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The advantages of using vacua in the hot pressing of refractory materials are demonstrated. A simple apparatus is described which enables powders to be pressed at temperatures up to 2500°C at gas pressures of 95% theoretical density can be prepared with an impurity oxygen content of the order of 0.01 wt.-%.

A study was made of the densification during hot pressing at 1300–1600°C of magnesium oxide activated by decomposing the hydroxide and the basic magnesium hydrocarbonate. During decomposition of these compounds at 500–700°C with a soak of 15 min, magnesium oxide forms that is actively compacted almost to the theoretical density (98.5–99.5%) at relatively low temperatures (1500–1600°C) and pressures of 150 kg/cm2.

Some refinements have been introduced into the hot press canning of internally and externally cooled fuel elements. This report outlines the specifications for the process including these refinements. Specifications cover components, dies, and punches, furnace condition, nickel plating, component cleaning, component assembly, sizing, hot pressing and inspection.

The hot press process has been altered so as to eliminate the slight wrinkling near the ID base. This was done by incorporating a three minute time delay in the pressing cycle. The pressing time was decreased to five minutes to restrict formation of the brittle intermetallic compound, Ni{sub 2}Al{sub 3}.

A small vacuum hot-press is described which is easily operated and maintained within a Harwell MK II glove box. The press incorporates a sliding vacuum seal.

In order to evaluate the performance of uranium slugs canned by the hot press method, several tubes of this metal were charged at C Pile and scheduled for irradiation until a specified number of ruptures had occurred. At the present time, all scheduled ruptures of hot-pressed slugs have been obtained. This report summarizes the irradiation experience under this test and the results obtained to the present time, and presents conclusions which are drawn from this experience.

Hot pressing has played a prominent part in research programs studying beryllium oxide, and has been considered on several occasions as a possible production tool. The desirable characteristics of the hot press are described by reference to advanced designs in three forms: (a) the basic research tool; (b) the vacuum hot press; and (c) the continuous hot press for production use. Techniques of operation have been learned for the reliable preparation of sound, uniform, high-purity BeO bodies of simultaneously very high density (99.7 to 100.0% of T.D.) and fine grain size (to a limit of 10μ average). The routine consists of a dwell at temperature without the application of pressure, an optimized time-temperature-pressure cycle, and rapid heating and cooling ramps. The parametric relations are described. Techniques for the controlled preparation of BeO of ultrafine grain size at somewhat less than full density have also been worked out. The resultant material parameters and corresponding mechanical characteristics are discussed, with particular reference to modulus of rupture at high temperatures. Average strengths of 48 000 psi at 1500° C have been recorded. The microstructural, size and shape limitations of hot-pressed BeO are reviewed with respect to reactor core requirements. Illustrations are taken from past experience to describe the preparation of hot pressed shapes as reactor component parts and the desired manner of conducting production runs. Cost elements of an hypothetical production activity are displayed, assuming continuous hot press operation and based on American economic conditions. A typical coldform-and-sinter operation is described for comparison.

It is said that the hot pressing gives better properties to WC-Co alloys than the cold presssinter method. At present time, graphite is mainly used as the die material for the hot pressing of WC-Co alloys. In this paper, the carbon impregnation to the sintered body which is caused by the contact of the powder (sintered body) and the graphite die was studied. The results obtained are as follows.(1) The layer depth of carbon impregnation increased parabolically with the increase of keeping time. However, it was assumed that the carbon impregnation which results in the excess carbon precipitation does not to occur during heating and also at the initial stage of keeping time, but assumed to begin to occur after the.sintering is completed. (2) The layer depth of carbon impregnation increased with an increase of hot press temperature. (3) The layer depth of carbon impregnation depended upon the property of the graphite used for the die. (4) The hot press pressure did not have a definite relation to the layer depth of carbon impregnation, but was affected by the behavior of metal which was squeezed from the die and other factors. (5) The metal which was squeezed from the die during hot pressing was mainly composed of cobalt and the WC content involved in it was by far lesser than that corresponding to Co-WC eutectic.

Sintering, hot-press forging, and gas-pressure bonding were evaluated as techniques for preparing cermet fuel materials containing at least 60 vol.% UO/ sub 2/ and having a minimum density of 90% of theoretical. Minus 325-mesh chromium, molybdenum, niobium, and Type 302B stainless steel were employed as matrix materials. Hydrothermal and spherical UO/sub 2/ powders were evaluated. Cermets containing 80 vol.% UO/sub 2/ and exhibiting densities in excess of 90% of theoretical were successfully prepared by both hot-press forging and by gas- pressure bonding mixed oxide and metal pcwders. Gas-pressure bonding produced specimens with a more uniform structure and was demonstrated to be capable of simultaneously densifying and cladding green-pressed cermet fuels. Spherical UO/ sub 2/ powders produced the more homogeneous microstructures. Excellent microstructures were also obtained by the use of UO/sub 2/ pcwder coated wit;i niobium by vapor-deposition techniques. So far as direct comparison is possible the cermets were superior in strength to UO/sub 2/. Strength, which was measured by bend and compression tests, was density dependent. Thermal-conductivity values for the cermets were far higher than values for UO/sub 2/. Electrical- resistivity data were also obtained. These data were used to develop a mathematical correlation of electrical and thermal conductivity but a complete analysis could not be made on the basis of present theories due to the limited number of measurements made. (auth)

