Effect Of Niobium Addition Research Articles

Effects of niobium alloying on microstructure, toughness and wear resistance of austempered ductile iron

Austempered ductile iron (ADI) is a heat-treated nodular iron variant that has for a given strength level much higher elongation than conventional iron with spheroidized graphite. This paper considers the effect of niobium addition on the graphite microstructure, bainite microstructure, bainite transformation process and properties such as hardness and impact toughness under given heat-treatment conditions. The resulting properties are significant with regard to the wear resistance of the material. The effects of niobium addition on the graphite morphology can be understood based on a detailed precipitation analysis of the niobium precipitation behavior in the liquid phase. Niobium influences the temperature and kinetics of pearlite as well as bainite transformation. Furthermore, niobium refines the bainite microstructure generated during austempering treatment. It was found that niobium addition in the range of 0.2–0.5 wt percent allows obtaining an optimum combination of hardness, impact toughness and wear resistance.

Effect of niobium addition in FeCoNiCuNbx high-entropy alloys

Abstract

Effect of niobium addition on the flux of submerged arc welding of low carbon steels

The present work evaluates the effect of adding 3 wt.% of NbC and Nb2O5 to a commercial SAW flux on the microstructure and mechanical properties of the weld metal of ASTM 131 AH31 plates. The analyses of the weld bead microstructure indicated the presence of three weld zones, as expected, enhancing the presence of fine and coarse HAZ. Microscopy and EDS indicated that Nb dissociates from the original compound and precipitates along the grain boundaries of the iron matrix as niobium oxide. Mechanical characterization evidenced that NbC and Nb2O5 added to a commercial SAW flux increased the microhardness values by ∼40% and ∼140%, respectively. The addition of NbC decreased the ductility of the weld metal, whereas the addition of Nb2O5 increased it. The results obtained indicate a potential product for high wear resistance applications.

Nb addition effect on microstructural properties of Ti–TiAl3 in situ composites produced by resistive sintering

In this study, as an alloying element, the effect of niobium addition by 5 mass% on the TiAl3 matrix in situ composites produced by resistive sintering method was investigated. As starting materials, aluminum, titanium and niobium powder with 35–44 µm size, having 99.9%, 99.8% and 99.9% purity, respectively, were used. DSC–TG analyzes were carried out in both an open and a protective atmosphere at a heating rate of 10 °C min−1 up to 1200 °C. The formation temperature of intermetallic compound for two different powders mixture determined by DSC–TG analysis was approximately 665 °C. The production of Ti–TiAl3 and Nb–Ti–TiAl3 in situ composites was carried out in electric activated assisted sintering system in open air with a uniaxial contact pressure of 35 MPa at 2000 A for 90 s. SEM studies showed that intermetallic compounds have low porosity and phase transformation has not been completed and unreacted titanium is in the body as desired. In this way, it is aimed to eliminate brittleness of intermetallic phase. The distribution of elements was confirmed by EDS analysis. The presence of metallic and intermetallic phases was determined by XRD analysis. The relative density of Ti–TiAl3 and Ti–TiAl3 + 5 mass% Nb was 98.7% and 92.1%, and the micro-hardness of materials was about 455 HV and 442 HV, respectively.

Effects of niobium addition on the microstructure and mechanical properties of laser-welded joints of NiTiNb and Ti6Al4V alloys

The dissimilar joining of shape memory alloys to Ti alloys is critically important in many industrial applications. However, joining these two alloys is a considerable challenge due to the formation of brittle intermetallics. In this paper, the dissimilar laser welding of 200-μm-thick NiTiNb and Ti6Al4V alloys was successfully achieved by the addition of a niobium filler wire with a diameter of 300 μm. The morphology, microstructure, phase composition and mechanical behavior of the obtained joints were studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, micro X-ray diffraction, and tensile testing. Variations in the laser power changed the degree of Nb dilution in the weld metal, which affected the amount of intermetallic compounds (IMCs), NiTi, and Ti2Ni formed. All the welds consisted of a dendritic (Nb, Ti) solid solution and varied IMCs. The tensile strength of the joints depended on the amount of IMCs, which decreased with increasing Nb addition. All the tensile specimens fractured along the continuous IMC region in the weld. The highest tensile strength of the joint reached 82% that of the weaker base metal, Ti6Al4V, when the niobium filler was melted completely.

