Nb Wt Research Articles

Nanostructuring and Hardness Evolution in a Medium‐Mn Steel Processed by High‐Pressure Torsion Technique

Severe plastic deformation (SPD) is performed on a newly developed medium‐Mn steel with the composition of Fe–7.66Mn–2Ni–1Si–0.23C–0.05Nb (wt%) to achieve a nanocrystalline microstructure. The SPD process utilizes the high‐pressure torsion (HPT) technique, resulting in a nominal shear strain of approximately 36 000% after processing the disk for 10 turns. In X‐Ray diffraction line profile analysis, an increase in dislocation density to around 230 × 1014 m−2 is observed. In addition, under high strains, a face‐centered cubic (fcc) secondary phase emerges within the body‐centered cubic (bcc) matrix. In analytical transmission electron microscopy, using energy‐dispersive X‐Ray spectroscopy, it is indicated that the secondary‐phase particles are enriched in Al, Mn, and Si. As the strain imposed during HPT increases, the simultaneous rise in dislocation density and nanostructuring lead to material hardening. However, the partial phase transformation from bcc to fcc contributes to material softening. As a result of these two opposite effects, the hardness exhibits a non‐monotonic variation with the shear strain, displaying, for 10 turns of HPT, a lower hardness compared to fewer turns, despite the continuous increase in dislocation density and decrease in crystallite size.

In situ production of low-modulus Ti-Nb alloys by selective laser melting and their functional assessment toward orthopedic applications.

This work aimed to manufacture Ti-28.5Nb and Ti-40.0Nb (wt%) alloys in situ via selective laser melting (SLM) from Ti and Nb elemental powders. X-ray diffraction analysis revealed complete β-phase (cubic) in Ti-40.0Nb and a mixture of (α'' orthorhombic + β cubic) phases in Ti-28.5Nb were formed, whereas few of the Nb particles remained only partially fused during manufacturing. The fraction of partially melted Nb particles was determined as ∼2 and ∼18% in Ti-28.5Nb and Ti-40Nb, respectively. Mechanical characterization revealed higher hardness and more strength in Ti-28.5Nb than in Ti-40.0Nb due to the presence of the α'' phase in the former. Tribocorrosion tests reveal a significantly better wear-corrosion resistance for Ti-40.0Nb, as determined from a lower total volume loss in Ti-40.0Nb (∼2 × 10-4 mm-3) than in Ti-28.5Nb (∼13 × 10-2 mm-3). The lower volume loss and better corrosion resistance behavior are attributed to the β phase, which was dominant in Ti-40.0Nb. Cell studies reveal no toxicity for up to 7 days. Both the alloys were better at supporting cell proliferation than wrought Ti6Al4V. This study presents a route to preparing Ti-Nb alloys in situ by SLM that are promising candidates for biomedical applications.

Synthesis and Ti-N Sputtering of Zr-Nb Alloys for Dental Implant Material

Synthesis and sputtering of the Zr-2.5Nb alloys were performed for the dental implant material candidate. The alloy was synthesized by casting process in an arc melting furnace with an argon atmosphere in the composition of Zr-2.5 Nb (wt %). Surface treatment was carried out by Ti-N sputtering process with the current of 20 Ampere for 45 minutes. Characterization of the microstructure was performed by the SEM-EDX test followed by the phase identification using the XRD analysis. The hardness was measured in the Vickers Hardness Number method to evaluate the relation of the microstructure to the mechanical property before and after the sputtering process. A homogeneous structure with relatively fine grain was found in the synthesis of Zr-2.5Nb alloy. The layer thickness of Ti-N was formed with the mean thickness of 0.5 micrometers. Increasing of hardness was observed in the surface of the alloy that predicted improving the compatibility for dental implant material.

