pseudo-elasticity that can reduce the accumulated strain.

Structural phase characteristics of rhenium- and ruthenium- containing high-temperature eutectic γ/γ'-NbC composites

Ingots of high-temperature nickel-based eutectic γ/γ'-NbC alloy of the Ni–Al–Re–Ru–Nb–C system with natural composite structure are produced using high-gradient oriented crystallization. Investigations are conducted involving alloy segregation along the composite zone of the ingot and its influence on the volume fraction of NbC whiskers, liquidus, solidus, and γ' solvus temperatures, and γ and γ' phase lattice spacing. The crystal-orientation correspondence between the γ/γ' matrix and NbC whiskers is established.

Effects of amount of pre-deformation on precipitation of NbC particles and shape memory effect of Fe17Mn5Si8Cr5Ni0.5NbC alloy during electropulsing treatment

To further enhance shape memory effect (SME) and improve treatment technique in Fe-based shape memory alloys, an Fe17Mn5Si8Cr5Ni0.5NbC alloy was subjected to electropulsing treatment after pre-deformation. The results show that the shape recovery ratio increases with the amount of pre-deformation up to 10%. The maximum shape recovery ratio after electropulsing treatment is 8% greater than that after ageing at 1073 K. The number of NbC particles induced by electropulsing treatment is increased and the size of the particles is decreased with the amount of tensile pre-deformation up to 10%, and NbC carbides are precipitated more quickly through electropulsing treatment than by ageing.

Effects of electropulsing treatment on stress-induced ɛ martensite transformation of a pre-deformed Fe17Mn5Si8Cr5Ni0.5NbC alloy

Effects of electropulsing treatment on stress-induced ɛ martensite transformation of a pre-deformed Fe17Mn5Si8Cr5Ni0.5NbC alloy were studied. The results showed that electropulsing treatment can strengthen austenite and decrease the critical stress for the stress-induced martensite transformation at room temperature due to the precipitation of more and smaller NbC particles. Therefore, more strain can be afforded by the stress-induced martensite transformation.

Further improvement of shape memory effect in a pre-deformed Fe–Mn–Si–Cr–Ni–Nb–C alloy by smaller NbC precipitated through electropulsing treatment

To further enhance shape memory effect (SME) and improve treatment technique in Fe-based shape memory alloys, a pre-deformed Fe17Mn5Si8Cr5Ni0.5NbC alloy was subjected to electropulsing treatment. The results showed that the maximum shape recovery ratio after electropulsing treatment was 12% greater than that after ageing at 1073 K. SEM observation showed that NbC carbides induced by electropulsing treatment were precipitated more quickly and the amount of NbC particles was increased and the size of NbC particles was smaller.

Martensite Transformation and Shape Recovery in Pre-Deformed Fe-15Mn-5Si-9Cr-5Ni-(0.5–1.5) NbC Alloys

The shape memory effect (SME) of Fe-15Mn-5Si-9Cr-5Ni-(0.5–1.5)NbC alloys pre-extended at room temperature was investigated. It shows that the pre-deformation result is similar for the SME of three composition alloys, i.e., the SME increased with increasing pre-extension and then decreased when they were over 12–14% pre-extended at room temperature. X-ray diffraction showed that there are two kinds of martensite transformations � (fcc) ! (hcp) and � ! ! � 0 (bcc) occurring in the Fe-15Mn-5Si-9Cr-5Ni-(0.5–1.5)NbC alloys when the alloys were deformed at room temperature. It was found by magnetic saturation measurements that when the alloy was 8% extended at room temperature, � 0 phase appeared and obviously increased with increasing deformation. Furthermore, TEM observations showed that � 0 phase exists in the cross section of the martensite and reverses in the different path of � ! . The effect of pre-deformation and aging on SME was correspondingly explained in view of martensite transformations and its nucleation, i.e., stacking faults and associated contribution of NbC precipitation, for � ! transformation. [doi:10.2320/matertrans.47.1328]

Effect of pre-deformation at room temperature on shape memory properties of stainless type Fe–15Mn–5Si–9Cr–5Ni–(0.5–1.5)NbC alloys

Substantial improvement of shape memory properties of the stainless type Fe–15Mn–5Si–9Cr–5Ni–(0.5–1.5)NbC (mass%) alloys has been achieved by pre-deformation at room temperature. It shows that a suitable pre-extension can result in excellent shape memory effect (SME). A 90% shape recovery of an initial 4% strain and 200 MPa shape recovery stress are attained when the Fe–15Mn–5Si–9Cr–5Ni–0.53Nb–0.06C alloy is 12% pre-extended at room temperature, being followed by aging at 1070 K for 10 min. If the pre-extension is more than 12%, the shape recovery is reduced with an increasing amount of the pre- extension. It is found by X-ray diffraction and transmission electron microscopy (TEM) that such a decrease in shape recovery is due to the formation of α′ phase (body-centered cubic). The mechanism to obtain a nearly perfect shape memory recovery at 12% pre-extension is studied by atomic force microscopy and TEM. It is concluded that the uniform distribution of stacking faults associated with fine NbC precipitates produces the single variant martensite plates, which is the key factor in obtaining an excellent SME.

