Effect Of Nb Addition Research Articles

Effect of Nb addition and Pre-strain on Hydrogen Embrittlement of Low-carbon Steels with Ferrite-pearlite Structure

The effect of pre-strain on the hydrogen embrittlement of Nb-free and Nb-added low-carbon steels with ferrite-pearlite structure was investigated in this study. After the steels were electrochemically charged with hydrogen, slow-strain rate tensile (SSRT) tests were conducted on them to examine hydrogen embrittlement behavior. The SSRT test results revealed that the Nb-added steel had a lesser decrease of elongation and reduction of area than the Nb-free steel. The formation of NbC carbide and grain refinement caused by the Nb addition improved resistance to hydrogen embrittlement. The loss of elongation and the reduction of area after hydrogen charging occurs when pre-strain is increased. The pre-strain increases dislocation density and thus increases the amount of reversible hydrogen trap sites associated with hydrogen embrittlement. 10% pre-strained specimens exhibited a significant loss in elongation and reduction of area, regardless of Nb addition. Based on the results of electron back-scatter diffraction, fractographic, and silver decoration analyses for Nb-free and Nb-added steels, the hydrogen embrittlement mechanism in low-carbon steels with different amounts of pre-strain is discussed in terms of dislocation density and hydrogen distribution.

Effect of Nb addition on the microstructural, mechanical and electrochemical characteristics of AlCrFeNiCu high-entropy alloy

AlCrFeNiCuNbx (x = 0.05, 0.15, and 0.26) high-entropy alloys (HEAs) were successfully fabricated using the laser metal deposition technique. The laser power of 1600 W and scanning speed of 1.2 m/min were used during laser processing of the alloys. The microstructural, mechanical, and electrochemical characteristics of the alloys were evaluated using various advanced characterization techniques. Results showed that the alloys exhibited a dual-phase structure with dendritic grains. The inclusion of Nb in the AlCrFeNiCu alloy matrix promoted the formation of fine eutectic structures and changed the shape of the grains from columnar to equiaxed. The Cu content decreased with the increase in the content of Nb, whereas the Al content increased with the increase in the content of Nb. The findings indicated that the presence of Nb in the alloy promoted the formation and enhanced the stability of the body-centered cubic (bcc) phase. All of the alloys that contained Nb also exhibited high hardness, compressive strength, and wear resistance. Furthermore, the low current density and positive shift in potential exhibited by HEAs with appropriate addition of Nb highlighted the superior anticorrosive properties.

Effects of Nb Addition and Different Cooling Methods on Microstructures and Properties of Cu-Cr Alloys

The Cu-Cr-Nb alloys were prepared by vacuum induction melting with different cooling methods. The effects of niobium contents and different cooling methods on the microstructures and properties of these alloys were investigated. The microstructures were characterized by optical microscope, scanning electron microscope and transmission electron microscope. The electrical conductivity, hardness and the tensile strength of Cu-Cr-Nb alloys were tested as well. The results showed that the as-cast microstructures of Cu-Cr-Nb alloys consist of primary α phase dendritic and eutectic phase. With the addition of element Nb, the microstructures were refined and the secondary dendritic arm spacing obviously decreased. Compared with the furnace cooling, the homogeneous and refined microstructures were obtained by the graphite mold, and the hardness of the alloys is enhanced greatly. After the heat treatment, two reinforcing phases of Cr and Cr2Nb are precipitated from the copper matrix. The comprehensive properties were obtained when the Nb content is 0.4%. The Cu-1.2Cr-0.4Nb alloy performed by direct aging treatment without solution treatment exhibits the higher performance, the hardness and electrical conductivity are 143HB and 84%IACS, respectively. In addition, the tensile strength and the elastic limit of the Cu-1.2Cr-0.4Nb alloy can reach up to 413.0 and 238 MPa.

