The effects of alloying and pressing routes in equal channel angular pressing of Cu-Fe-Cr and Cu-Fe-Cr-Ag composites

Abstract

Equal channel angular pressing (ECAP) was carried out on Cu-Fe-Cr and Cu-Fe-Cr-Ag composites at room temperature. ECAPed Cu-Fe-Cr and Cu-Fe-Cr-Ag exhibited ultrafine-grained microstructures with the shape and distribution of Fe-Cr phase were dependent on the processing routes. In route A, the initial dendrites of Fe-Cr phase were elongated along the shear direction and developed into filaments, whereas in route Bc the initial dendrites became finer by fragmentation with no pronounced change of the shape. The hardness of ECAPed Cu-Fe-Cr-Ag is greater than that of ECAPed Cu-Fe-Cr. The higher hardness in Cu-Fe-Cr-Ag is ascribed to the more effective matrix strengthening due to the dislocation storage and the precipitation hardening. The hardness of ECAPed Cu-Fe-Cr was lower than that of the drawn Cu-Fe-Cr at the same deformation strain because of the less effective refinement and elongation of the two-phase filamentary microstructure. The addition of silver was found to increase the hardness of the ECAPed composite above the strength level of heavily drawn Cu-Fe-Cr, rendering the processing method of applying alloying and ECAP to Cu-Fe-Cr composite an attractive approach to producing bulky high strength Cu base composites.

The effectiveness of Equal Channel Angular Pressing and rod rolling for refining microstructures and obtaining high strength in a Cu–Fe composite

“…wires) thick enough for the applications. The ECAP processing here has been carried out using the socalled route A [20], whereby there is no rotation of sample between successive ECAP passes, since other routes can lead to ribbon fragmentation during processing [22]. Such fragmentation should be avoided since the presence of Fe phase as relatively long ribbons is believed to be important for achieving high strength [4][5][6]8,[11][12][13][14][15][16][17].…”

“…The most likely explanation for the observed inefficiency of the ECAP + rolling processing for microstructural refinement is the slow build up of substructure during ECAP by route A. A number of previous studies have shown that altering strain paths, for example by using route B or C for ECAP [20] or using rolling or drawing methods, is more effective at strengthening by microstructural refinement than using route A for ECAP [22,[34][35][36][37][38][39]. It seems likely that the preliminary ECAP stage sets up a relatively coarse deformation substructure, based on a given set of operating slip systems, and there will be a change of suitable slip systems when further plastic strain is imposed by rolling.…”

“…The ECAP process has been shown to be capable of producing microstructural refinement (of the matrix) and also to be able to shear the bcc dendrites towards ribbon morphology [21,22]. This preliminary work [22] has also demonstrated that it is important to use the socalled route A for ECAP processing (whereby there is no rotation of sample between repeated ECAP passes) such that the ribbons are not sheared to fine fragments. The presence of the second phase as elongated ribbons is believed to be important for increasing material strength [4][5][6]8,[11][12][13][14][15][16][17].…”

“…ECAP was carried out using a die of angle near 118 • , producing a true strain of 0.7 per pass, and material given three passes without rotation of the bar (route A [20]) to allow the build up of substructure in the Cu matrix and shear the Fe dendrites to ribbons without fragmenting them into short lengths [22]. Rod rolling was carried out using a laboratory rolling mill with 8 cm diameter rolls turning at approximately one turn per second.…”