Improved shape memory properties and internal structures in Fe-Mn-Si-based alloys containing Nb and C

It has recently been found that the shape memory properties of Fe-Mn-Si-based alloys are notably improved by addition of small amounts of Nb and C elements. In these newly modified alloys, the so-called training process is replaced by a simpler thermomechanical treatment. For example, in an Fe-28Mn-6Si-5Cr-0.5NbC alloy (mass %), a combination of pre-rolling at 870 K followed by 10 min ageing at 1070 K results in a shape recovery of 90% for 4% initial strain and a shape recovery stress of 295 MPa for 4.5% initial strain. In this work, we present the shape memory properties of the samples pre-rolled up to 20% in Fe-28Mn-6Si-5Cr-0.5NbC, and atomic force microscopy (AFM) and transmission electron microscopy (TEM) observations of the stress-induced martensite. Detailed discussion is made on the relations between the microstructures observed by AFM and TEM and the shape recovery and shape recovery stress, and the main factors responsible for drastic improvement of the shape memory properties in this alloy system are drawn.

The influence and its mechanism of NbC precipitates on the shape memory effect of Fe-Mn-Si-Cr-Ni shape memory alloy

In order to evaluate the effect that the existence of small coherent NbC precipitates in austenitic matrix greatly influences the shape memory recovery, seven FeMnSiCrNi shape memory alloys containing (0.1∼0.5%) NbC and (3∼5%) Si have been prepared and investigated in this paper. The result shows that solution-aging treatment correlated with the NbC precipitates and the Si content is the most important to the shape memory effect. Among these alloys, the shape memory recovery rate with 0.5% NbC and 3%Si addition is the lowest. The best result has been achieved in the Fe14Mn5Si9Cr5Ni0.5NbC alloy by solution treated at 1200°C for lOh and then aging at 800°C for 6h. Under 5% deformation, its shape memory recovery rate is up to about 3.7%, which is comparable of the result of thermomechanical cycle. The NbC precipitates were observed by TEM in the paper. Its influence and mechanism on shape memory effect and the relationship between the second phase precipitates and the resultant good shape memory are discussed in details. The pre-requirement for the FeMnSiCrNi alloy to get training free has been proposed.

Thermotransport of carbon in two-phase V-C and Nb-C alloys

Thermotransport experiments were performed on two-phase V-C and Nb-C alloys for various times, temperature ranges, and compositions. A one-phase region develops in the hotter portion of the sample accompanied by an increase in carbide concentration in the colder region. A mathematical equation in which the direction of transport is described by the sum of the heat of solution,A―H, and the heat of transport,Q*, was fitted to the experimental data for all of the alloys studied. No evidence was found to support the physical motion of the carbide particles predicted by some models. On the assumption that local equilibrium exists between the particles and the matrix, points on the V-C solvus were determined from the temperature corresponding to the one-phase/two-phase interface in the different experiments. The solid solubility for carbon in vanadium was determined to be log C (at. pct C) = 2.918 - 4536/T with a heat of solution of 86.8 ± 2.9 kJ/mol.

Molybdenum in Nb-C alloys

The effects of molybdenum alloying additions to niobium on the carbide phases and their precipitation behavior were investigated. The experimental alloys included Nb-0.1C, Nb-15Mo-0.1C, and Nb-30Mo-0.1C. After selected heat treatments the microstructural changes were determined by metallography and the carbide phases were extracted and identified by X-ray diffraction and chemical analysis. The results are essentially in agreement with recent phase diagram determinations. Additions of 30 wt pct Mo appears to slightly increase the solubility of carbon in niobium at temperatures around 1650°C. The solubility of molybdenum in Nb2C is very small. Discontinuous precipitation of β-Nb2C was found to occur in the Nb-30Mo-0.1C alloy during annealing at 1200°C. The important, overall effect of molybdenum in Nb-C alloys is to decrease the rate of niobium carbide precipitation so that appreciable carbon supersaturation can be achieved even after comparatively slow furnace cooling.

Microstructural development during the liquid-phase sintering of two-phase alloys, with special reference to the NbC/Co system

An investigation was made of the grain growth and other microstructural changes occurring during the liquid-phase sintering of NbC alloys with ∼20 wt % cobalt. The effects of sintering time, sintering temperature, and small alloying additions were studied. It was found that the grain growth of NbC in liquid cobalt, at 1420° C, can be described by the equation: $$\bar d^3 - \bar d_0 ^3 = {\text{K}}t$$ where $$\bar d$$ is the mean linear intercept of the grains after time t, and $$\bar d_0$$ the initial mean intercept, K being a temperature-dependent constant with an “activation energy” of 95±15 kcal/mole. This equation suggests that grain growth occurs by a solution/ precipitation process controlled by diffusion in the liquid phase. Small alloying additions of WC, TiC or NbB2 inhibit the growth and/or alter the growth process, as well as affecting such properties as the shape and contiguity of the carbide grains. The relative significance of grain coalescence to grain growth in a liquid phase is discussed. By examining theoretically the effect of anisotropy of interface energy on the cube ⇌ sphere grain-shape change, it has been possible to explain the observed sensitivity of grain shape towards sintering conditions.