Effects of Nb Addition and Heat Treatment on the Crystallization Behavior, Thermal Stability and Soft Magnetic Properties of FeSiBPCuC Alloys

In this paper, the effect of the replacement of Fe by Nb on the glass forming ability (GFA), the thermal stability and the crystallization behavior of Fe84.5−xSi0.5B10.5P3.5C0.7C0.3Nbx (x = 0, 1, 2) alloys were investigated. The results show that the addition of Nb increases the GFA. Increasing Nb content can enhance the first onset crystallization temperature (Tx1), the second onset crystallization temperature (Tx2) and ΔTx (ΔTx = Tx2 − Tx1), which broadens the range of annealing temperatures. The coercivity (Hc) of ribbons decreases with increasing Nb content after annealing at a low heating rate and reach as a minimum of 24.5 A/m when the Nb content is 2 at.%. The process of annealing at a high heating rate distinctly decreases Hc, and all samples present excellent soft magnetic properties. The nanocrystalline alloy exhibits the lowest Hc of 6.4 A/m after annealing at 460 °C for 5 min.

Novel (CoFe2NiV0.5Mo0.2)100−xNbx Eutectic High-Entropy Alloys with Excellent Combination of Mechanical and Corrosion Properties

The emergence of eutectic high-entropy alloys (EHEAs) offers new insights into the design of next generation structural alloys, which is due to their stable dual-phase microstructure and outstanding mechanical properties from room to elevated temperatures. In this work, a series of (CoFe2NiV0.5Mo0.2)100−xNbx (0 ≤ x ≤ 12) EHEAs were designed and prepared via vacuum arc-melting. Typical eutectic microstructure composing lamellar face-centered cubic solid solution phase and C14 Laves phase appears in the as-cast EHEA when x = 9. The microstructure turns to hypoeutectic or hypereutectic when x is below or beyond that critical value accordingly. The volume fraction of the hard Laves phase is proportional to the Nb addition, leading to the strength increment yet at the expense of ductility at room temperature. In particular, the EHEA having 4 at% Nb shows a compressive strength of 2.1 GPa with an elongation to fracture of 45%, while EHEAs containing 9 and 10 at% Nb exhibit ultrahigh yield strengths of over 1.4 GPa. The effect of Nb addition on the corrosion resistance of this Cr-free EHEA system was also studied. The EHEA containing 9 at% Nb has the best anti-corrosion performance in the 3.5 wt% NaCl solution at 298 ± 1 K, indicating a good combination of mechanical and corrosion properties.

Effect of Nb addition on the stability and biological corrosion resistance of Ti-Zr alloy passivation films

The effect of Nb addition on the biological corrosion behavior and passivation film characteristics of Ti-Zr alloys in simulated body fluid solution has been systematically investigated. Potentiodynamic polarization analysis, Mott-Schottky analysis, and electrochemical impedance spectroscopy analysis revealed that, with increasing Nb content, the corrosion resistance of alloys first decreases and then starts to increase when the amount of Nb added is 20 at%. The addition of Nb can stabilize the passivation film of Ti-Zr alloys and reduce pitting sensitivity. The mechanisms of the effect of Nb on the corrosion resistance and stability of the passivation film have been extensively discussed.

Effect of Nb Additions on the High-Temperature Performances of NiFe2O4 Spinel Coatings Fabricated on Ferritic Stainless Steel

Ni–Fe alloy coatings with Nb contents of 0, 4.2 at.%, 7.0 at.% and 9.0 at.% were electrodeposited on ferritic stainless steels for intermediate-temperature solid oxide fuel cell (SOFC) interconnect application. The oxidation behavior, scale-growth mechanisms and electrical performances of the Ni–Fe- and NiFe–Nb-coated steels were then investigated in air at 800 °C corresponding to the cathode environment of SOFC. It was found that the scales formed are mainly composed of an external NiFe2O4 layer and an inner Cr2O3-rich layer after oxidation, with some Nb-rich oxides also observed for the Nb-containing coatings. Doping 4.2 at.%Nb into the coating decreased the growth rate of Cr2O3 and suppressed the formation of voids at the scale/alloy interface, whereas excess Nb impaired the oxidation resistance of the steel. The Nb addition affects the oxide growth direction by suppressing the cation transport. All the coatings decreased the area-specific resistance (ASR) of the steel, with the NiFe–4.2 at.%Nb-coated sample exhibiting the lowest ASR value. The effects of Nb on the oxidation mechanism and electrical properties of the Ni–Fe-coated steels are discussed.

