Nickel Alloy Matrix Research Articles

Magnetic Instability in ${\hbox{MgB}}_{2}$ Monofilamentary Tapes

The magnetic instability in MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> monofllamentary tapes with nickel alloy matrix has been investigated by measuring hysteresis loops and magnetic relaxation. The measurements have been performed in the temperature range from 2 K up to 39 K, applying an external magnetic field up to 20 kOe both parallel and perpendicular to the filament direction. We have analysed the magnetic instability by using an adiabatic and dynamical approach and taking also into account the effects of the samples geometry on the magnetic properties. In this work we discuss the observed dependence of the flux jumps on the temperature and on the applied magnetic field taking into account the recent results on the magnetic instability in a superconductor placed in a perpendicular magnetic field.

Magnetic relaxation in MgB 2 monofilamentary tapes

To study the flux creep in MgB 2 monofilamentary tapes embedded in nickel alloy matrix, we have measured the magnetic relaxation M( t) in the temperature range from 4.2 K up to 30 K applying an external magnetic field of 10 kOe both parallel and perpendicular to the filament direction. We have analyzed the experimental curves including the first seconds of the magnetic relaxations. In this work, we discuss the dependence of the M( t) creep rate and the effective pinning energy on the temperature in presence of an applied magnetic field, taking also in account the sample geometry.

Silicon-boronising of Nimonic 90 superalloy

In the present work, Nimonic 90 alloy surface has been modified to increase its abrasive wear resistance by using a self-protective silicon-boronising paste agent. A multilayer consisting of intermetallic compounds, or a composite layer containing different intermetallic compounds, was formed at the surface. In the former case, the multilayer coating consisted of an outer layer of (Ni,Co) 2Si, an intermediate layer of (Cr,Co) 2B, and an inner layer of Ti-rich nickel silicide. The total thickness of these layers was 40–90 μm, depending on the temperature and the holding time. In the latter case, the composite layer contained lathlike (Ni,Co) 5Si 2, ‘flower patterns’ of CrB and modified nickel alloy matrix. The composite layers were about 500 and 800 μm thick after 2 h and 8 h of treatment, respectively. The microhardness of the coatings was about 3 times higher than that of the Nimonic 90 substrate. The abrasive wear resistance of Nimonic 90 was raised by 2.5–5 times, depending on the employed surface treatment parameters.

Self-Lubricating Composite Coating on Air Foil Bearing Shaft by Hollow Cathode Plasma Jet

The self-lubricating composite films were deposited on Inconel 718 by Hollow Cathode Plasma Jet (HCPJ). These composite materials consist of chrome nickel alloy matrix and Ag, BaF2/CaF2 solid lubricants. The Cr2O3-NiCr-Ag composite thin film was crystallized and had the main peaks of Cr2O3 (012) and Ag (111). The deposition rate of 200 nm /min by HCPJ was much faster than the ordinary R.F planar magnetron sputtering. The surface roughness of coated shaft was 30 nm.

A model for heterogeneous materials including phase transformations

A model is developed for particulate composites, which includes phase transformations in one or all of the constituents. The model is an extension of the method of cells formalism. Representative simulations for a single-phase, brittle particulate (SiC) embedded in a ductile material (Ti), which undergoes a solid–solid phase transformation, are provided. Also, simulations for a tungsten heavy alloy (WHA) are included. In the WHA analyses a particulate composite, composed of tungsten particles embedded in a tungsten–iron–nickel alloy matrix, is modeled. A solid–liquid phase transformation of the matrix material is included in the WHA numerical calculations. The example problems also demonstrate two approaches for generating free energies for the material constituents. Simulations for volumetric compression, uniaxial strain, biaxial strain, and pure shear are used to demonstrate the versatility of the model.

Abrasion resistance of thermal sprayed composite coatings with a nickel alloy matrix and a WC hard phase. Effect of deposition technique and re-melting

Coatings resulting from the spraying of mixtures with different proportions of two commercial alloys, a nickel self-fluxing alloy and a tungsten carbide with cobalt, have been produced using two flame-spraying techniques: HVOF, and powder oxy-acetylene flame spraying. The effect of both hard-phase content and coating-spraying technique on abrasion resistance is discussed in terms of the coatings' mechanical properties and microstructure.

