The plastic deformation of polycrystals II. Aluminium at 77 K

60 Years of Hall-Petch: Past to Present Nano-Scale Connections

“…Other Narutani and Takamura 54) nickel results to be described with regard to H-P influence on the strain rate sensitivity, showed a constant value of k ¾ throughout the stressstrain curve and of value near to that mentioned for ¾ = 0.01. The relatively pure aluminum results of Hansen 49) and of Al-Haidary et al 50) showed a relatively constant value of k ¾ = ³1.4 MPa·mm 1/2 with straining; and, this strain independence of k ¾ seems more often than not to be generally observed.…”

“…32,48) Detailed observations of H-P dependencies for the complete stressstrain behaviors of relatively pure aluminum materials have been reported by Hansen 49) and by AlHaidary, Petch and de Los Rios. 50) Figure 4 shows a log/ log compilation of other H-P results reported for aluminum at conventional and nanopolycrystal grain sizes and includes comparison with copper and nickel material results. On a log/log basis, the H-P relation leads at large grain size to a relatively constant value of · 0¾ and, at limiting small grain size, goes over to a linear dependence of slope (¹1/2).…”

The Effect of Grain Size, Strain and Temperature on the Monotonic Stress‐strain Behaviour of Polycrystalline Aluminium and Al Alloys

“…At tensile yield, ky=0.139, 0.198 and 0.596 MPam1/2, for the pure metal, the Al-2.63Mg and Al-2.07Li alloys respectively, and can be understood in terms of the action of solute-locking, solution and precipitation hardening. (9) The grain size dependent, slip band stress intensities, ky, show similar behaviour with increasing strain at each temperature studied. At tensile yield, k,,, varies from 0.67 MPam1/2 at -196°C to 0.0486 MPam'l2 at 4WC, so increasing temperature lowers the stress required to force a dislocation loop out of the grain boundary and transfer slip across the grain boundary.…”

“…At tensile yield, k,,, varies from 0.67 MPam1/2 at -196°C to 0.0486 MPam'l2 at 4WC, so increasing temperature lowers the stress required to force a dislocation loop out of the grain boundary and transfer slip across the grain boundary. (10) At all temperatures studied, k, falls following initial yielding and is most dramatic at 20°C, and may be associated with the generation of new, unlocked dislocation sources during deformation.…”

“…Following initial yielding, the value of k, for Al8090 falls at each temperature studied. The fall is most significant at 20"C, from 0.596 MPam'" to 0.40 MPaml", and has been associated with the generation of new, unlocked dislocation sources during deformation [8][9][10]. After yielding, as strain proceeds and dislocations accumulate, the blocked slip bands can use, more easily, the fresh unlocked sources within the grain so k, drops accordingly.…”