Effect of Nb content on mechanical reinforcement of the Cu-10Fe composites

The Cu-10Fe-based composites with different Nb content were fabricated by vacuum mold casting. The effect of Nb content on the solidification behavior and microstructure was investigated systematically and the optimal composition was determined as Cu-10Fe-1.0 Nb (wt%). The as-cast samples were rolled by 90% reduction at room and then aged at 250 ℃ for different time. The properties results showed that, after aging for 1800 min, microhardness, tensile strength and elongation of the Cu-10Fe-1.0 Nb samples reached 145 HV, 553 MPa and 21.5%, respectively. The microstructure results showed that the primary Fe-rich phases in the Cu-10Fe-1.0 Nb samples were significantly refined due to the heterogeneous nucleation induced by Fe2Nb phases, and then led to the refinement of the matrix. The enhanced mechanical properties could be attributed to the Orowan strengthening, refinement strengthening and work hardening resulted from the numerous submicron-/nano-sized Fe particles, fine sub-grains and high-density dislocation in the matrix formed during thermo-mechanical treatment.

The Oxidization Behavior of Zr–2.5Nb(wt%) Alloy in Dry Air

The oxidation behavior of Zr–2.5Nb alloy at 500 °C, 600 °C and 700 °C from 0.5 to 24 h in a tubular furnace with dry air was systematically investigated by scanning electron microscope, transmission electron microscope and nanoindentation techniques. The results indicate that there is an oxidation rate transition related to grain morphologies of the oxide layer. It showed that the equiaxed grains are good for the oxidation in pre-transition, while the columnar grains are unfavorable to the oxidation in post-transition. The oxide layers first grow with small equiaxed grains and then, become columnar grains. Both t-ZrO2 and m-ZrO2 were identified in the equiaxed grains, while only m-ZrO2 was identified in the columnar grains. Some sub-oxides with different morphologies were observed in the substrate at the beginning of oxidation and were not found after long time oxidation. The occurrence of the oxygen-assisted eutectoid phase transformation of βZr → αZr + βNb results in the decomposition of βZr phase and the precipitation of βNb phase in the microstructure near oxide layer/substrate interface. As the oxide layer thickens, its nano-hardness firstly increases and then decreases, while its adhesion increases gradually. The present study suggests that thicker oxide layers with limited microcracks may also be suitable for the bearing surface of artificial joints.

Investigation of coherent/Compton scattering differential cross section ratios in Cu alloys as depending on chemical environment and scattering angle

In this study, seven alloys with a nominal composition of (CuO2)0.5 M0.5 (M = Fe, Co, Ni, Cu, Zn, Y, and Nb wt%) were produced via the powder mixed method. Alloys and pure metals were excited with 59.54 keV photon energy emitted from Am-241 radioactive source at 25°, 35°, 45°, 55°, 65°, 75′ and 85° scattering angles. The spectra of the coherent/Compton peaks were obtained by Si(Li) detector. First of all, chemical shift, (ΔE) peak energies, (E) asymmetry index (As) and full width half maximum (FWHM) values were found in the Compton/Coherent scattering spectra obtained depending on the scattering angle and the chemical environment of the transition metals. Then the ratios of the Coherent/Compton scattering differential cross-section (dσcoherent/dσCompton) were obtained experimentally. The experimental dσcoherent/dσCompton ratios of the selected 3d-4d transition metals were found to be compatible with the data in the literature. Asymmetry and chemical shifts were observed in almost all samples, especially in Compton peaks, with increasing scattering angles. The chemical shifts of Compton and Coherent peaks of the alloys were found in the range of 1–932 eV. The experimental dσkoherent/dσCompton ratios for the alloys obtained by adding Fe, Co, Ni, Cu, Zn, Y, and Nb to Cu2O were found as 0.697, 0.689 0.678, 0.698, 0.736, 0.755, 0.798, 0.835 at 45° scattering angle, respectively. It has been determined that the experimental dσcoherent/dσCompton ratio for each alloy increases with increasing atomic number, while it decreases with increasing scattering angle.

