Creep of metals at elevated temperatures

Creep of metals at elevated temperatures

620 U.S. BUREAU OF STANDARDS NOTES. [J. F. I. than at room temperatures. High-alloy steels have lower thermal conductivities than low-alloy steels...

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620

U.S.

BUREAU OF STANDARDS NOTES.

[J. F. I.

than at room temperatures. High-alloy steels have lower thermal conductivities than low-alloy steels. An increase in the a m o u n t of alloy constituents in iron causes, in general, an increase in the t e m p e r a t u r e coefficient of thermal conductivity. CREEP OF METALS AT ELEVATED TEMPERATURES.

Solid metals m a y flow or " c r e e p " if they are subjected to a constant or continued load, which behavior is particularly noticeable when the metal is at a temperature above normal atmospheric temperature. In studying the " c r e e p " of metals, the Bureau has prepared single crystals of silver and has been measuring the very slow flow or creep of these single crystals when sustaining constant loads at 4oo ° C. With this type of specimen the influence of the g r a i n or crystal boundaries on the creep of metals is eliminated. Some of these single crystals have now been under load and slowly creeping for over nine months. T h e rate of creep of a silver crystal at 4oo ° C. is influenced by the direction of the stress in the crystal relative to the crystal axes. The rate of creep is relatively low when the load acts in a direction approaching t h a t of a perpendicular to the cube face of the silver crystal. The rate of creep is distinctly higher when the crystal is loaded in a direction m a k i n g an angle of 3 °0 to 45 ° with this same perpendicular. WEATHERING OF SHEET ALUMINUM ALLOYS.

T h e investigation of the corrosion of a l u m i n u m alloy sheet materials has been in progress at the Bureau since I925. Its purpose is to s t u d y and develop m e t h o d s for the elimination of corrosion-embrittlement in the alloys utilized in aircraft, more particularly duralumin. Extensive laboratory corrosion tests, supplemented by actual exposure of specimens to the weather at Washington, D. C., H a m p t o n Roads, Va., and Coco Solo, C. Z., have furnished d a t a on the behavior of these materials under conditions conducive to corrosion. Corrosive a t t a c k of the intercrystalline type is most undesirable in sheet a l u m i n u m alloys, since it results in