Effect of Nb addition on the microstructure of Ni–12Mo–7Cr based superalloy

The effects of Nb addition on the microstructures of Ni–12Mo–7Cr based superalloy have been systematically investigated in this study. If no Nb addition, the granular and thin rod-like M2C carbides distribute in the matrix and at the grain boundaries. In the alloy with 1 wt % Nb, the needle-like Mo-riched MC carbides and the granular Nb-containing M2C carbides form in the matrix and at the grain boundaries respectively. The needle-like MC carbides were found to grow along the {1 0 0} planes of the matrix and possess a cube-on-cube orientation relationship (OR) with the matrix. In the case of the alloy with 4 wt % Nb, the thick rod-like NbC carbides with few other metal elements were found to form in the matrix, which grow along the {1 1 1} planes and possess a twin-like OR with the matrix with a small-angle deviation. Based on the interface energy analyses, the morphology differences between MC and NbC carbides were found to result from their different ORs and interface structures.

Effect of Nb addition on the microstructure and corrosion resistance of ferritic stainless steel

The effects of Nb addition on the microstructure and corrosion resistance of the as-rolled Ti-stabilized Fe-17Cr ferritic stainless steels were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, pitting tests, and electrochemical measurements. TiN precipitate tends to form in the microstructure of Ti-stabilized Fe-17Cr ferritic stainless steel. After 0.1 wt. % Nb addition, (Ti, Nb) (C, N) composite precipitates with MgO and Al2O3 core form in the microstructure. After adding 0.1 wt. % Nb, the corrosion rate of the Ti-stabilized Fe-17Cr ferritic stainless steel in FeCl3 solution is decreased significantly. The corrosion current densities decrease in HNO3, NaOH, and NaCl solutions, and the pitting corrosion potentials can be improved in NaCl solution for the Fe-17Cr ferritic stainless steel with 0.1 wt. % Nb addition.

Effect of Nb addition on mechanical properties and corrosion behavior of Ti6Al4V alloy produced by selective laser melting

Abstract

Effect of Nb addition on high-temperature oxidation behavior, oxide layer structure, and its exfoliation resistance of Ti-Nb Alloys

The authors proposed an oxide coating on Ti alloys for the dental abutment tooth, and they had reported that Ti–29Nb–13Ta–4.6Zr (TNTZ) alloy forms a dense oxide layer by high-temperature oxidation. On the other hand, CP Ti forms a multilayered oxide consisted of rutile monolayers and the void layer. This morphological change by alloying is supposed to be mainly caused by Nb addition in Ti since the dense oxide layer of TNTZ mainly consists of rutile TiO2and TiNb2O7.Therefore, in this study, oxidation behaviors of various range of Nb content of Ti-xNb alloys (x = 1 ~ 32 mol%) were investigated, and exfoliation resistance was evaluated. And in this paper, the oxide/metal interfacial microstructure of oxidized CP Ti, TNTZ alloy, and Ti-Nb alloy was studied by a transmission electron microscopy (TEM) and by a scanning transmission electron microscopy with an electron dispersive spectroscopy (STEM-EDS).The cross-sectional observations suggested that the substrate was gradually oxidized during heat treatment, and nucleation and grain growth of TiO2and TiNb2O7proceed at the metal/oxide interface. Consequently, the gradual oxidation process in TNTZ and Ti-Nb alloys could lead to its continuous interfacial microstructure and dense oxide structure, which can achieve high exfoliation resistance.

