Effect Of Niobium Addition Research Articles

Effects of niobium addition on the sustained-load cracking characteristics in lamellar microstructure γ-base TiAl

Substained-load cracking characteristics of lamellar microstructure binary and niobium-alloyed γ-base titanium aluminides are investigated. Crack growth was observed under sustained load at stress intensities much lower than the fracture toughness of the matieral. Addition of niobium improved the sustained-load cracking characteristics significantly. The threshold stress intensity factor for the sustained-load crack growth in vacuum was found to be higher than that in air indicating the strong influence of environment. Crack growth under sustained load was attributed to the stress corrosion cracking. Less deformation at the crack tip due to addition of niobium might have caused less diffusion of embrittling species and improved the environmental resistance.

Effect of niobium addition on the NdFeB alloy and magnet

The effect of niobium addition on the microstructure and phase compositions of an Nd 2(Fe 0.98Nb 0.02) 14B alloy and an Nd 16Fe 76.3Nb 0.3B 7.4 magnet have been investigated. The microstructure of the as-cast alloy contains four phases, the Nd 2Fe 14B matrix phase, an NbFeB ternary phase, Nd-rich regions and free iron. After homogenisation the alloy contains only the first two phases and very small amounts of Nd-rich phase. Quantitative electron probe microanalysis of the NbFeB phase revealed a composition of approximately Nb 26Fe 32B 42. This ternary phase was found in the as-cast alloy, the homogenised alloy and also, to a lesser extent, in the magnet. The shape of this phase in the as-cast and the sintered magnet was hexagonal whereas, in the homogenised alloy, it was also observed in an acicular form. In the as-cast alloy the ternary phase was found to nucleate within the free iron phase and then grows at the expense of the surrounding free iron. This provides strong evidence for the role of Nb in the removal of free iron from the microstructure. The results indicate that, by controlling the solidification behaviour of the alloy, free iron may be prevented from nucleating or at least reduced to a very thin film near the surface of the ingot which can be removed by machining to produce NdFeB material without free iron.

The effect of niobium additions on the fracture of Ni19Si-based alloys

The mechanical properties of Ni19Si polycrystals alloyed with niobium and boron were investigated by microhardness and tensile tests. The microstructure change caused by the addition of niobium was also examined by X-ray diffraction, high temperature differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. The results reveal that the cast Ni19Si xNb alloys of two phases, α (f.c.c.) and β(Li 2). The addition of niobium, which substitutes for silicon in these alloys, will decrease their melting points, but increase their hardness and yield strengths. This strengthening effect arises owing to the lattice expansion of the β phase matrix by the addition of niobium and the hardening by the hard niobium-rich precipitates in the β matrix. In addition, it appears that with 5 at.% Nb, the β phase formed directly from the melt, instead of a liquid-solid or solid-solid reaction. The fracture behavior of the Ni-19Si3.5Nb alloy with boron doping also exhibits significant ductility improvement.

Effect of niobium additions on the structure and magnetic properties of equiatomic iron-cobalt alloys

The structure of equiatomic iron-cobalt alloys containing 1, 2 and 3 wt% niobium has been studied using a variety of techniques, including X-ray diffraction, scanning and transmission electron microscopy and differential thermal analysis. It has been found that niobium is effective in reducing the kinetics of ordering to the B2 structure and of anti-phase domain growth, even though the solubility is only 0.3–0.5 wt%. The magnetic properties (coercive force and saturation magnetization) and the electrical resistivity of the three alloys have also been determined.

Effect of niobium additions on the structure and magnetic properties of equiatomic iron-cobalt alloys

Effect of niobium additions on the structure and magnetic properties of equiatomic iron-cobalt alloys

Microstructure and creep behavior of a niobium alloyed cast heat-resistant 26 pct Cr steel

The effects of niobium additions to a “straight chromium” alloy were investigated by optical metallography and creep testing at 1033 K. The results indicate that by increasing the amount of interdendritic constituent, niobium adds to creep strength and fracture ductility. Optimum alloy design requires balancing niobium, chromium, and carbon content.

The effect of niobium additions on an FeCrCo permanent magnet alloy

The effect of niobium additions on an FeCrCo permanent magnet alloy

The Effect of Niobium Additions on the Corrosion Behavior of Zircaloy-4

Alloying additions of 0.5 and 1.0 wt% niobium, respectively, have been added to Zircaloy-4 in an attempt to improve its high-temperature corrosion resistance. Ingots of these modified alloys were fabricated to a 0.76-mm-thick sheet via a processing sequence compatible with commercial tubing production and were given one of four different final anneals. Subsequent testing indicated that the niobium additions had little or no effect on corrosion resistance in 360°C water. In 427°C steam, however, the 0.5%-niobium addition provided increased resistance to spalling, while the 1.0%-niobium addition decreased both cumulative weight gains and post-transition corrosion rates. The weight gains exhibited by the 0.5%-niobium alloy were relatively insensitive to final heat treatment, whereas the 1.0%-niobium alloy suffered a degradation in properties as the extent of the final anneal increased. These trends in corrosion performance were subsequently correlated with the second-phase particle size distributions present in the alloys, the best performance being obtained when the mean particle diameter was <400 to 500 Å. It was concluded that both niobium additions improved the corrosion performance of Zircaloy-4 at elevated temperatures, but that the best performance was obtained at the 1.0-wt%-niobium level.