Enhancement of wear resistance and impact toughness of as cast hypoeutectic high chromium cast iron using niobium

The effect of niobium additions on the as-cast microstructure of a hypoeutectic high-Cr cast iron containing 2.2 wt.% C and 16.5 wt.% Cr was investigated. With increasing niobium content, the eutectic M7C3 carbides were refined and became less elongated as well as its volume fraction was decreased gradually. The first precipitated NbC particles could be act as heterogeneous substrate of proeutectic austenite and a barrier to M7C3 grain growth. The morphology of NbC carbides changed with increasing niobium content. Such NbC particles were increased with increasing Nb content and subsequently contributed to increased hardness. Optimum toughness was obtained for the irons alloyed with 2.14% Nb. The effects of applied load and Nb-additions on wear resistance of high chromium cast iron have been studied. The results showed that wear resistance increases with increasing Nb addition. Furthermore, the effectiveness of the NbC particles on the weight loss was more evident at higher loads.

Optimization of Micro-Alloying Elements for Mechanical Properties in Normalized Cast Steel Using Taguchi Technique

Abstract In this study, Taguchi method is used to find out the effect of micro alloying elements like vanadium, niobium and titanium on the hardness and tensile strength of the normalized cast steel. Based on this method, plan of experiments were made by using orthogonal arrays to acquire the data on hardness and tensile strength. The signal to noise ratio and analysis of variance (ANOVA) are used to investigate the effect of these micro alloying elements on these two mechanical properties of the micro alloyed normalized cast steel. The results indicated that in the micro alloyed normalized cast steel both these properties increases when compared to non-micro-alloyed normalized cast steel. The effect of niobium addition was found to be significantly higher to obtain higher hardness and tensile strength when compared to other micro alloying elements. The maximum hardness of 200HV and the maximum tensile strength of 780 N/mm2 were obtained in 0.05%Nb addition micro alloyed normalized cast steel. Micro-alloyed with niobium normalized cast steel have the finest and uniform microstructure and fine pearlite colonies distributed uniformly in the ferrite. The optimum condition to obtain higher hardness and tensile strength were determined. The results were verified with experiments.

Comment on “Effects of niobium addition on microstructure and tensile behavior of as-cast ductile iron” by Chen et al. [Mater. Sci. Eng. A 688 (2017) 416

This letter attempts to comment on the article by Chen et al. [Mater. Sci. Eng. A 688 (2017) 416] in the aspects of microstructure and tensile properties of ductile iron with niobium additions.

Effect of niobium addition on hot deformation behaviors of medium carbon ultra-high strength steels

The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map, and the effect of niobium addition on the hot deformation behavior of medium carbon steel was determined. The hot compression tests were conducted on a Gleeble-3500 thermo-mechanical simulator deformed at temperatures from 850 to 1 200 °C and strain rates from 0.001 to 1 s−1. The processing maps of two test steels were built at a true strain of 0.7 based on dynamic materials model (DMM). There are two peak efficiency domains and two flow instability regions in both test steels. However, the peak efficiency domains of Nb-bearing steel move to higher temperature due to the inhibition of dynamic recrystallization (DRX), and the instability domains of Nb-bearing steel are enlarged due to the precipitation of Nb-containing particles during hot deformation. The optimum process parameters of Nb-bearing and Nb-free steels for industrial production were determined according to the processing map and the microstructural observation.

Effects of niobium addition on microstructure and tensile behavior of as-cast ductile iron

The effects of niobium addition up to 0.11wt% on the microstructure and tensile properties of as-cast ductile iron (ACDI) were investigated. Metallographic analyses by both optical microscopy (OM) and scanning electron microscopy (SEM) indicated that niobium (Nb) promoted the formation of pearlite, reduced pearlite lamellar spacing and decreased the extent of graphitization taking place in the Nb-alloyed ACDI. The nodularity and nodule counts of graphite changed insignificantly when the Nb content was less than 0.08wt% in the ACDI. The analysis of precipitates by transmission electron microscopy (TEM) revealed that nano and micro sized (Nb, Ti)C carbides acted as nucleation site for graphites, and promoted the formation of large graphite nodules with low roundnesses as Nb content rose above 0.08wt%. The results of tensile testing showed that the yield strength, ultimate tensile strength and elongation of the ACDI with 0.08wt% Nb increased by 12.1%, 11.2% and 14.3% over those of the Nb-free ACDI, respectively. The optimum values of the yield strength, tensile strength and elongation of the Nb-alloyed ACDI were found to be 418MPa, 746.0MPa and 8.0%, respectively, at the Nb content of 0.08wt%. The high strain hardening rates of the Nb-containing ACDIs implied that they were capable of spontaneously strengthening itself increasingly to a large extent, in response to a slight plastic deformation after yielding.