Effects of Nb addition and heat treatment on the microstructure, mechanical property and internal friction behavior of FeCrAlMo cladding alloys

FeCrAl based alloy was a good candidate as an accident tolerant fuel (ATF) cladding material, this research investigated the influence of Nb addition and heat treatment on the evolution of dispersed Fe2Nb precipitates, the mechanical property and Internal Friction (IF) behavior of Nb containing Fe-13Cr-4.5Al-2Mo alloys. Fe-13Cr-4.5Al-2Mo-1.5Nb (wt%) annealed at 1000 °C exhibited the highest ultimate tensile strength (UTS) and an acceptable ductility at each tested temperature (room temperature, 300 °C, 500 °C or 800 °C). For example, the UTS of FeCrAlMo-1.5 wt% Nb at 800 °C was 95 MPa, 73% higher than that of Nb-free FeCrAlMo alloy at the same test temperature. Comparing with IF results of the cold-rolled Nb-free FeCrAlMo alloy in the first heating cycle, a high IF peak (∼P2) located at about 680 °C disappeared in the Nb containing FeCrAlMo alloy. Based on the optical micrographs analysis, the reason may be the pinning effect by the high density nanoscale Fe2Nb particles on dislocations, P2 peak would be expected to find at higher temperature; Likewise, the disappearance of P3 in the Nb containing FeCrAlMo alloys proved the pinning effect of Fe2Nb particles on grain boundaries. Based on the IF theory and microstructure characterization, the disappearance of P2 (recrystallization peak) and P3 (grain boundary peak) in the Nb containing FeCrAlMo alloys well proved that this pinning effect by high density Fe2Nb nanoscale particles was the main reason for improving the tensile strength of the Nb containing FeCrAlMo alloys.

Partial austenitisation and TBF steel composed of ferrite, bainitic ferrite, and austenite

A TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe–0.19C–1.7Mn–1.09Si–0.51Al–0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350°C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770°C showed a good combination of ultimate tensile strength and total elongation.

Insights into the surface and biocompatibility aspects of laser shock peened Ti-22Nb alloy for orthopedic implant applications

This paper reports the effect of varying laser-peening fluences (3, 6 and 9 GW/cm2) on surface topography, oxide composition and wettability of low modulus Ti-22Nb at.% (Ti-35.4Nb wt.%) alloy with specific focus on the ensuing fretting wear and biocompatibility. Microtopography with nano-sized pores were generated during the laser interaction. LP-6 and LP-9 GW/cm2 surfaces displayed nano-porous distribution, with topographies characterized by negative skewness and platykurtosis. X-ray photoelectron studies revealed the development of mixed oxide layers rich in Ti4+ and Nb5+ when laser fluence was increased. Improved hydrophilic behavior was observed with increment in laser fluence displaying contact angles of 47.1° and 43.2° for LP-6 and LP-9 GW/cm2. Based on the preliminary surface characterizations, LP-6 and LP-9 GW/cm2 which displayed a platykurtic surface with negative skewness, Ti-Nb based mixed oxides and stable hydrophilic nature were selected for further analysis. Presence of Nb5+ ions rendered the oxide surfaces less defective, thereby improving fretting wear resistance. In particular, well-spread cells and up-regulation of beneficial genetic-markers (Ki67) on laser-peened surfaces demonstrated the role of nano-sized cues and oxide-layer in improving osseointegration aspects. Results demonstrate that LP-6 and LP-9 GW/cm2 surfaces on low modulus Ti-22Nb alloy can beneficially contribute towards the fretting wear and biocompatibility.

Microstructure and Mechanical Properties of Nb-API X70 Low Carbon Steel

The oil and gas production has grown steadily, and the care with its transportation grid needs to be maintained and expanded. The pipeline used in the transport of gas and oil by-product requires materials with high mechanical strength, toughness, and fatigue resistance. The chemical composition and distribution, amount, and morphology of the final microconstituents of the steel are of paramount importance once it will directly influence the mechanical properties. The fracture toughness is one of the most important mechanical properties for the suitability of the steel for pipeline usage, and is most of the literature with pipelines study does not present tests such as crack tip opening displacement (CTOD), with a steady and controlled crack growth behavior, to evaluate its fracture toughness. This study compares the fracture toughness of the API 5L X70 steel between two plates of steel with different Nb content, 0.06 and 0.09 Nb wt.% by CTOD tests. The mechanical response was correlated to the grain size and distribution. The CTOD parameter was used to assess the fracture toughness at 25 °C and − 60 °C. The microstructures and microconstituents of the two plates of steel were similar. The matrices were composed of ferrite, with bands of secondary products, including degenerated pearlite. Results showed a prone to the formation of a bimodal microstructure, coarse and fine grains, due to the addition of Nb. High-Nb steel presented better fracture toughness than normal-Nb steel at low-temperature.

