Abstract
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 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.
Highlights
Compared with traditional coarse polycrystalline materials, ultrafine grained (UFG) materials and nanocrystalline materials (NCMs) exhibit better physical, mechanical, and chemical properties due to their high density of defects and large volume percentage of grain boundary [1,2]
The experimental material used in this study was commercial pure copper, which was in the form of a circular tube with an external diameter of 70 mm, an internal diameter of 60 mm, and a length of
The microstructure evolutions of pure copper after large strain extrusion machining (LSEM) and annealing treatments were whose internal misorientation was under 2◦ but the misorientation from subgrain to subgrain was observed by a field emission scanning electron microscope NOVA NANOSEM 430
Summary
Compared with traditional coarse polycrystalline materials, ultrafine grained (UFG) materials and nanocrystalline materials (NCMs) exhibit better physical, mechanical, and chemical properties due to their high density of defects and large volume percentage of grain boundary [1,2]. Their preparation methods have become a hot topic in various fields. On the basis of retaining and even enhancing the ability of severe plastic deformation in traditional cutting, a potential process, namely, large strain extrusion machining (LSEM), was proposed for the preparation of NCMs and UFG materials by Iglesias [12,13] and Moscoso [14], who learned from Cliffre’s “extrusion cutting”
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