Influence of Strain Amplitude on the Microstructural Evolution and Flow Properties of Copper Processed by Multidirectional Forging

Abstract

The search for the development of metals with high mechanical strength has raised intense interest in severe plastic deformation (SPD) methods. [1,2] These involve the application of intense straining to ultimately produce ultrafine-grained (UFG) materials. Among the available SPD techniques, multidirectional forging (MDF) [3-5] is one of the simplest procedures and can be readily applied in industry. During MDF processing, a cuboid workpiece is successively submitted to the same compression strain along its three orthogonal axes, so that after each three compressions (a so-called MDF cycle) the dimensions of the sample return to the unprocessed state. [4,6] MDF processing allows the determination of the material in situ stressstrain curves for every compression step and can be performed with or without the use of dies confining the plastic flow. [3,7] Although the grain refinement mechanisms associated with SPD are still not fully understood, it is generally accepted that it is caused by the fragmentation of the original grains in the material by boundaries formed from dislocation arrangements created during straining. [8] Sakai et al. [3] have emphasized the importance of the development of micro shear bands (MSBs), which are localized planar sheared regions within the initial grains, in the development of UFG structures in metals processed by different SPD procedures [3,7,9-18] This microstructural evolution is also referred to in the literature as continuous dynamic recrystallization [3,7,9,12,19] and the successive deformation at mutually orthogonal

Influence of processing temperature on microhardness evolution, microstructure and superplastic behaviour in an Al–Mg alloy processed by high-pressure torsion

“…Therefore, different strategies have been carried out to improve the microstructural stability of materials processed by SPD such as (i) the development of alloys containing elements which originate as nanosized precipitates during heating [17][18][19][20], (ii) the application of SPD procedures at warm conditions [21][22][23][24][25], (iii) the use of cyclic deformation with low strain amplitudes [26][27][28] and (iv) the formation of nanosized particles and solute segregation at grain boundaries concurrently with deformation in microstructures having secondary phases prior to processing [29][30][31][32][33][34][35].…”

Hardness, Microstructure and Strain Distributions in Commercial Purity Aluminum Processed by Multi Directional Forging (MDF)

“…It is recognized that the simulation results for the specimen shape, strain and stress distributions are approximate due to the following points: the constitutive behavior is described by a monotonically increasing flow stress corresponding to the envelope of the individual stress stress-strain curves for each MDCF compression. These display decreased yield strengths in relation to the corresponding flow stress in the envelope curve, as well as initial mild stress peaks 20,50 , associated with the strain path changes as the specimen is rotated. These phenomena cannot be accounted for in the current state of finite element simulations.…”