Effect of Milling Parameters on the Development of a Nanostructured FCC–TiNb15Mn Alloy via High-Energy Ball Milling

In this work, a blend of Ti, Nb, and Mn powders, with a nominal composition of 15 wt.% of Mn, and balanced Ti and Nb wt.%, was selected to be mechanically alloyed by the following two alternative high-energy milling devices: a vibratory 8000D mixer/mill® and a PM400 Retsch® planetary ball mill. Two ball-to-powder ratio (BPR) conditions (10:1 and 20:1) were applied, to study the evolution of the synthesized phases under each of the two mechanical alloying conditions. The main findings observed include the following: (1) the sequence conversion evolved from raw elements to a transitory bcc-TiNbMn alloy, and subsequently to an fcc-TiNb15Mn alloy, independent of the milling conditions; (2) the total full conversion to the fcc-TiNb15Mn alloy was only reached by the planetary mill at a minimum of 12 h of milling time, for either of the BPR employed; (3) the planetary mill produced a non-negligible Fe contamination from the milling media, when the highest BPR and milling time were applied; and (4) the final fcc-TiNb15Mn alloy synthesized presents a nanocrystalline nature and a partial degree of amorphization.

Isothermal transformation of austenite to ferrite and precipitation behavior in 9Cr-1.5Mo-1.25Co-0.1C-VNb heat-resistant steel

This study explored the transformation of austenite to ferrite and precipitation behavior during the isothermal annealing of heat-resistant steel based on Fe-9Cr-1.5Mo-1.25Co-0.1C-0.2 V-0.05Nb (wt%). For this purpose, the samples used here were initially reheated to the full austenitization temperature and thereafter directly annealed at 710 °C and 730 °C, a temperature range in which the transformation to ferrite takes place, for up to 196 h. In addition, we modified the prior austenite grain size (PAGS) by changing the reheating temperature and then analyzed the effect of PAGS on the kinetics of the isothermal transformation to ferrite. In the early stage of annealing, Cr-enriched M23(C,B)6 carbides initially precipitated along the prior austenite grain boundaries (PAGB). As annealing progressed, the ferrite began to nucleate at the PAGB and then grew into the austenite. The initial stage of the transformation to ferrite was then accompanied with the cellular precipitation of M23(C,B)6 particles. Interestingly, we also found the interphase precipitation of V- and Nb-enriched MX particles resulting from the partitioning of the C concentration at the moving austenite/ferrite interface during the austenite to ferrite transformation. The transformation was finished after annealing for more than 48 h. The time taken to complete the process was prolonged with an increase in the PAGS, indicating that the kinetics of the transformation decreased with an increase in the PAGS.

Quantitative investigation on deep hydrogen trapping in tempered martensitic steel

In this work, the correlation between different microstructural components and hydrogen trapping with high density in tempered niobium carbide (NbC)-precipitated martensitic steel was quantitatively investigated using a combination of electrochemical hydrogen permeation experiments and thermal desorption spectroscopy. The martensite lath and a high density of dislocations, which constitute the reversible hydrogen trapping sites, with a density of 2.24 × 1020 cm−3 in Fe-0.05C-1.10Mn-4.50Ni-0.50Cr-0.50Mo-0.05Nb wt.% martensitic steel. The dislocation with high density could disperse the hydrogen distribution. Furthermore, the uniformly distributed NbC nanoprecipitates, the high-angle grain boundaries, and the grain-boundary precipitates were found to act as irreversible hydrogen traps, with a density of 1.00 × 1020 cm−3. These deep hydrogen trapping sites could not only trap hydrogen irreversibly, but also can inhibit the accumulation of hydrogen. The interpretation of hydrogen trapping is significant to enhance the hydrogen embrittlement resistance of high-strength martensitic steels.