Effect of niobium addition in support catalysts applied in satellite propulsion

Catalysts composed of iridium as the active phase dispersed in aluminum oxide (Ir/Al2O3) are used in propulsion systems that employ hydrazine as monopropellant in the control of satellite orbit and attitude. The aluminum oxide (Al2O3) utilized as support must present high values of specific surface area, pore volume, and crush strength. The niobium effect was evaluated in this work, in its oxide form (Nb2O5), by 3 different methods: with the employment of a NbCl5 precursor solution, by wet impregnation and dry impregnation of an alumina obtained from a mixture of gibbsite and boehmite and by physical mixing of gibbsite and hydrated niobium oxide, both autoclaved separately. Aluminum oxides were prepared in both cases containing Nb2O5 contents of 10, 20, and 30% w/w. The acid impregnating NbCl5 solution in the wet impregnation method caused a strong attack to the Al2O3 support, altering and compromising its initial structure and morphology. This process did not occur in the supports prepared by dry impregnation. However, results indicated that the use of this methodology with Nb2O5 contents of 20% and 30%, caused an extensive coverage of the support by Nb2O5, modifying the nature and amount of alumina sites responsible for anchorage of the iridium precursor. In the case of supports prepared through physical mixture (Nb2O5-Al2O3) from aluminum hydroxide and niobium acid precursor compounds, with both being previously autoclaved separately, the 20% and 30% Nb2O5 contents presented the most promising properties, since the binder effect caused by amorphous Nb2O5 increased the crush strength of the support, without compromising the aluminum oxide morphology and texture. Despite of existence of stronger acid sites due to the addition of niobium oxide to aluminum oxide, no increase in the acidity of the materials was observed due to the presence of niobium oxide. This can be attributed to the high calcination temperature used, as well as, to the procedures used for the preparation of such materials.

Effect of niobium addition on magnetization reversal behavior for SmCo-based magnets with TbCu7-type structure

AbstractThe effect of Nb addition on the microstructure and magnetic properties of nanocrystalline Sm(CobalNbxZr0.02)7 permanent magnet were investigated. The magnetization reversal behavior for ball milled Sm(CobalNbxZr0.02)7 samples with high coercivity was investigated by analyzing hysteresis curves and recoil loops of demagnetization curves. Nb addition proved to result in relevant improvement in the magnetic properties, especially in the coercivity Hc. It was shown that the magnetic properties of Sm(CobalNbx- Zr0.02)7 nanocrystalline magnets were improved by an additional 0.06 at.% Nb. In particular, Hc was improved from 602 to 786 kA/m at room temperature. The maximum value of the integrated recoil loops area for 0.06 at.% Nb-doped samples of 1.81 kJ/m3 was much lower than that of the Nb-free sample, which could be explained by a smaller recoverable portion of the magnetization remaining in the Nb-doped sample when the applied field was below the coercivity Hc. The nucleation field Hn for irreversible magnetization reversal of the magnetically hard phase were calculated by analyzed in terms of the ΔMirrev-H curve and the Kondorsky model.

Effects of Niobium Addition into TiO2 Layers on CH3NH3PbI3-based Photovoltaic Devices

Abstract TiO2/CH3NH3PbI3-based photovoltaic devices were fabricated by a spin-coating method using a mixture solution of niobium(V) ethoxide, and the effects of niobium (Nb) addition to TiO2 layers were investigated. The lattice distance and energy gap of the TiO2 were almost same after Nb addition. The elemental mapping and sheet resistance measurements indicated a wide distribution of Nb and Ti, and a decrease in sheet resistance by Nb addition. The external quantum efficiency and internal quantum efficiency increased by Nb addition to compact TiO2 and mesoporous TiO2 layers, which resulted in an increase in the current density and conversion efficiency of the cell.

Effect of Niobium Additions on Austenite Grain Coarsening Behavior of GCr15 Bearing Steel

The effect of 0.018% niobium additions on austenite grain coarsening behavior of GCr15 bearing steel was studied. Results indicate that the coarsening temperatures of No.1 and the No.2 experimental steel were 950°C and 1100°C. The austenite grain coarsening temperature was increased by 150°C by the addition of 0.018% Nb in bearing steel. The grain growth equations of two experimental steels at different soaking temperatures from 850°C to 1250°C with the soaking time of 30 min are as follows: the equation of No.1 steel is D1=1.85×105·exp (-6.57×104/RT); the equations of No.2 steel below and above 1100°C is D2=5.08×102·exp (-2.49×104/RT) and D2=1.06×108·exp (-1.31×105/RT), respectively. The grain growth equations of two experimental steels at different soaking time from 15 to 120 min with the soaking temperature of 840°C are as follows: the equation of No.1 steel is D1=4.83×10-2·t0.72 while that of No.2 steel is D2=1.25·t0.18.

Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

The effect of Nb substitution for Ni in Ni45Co5Mn40Sn10 magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni45Co5Mn40Sn10 alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni45Co5Mn40Sn10 alloys potential candidates for solid state refrigeration near room temperature.

The Effect of Niobium Addition and Heat Treatment on the Phase Structure of Fe3Al - Type Intermetallic Alloys

The iron aluminides seem to be a promising materials for high-temperature applications. They have a wide range of positive properties, but unfortunately also some negative (for example low ductility at room temperature or sharp drop in strength above 600°C). The addition of third element into the alloy can be the way to improvement of the properties. Nb, Zr or Ta seem to be appropriate elements. The niobium addition to the Fe-Al matrix leads to the formation of Laves phase. If the Laves phase is presented in an appropriate shape, it could enhance high temperature mechanical properties. These properties are dependent on the structure of alloy - mainly on second phase distribution and type.Two alloys with different content of niobium were investigated. The influence of niobium content and heat treatment on the structure and mechanical properties of the alloys were studied. The phase composition was determined using scanning electron microscopy (SEM) equipped by energy dispersive analysis (EDX) and electron backscattered diffraction detector (EBSD). This paper is the first part of study and it deals with description of the alloy structure and phases in the investigated materials.

Effect of niobium additions on initial hydriding kinetics of uranium

To study the behavior of hydrogen corrosion at the surface of U, U–2.5wt%Nb alloy and U–5.7wt%Nb, a gas–solid reaction system with an in situ microscope was designed. The nucleation and growth of the hydride of the alloy were continuously observed and recorded by a computer. The different characteristics of the hydrides on U metal and U–2.5wt%Nb showed that the later alloy is more susceptible to hydrogen corrosion than the former. The growth rate of hydride of U–2.5wt%Nb, calculated by measuring the perimeter of the hydride spots recorded by the in situ microscope, exhibited a reaction temperature dependency in the range of 40–160°C, for pressure of 0.8×105Pa. An Arrhenius plot for growth rate versus temperature yielded activation energy of 24.34kJ/mol for the hydriding of U–2.5wt%Nb alloy. The maximum hydriding rate was obtained at 125°C, whose thermodynamics reason was discussed.

NaCl 용액에서 Nb 첨가가 Ti 합금의 부식 거동에 미치는 영향

In this study, the effect of niobium addition on the passivation behavior of Ti alloys in NaCl solution was investigated using various electrochemical methods. An -phase in Ti alloy was transformed into a -phase and martensite structure decreased as Nb content increased. The corrosion and passivation current density() decreased as Nb content increased, and thereby a stable passive film was formed on the Ti alloy. Potential of Ti-xNb alloy in the passive region increased, whereas, current density decreased with time from results of potentiostatic and galvanostatic tests. Also, the corrosion morphology showed the smaller pits as Nb content increased. Consequently, Ti alloy contained high Nb content showed a good resistance to pitting corrosion in 0.9% NaCl solution.

Effect of Niobium Addition on the Mechanical Properties of Ti Stabilized Interstitial-Free Steel

Two interstitial-free steel grades, one based on combined niobium and titanium additions and the other based on titanium only addition, were investigated. Annealing experiments were used to study the effect of niobium on the mechanical property. And tensile-shear fatigue tests were used to study the effect of niobium on the fatigue property of spot welding. The experimental results show that niobium addition not only can significantly improve the mechanical properties of the basic materials by way of grain refinement, but also has beneficial effects to the fatigue strength of spot welding.

Effects of Niobium Addition on Microstructures and Formability in Si‐Al‐Mn TRIP Cold‐rolled Steels

AbstractThe effects of Nb addition on microstructures and formability in Si‐Al‐Mn TRIP cold‐rolled steels were investigated. These steels were intercritical annealed at 770 °C for 5 min, and isothermally treated at 400 °C for 3 min. Microstructural observation, tensile tests and forming limit diagram (FLD) tests were conducted, and the changes of retained austenite volume fraction as a function of tensile strain were measured by using an X‐ray diffractometer. The results showed that Nb addition makes grain size refined, the volume fraction of ferrite increase and that of bainite decrease, however, obviously it does not affect the volume fraction and carbon content of retained austenite. The Nb addition increased the stability of retained austenite owing to grain refinement. With Nb addition, increase in strength, ductility, strain hardening exponent and formability could be achieved simultaneously. These findings indicate that Nb addition can be a new direction of microalloying design for the low carbon TRIP steels with excellent formability and high stability of retained austenite.