The effects of rapid cooling upon metals and alloys

Abstract

It is of great importance to the engineer to be as fully acquainted as possible with the mechanical properties of the metals and alloys which he employs. Many series of experiments have been carried out by various observers with the object of determining the manner in which the mechanical properties of an alloy vary with its composition and with its previous history, but no general principles have been deduced from these scattered observations. During a preliminary study of the available data, the writer strongly felt the necessity of knowing the constitution and structural arrangement of the various alloys of which the mechanical properties had been determined. Many observations of the structure of metals and alloys subjected to various thermal and mechanical treatments have been made, out the results of these leave several difficulties unsolved. Accordingly the present investigation of the effect of rapid cooling was undertaken.The physical properties of a metal which has solidified quickly may differ greatly from those of the same metal allowed to crystallite slowly. The difference in properties produced by varying the rate of cooling is accompanied by variation in the structure of the metal, that is, in the size and shape of the crystal aggregates or grains. In alloys, still greater relative change in properties may be caused by varying the rate of cooling, and the change in structure is not necessarily confined to the size and shape of the grains, but the manner of distribution of the grains, and even the proximate constitution of the mixture may be more or less completely altered. The exact connection between change of structure and change of properties cannot be exactly specified at present, but in general an alteration of constitution is more important than one of crystal size.It had seemed likely to the writer for some time that the constitution of a rapidly cooled alloy should be possible of calculation from the equilibrium diagram; Part I deals with this problem in a fairly thorough manner. The conditions which govern crystal growth are but imperfectly apprehended at present, so that structure must be investigated experimentally; Part II deals with the structum of various selected metals and alloys, but though the observations are numerous the results are not of general applicability like those of Part I, since each metal and each series of alloys exhibits its own structural peculiarities, and there is great difficulty when studying one cause of structural variation to eliminate all others.