The heat developed during plastic extension of metals

When a soft metal, such as annealed copper or aluminium, is deformed while cold, either by stretching, hammering, rolling, or other method of ‘‘cold working’’ it hardens; that is, the forces necessary to deform it increase as the amount of plastic deformation increases. The physical state of “cold worked’’ metal is undoubtedly different from that of the metal in its original soft or annealed state, and various explanations have been put forward to account for the difference. Some of these explanations involve the hypothesis that the process of hardening is associated with the formation of amorphous material at the crystal planes where slipping occurs during the deformation. The formation of amorphous material from a crystalline mass would involve a phase change, which would in general be accompanied by a change in the internal energy of the material. It has been suggested that the phase change could detected by measuring the heat evolved during a deformation, and com-ring with the heat equivalent of the work done on the metal by the forces inducing the deformation. Any difference between the two would imply change in the internal energy of the metal. It is curious that very few measurements of this type appear to have been inside. The only reference which we have been able to find occurs in Dr. Rosen-Inde article on “ Metals,” in the 4 Dictionary of Physics,5 where he quotes the previously unpublished observations made by Dr. Sinnat.