Effect of Nb Addition on Oxide Formation on Ti–xNb Alloys

Effect of Nb Addition on Oxide Formation on Ti–xNb Alloys

Effect of Nb Addition on Oxidation Mechanisms of High Cr Ferritic Steel in Ar–H2–H2O

High chromium ferritic steels are being used as construction materials for interconnects in solid oxide electrolysis cells (SOEC). Addition of niobium in the range of a few tenths of a percent is suitable for increasing the high-temperature creep strength of this type of ferritic steel. In the present work, the high-temperature isothermal oxidation behavior of a niobium containing ferritic steel at 800 °C was investigated in Ar–4%H2–4%H2O gas simulating the service environment in an SOEC (cathode side) and compared with that of a Nb-free counterpart alloy. Gravimetric data were correlated with the results from microstructural analyses using, among others, scanning and transmission electron microscopy as well as glow discharge optical emission spectroscopy. Atom probe tomography was used for obtaining atomic-scale insight into the segregation processes in external oxides and their interfaces. The oxidation rate was substantially higher for the Nb-containing than for the Nb-free alloy. Both alloys formed double-layered oxide scales consisting of inner chromia and outer MnCr2O4 spinel. Additionally, a thin layer of rutile-type Nb(Ti,Cr)O2 oxide of 200–300 nm thickness was observed at the scale–alloy interface in the Nb-containing steel. Nb addition to the alloy led to its segregation at chromia grain boundaries which affected the diffusion of Cr and other solute species such as Ti, Mn and Si.

Effect of Nb Addition on Microstructure and Thermal and Mechanical Properties of Fe-Co-Ni-Cu-Cr Multiprincipal-Element (High-Entropy) Alloys in As-Cast and Heat-Treated State

The microstructure and thermal and mechanical properties of (FeCoNiCuCr)100−x-Nbx multiprincipal-element alloys have been investigated in the as-cast and heat-treated state. The alloys were smelted by arc-melting in argon atmosphere. As-cast samples were produced by copper mold casting. The structure was studied by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The calculated phase diagrams of the Fe-Co-Ni-Cu-Cr-Nb system were used to predict the phase composition. The predicted thermodynamic temperatures and phase areas were compared with those obtained using differential scanning calorimetry (DSC) and the results of SEM observation, respectively. Addition of 10 at.% Nb caused phase separation of the alloy in the liquid state. Addition of Nb caused an increase in the yield strength by solid-solution hardening and by the formation of intermetallic compounds. Heat treatment also affected the mechanical properties of the studied alloys.

Effects of Nb additions on structure and mechanical properties evolution of CoCrNi medium-entropy alloy

Effects of Nb additions on structure and mechanical properties evolution of CoCrNi medium-entropy alloy

Effect of Nb additions on microstructure and properties of γ-TiAl based alloys fabricated by selective laser melting

Abstract The γ-TiAl based Ti–Al–Mn–Nb alloys with different Nb additions were fabricated by selective laser melting (SLM) on the TC4 substrate. The effects of Nb content on microstructure and properties of the alloys were investigated. The results reveal that the alloys consist of γ-TiAl phase with tetragonal lattice structure and α2-Ti3Al phase with hcp lattice structure, and show a sequential structure change from near full dendrite to near lamellar structure with the increase of Nb addition. Owing to the higher Nb content in γ-TiAl phase and the formation of near lamellar structure, the alloy with 7.0 at.% Nb addition has the best combination of properties among the studied alloys, namely, not only a high hardness of HV 2000, a high strength of 1390 MPa and a plastic deformation of about 24.5%, but also good tribological properties and high-temperature oxidation resistance.

