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Chemical vapor deposition welding below recrystallization temperatures for low temperature joining of refractory and nonrefractory metal aerospace structures
Cold machining process, which uses a sub-zero refrigerated cutting fluid, is used for machining refractory or reactive metals and alloys. Special carbide tools for turning and drilling these alloys further improve the cutting performance.
Development of aerospace structural materials - heat resistant alloys, refractory materials, transition metals, and composite materials
Production of refractory bodies with controlled porosity by pressing and heating mixtures of refractory and inert metal powders
Freeze casting of metal ceramic and refractory compound powders into plastic slips
This paper presents the results of a program to evaluate thermal insulations for use under the radiative TPS of a shuttle orbiter vehicle. Evaluations were made for survival under the multimission requirements of shuttle acoustic/vibration loads and thermal profiles. During the first year of the program a total of 1100 specimen-cycles were completed using metal foil packaged refractory fiber insulations.
High temperature oxidation resistance, high hardness and high abrasion and wear resistance are properties of cermet compositions particularly to provide high temperature resistant refractory coatings on metal substrates, for use as electrical insulation seals for thermionic converters. The compositions comprise a sintered body of particles of a high temperature resistant metal or metal alloy, preferably molybdenum or tungsten particles, dispersed in and bonded to a solid solution formed of aluminum oxide and silicon nitride, and particularly a ternary solid solution formed of a mixture of aluminum oxide, silicon nitride and aluminum nitride. Ceramic compositions comprising a sintered solid solution of aluminum oxide, silicon nitride and aluminum nitride are also described.
The NASA/University of Arizona Space Engineering Research Center is dedicated to research on the discovery, characterization, mapping, beneficiation, extraction, processing, and fabrication of useful products from extraterrestrial material. Schemes for the automated production of low-technology products that are likely to be desired in large quantities in the early stages of any large-scale space activity are identified and developed. This paper summarizes the research program, concentrating upon the production of (1) propellants, both cryogenic and storable, (2) volatiles such as water, nitrogen, and carbon dioxide for use in life-support systems (3) structural metals, and (4) refractories for use in aerobrakes and furnace linings.
Through the support of the NASA SBIR program, Control Vision, Inc. developed novel video techniques for clear, high resolution, real-time imaging of high temperature, high-energy industrial processes, such as welding, plasma arc spraying (coating), arc furnaces, metal casting and refractories (ceramics) melting. The Control Vision systems use reflected laser or strobe illumination, combined with ultra-short exposure times to create video, including the allowance of particle imaging velocimetry (PIV) of fast moving powder particles buried within a plasma stream.
We are currently studying the chemical interrelationships between the main rockforming components of carbonaceous chondrites (hereafter CC), e.g. silicate chondrules, refractory inclusions and metal grains, and the surrounding meteorite matrices. It is thought that the fine-grained materials that form CC matrices are representing samples of relatively unprocessed protoplanetary disk materials [1-3]. In fact, modern non-destructive analytical techniques have shown that CC matrices host a large diversity of stellar grains from many distinguishable stellar sources [4]. Aqueous alteration has played a role in homogeneizing the isotopic content that allows the identification of presolar grains [5]. On the other hand, detailed analytical techniques have found that the aqueously-altered CR, CM and CI chondrite groups contain matrices in which the organic matter has experienced significant processing concomitant to the formation of clays and other minerals. In this sense, clays have been found to be directly associated with complex organics [6, 7]. CR chondrites are particularly relevant in this context as this chondrite group contains abundant metal grains in the interstitial matrix, and inside glassy silicate chondrules. It is important because CR are known for exhibiting a large complexity of organic compounds [8-10], and only metallic Fe is considered essential in Fischer-Tropsch catalysis of organics [11-13]. Therefore, CR chondrites can be considered primitive materials capable to provide clues on the role played by aqueous alteration in the chemical evolution of their parent asteroids.
Device output and durability increased. Photosensitive GaAs Schottkybarrier device modified by addition of intermediate layer of refractory or alkaline earth metal. Photovoltaic cells and photosensors made with new design put out higher short-circuit currents and better able to withstand rigors of handling and connection to other circuit components.
