Influence Of Niobium Additions Research Articles

Characterization of NiTiNb10.5 shape memory alloy: microstructural aspects and high-temperature oxidation behavior

The influence of Niobium addition on the high-temperature oxidation behavior of NiTi shape-memory alloys was investigated. Mass-gain kinetics were determined for up to 100 h oxidation at 800, 900 and 1000 °C. Niobium addition drastically reduced the oxidation rates. The surface and cross-section of the resulting oxide layers were characterized by XRD and SEM/EDS. The presence of Nb changed the morphology, phase assemblage, and composition of the scale product, which directly influenced the observed results. The postulated reasons for the improved oxidation resistance were the Nb-doping of TiO2 and the formation of an Nb-rich layer at the scale/alloy interface.

Influence of Niobium Addition on Microstructure and Machinability of High Chromium Cast Iron

High Chromium Cast Iron (HCCI) is mostly utilised in environments under severe abrasion and corrosion wear conditions, and research on this material with added niobium obtained positive results regarding wear resistance. The casting process has surface finish and dimensional accuracy limitations compared to machining processes. There are too few studies about HCCI machinability and no one about HCCI with niobium additions. HCCI machinability studies may allow new applications for this material when excellent surface finish and high dimensional accuracy are required. This study analyses the influence of 0.5% Nb addition on the microstructure and machinability of a HCCI alloy with 25.6% Cr and 3.2% C. The samples were heat treated and subsequently machined in dry cutting conditions. Annealing was used to facilitate the pre-machining of the samples, which were later quenched and tempered. Microstructure and hardness were analysed at each stage of the heat treatment. The material was machined after tempered using polycrystalline cubic boron nitride (pcBN) tools. The alloys solidified in the hypereutectic condition. The addition of niobium reduced the hardness and carbide volumetric fraction, increased the service life of the cutting tools in all tests, provided better surface finishing and modified the wear mechanisms.

The Influence of Niobium Additions on Creep Resistance of Fe-27 at. % Al Alloys

Results of creep tests of two Fe-27 at. % Al-based alloys with additions of 2.7 and 4.8 at. % of niobium conducted in the temperature range from 650 °C to 900 °C in the authors’ laboratory are presented. The purpose of the study is to supplement previous work on Fe-Al-Nb alloys to obtain a more complete overview of creep properties from the dilute alloy with 1% of Nb up to the eutectic alloy with 10% of niobium. At higher temperatures and lower stresses, the creep resistance of the 10% niobium alloy is better than that of the lower niobium alloys. On the other hand, the eutectic alloy loses its preference at lower temperatures and higher deformation rates. This phenomenon is similar to that reported by Yildirim et al. for Fe-50 at. % Al-based alloys and is probably associated with an increased stress sensitivity of the eutectic alloy.

Influence of niobium addition on structure and mechanical properties of W-Nb-N coatings

W-Nb-N coatings with Nb content ranging from 0 to 13.2 at.% were deposited by reactive magnetron sputtering technique. The influence of Nb content on the structure and mechanical properties was investigated. The results show that Nb atoms substitute W atoms forming the solid solution W-Nb-N. All the coatings exhibit a single-phase face-centered cubic (fcc) structure and the preferred orientation changes from (200) to (111) with Nb addition. The grain size of W-Nb-N coatings decreases with the increase of Nb content. The hardness and elastic modulus of W-Nb-N coatings increase gradually from 28.0 GPa to 320 GPa at 0 at.% Nb to 36.0 GPa and 386 GP at 13.2 at.% Nb, respectively. The adhesion between coatings and Si substrate also could be improved by Nb addition.

Effect of Niobium on Phase Transformations, Mechanical Properties and Corrosion of Supermartensitic Stainless Steel

The influence of niobium addition in a supermartensitic stainless steel with 13Cr-5Ni-2Mo has been studied. The steel with Nb tempered at 600 °C for 2 h showed improved mechanical resistance properties and lower degree of sensitization, without compromising elongation and pitting corrosion resistance, when compared to the reference steel. In order to understand the Nb effect in such steel, mainly regarding phase transformation, different tempering time intervals have been studied. The better performance of the SM2MoNb is attributed to the hindering effect that Nb has in the kinetics of the phase transformations during tempering, delaying the precipitation start and coarsening stages of the present phases.

