Fundamental Study, and Equipment for Sintering and Testing of Cermet Bodies, I–iii*

Abstract

Cermet b0dies.t composed of metals and oxides, are being developed for high-temperature service. Part I covers the theoretical aspects of experiments of a fundamental chemistry nature which accompanied the laboratory development of test specimens. Compacts of metal powders (Xi, Fe, Co, Cr, and Cr-B) were !ired at 2880" to 3500'F. on pure A1201 tile in various controlled atmospheres. The results indicate that a controlled layer of oxide on the surfaces of the metal-powder grains is essential for good bonding. Special furnaces, described in Part 11, were necessary for the fundamental study and for sintering cermet specimens. Equipment for determining instantaneous modulus of rupture and tensile rupture, and longtime stress-rupture in bending at temperatures up to 2400°F.. is described in Part 111. ForewordThe advent during World War I1 of new aircraftpropulsion mechanisms with optimum temperatures above the physical limits of metals aroused interest in ceramic materials as potentially capable of withstanding the severe conditions of temperature and stress encountered. Investigations of ceramic materials and compositions for such uses were under way before the war ended, and one of the first studies was the testing of the high-temperature praperties of existing commercial ceramic bodies. Outstanding among these was a composition consisting of a combination of ceramic material and metal.$ A'hen the war with Germany ended, it was learned that the Germans had been interested in combinations of iron and aluminas for gas turbine blade application and had begun an active study of this material.On the basis of this information and additional theorizing on the potentialities of such compositions, it seemed plausible that combinations of metals and ceramic oxides or carbides would incorporate desirable properties of both in the end product, which would be better suited to the service requirements than either material alone. Consequently, a full-scale investigation was undertaken.An investigation of such combinations required the development of special high-temperature equipment for fabrication purposes and for determining the properties of the material at elevated temperatures, as well as a fundamental study of the mechanics of bond developed in cermet bodies.

A Fundamental Study of Synthetic Sapphire as a Bearing Material

“…Above this point the increased friction is attributed to a softening and wearing away of the metal plating. 8 . A reversible effect in friction is observed for these couples in heli um when cycled between room temperature and -120°C.…”

Refractory Bodies Composed of Boron and Titanium Carbides Bonded with Metals

“…In each ease there was sufficient boron available from the decomposition of the B4C to form the boride with the highest boron content. It is probable that the betides of chromium, especially those high in boron, have high melting points and therefore would require high temperatures for sintering (18). On the other hand, the iron borides must have lower melting points and tend to create a bonding phase at the temperatures used in this investigation.…”

“…The "d"-spacings ascribed to chromium borides were similar to those obtained from an x-ray pattern of a sample of "Chromium-Boron" obtained from Wall-Colmonoy Corporation. Blackburn, Shevlin, and Lowers (18) reported the Wall-Colmonoy material to be a mixture of CrB, CrB2, and Cr3B2 in unknown proportions. This seems to strengthen the assumption that chromium borides were formed in the experimental bodies, but, at the same time, does not permit positive identification.…”