Papers by Keyword: Niobium

Abstract: Incremental sheet forming is a viable method for manufacturing highly customized components from non-conventional materials. Among these, niobium is a metal of growing interest due to its potential in various technological applications. In this experimental study, the incremental forming of high-purity annealed niobium sheets was investigated, with particular attention given to the surface finish of the formed parts. To this end, the surface morphology of the components, specifically fixed wall conical frusta, and the forming forces were analyzed. The results indicate that, despite the material’s notable formability, the incrementally formed niobium surfaces exhibit poor quality. This is attributed to the unique properties of niobium, suggesting that the development of surface treatment strategies is advisable to improve this aspect.

Abstract: The mechanical properties of anodic oxide films of Nb, Ta and Zr were studied by the nanoindentation method. Anomalously high elastic recovery after deformation was observed for oxides with thickness of 20 nm. An analogue of this behavior can be elastic membrane fixed on soft base that does not prevent the membrane from bending. Increase of the oxide thickness to 300 nm reduced the effect associated with the high elasticity of oxide and easy deformation of the soft metal substrate, and was accompanied by an increase in the plastic component of deformation, which is similar to the behavior of ceramic materials with low elastic and significant residual plastic deformation.

Abstract: Niobium is added to carbon steels in small amounts (< 0.1weight %), thus being called a microalloying element, to increase mechanical strength and toughness. When added to steel, niobium is partly soluble in the matrix and another part combines with carbon and nitrogen forming a family of Nb_xC_yN_z precipitates (niobium carbides, nitrides or carbonitrides), where the values ​​of x, y, z depend on the temperature and the chemical composition of the steel. The solubility equations for niobium in austenite available in the literature only provide the niobium content that could be solubilized at a given temperature. But when niobium is added above the solubility limit, the excess niobium will not only form the Nb_xC_yN_z family of precipitates. This is what the proposed model calculates. The proposed model is easy to apply and provided results are very close to those determined experimentally by different researchers, who used different techniques such as atom probe, or matrix dissolution with precipitate filtration, for example. Although the proposed model has been used to calculate niobium in solution in austenite, the same can be applied to any other precipitate, such as carbides, nitrides or carbonitrides of vanadium and titanium, for example.

Abstract: Our research novel Ti-22Nb biomedical alloys made by powder metallurgy and analyze the effect of adding silicon at various weight ratios to the base alloy (0.4, 0.8, and 1.2 %at Si). In this work, the wear characteristics of Ti-Nb-Si alloys in dry conditions are examined, as well as the wear process. To measure the wear rate, a pin-on-disc wear testing apparatus was employed. The optical microstructure analysis showed that the microstructure had a mixture-like appearance and included only a small quantity of another phase. XRD results showed that the stability of the β phase increased with silicon concentration. The (Ti-22Nb) alloy's hardness and compressive strength both increased once silicon is added. Hardness also rises as the amount of silicon additions increases, with the maximum percentage (1.2 percent Si) resulting in the highest hardness and compressive strength

Abstract: Niobium is added to carbon steels in small amounts (< 0.1weight %), thus being called a microalloying element, to increase mechanical strength and toughness. When added to steel, niobium is partly soluble in the matrix and another part combines with carbon and nitrogen forming a family of Nb_xC_yN_z precipitates (niobium carbides, nitrides or carbonitrides), where the values of x, y, z depend on the temperature and the chemical composition of the steel. The effects of niobium dissolved in the matrix or as precipitates are distinct and sometimes antagonistic. Thus, two samples of the same carbon steel microalloyed with niobium may differ in: microstructure, ferritic grain size or interlamellar spacing of the pearlite, depending on the thermomechanical processing to which they were submitted, which will result in different mechanical properties. In order to make good use of the possible beneficial effects of adding niobium to carbon steels, it is necessary to clearly understand its complex physical metallurgy. To analyze the effects of niobium, six steels were used (0.2/0.4/0.8 C/ 1 Mn, with and without the addition of 0.03 Nb, weight %). Using an ARL ion microprobe, with oxygen ions and mass spectroscopy reading on niobium steel, after partial isothermal transformation at 700 oC, we observed the partition of niobium between ferrite and austenite. Thus, the formation of ferrite is slower, shifting the TTT curve to longer times and separating the pearlite and bainite bays. The same occurs in continuous cooling transformation, where the diffusional components (ferrite, pearlite and bainite) are formed at lower temperatures and with a longer time. With pearlite forming at lower temperatures, there is a decrease in the interlamellar spacing, increasing its hardness and, consequently, the mechanical strength. Niobium also forms carbonitrides, and these finely precipitated particles anchor the grain boundary, making it difficult to move and thus producing a smaller austenitic grain size than in steel without the addition of niobium, increasing mechanical strength and toughness of steel.