Influence of Niobium Content on the Hot Mechanical Behavior of Nickel Alloys

Nickel-base superalloys are usually employed for large forged parts in aerospace industry. A comprehensive understanding of their mechanical behavior during hot working is required, especially for manufacturers in order to enhance the in-service properties. In this context, the first part of the work aims at investigating the mechanical behavior of nickel during hot deformation, with particular emphasis on the influence of niobium additions in solid solution. For this purpose, a series of wrought model alloys including pure nickel and Ni-Nb alloys (Ni-0.01, 0.1, 1, 2, 5 and 10 wt. % Nb) were prepared and deformed by hot torsion at temperatures ranging from 800 to 1000 °C degrees and at three (von Mises equivalent) strain rates of 0.03, 0.1 and 0.3 s-1. Afterwards, the key rheological parameters that characterize strain hardening and dynamic recovery were determined through a simple analytical method based on the classical Laasraoui-Jonas constitutive equation, allowing reasonable fit for the flow curves for all studied Ni-Nb alloys. In this way, the effect of niobium solutes on the fundamental mechanisms of deformation was well highlighted. In the second part, three usual models describing strain hardening and dynamic recovery, referred to as the Laasraoui-Jonas (LJ), Kocks-Mecking (KM), and power law (PW) equations are compared within the range of moderate strains. Transformation formulae are derived, allowing the parameters of one law to be computed from the parameters of any of the two others. The theoretical derivations are illustrated by the specific case of a Ni-Nb alloy in the solid solution domain.

Influence of Niobium Addition in Iridium on High Temperature Plasticity

Discussed the characteristics of iridium generally, illustrated the importance of exploring and studied the plasticity about iridium. We analyzed high temperature plasticity about Nb alloying effects based on first-principles density functional theory. Calculated cohesive energies and formation enthalpies of IrXNb32-X in different amounts of Nb, then calculated and analyzed elastic constants of IrXNb32-X, and finally summarized the influence of Nb addition in Ir on high temperature plasticity.

Influence of niobium addition on the high temperature mechanical properties of a centrifugally cast HP alloy

The influence of niobium addition on the mechanical properties at high temperature of HP alloy has been investigated. Two HP alloys were centrifugally cast with a similar chemical composition differing only in the niobium content. Low strain rate high temperature tensile tests and creep-rupture tests were performed in the range of 900–1100°C, and the results compared between the alloys. According to the results, the high temperature mechanical behavior of both alloys is controlled by several factors like solid solution, network of eutectic carbides, intradendritic precipitation and dendrite spacing. A significant increase in the mechanical properties for the HP alloy with niobium addition was found within the temperature range of 900–1050°C. Beyond this temperature the mechanical behavior of both alloys is basically the same.

Influence of niobium addition on microstructure, mechanical properties and oxidation resistance of ZrN coatings

In this study, Zr-Nb-N coatings with 0–3.8at.% Nb addition were deposited by magnetron co-sputtering deposition. The results reveal that Nb atoms substitute Zr atoms in Zr-N lattice, forming the solid solution structure. All the Zr-Nb-N coatings illustrate a dense columnar structure with the preferred orientation of (200), showing independent of Nb addition. Nanoindentation result reveals a promoted hardness of the Zr-Nb-N coatings from 23.9±0.7GPa to 28.4±0.5GPa with enhanced Nb content from 0 to 2.8at.% due to both the solid solution strengthening and Hall–Petch effect. Scratch tests show that adhesion between substrates and coatings can be improved by Nb addition. After oxidation in air at 600°C for 2h, microstructural studies indicate the oxide scales consist of monoclinic-ZrO2 outer layer and tetragonal-ZrO2 inner layer. Moreover, ZrO2 can be stabilized in the tetragonal phase by Nb doping. The Zr-Nb-N coating with 1.3at.% Nb addition exhibits superior oxidation resistance, while excess Nb addition produces detrimental effects on oxidation resistance.

Influence of niobium additions on high-temperature-oxidation behavior of Ti3Al alloys and coatings

In this study, the oxidation properties of Ti3Al+Nb bulk alloys, as well as IMI 829 alloy, coated with a Ti3Al+Nb layer, have been considered. Model alloys have been prepared, with 5–25 at.% niobium contents; 50-μm-thick Ti3Al+10 at.% Nb coatings have also been deposited on IMI 829 by triode sputtering. Bulk alloys and coated substrates have been exposed to cyclic and isothermal oxidation in air between 700 and 800°C. Niobium additions generally caused the oxidation rate of Ti3Al to decrease significantly. In all cases rutile is the main oxide formed. It is believed that the ability of niobium to dissolve in the rutile lattice, and therefore to lower the oxygen diffusion rate through the oxide layer, is a contribution to the observed oxidation resistance enhancement. The formation of niobium oxide has also been envisaged for this matter.

Effects of recrystallization and Nb additions on texture and mechanical anisotropy of Zircaloy

Abstract The effect of recrystallization on the crystallographic textures and anisotropic mechanical properties of Zircaloy-4 sheets was investigated. In addition, the influence of niobium additions on these properties was studied using three different alloys. The mechanical anisotropy parameters were determined by mechanical testing of gridded tensile samples. The textures were characterized by X-ray pole figure measurements and crystallite orientation distribution functions (CODFs). The CODFs were combined with a crystal plasticity model to predict the anisotropy parameters based on the dominance individually of basal, prism and pyramidal slip systems. Good agreement was noted between the experimental results and model predictions based on prism slip for the recrystallized materials, while the results on cold-worked sheets differed from model predictions for all the three slip systems.