THE HEAT TREATMENT OF PLUTONIUM

Two groups of plutonium bars, one group containing 165 ppm iron and the other 678 ppm iron were end-quenched from the beta, gamma, delta, delta-prime, and epsilon phases. In general, cooling rate was found to have three striking effects on microstructure. The alpha grain size was found to decrease with increasing cooling rate during cooling from all phases. Upon cooling high-iron plutonium from the epsilon phase, the size of the Pu--Pu6/sub 6/Fe eutectic network decreased with increasing cooling rate. Cooling high-iron plutonium from temperatures between 413 and 460 deg C produced a wide variety of Pu --Pu/sub 6/ Fe configurations in the microstructure. Finally, the size of an unidentified spheroidal inclusion, soluble in the delta and higher temperature phases, decreased as cooling rate increased across the delta to gamma transformation. These effects of cooling rate can be used to indicate the cooling rate or thermal history that a particular plutonium specimen has encountered. A linear relationship between the alpha grain size and the Pu--Pu/sub 6/Fe eutectic network size was observed. The network size was roughly two times larger than the alpha grain size. Hardness traverses on each of the bars indlcated no apparent effect of coollng rate during quenchlng on hardness. A density decrease was noted near the quenched end of both low and high-iron bars which lndicated that faster cooling rates promote microcracklng. However, a greater decrease in density was obtained for the low-iron bars which was attributed to their greater tendency to microcrack. The presence of the Pu--Pu/sub 6/Fe eutectic network in the high-iron bars inhibits microcracking. (auth