Abstract: Pure Niobium is a material of interest for high-energy-physics applications including superconducting accelerators. Cold-rolled sheets of Nb exhibit significant plastic anisotropy. Here we report on the mechanical and forming properties of 99.95% pure, 1.02 mm thin, cold-rolled sheet. Uniaxial tension, biaxial tension and disc compression experiments are performed, the first two at multiple angles to the rolling direction of the sheet. The material is very ductile (uniform elongation ~30%), and exhibits significant plastic anisotropy (e.g., the R-values range from 1.2 in 45^o to 2.5 in 90^o). The results are used to calibrate the Yld2000-2D anisotropic yield function, with an exponent of 6 as Nb is BCC. They are also used to extract the hardening curve beyond the limit load in uniaxial tension. Deep-drawing experiments are performed using a die of 27.6 mm dia. and a punch of 25.4 mm dia. Blanks of various diameters are used. The successfully drawn cups exhibit significant earing. The experiments are simulated using Abaqus/Standard and shell elements. It is shown that a properly calibrated material model enables the numerical simulations to match the experiments.

Abstract: We investigated the possibility of using an organofluorine coating on parts of the "Screen" type made by cold stamping from refractory metals, in particular niobium. The paper also presents the results of a study of the mechanical characteristics of samples with acoustic-emission accompaniment and the hardness values before and after applying the organofluorine composition. The surface of parts with and without coating after convolution is studied. It is shown that it is possible to prevent loss of stability during the first operation of the technological process, as well as to reduce the number of operations by eliminating annealing between subsequent operations of drawing with thinning.

Abstract: Pure niobium substrates were coated using laser cladding method. Pure molybdenum, Yttria Stabilized Zirkonia (YSZ) and corundum (Al₂O₃) powders were used as coating materials. Coatings were deposited on specimens as seperate paths with 3÷10mm width and 40mm of length. Two different laser power 3kW and 4kW were tested during deposition. In order to assess the quality of the Mo-YSZ and Mo-Al₂O₃ coatings, the light microscopy, Scanning Electron Microscopy (SEM), chemical analysis (EDS) and Vickers hardness test investigation were performed. The surface roughness and wear volume were also measured. As a result of YSZ-Mo powder cladding on the Nb substrate the composite layers were obtained without cracks and porosity not exceeding 1 μm. In addition, an increase in hardness of about 450 HV0.5 was revealed. As a result of Al₂O₃-Mo powder cladding on the Nb substrate the composite layers with many voids and cracks were obtained for each of the cladding variants.

Abstract: The authors conducted the study at micro-scratching of titanium, zirconium, niobium and molybdenum alloys. The content of the main element in alloys was from 99.5 to 99.7 %. Micro-cutting was carried out by specially prepared indenters with silicon carbide mono-crystals of a given shape. The state of the relief and the chemical composition of the wear area were studied using a scanning two-beam electron microscope. The micro-scratching speed was 35 m/s without cooling. The condition of the contact surfaces of silicon carbide and metals was studied at a magnification up to 100,000 times with the rotation and tilt of the microscope slide. The content of chemical elements was determined at individual spots of an object by scanning along the line and area. The authors also studied the condition of the wear area after micro-scratching of metals and after removal of metal adhesions by chemical etching. The intensity of metal transfer was determined by the average concentration of metal atoms at the wear area. The article also gives a classification of metals according to the intensity of transfer immediately after grinding and removal of metal adhesions. The influence of metal and the depth of micro-scratching on the morphology of the wear site is shown. It was found that molybdenum, having a low adhesive activity to silicon carbide, is able to penetrate microcracks and other surface defects during micro-scratching. The width of microcracks and the depth of metal penetration were determined

Abstract: Niobium is an important constituent of Zr-Nb alloys being used widely in the nuclear industries as fuel claddings and pressure tubes. In this article, MD based simulations are performed to obtain grain boundary (GB) energies in ∑3 symmetrical and asymmetrical tilt grain boundaries (ATGBs) along <110> tilt axis. Grain boundary energies are also obtained analytically by utilizing the equation establishing the relationship between inclination angle and grain boundary energy for ATGBs. It is observed that in both the cases the GB energies increase with the increase in inclination angle of the ATGBs. The increase in the GB energy follows the same trend with a little offset between the results obtained analytically and MD based simulations. The offset between both the results can be attributed to the limitations of the potentials employed for the simulations. MD based simulations thus provide an accurate method to calculate the GB energies.