Micromechanical modelling of microstress fields around carbide precipitates in alloy 600

Elastic stresses in the grain boundary regions caused by the mismatch between the elastic properties of a carbide precipitate and a nickel alloy matrix were studied by finite-element modelling. The effects of the metal matrix elastic anisotropy, the precipitate elastic anisotropy and the external stress state on the microstress fields around the precipitate were analysed. An intragranular carbide precipitate is not as effective a stress raiser as a carbide precipitated at a grain boundary triple point due to the contributing effect of strain incompatibilities between the grains in the latter case. The precipitate, which has an effective elastic modulus that is higher than that for the surrounding grains, experiences more stress than the matrix, i.e. the stresses inside the precipitate are higher than in the alloy grains. The mismatch between the elastic moduli of the alloy and the precipitate has a pronounced effect on the stress distribution; the higher the precipitate modulus compared with the matrix modulus, the higher is the local stress concentration in the grains of the alloy matrix. The shape of the inclusion plays a role in the stress distribution in the grain boundary regions; sharp corners raise stresses more effectively than rounded edges of oblong-shaped precipitates. Shear anisotropy in the precipitates affects the distribution of the von Mises (shear) stresses, and the compression anisotropy affects the state of the hydrostatic pressure: the higher the elastic anisotropy, the higher are the corresponding stress concentrations. The selection of the external stress state (shear versus hydrostatic) can reduce or enhance the effects of the precipitate elastic anisotropy. Equi-biaxial loading provides for a more uniform distribution of stresses than does uniaxial loading. The high stress fields are confined to the vicinity of the precipitate (their range is much smaller than the size of the precipitate). When the spacing between carbides at the grain boundary becomes large, their elastic interactions become insignificant.

Ｎｉ‐Ｍｏ‐ＴｉＣ基粉末の混合・粉砕による組成変動と合金化

By using the stirrer-type ball mill which is used for mechanical alloying, nickel rich Ni-Mo-Cr-Co metal powders added with titanium carbide powder were mixed and pulverized in wet condition for a total time of 120 hours. With increase in processing time, the shapes and sizes of the powder particles tended to be uniform and the contents of nickel, titanium, molybdenum, carbon and cobalt were decreased but the contents of chromium and iron were increas-ed. Especially the content of iron which was not added to the starting mixed powders increased up to a few percents.The hot-pressed specimens of the powders mixed in wet and dry condition were compared in their hardness and microstructure. In the former, fin titanium carbide particles were dispersed in nickel alloy matrix whereas in the latter, titanium carbide particles which have high hardness were extinguished to alloy with nickel and then the hardness of the latter decreased to be about 1/5 that of the former.

Chemical partitioning of elements in Ni-base MC-carbide reinforced eutetic superalloys

The plane-front solidified eutectic alloys consisting of aligned tantalum monocarbide fibers in a nickel alloy matrix are currently under consideration for future aircraft and gas turbine blades. The MC fibers provide exceptional strength at high temperatures. In these alloys, the Ni matrix is strengthened by the precipitation of the coherent γ' phase (ordered L12 structure, nominally Ni3Al). The mechanical strength of these materials can be sensitively affected by overall alloy composition, and these strength variations can be due to several factors, including changes in solid solution strength of the γ matrix, changes in they γ' size or morphology, changes in the γ-γ' lattice mismatch or interfacial energy, or changes in the MC morphology, volume fraction, thermal stability, and stoichiometry. In order to differentiate between these various mechanisms, it is necessary to determine the partitioning of elemental additions between the γ,γ', and MC phases. This paper describes the results of such a study using energy dispersive X-ray spectroscopy in the analytical electron microscope.

Development of oxide diffusion-barrier on refractory metals

A new approach to the development of diffusion-barrier coatings which can effectively reduce the interaction of refractory filaments such as tungsten and tantalum with a nickel-alloy matrix is presented. This consists of reacting the oxide film deliberately grown on these metals with a nickel coating prior to fabricating the composite. The nickel-oxide film reactions proceed under vacuum conditions in the temperature range 650 to 800° C with the formation of intermediate phases which produce sufficiently strong bonds for composite strengthening.

Interfacial Stability and Mechanical Behavior of Nichrome-Tungsten Filamentary Composites

Filamentary composites are frequently fabricated by an elevated-temperature process such as diffusion bonding. Because of differences in chemical potential of the elements at the interface, processing or subsequent elevatedtemperature exposure is accompanied by interdiffusion and/or reaction. Generally, this is reflected in the degradation of mechanical properties since it is the interface that controls stress transfer from matrix to reinforcement. The purpose of this study was to characterize the interfacial dependence of mechanical behavior in potential high-temperature nickel-alloy matrix composites reinforced with refractory metal wires, and to determine the effectiveness of diffusion barrier layers between fiber and matrix.Tungsten wire-reinforced nichrome composites (Vf in range 10% to 20%; wire diameter 0.010“) were diffusion bonded under vacuum for one hour at 1100°C.