Characterization of Special Grain Boundaries and Triple Junctions in Cu_xNi_1‐x Alloys upon Deformation and Annealing

Abstract

We compare two quantities to describe a microstructure: the length fraction of normalΣ3/normalΣ9‐grain boundaries and the number fraction of normalΣ3‐x‐x/normalΣ3‐normalΣ3‐normalΣ9‐triple junctions using Cu, Ni and four of their alloys in several microstructural states. The fractions of normalΣ3‐grain boundaries show similar tendencies as the respective fractions of normalΣ3‐x‐x‐triple junctions in relation to the grain size upon deformation and annealing. However, the fraction of normalΣ9‐grain boundaries stagnates at certain grain sizes, while there is still a considerable change of normalΣ3‐normalΣ3‐normalΣ9‐triple junctions during grain growth, meaning that the normalΣ3‐normalΣ3‐normalΣ9‐triple junction microstructure is still evolving. To analyze the evolution of the triple junction microstructure, a program, such as pythorient, is necessary.

Hall–Petch Relations of Severely Deformed Cu, Ni, and Cu–Ni Alloys: Analysis of the Dislocation Blockage Strength of Deformation‐Modified Grain Boundaries

“…It should be noted that annealing ensures also a steady state of the GB distribution and triple junction types. [ 16 ] Pure Cu showed a decrease in hardness for 0.25 mm. This shows that dynamic recovery and recrystallization lead to grain size saturation in pure Cu at shear strain values ϵ larger than 8 (i.e., for 0.25 and n = 5, see Equation () in the Experimental section).…”

“…This difference in the behavior of pure materials and alloys must be caused by the additional solid‐solution effect in alloys, making it possible to obtain higher hardnesses and smaller grain sizes. [ 16 ] The difference in hardening behavior is then related to dislocation and GB mobility and its influence during (dynamic) recovery and recrystallization.…”

“…To reach the central goal of this study, i.e., the evaluation of the dislocation blockage strength of deformation‐modified GBs after SPD, a series of Cu–Ni alloys (Cu 90 Ni 10 , Cu 65 Ni 35 , Cu 50 Ni 50 , and Cu 10 Ni 90 ) including the pure end members Cu and Ni has been selected. Cu and Ni are completely miscible in the liquid and the crystalline states, thus offering the opportunity to study the isostructural influence of the alloy composition and the stacking fault energy [ 16 ] on the deformation characteristics in a comparably simple system. Most importantly, the microstructure‐hardness correlation for the present alloys can be evaluated without convoluting contributions from precipitates or GB segregation which alters the GB strength.…”

Grain Boundaries and Diffusion Phenomena in Severely Deformed Materials

“…With this analysis, at the same time, also the triple junctions as well as their nature were determined. 39) For this reason, a specially designed software tool, "pythorient" 40) has been created that determines triple junction maps and that is available as freeware.…”