The production of single crystals of aluminium and their tensile properties

The crystals of which metals and alloys are composed are allotriomorphic. They are generally very small, and cannot usually be distinguished without the aid of a microscope. It is quite true that in the case of large castings weighing many tons, crystals of several cubic inches’ capacity may be formed under special conditions of cooling. These, however, are quite rare, and possess the well-known dendritic or skeleton form. The majority of metals and alloys which have been hot-worked, have from 150 to 300 crystals to the linear inch, but frequently the size is still smaller, especially in steel. Rosenhain and Humphry counted the number of crystals in a known area of mild steel, and from that calculated the areas of individual crystals. The figures they give are from 1·5 to 7·5 × 10-6 square inches, according to the condition of the steel. Sykes has recently given as the diameters of crystals in molybdenum wire figures varying from 0·0011 to 0·0002 of an inch in diameter. These correspond to approximately from 1000 to 5000 crystals to the linear inch. Admittedly, in this case, the wire was severely worked. Sauveur was one of the first investigators to show that by carefully straining and subsequently heating such metals, crystals of a much larger size could be produced, and suggested that there was a critical stress which produced the largest crystals.