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SLOW KKCOVERY AND PEHMAXENT SET IN ('OrPEH, ALT^MIMM. 

 AND LEAD. 



Albert E. Woodruff. 



When a copper wire is strained and the stress is removed there is an 

 instantaneous recov(»ry followed by a slow recovery vvith time. This slow 

 recovery may be accounted for by the hypothesis that it is due to the re- 

 crystallization of the metal. The fact that there is a recovery with time is 

 not new. Even the mafjnitude of the recovery as a function <»f time has 

 been investigated exiierimentally and is fairly definitely known. liut so far 

 no one seems to have been sutticiently interested to seek for an explanation 

 of the cause of recovery. 



Andrade (1) has done much experimental work on the flow of soft 

 metals under stress. Knowing from the micro-photographic work of 

 Quincke (2). Ewing and liosenhain (.'?). and Beilby (4) that when a metal 

 is strained there is a breaking down of the crystallar structure of the metal, 

 he reasons that since the two take place simultaneously the one is due to 

 the other, and he is able to substantiate bis theory by exi)eriraent. both from 

 observed phenomena of a strained wire and by looking into a uiicrosct)i)e 

 and seeing what actually takes place in the metal. 



But the work of Quincke. Ewing and Kosenhain. and Beilby does not stop 

 with the observation that the crystallar structure of a metal breaks down 

 under exces.sive strain. They find that as soon as the stress is removed 

 that the crystals of the metal begin to reform. For copper at ordinary 

 temperatures this process is very slow. But if the temperature is raised, 

 to say three or four hundred degrees the process of recrystallization is ex- 

 ceedingly rapid, almost instantaneous, and the specimen becomes annealed. 

 The object of this paper is to present facts which show that slow i-ecovery 

 is due to recrystallization of the metal. 



Plate I shows that an unannealed si)ecimen of copper has a much more 

 decided recovery than an annealed si>ecimen subjected to the same strain. 

 Plate III shows the same thing for aluminium. Plates II. IV and VI show 

 tliat for all three metals investigated the larger the stress applied, other 

 conditions being equal, the greater the recovery. Plates I. Ill and V show 

 that the longer the time of applying the stress the greater the recovery, the 

 stresses being equal. It will be noticed from these same curves that per 

 unit of length per unit of stress the amount of recovery of the different 

 metals is in the same order as the tempei'atures at which the metals 

 annual. All these facts support the hypothesis that the reco\ery of a metal 

 after the stress has been removed is connected with the process of recry- 

 stallization. 



In the first instance the material of a drawn wire that has not been 

 annealed is largely reduced to the amorphous phase. Such crystals and 

 parts of crystals as remain are under strain which is the result of drawing. 

 Most of the strain was relieved when the tension of the drawing process 

 was released. But the fine amorphous particles fill the spaces about the 

 remaining crystals leaving the metal still in a state of strain. Annealing 

 or recrystallization immeiliately begins and the amorphous [tarticles begin 