Influence of B and Nb Additions and Heat Treatments on the Mechanical Properties of Cu-Ni-Co-Cr-Si Alloy for High Pressure Die Casting Applications

During the high pressure die casting process (HPDC), it is necessary to develop new designs and alloys for the copper plungers. In this research, two alloys Cu-9Ni-1Co-1.6Cr-2Si-1.3Fe-0.25B wt.% (A1) and Cu-9Ni-1Co-1.6Cr-2Si-0.1Fe-0.2Nb wt.% (A2) under different heat treatments (HT) were studied. Optical microscopy technique was applied to reveal the regions of dendritic morphology, also lower Secondary Dendrite Arm Spacing (SDAS); and different grain orientations. The results reveal that the solidification sequence is primary Cu dendrites and secondary intermetallics; heat treatments increase the redistribution of alloying elements in the interdendritic regions. During the heat treatments, some precipitates were found in the grain boundary after aging heat treatments for both alloys, which were determined by X-ray diffraction. Hardness test HRB presented a decrease with the solution heat treatment and an increase with the aging heat treatments proposed for both alloys. Finally, the wear resistances for both alloys were compared with a commercial alloy C17530, with decreased A1 with B additions having the best result in the as-cast condition 4.07 × 10−4 mm3/Nm, while for A2 with Nb additions wear resistance increased, with the best result in the one with aging heat treatment 1.69 × 10−4 mm3/Nm while for the C17530 alloy this was 2.74 × 10−4 mm3/Nm.

Влияние ультрамелкозернистого состояния на теплофизические свойства сплавов Zr - 1 мас. % Nb и Ti - 45 мас. % Nb и процессы диссипации и накопления энергии при деформировании

The results of studying the thermal conductivity and specific heat capacity of Zr-1 wt.% Nb and Ti-45 wt.% Nb in coarse-grained and ultrafine-grained states are presented. The influence of the utrafine-grained state on the thermo physical properties and the processes of dissipation and accumulation energy during deformation of the alloys are estimated. It is shown that formation of the ultrafine-grained state in the Zr-1 wt.% Nb alloy by abc -pressing and subsequent rolling leads to a decrease in its thermal conductivity and specific heat capacity by 10 and 20%, respectively, due to substructural hardening under severe plastic deformation. It is found that thermal conductivity and specific heat capacity of the ultrafine Ti-45 wt.% Nb alloy increase by 7.5 and 5%, respectively, due to dispersion hardening of the ω phase by nanoparticles and formation of a new α phase. It is established that the ultrafine-grained structure has a significant influence on the regularities of the dissipation and accumulation energy during plastic deformation, which in turn depend on their thermo-physical characteristics and on the structural and phase state.

Влияние длительности термического воздействия на микроструктуру и механические свойства ультрамелкозернистых биоинертных сплавов Zr - 1 мас. % Nb и Ti - 45 мас. % Nb

The results for thermal stability of the microstructure and mechanical properties of ultrafine-grained alloys Zr-1 wt. % Nb and Ti-45 wt. % Nb alloys after long-term thermal annealing at temperature of 400°C are presented. It is shown that in the Zr-1 wt.%Nb alloy in the ultrafine-grained state, increase in the annealing duration from 5 to 360 hours leads to growth of the structural elements (grains, sub-grains, fragments) of the matrix phase a - Zr and the particles β-Nb. This fact is due to the processes of recrystallization. It leads to softening of the alloy and decrease of microhardness and yield stress. It was also found that annealing up to 360 hours does not affect the size of the structural elements of the matrix β-phase in the Ti-45 wt. % Nb alloy, but contributes to the noticeable growth of the α-phase and ω-phase grains. According to our results, softening of the Ti-45 wt. % Nb alloy and decrease in its mechanical characteristics are associated with the processes of return at the grain boundaries, as well as with growth of the nanoscale grains of α-phase and ω-phase and decrease in their contribution to dispersion hardening.

Replacement of Ni by Mn in Commercial High-Ni Austenitic Cast Steels Used for High-Performance Turbocharger Housings

High-Ni austenitic cast steels were fabricated by replacing the expensive Ni content by inexpensive Mn in a commercial DIN 1.4849 steel (0.4C-2.0Mn-1.5Si-20Cr-38Ni-1.5Nb (wt pct)), and their high-temperature tensile properties were enhanced by controlling the volume fraction and distribution of carbides. The 14-pct-Ni-containing steel showed the highest total fraction and most homogeneous distribution of carbides due to the smallest cell size, which played a role in improving high-temperature properties far better than those of the DIN 1.4849 steel.

