Ultrafine grained (UFG) pure copper chips with improved material strength have been successfully prepared by large strain extrusion machining (LSEM). However, the thermal stability of the UFG chips has been a key characteristic that has restricted their use in practical applications. To understand the influence of annealing temperature and annealing time on their microstructures and mechanical properties, the UFG chips were subjected to isochronous and isothermal annealing treatments as well as

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... Vickers hardness tests in the present study. From the results, we found that the UFG chips maintain high hardness when annealing at temperatures up to 160 • C but begin to exhibit a reduction in their hardness while the annealing temperature reached above 200 • C. When annealed at 280 • C for 10-240 min, the grain size increased slightly and reached a stable value of 2 µm with an increase in annealing time and with a decrease in the hardness of the chips. These results indicated that UFG pure copper chips have good thermal stability at temperatures below 160 • C.