Babak Omranpour Shahreza

In this work, we investigated a modern combined processing technique for the synthesis of lightweight superhard composites based on boron–carbon. We used traditional B4C with precipitates of free graphite and Al powder as initial materials. In the first stage, the composites were fabricated by the self-propagating high-temperature synthesis (SHS) with the subsequent hot pressing of the compound. Further, by the disintegration and attrition milling, the ultrafine-grained powder was obtained. We used HCl and HNO₃ acids for the chemical leaching of the powder to remove various impure compounds. At the last stage, a solid composite was obtained by the spark plasma sintering (SPS) method under nitrogen pressure. The main feature of this approach is to implement different synthesis techniques and chemical leaching to eliminate soft phases and to obtain superhard compounds from low-cost materials. The phases were studied by X-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy. The composites compacted by the SPS method contained superhard compounds such as B13C2, B11.7C3.3, and c-BN. The fabricated composite has an ultrafine-grained microstructure. Using a Berkovich indenter, the following nanohardness results were achieved: B13C2 ~ 43 GPa, c-BN ~ 65 GPa (all in Vickers scale) along with a modulus of elasticity ranging between ~ 400 GPa and ~ 450 GPa.

In the present work, we use a modified Equal Channel Angular Pressing technique for structure and properties change of Tantalum and Niobium at room temperature. The main advantage of this modified technique is the possibility to produce relatively large samples with ultrafine-grained microstructure in all volume of the workpiece by reduced deformation load up to 25% via friction decrease, and also to prevent the punch fracture under high compression stress during pressing. The various microstructures and properties were produced in metals by using different von Mises strain levels up to Ɛ_vM = 13.8. The changes in microstructure were studied by using SEM and TEM techniques. The change of mechanical properties was measured by using various tension and hardness testing setups. We can conclude that during processing the ultrafine-grained microstructure in as-cast Nb and Ta was formed. The uniaxial tensile strength, Vickers hardness, and plasticity of Nb and Ta significantly increased as compared to coarse-grained counterparts. We believe that the relatively large workpieces of pure bulk Ta and Nb metals with improved microstructure and exploitation properties are suitable materials for the modern industry.

Hydrogen is expected to be a viable solution for green-energy investment in future. However, hydrogen storage is a big challenge for stationary and mobile applications. Severe Plastic Deformation (SPD) techniques are well-known to be effective in enhancement of hydrogenation in metals hydrides. This paper shows the effect of a novel SPD technique named “High Pressure Torsion Extrusion-HPTE” on the hydrogenation of metal hydrides and compare it with the conventional method of ECAP. Results of mechanical testing and X-ray diffraction patterns showed significant enhancement in hardness and microstructural refinement in materials after HPTE. Accordingly, hydrogenation kinetics improved dramatically. This achievement could be an initiative to implement HPTE in synthesis of metal hydrides for clean energy applications.

High Pressure Torsion Extrusion (HPTE) is a novel technique which has been recently introduced to the society of Nano-SPD researchers. HPTE exploits the deformation mechanics of HPT but in a larger scale within rod-shape samples and is capable of applying high values of strain to materials in one pass. This research aims to evaluate the effect of HPTE on mechanical properties of materials and also to study the effect of geometry of HPTE die on strain distribution in deformed samples by using Finite Element Method (FEM). Commercial pure Aluminium AA1050 was used for experimental work; and eccentric dies with parallel-misaligned channels were developed for evaluation by numerical modelling. Results of this research will help us better understand the effect of process parameters and also geometry of the die on materials.

Equal channel angular pressing (ECAP) is a type of severe plastic deformation procedure for achieving ultra-fine grain structures. This article investigates artificial neural network (ANN) modeling of ECAP process based on experimental and three-dimensional (3D) finite element methods (FEM).In order to do so, an ECAP die was designed and manufactured with the channel angle of 90° and the outer corner angle of 15°. Commercial pure aluminum was ECAPed and the obtained data was used for validating the FEM model. After confirming the validity of the model with experimental data, a number of parameters are considered. These include the die channel angles (angle between the channels Φ and the outer corner angle Ψ) and the number of passes which were subsequently used for training the ANN. Finally, experimental and numerical data was used to train neural networks. As a result, it is shown that a feed forward back propagation ANN can be used for efficient die design and process determination in the ECAP. There is satisfactory agreement between results according to comparisons.