Plastic anisotropy of low-carbon, low-manganese steels containing niobium

The effect of niobium additions (up to 0.23 pct) on the plastic anisotropy of cold-rolled and annealed low-carbon, low-manganese steels has been studied. When hot-rolling conditions involving coiling temperatures below 1150°F were used, increased concentrations of niobium were deleterious to the development of high plastic anisotropy. Isothermal transformation studies and special hot-rolling studies showed that when transformation from austenite to ferrite and precipitation of carbonitrides occurred at high temperatures (\s>1350°F), excellent plastic anisotropy (•gn about 2) was obtained after cold rolling and annealing. The results are interpreted on the basis of an effect of critical particle sizes or dispersions on the selection of preferred orientations during recrystallization. From electron microscope studies, the critical carbonitride size and interparticle spacing, necessary for the development of high plastic anisotropy, was estimated to be 40 to 500A and 0.04 to 0.5 μm, respectively. However, the presence of a large amount of niobium in solid solution in ferrite is apparently deleterious to the development of high plastic anistropy, even though carbonitrides having the critical size and spacing are present. On the basis of these observations and other published work, it is suggested that second-phase particles influence the development of plastic anisotropy in rimmed and aluminum-killed steels as well as in niobium-and titanium-containing steels. Thus, the degree of plastic anisotropy produced in these steels is influenced by textures developed during annealing, which in turn is dependent on the dispersion characteristics of the particular second-phase particles present.

極低炭素冷延鋼板の集合組織に及ぼすニオブの影響

極低炭素冷延鋼板の集合組織に及ぼすニオブの影響

Ni-Mn系新高透磁率合金「Nimalloy」の特性におよぼすNb添加の影響について

Ni-Mn系新高透磁率合金「Nimalloy」の特性におよぼすNb添加の影響について

Nb添加非調質高張力鋼板に関する研究(第1報)

At first the effect of niobium addition on the mechanical and welding properties of low carbon steel small plate as rolled was investigated in laboratory as compared with vanadium addition. Then the properties of large plate as rolled in works of killed and semikilled steel containing niobium, especially the toughness of the plate were investigated.1) To increase the tensile strength of low carbon steel plate as rolled by 5-6 Kg/mm2 the addition of about 0.05% vanadium is a little more effective than the one of niobium equivalent to 0.05% vanadium with respect the impact properties of the plate. But niobium increases the tensile strength of the plate more than vanadium in the range up to about 0.05% individually.2) It may be said that we have had for the first time nonheat-treated weldable high tension steel plate with both tensile strength over 60 kg/mm2 and structure consisting of ferrite and pearlite. The addition of both niobium and vanadium to the low alloy steel containing lower content of carbon further improves the impact properties of the plate as rolled.3) The high tension steel plate containing niobium has a higher yield ratio as well known and can be welded easily, but the absorbed energy in Charpy impact test of the plate is comparativelly small and this phenomenon is especially controversial in the transverse direction to rolling one. The absorbed energy in Charpy test being small is probably due to the higher tensile strength for the structure consisting of ferrite and pearlite. But the transition temperature of fracture surface in Charpy test is comparativelly good and not worse than the one of low tension steel plate containing no niobium.4) The new evaluation criteria for brittle fracture characteristic of structural steels for low temperature application (recently proposed by Japan Welding Engineering Society) adopt the evaluation method by transition temperature of fracture surface in Charpy test, rejecting the one by the absorbed energy. The transition temperature of fracture surface of high tension steel plate containing niobium being good, the small absorbed energy of the plate seems not to be a large defect.5) The fracture tests on a larger scale such as press-notch crack starter test (wedge impact test) and double tension test of the plate were also carried out. The results of these fracture tests matched the transition temperature of fracture surface in Charpy test and supported the evaluation results by the above new criteria.6) The tensile strength of carbon steel plate containing no niobium coiled immediately after hot-rolling is lowered in general due to the pearlite structure being globularized during slow cooling from coiling temperature, but the one of coiling plate containing niobium is little lowered by precipitation hardening of niobium carbo-nitride. The method to apply globularizing annealing to uncoiled flat plate after hot-rolling may be suitable to improve the impact properties of large plate unable to be coiled.