Purification of alkali metals for use in advanced refractory alloy corrosion loop
Static and thermal convection loop tests for refractory alloy corrosion in lithium
Amorphous coatings of refractory metal/metalloid-based alloys deposited by magnetron sputtering provide extraordinary hardness and wear resistance. Sputtering target fabricated by thoroughly mixing powders of tungsten, rhenium, and boron in stated proportions and pressing at 1,200 degrees C and 3,000 lb/in. to second power (21 MPa). Substrate lightly etched by sputtering before deposition, then maintained at bias of - 500 V during initial stages of film growth while target material sputtered onto it. Argon gas at pressure used as carrier gas for sputter deposition. Coatings dense, pinhole-free, extremely smooth, and significantly resistant to chemical corrosion in acidic and neutral aqueous environments.
Refractory niobium alloy corrosion tests in potassium liquid at 2000 to 2200 degrees F
Temperatures high enough to vaporize even refractory solids existed in the midplane of the solar nebula during its earliest evolutionary stages and played an important role in the processing of materials that went into the formation of the inner planets and asteroids. A variety of such high-T materials have been identified in primitive chondritic meteorites. These include chemically zoned FeNi metal grains that are generally believed to have formed directly by gas-solid condensation from a gas of approximately solar composition. These FeNi particles provide important information about the times scales of formation and physical transport mechanisms in the nebula, as well as formation temperature, pressure and gas chemistry. Currently, however, the interpretation of the chemical signatures in these FeNi particles rests on less than perfect information about the condensation sequence of siderophile elements. For example much, if not all, of the thermodynamic data for the vapor pressures of moderately refractory metals , such as Fe, Ni and Co, do not cover the desired temperature range. As a result, quite large extrapolations are needed. These extrapolations can be complex and uncertain due to factors such as oxygen fugacity or the presence of hydrogen gas.
Additive friction stir deposition (AFSD) is a solid-state metal additive manufacturing technique, which utilizes frictional heating and plastic deformation to create large deposits and parts. Much like its cousin processes, friction stir welding and friction stir processing, AFSD has seen the most compatibility and use with lower-temperature metals, such as aluminum; however, there is growing interest in higher-temperature materials, such as titanium and steel alloys. In this work, we explore the deposition of an ultrahigh-temperature refractory material, specifically, a tantalum–tungsten (TaW) alloy. The solid-state nature of AFSD means refractory process temperatures are significantly lower than those for melt-based additive manufacturing techniques; however, they still pose difficult challenges, especially in regards to AFSD tooling. In this study, we perform initial deposition trials of TaW using twin-rod-style AFSD with a high-temperature tungsten–rhenium-based tool. Many challenges arise because of the high temperatures of the process and high mechanical demand on AFSD machine hardware to process the strong refractory alloy. Despite these challenges, successful deposits of the material were produced and characterized. Mechanical testing of the deposited material shows improved yield strength over that of the annealed reference material, and this strengthening is mostly attributed to the refined recrystallized microstructure typical of AFSD. These findings highlight the opportunities and challenges associated with ultrahigh-temperature AFSD, as well as provide some of the first published insights into twin-rod-style AFSD process behaviors.
A phenomenon of "phase inversion", presumably the first ever experimental evidence in metallic alloys, is shown in a refractory high entropy alloy (RHEA), Al0.5NbTa0.8Ti1.5V0.2Zr. Phase inversion in crystalline solid systems is driven by the differences in elastic modulus of the two phases. Quenching from a high-temperature single phase field, the RHEA exhibits a co-continuous mixture of a disordered BCC and an ordered B2 phase, that upon isothermal annealing at 600°C develops via spinodal decomposition into a continuous B2 matrix with discrete cuboidal BCC precipitates aligned along the <001> directions. Longer term annealing at 600°C results in the development of necking constrictions along the B2 channels, eventually pinching-off these channels and making the BCC phase continuous with discrete B2 precipitates. This inversion the process can be related to the simultaneous operation of two processes:(i) spheroidization of the initially discrete cuboidal BCC precipitates driven by a reduction in the total interface energy and (ii) an increase in the stiffness of the B2 phase, relative to the BCC phase, due to chemical composition changes during annealing, forcing the B2 regions to become discrete driven by the reduction in the total elastic strain energy.