Tensile tests on alloy crystals. Part II.—Solid solution alloys of copper and zinc

Abstract

A previous paper has described the method of making rods of metal in the form of one crystal by slowly lowering graphite tubes containing a rod of the required metal through a furnace, so that cooling and solidification begins from the bottom of the tube. Copper, silver and gold crystals were made by this method and showed the same properties on distortion as aluminium crystals made by another method. The present paper describes some tensile tests carried out on brass crystals made in this way. Some rods 0⋅25 inch in diameter of a brass containing 70 per cent. copper and 30 per cent. zinc were kindly given to the author by Mr. Leonard Sumner, of the Broughton Copper Company, Manchester. Lengths of 9 inches exactly fitted into graphite tubes and these were lowered through a platinum wound furnace which was maintained at 1,150°C. Nitrogen was passed slowly through the tube to prevent oxidation. The whole process was carried out as quickly as possible in order to reduce the loss of zinc. In spite of this a considerable amount of zinc distilled off and collected at the end of the tube and on the nickel-chrome wire by which the graphite tube was suspended. This made the wire very brittle and if the temperature were too high or the wire too long in the furnace, it broke away. A number of crystals were successfully prepared and the copper was estimated in samples from each end of the rod. As it was desired to preserve the part upon which distortion measure­ments had been made it was only possible to cut off a small piece at each end of the crystal where it had been held in the testing machine, and in the case of the top of the ingot this was not always sound. Only one analysis was made of Crystal I as the portion measured was comparatively small, near the centre of the rod, and the sample for analysis was taken as close to this as possible. As was to be expected, very variable results were obtained, according to the time taken in melting and lowering the crystal, and the temperature of the furnace. The differences obtaining between each end were also variable, ranging from 0⋅51 per cent, to 3⋅28 per cent, in the amount of copper. It will also be seen that the amount of zinc lost, judged by the copper content, varies from about 1 per cent, to 10 per cent. Some of the crystals had a bright-yellow colour at the top, and it is probable that this was due to the increased amount of zinc which distilled out of the rest of the metal and re condensed as the tube cooled.