Consolidation of Particles by Severe Plastic Deformation: Mechanism and Applications in Processing Bulk Ultrafine and Nanostructured Alloys and Composites

Abstract

Severe plastic deformation (SPD) can be used to consolidate particles into bulk ultrafine and nanostructured materials. SPD consolidation relies on plastic deformation of individual particles, rather than diffusion, to achieve bonding and thus can be carried out at much lower temperatures. Using examples of consolidation of Al particles by back pressure equal channel angular pressing (BP‐ECAP), it is demonstrated that full consolidation is achieved when the particles are sheared to disrupt the surface oxide layer whereas consolidation is impossible or incomplete in the case of particles sliding over each other. The effects of particle characteristics such as size, shape, strength and surface condition, as well as processing parameters including temperature and back pressure, are discussed to shed light on the mechanism of SPD consolidation. Potential applications of SPD in powder consolidation and processing of bulk ultrafine and nanostructured materials are discussed.

Al/Al₂O₃ Nanocomposite Produced by ECAP

“…In order to achieve a further dispersion of the ceramic nanoparticles, 12 ECAP passes were performed. ECAP involves very high shear deformation of the material, which should act by promoting the hard particles dispersion and the breaking of the clusters [15]. This effect was confirmed by the present experimental tests on 12 ECAP passes but the amount of shear was apparently not enough to completely destroy all the oxide layers and to homogeneously spread all the nano-particles into the matrix of samples Al-SFT-300 and Al/Al 2 O 3 -SFT-300 (Fig.…”

Al/Al₂O₃ Nanocomposite Produced by ECAP

“…In order to achieve a further dispersion of the ceramic nanoparticles, 12 ECAP passes were performed. ECAP involves very high shear deformation of the material, which should act by promoting the hard particles dispersion and the breaking of the clusters [15]. This effect was confirmed by the present experimental tests on 12 ECAP passes but the amount of shear was apparently not enough to completely destroy all the oxide layers and to homogeneously spread all the nano-particles into the matrix of samples Al-SFT-300 and Al/Al 2 O 3 -SFT-300 (Fig.…”

Microstructure, Mechanical Properties, and Thermal Stability of Al-Al2O3 Nanocomposites Consolidated by ECAP or SPS from Milled Powders

“…The higher the hardness, the higher the density and length of the cracks. Such a problem, previously reported in the literature, was attributed to shear strain localization [17], a lack of ductility of hard, nanocrystalline, or severely milled powder [42], the inability of hard powder particles to increase their mutual contact surface by shear flow, and their tendency to roll on each other [18]. An additional explanation will be suggested further on.…”

Mg–3Zn–0.5Zr/HA nanocomposites fabricated by high shear solidification and equal channel angular extrusion

“…ECAE processing is effective in the consolidation of particle aggregates when the particles are deformable so that the relative movement between the particles will involve plastic deformation by simple shear. The consolidation effect is limited and porosities are difficult to remove when the particles are hard and their relative movement is by sliding [28]. In the present investigation, the HA aggregates were fully consolidated and a dispersion of HA particles began to develop in the second pass ECAE.…”

Al/Al₂O₃ Nanocomposite Produced by ECAP

“…In order to achieve a further dispersion of the ceramic nanoparticles, 12 ECAP passes were performed. ECAP involves very high shear deformation of the material, which should act by promoting the hard particles dispersion and the breaking of the clusters [15]. This effect was confirmed by the present experimental tests on 12 ECAP passes but the amount of shear was apparently not enough to completely destroy all the oxide layers and to homogeneously spread all the nano-particles into the matrix of samples Al-SFT-300 and Al/Al 2 O 3 -SFT-300 (Fig.…”

Microstructure, Mechanical Properties, and Thermal Stability of Al-Al2O3 Nanocomposites Consolidated by ECAP or SPS from Milled Powders

“…The higher the hardness, the higher the density and length of the cracks. Such a problem, previously reported in the literature, was attributed to shear strain localization [17], a lack of ductility of hard, nanocrystalline, or severely milled powder [42], the inability of hard powder particles to increase their mutual contact surface by shear flow, and their tendency to roll on each other [18]. An additional explanation will be suggested further on.…”

Mg–3Zn–0.5Zr/HA nanocomposites fabricated by high shear solidification and equal channel angular extrusion

“…ECAE processing is effective in the consolidation of particle aggregates when the particles are deformable so that the relative movement between the particles will involve plastic deformation by simple shear. The consolidation effect is limited and porosities are difficult to remove when the particles are hard and their relative movement is by sliding [28]. In the present investigation, the HA aggregates were fully consolidated and a dispersion of HA particles began to develop in the second pass ECAE.…”

Al/Al₂O₃ Nanocomposite Produced by ECAP

“…In order to achieve a further dispersion of the ceramic nanoparticles, 12 ECAP passes were performed. ECAP involves very high shear deformation of the material, which should act by promoting the hard particles dispersion and the breaking of the clusters [15]. This effect was confirmed by the present experimental tests on 12 ECAP passes but the amount of shear was apparently not enough to completely destroy all the oxide layers and to homogeneously spread all the nano-particles into the matrix of samples Al-SFT-300 and Al/Al 2 O 3 -SFT-300 (Fig.…”

Microstructure, Mechanical Properties, and Thermal Stability of Al-Al2O3 Nanocomposites Consolidated by ECAP or SPS from Milled Powders

“…The higher the hardness, the higher the density and length of the cracks. Such a problem, previously reported in the literature, was attributed to shear strain localization [17], a lack of ductility of hard, nanocrystalline, or severely milled powder [42], the inability of hard powder particles to increase their mutual contact surface by shear flow, and their tendency to roll on each other [18]. An additional explanation will be suggested further on.…”

Mg–3Zn–0.5Zr/HA nanocomposites fabricated by high shear solidification and equal channel angular extrusion

“…ECAE processing is effective in the consolidation of particle aggregates when the particles are deformable so that the relative movement between the particles will involve plastic deformation by simple shear. The consolidation effect is limited and porosities are difficult to remove when the particles are hard and their relative movement is by sliding [28]. In the present investigation, the HA aggregates were fully consolidated and a dispersion of HA particles began to develop in the second pass ECAE.…”