Influence of niobium microalloying on the microstructure and mechanical properties of high carbon nano bainitic steel

Carbide free nano bainitic steels have recently become a promising material for several applications such as rails, armour etc. because of their impressive combination of mechanical properties. Very high strengths up to 2500 MPa have been achieved because of the very fine nano-scale microstructure obtained through transformations at low austempering temperatures. However, the low ductility and impact toughness are the limiting factors which prevent their use in several applications. It is well known that alloying elements such as Nb and V are added in very small quantity in order to improve strength and ductility of low and medium carbon steels through Nb, V (C, N) precipitates. Influence of these microalloying elements on the mechanical properties of nano bainitic steel is not well understood. In the present study, mechanical properties of two high carbon nano bainitic steels with 0.037 wt% Nb and without Nb addition have been studied. Nb addition results in a substantial increase in ductility (total % elongation) from 16 % to 28 %. Effect of Nb addition on transformation kinetics, microstructure and mechanical properties is also discussed.

Influence of Nb Content on Sensitization and Pitting Corrosion of Welded AISI 430 Ferritic Stainless Steel

Abstract In this work, the effect of Nb addition on sensitization and pitting corrosion of welded AISI 430 ferritic stainless steel subjected to autogenous GTAW was investigated by microstructural characterization and electrochemical techniques. The three distinct regions of welding process, weld metal, heat affected zone and base metal of AISI 430 steel with and without Nb were evaluated. The degree of sensitization was measured by double loop electrochemical potentiodynamic reactivation and pitting corrosion was studied by potentiostatic polarization test. The microstructural analyses reported martensite network in the weld metal and heat affected zone of AISI 430 non stabilized. The electrochemical studies revealed that the highest degree of sensitization and the lowest pitting potential are in the weld metal of AISI 430 without Nb.

Effect of Nb addition on microstructure and properties of laser cladding NiCrBSi coatings

ABSTRACTNiCrBSi coatings with different Nb additions have been prepared by laser cladding. The microstructure, phase composition, hardness, and wear resistance of the coatings were studied by scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. The results show that the phases in the NiCrBSi coating without Nb addition include γ-Ni, Cr23C6, Cr7C3, Ni3B, Ni3Si2 and CrB. The NbC phase appears in coatings after the addition of Nb element. When the addition of Nb is 2 wt-%, the NbC particles with a size of about 1.2 μm were found in the coating, and the amount of NbC is about 1.8 vol.-%. With the increase of Nb addition, the size and amount of NbC in the coatings also increased. When the addition of Nb is 6 wt-%, the size of NbC is about 2.3–6.1 μm and the morphology of NbC changed from particle to quadrangular and petaloid shaped. In addition, when the addition of Nb is 2 wt-%, the hardness and wear resistance of the coating are the best, and the wear resistance of the coating is 104% higher than that without Nb addition.

Effect of Nb Addition on Dendrite Growth and Equiaxed Grain Ratio of Fe-20 Pct Cr High-Purity Ferritic Stainless Steel

The acquisition of a high equiaxed zone ratio (EZR) is crucial for ferritic stainless steel (FSS). The main method of achieving this is to use effective particles to promote heterogeneous nucleation. In this study, an increased EZR was obtained owing to dendritic growth kinetics influenced by Nb addition. The EZR increased from 12 to 44 pct when 0.7 wt pct Nb was added to the FSS. The mechanism of increase of the EZR was analyzed by modified dendritic growth kinetics using the Kurz–Giovanola–Trivedi model coupled with thermodynamic data from ThermoCalc. The dendritic growth kinetics for Fe-20 pct Cr and Fe-20 pct Cr-0.7 pct Nb can be expressed as $$ V = 2.258 \times 10^{ - 5} \cdot \Delta T^{3.617} $$ and $$ V = 5.755 \times 10^{ - 7} \cdot \Delta T^{3.248} $$ , respectively, which means that undercooling (ΔT) of Fe-20 pct Cr-0.7 pct Nb was larger than that of Fe-20 pct Cr under the same solidification velocity (V). The undercooling enlarged at the dendrite tip then provided favorable nucleation conditions for FSS and increased the EZR. The as-cast structure, simulated by the cellular automaton–finite element model combined with modified dendritic growth kinetics, compared well with an actual ingot.