JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V OCTOBER 19, 1915 No. 17 



PHYSICAL CHEMISTRY.— Microstrudural changes accom- 

 panying the annealing of bronze. Henry S. Rawdon, 

 Bureau of Standards. ^ 



A study of the structural changes in bronze induced by an- 

 neahng was made to supplement the investigation of the stand- 

 ard zinc-bronze (88 Cu, 10 Sn, 2 Zn) recently carried out at the 

 Bureau of Standards. The various changes together with 

 the temperatures at which such changes are completed were 

 determined. 



After casting, the alloy exhibits a complex structure compris- 

 ing a dendritic matrix consisting of a solid solution of tin (and 

 zinc) in copper, in which are embedded nmiierous particles of a 

 hard and brittle eutectoid similar in structure and formation to 

 pearlite in steel. Upon anneaUng, the alloy is first rendered 

 homogeneous by the absorption of the eutectoid by the matrix 

 and the disappearance of the dendritic structure of the same 

 matrix by diffusion. If the alloy has received no deformation 

 previous to annealing, no other changes are observed, the crystal 

 or "grain" size remains unchanged. The characteristic poly- 

 hedral twinned crystals seen in annealed brass and bronze rich 

 in copper are obtained only after the structure has been dis- 

 torted. Samples which had been cooled in a very drastic man- 

 ner, thus inducing severe internal stresses, behaved similarly upon 

 annealing to those which had been mechanically deformed be- 

 fore annealing. 



1 To appear in full as a Scientific paper of the Bureau of Standards. 



589 