Creep deformation of sintered zirconium diboride were studied at 1690°-1890°C under compressive stress of 160-500kg/cm2 using hot-press furnace. The samples for this experiment were prepared by hot-pressing and grouped into three porosities.Deformation of zirconium diboride was remarkable above 1800°C. The higher load was applied, the more quick deformation occured. Deformation rates also increased with increasing porosity. But it's temperature dependences were independent of porosity and load. Activation energy for deformation was 100-120kcal/mole. Sintered zirconium diboride showed plastic behavior and yield loads were 130-160kg/cm2 for samples with 19-20% porosity at the temperature range of this experiment. The effects of porosity and grain size on deformation rates were discussed. Viscosity calculated from this experiment was compared with that from densification experiment.

This paper describes the powder metallurgical processing of beryllium into fine-grained forms from which finished shapes are made. Emphasis is given to the vacuum-hot-press-machine process which is used for the majority of beryllium parts being made today.

Laboratory measurements of dissolution rates of thorium in mixtures of nitric and hydrofluoric acids show that thorium can be dissolved with practicable time cycles in large-scale processing. The corrosion of stainless steel during the dissolution of thorium is acceptable, except that when the thorium is coated with Al-Si alloy, frequently used as a bonding material for aluminum cans, severe local corrosion of the stainless steel occurs at areas of contact with residual Al-Si. This contact corrosion does not occur when the cans are hot-press-bonded to the thorium without Al - Si. (auth)

Aluminum-based P/M hand forgings and extrusions in two Al-Zn-Mg-Cu alloys have been studied to evaluate the effects of powder processing variations on forging quality and properties and extrusion properties. High quality hand forgings with high strength and ductility have been produced directly from hot pressed aluminum powder compacts without an intermediate extrusion operation. The processing conditions leading to maximized hand forging properties are: Cold press to at least 70% green density; preheat 1 hour at 1,000 F in dry argon; hot press at 90 ksi; forge at a temperature appropriate for the specific alloy; forge by any standard hand forging press technique with as much total reduction as possible.

Fabrication techniques for making metal-ceramic fuel elements containing 80 to 90 vol. f UN or UO/sub 2/ in a Type 302B stainless steel matrix were investigated. A hot press-forging procedure was most successful for of theoretical or better. This procedure consisted of sealing the cold-p;ressed core compacts in stainless steel picuture-frame packs, heating to 1900 deg F, and pressing to a total reduction in thickness of 35%. A pressure approximately 50 tsi was used specimens produced by this method were evaluated on the basis of their microstructure, modulas of rupture, electrical conduuctivity, and resistance to thermal shock. Microscopic and macrcscopic examination showed the presence of a continuous metal skeleton even in specimens containing 90 vol. a fuel. The modulus cf rupture at rcom amperature varied from 22,500 psi for a specimen containing; 63 vol. % UO/sub 2/ to 9,200 psi for a specimen containing 87 vol.% UO/sub 2/. Both the electrical conductivity and resistance to thermal shock of UO/sub 2/ were improved by the addition of a small volume of metal. Gaspressure-bonding techniques appear promising for cladding these cores into composite elements. (auth)

The program attempts to develop an understanding of the diffusion bonding of titanium alloys; in particular, the alloy Ti-6Al-4V. The accomplishments of the second quarter of the program are as follows: Instrumentation for the vacuum hot press was completed and calibrated. Tests were performed on the effects of temperature, pressure, time, and surface roughness on bond shear strength. The results of the bonding parameter studies indicate a dependence on plastic deformation but not a direct dependence on temperature or bonding pressure. An empirical fit has been made to the data and work is in progress to refine the mathematical description which was proposed during the first quarter. Tensile and bend tests were initiated. It was determined that the electron-beam microprobe is not sufficiently sensitive to detect the diffusion of oxygen or nitrogen in the alloys Ti-6Al-4V. (Author)

Platinum is being investigated as a ductile, oxidation resistant coating for protection of columbium and molybdenum alloys at temperatures to 3000F. While its oxidation resistance has been found to be excellent, its value as a protective coating for the given substrate alloys rapidly deteriorates as a result of platinumsubstrate alloy interdiffusion. It is the prime concern of this contract, therefore, to develop a barrier to this degrading interdiffusion. Twelve materials have been selected for initial evaluation potential diffusion barriers. Roll bonding, hot press bonding, electron beam evaporation and chemical vapor deposition techniques are being used for fabrication of composite coating-barrier-substrate test samples. Screening tests will be conducted in flowing air at 2550F to determine the relative merits of the various coating-substrate combinations. (Author)

A research program is currently being conducted for developing new cemented-carbide tool materials which will be capable of exhibiting exceptional hardness, toughness, strength and oxidation resistance at elevated temperatures. A series of refractory binder alloys in combinaticn with various carbides is being investigated. Liquid phase sintering during the simultaneous application of pressure in a controlled atmosphere hot press is used as the method of densification.