Structure Refinement and Fragmentation of Precipitates under Severe Plastic Deformation: A Review

During severe plastic deformation (SPD), the processes of lattice defect formation as well as their relaxation (annihilation) compete with each other. As a result, a dynamic equilibrium is established, and a steady state is reached after a certain strain value. Simultaneously, other kinetic processes act in opposite directions and also compete with each other during SPD, such as grain refinement/growth, mechanical strengthening/softening, formation/decomposition of solid solution, etc. These competing processes also lead to dynamic equilibrium and result in a steady state (saturation), albeit after different strains. Among these steady-state phenomena, particle fragmentation during the second phase of SPD has received little attention. Available data indicate that precipitate fragmentation slows down with increasing strain, though saturation is achieved at higher strains than in the case of hardness or grain size. Moreover, one can consider the SPD-driven nanocrystallization in the amorphous phase as a process that is opposite to the fragmentation of precipitates. The size of these crystalline nanoprecipitates also saturates after a certain strain. The fragmentation of precipitates during SPD is the topic of this review.

Sustainable Manufacturing of Ultra-Fine Aluminium Alloy 6101 Wires Using Controlled High Levels of Mechanical Strain And Finite Element Modeling

The evolution of grain size and component mechanical behaviour are fundamental aspects to analyse and control when manufacturing processes are considered. In this context, severe plastic deformation (SPD) processes, in which a high shear strain is imposed on the material, are recognized as the main techniques to achieve microstructural changes and material strengthening by the recrystallization, attracting both academic and industrial investigation activities. At the same time, nowadays, sustainable manufacturing design is one of the main responsibilities of the researchers looking at UN2030 agenda and the modern industrial paradigms. In this paper a new severe SPD process is proposed with the aim to steer manufacturing to fourth industrial revolution using some of Industry 4.0 pillars. In particular, additive manufacturing (AM) and numerical simulations were setup as controlling and monitoring techniques in manufacturing process of wires.Strengthening effect (yield and ultimate tensile strength, plasticity and hardness) and microstructural evolution (continuous dynamic recrystallization -CDRX-) due to severe plastic deformation were experimentally analysed and numerically investigated by an innovative finite element (FE) model able to validate the effectiveness of a properly modified process for ultra-fine aluminium alloy AA6101 wires production designed with the aim to avoid any post manufacturing costly thermal treatment.The study provides an accurate experimental study and numerical prediction of the thermo-mechanical and microstructural phenomena that occur during an advanced large plastic deformation process; it shows how the combination of smart manufacturing and simulations control represents the key to renew the traditional manufacturing methods in the perspective of the Industry 4.0, connecting and integrating the manufacturing process for the industrial evolution in production.

Hardness and Microstructure Homogeneity of Pure Copper and Iron-Chromium Alloy Processed by Severe Plastic Deformation

Hardness and microstructure homogeneity of pure copper and iron-chromium alloy processed by severe plastic deformation (SPD) were investigated in grain refinement. Equal channel angular pressing (ECAP) is one of the well-known techniques of the SPD technique due to their up-scale ability and other methods. SPD was applied to pure copper and iron-chromium alloy at comparable temperatures up to four passes. The microstructure and microhardness were observed and measured in the transverse plane for each billet. The homogeneity observation was carried out from the sub-surface until in the middle of the billet. The result showed that the deformed structure appeared adequately after the first pass and had a higher hardness level. The first pass showed a higher inhomogeneity factor than the fourth pass due to the homogeneity microstructure. The hardness also showed homogeneous value along the transverse plane, and it was concluded that ECAP could achieve complete homogeneity in grain refinement

Severe Plastic Deformation and Phase Transformations in High Entropy Alloys: A Review

This review discusses an area of expertise that is at the intersection of three large parts of materials science. These are phase transformations, severe plastic deformation (SPD), and high-entropy alloys (HEA). First, SPD makes it possible to determine the borders of single-phase regions of existence of a multicomponent solid solution in HEAs. An important feature of SPD is that using these technologies, it is possible to obtain second-phase nanoparticles included in a matrix with a grain size of several tens of nanometers. Such materials have a very high specific density of internal boundaries. These boundaries serve as pathways for accelerated diffusion. As a result of the annealing of HEAs subjected to SPD, it is possible to accurately determine the border temperature of a single-phase solid solution area on the multicomponent phase diagram of the HEA. Secondly, SPD itself induces phase transformations in HEAs. Among these transformations is the decomposition of a single-phase solid solution with the formation of nanoparticles of the second phase, the formation of high-pressure phases, amorphization, as well as spinodal decomposition. Thirdly, during SPD, a large number of new grain boundaries (GBs) are formed due to the crystallites refinement. Segregation layers exist at these new GBs. The concentration of the components in GBs differs from that in the bulk solid solution. As a result of the formation of a large number of new GBs, atoms leave the bulk solution and form segregation layers. Thus, the composition of the solid solution in the volume also changes. All these processes make it possible to purposefully influence the composition, structure and useful properties of HEAs, especially for medical applications.