Epoxidation of Karanja (Millettia pinnata) Oil Methyl Esters in the Presence of Hydrogen Peroxide over a Simple Niobium-Containing Catalyst

The synthesis, characterization and catalytic performance of a conceptually simple, novel NbOx-SiO2 catalyst are here described. The niobium(V)-silica catalyst was prepared starting from cheap and viable reactants, by alkaline deposition of NH4Nb(C2O4)2·H2O in the presence of fructose as a stabilizer and subsequent calcination. The NbOx-SiO2 solid (0.95 Nb wt.%) was tested in the liquid-phase epoxidation with aqueous hydrogen peroxide of methyl oleate, as a model substrate. It was then tested in the epoxidation of a mixture of methyl esters (FAMEs) obtained by transesterification with methanol and purification of karanja oil, extracted from the autochthonous Indian variety of Millettia pinnata tree. The catalyst showed a promising performance in terms of methyl oleate conversion (up to 75%) and selectivity to epoxide (up to 82%). It was then tested on the FAME mixture from karanja oil, where interesting conversion values were attained (up to 70%), although with lower selectivities and yields to the mixture of desired epoxidized FAMEs. The solid withstood four catalytic cycles overall, during which a non-negligible surface reorganization of the Nb(V) sites was observed. However, this restructuring did not negatively affect the performance of the catalysts in terms of conversion or selectivity.

Formability of quenching-partitioning-tempering martensitic steel

ABSTRACTA Fe-0.20C-1.49Mn-1.52Si-0.58Cr-0.05Nb (wt%) steel was treated by a novel quenching-partitioning-tempering (Q-P-T) process and traditional quenching and tempering (Q&T) for comparison, respectively. The researches of the mechanical properties and forming limit diagrams reveal that Q-P-T martensitic steel has more retained austenite (10.8%) than the Q&T martensitic steel (less than 3%), which makes Q-P-T martensitc steel possess higher strain hardening exponent and true uniform elongation than the Q&T martensitic steel. The high value of hardening exponent (n) and true uniform elongation (εu) stem from the low initial dislocation density in martensitic matrix in Q-P-T martensitic steel before deformation and the high strain hardening rate and dislocation absorption by retained austenite (DARA) effect of retained austenite during deformation. Moreover, the n, or the εu, is a most important parameter in all the apparent parameters affecting the formability of metal sheets, and this conclusion is of practical importance in the comparison of several steels’ formability.

Microstructure and properties of Cu-Cr-Nb alloy with high strength, high electrical conductivity and good softening resistance performance at elevated temperature

Cu-0.47Cr-0.16 Nb (wt%) alloys were designed and prepared, and the microstructures of the Cu-Cr-Nb alloy were investigated using transmission electron microscopy and three-dimension atom probe tomography technique. After homogenizing at 950 °C for 4 h, cold rolling by 80% reduction, then aging at 450 °C for 30 min, the micro-hardness, electrical conductivity, tensile strength, yield strength and elongation of the alloy were up to 150 HV, 89.1%IACS, 453 MPa, 443 MPa and 11.4%, respectively. The tensile strength / elongation of the alloy approached 399 MPa / 22.9% as test at 200 ℃, 334 MPa / 14.8% for 300 ℃, and 282 MPa / 12.3% for 400 ℃, respectively. The Cr2Nb phase with an average size of 700 nm and Nb phase with an average size of 500 nm formed during the solidification process, while the nano-scale Cr-rich phases precipitated from the solid solution during the aging process. The sizes of Cr2Nb and Cr-rich phases were close to each other during aging. These precipitates located in the grain and sub-grain boundary could effectively pin the movement of boundary, resulting in a high strength of the alloy at the elevated temperature. The addition of Nb can promote the precipitation of Cr from the solid solution during aging, thus both strength and electrical conductivity of the alloy were improved.