I. Sabirov

Deformation modes and anisotropy in magnesium alloy AZ31

Abstract A strongly textured sheet of magnesium alloy AZ31 has been subjected to tensile testing at temperatures between ambient and 300 °C. Structures have been examined by optical and transmission electron microscopy and also by atomic force microscopy to quantify surface displacements seen at grain boundaries. Plastic anisotropy varies strongly with test temperature as was observed previously by Agnew and Duygulu. The present findings do not support the view that crystallographic becomes a major contributor to deformation at higher temperatures. Rather, the material behaviour reflects an increasing contribution from grain boundary sliding despite the relatively high strain rate (10– 3 s– 1) used in the mechanical tests.

Nanostructured Al and Cu alloys with superior strength and electrical conductivity

Mechanical strength and electrical conductivity are the most important properties of conducting metallic materials used in electrical engineering. Today, there is a growing need in this field for innovative conductor materials with improved properties. Meanwhile, the main issue is that high electrical conductivity and high strength are usually mutually exclusive due to physical nature of these properties. Alloying of pure metals results in significant increase of their mechanical strength, whereas electrical conductivity dramatically drops due to the scattering of electrons at solutes and precipitates. Recent studies have shown that intelligent nanostructural design in Al, Cu, and their alloys can improve combination of high mechanical strength with enhanced electrical conductivity. It was demonstrated that mechanical strength and electrical conductivity of these materials are primarily controlled by their microstructure, of which grain size, morphology of second phases, and their distribution, as well as dislocation structure, are the most important parameters. Rapid development of the state-of-the-art methods for the microstructural characterization at nano- and atomic scale has allowed a deeper insight into microstructure–properties relationship. The approach of intelligent nanostructural design of Al and Cu alloys has even enabled to increase the material strength with simultaneous improvement of its electrical conductivity. In this case, recent works on nanostructuring alloys by severe plastic deformation are of special interest, which gives rise to fundamental questions dealing with new mechanisms of strength and electrical conductivity as well as innovation potential of practical application of nanostructured materials. These issues are considered and discussed in the present progress article.

Biaxial Deformation Behavior and Enhanced Formability of Ultrafine-Grained Pure Copper

Coarse-grained commercially pure Cu was subjected to equal channel angular pressing at room temperature for 2 passes and 12 passes resulting in grain refinement down to the ultrafine scale. Uniaxial tensile testing revealed that as-ECAP Cu samples have very high strength, but low uniform elongation and elongation to failure, whereas small punch testing showed that strain in biaxial stretching of the as-ECAP Cu specimens was comparable to that in the coarse-grained Cu. Analysis of surface relief demonstrated extensive microlocalization of plastic flow into microshear bands during biaxial stretching of the as-ECAP Cu specimens. The effect of microstructure and stress state on formability of the material and the mechanisms governing its plastic deformation are discussed. It is suggested that although the high strength as-ECAP Cu exhibits poor ductility in uniaxial tension, in other strain paths such as biaxial stretching, it can show high formability which is sufficient for metal-forming processes.

Ultra-fine grained pure Titanium for biomedical applications

Ti-based materials are one of the most important materials used in biomedical engineering. Recently, commercially pure (CP) Ti has attracted significant attention of research community due to its full biocompatibility with human body, and there is an ongoing demand to improve its mechanical properties without sacrificing other beneficial properties. A possible approach to achieving this aim is to use the method of severe plastic deformation (SPD) to obtain an ultra-fine grained (UFG) microstructure. Significant grain refinement by SPD processing leads to an improvement in mechanical and functional properties. This paper gives an overview of a range of the properties that can be achieved in the UFG CP Ti including microstructural features, mechanical properties, corrosion performance and biocompatibility. Attention is paid to the main SPD processing techniques developed for the fabrication of UFG CP Ti. Current and potential applications of UFG CP Ti in biomedical engineering are also considered.

Deformation Behaviour of Ultrafine Grained Steel Produced by Cold Rolling of Martensite

Abstract An ultrafine grained Nb microalloyed steel was produced by cold rolling of martensite followed by annealing heat treatments at different times to study its effect on the microstructure and mechanical behaviour of the ultrafine grained steel. High strength was achieved by this thermomechanical processing due to the formation of cell and subgrain dislocation substructure; however annealing reduced both strength and elongation.

Physical Simulation of Hot Rolling of Ultra-fine Grained Pure Titanium

Complex thermo-mechanical processing routes are often developed for fabrication of ultra-fine grained (UFG) metallic materials with superior mechanical properties. The processed UFG metallic materials often have to undergo additional metalforming operations for fabrication of complex shape parts or tools that can significantly affect their microstructure and crystallographic texture, thus further changing their mechanical properties. The development of novel thermo-mechanical processing routes for fabrication of UFG metallic materials or for further metalforming operations is very time-consuming and expensive due to much higher cost of the UFG metallic materials. The objective of this work is to perform physical simulation of hot rolling of UFG pure Ti obtained via severe plastic deformation and to analyze the effect of hot rolling on the microstructure, crystallographic texture, and hardness of the material. It is demonstrated that physical simulation of metalforming processes for UFG metallic materials can significantly reduce the amount of material required for development of processing routes as well as to increase the efficiency of experimental work.

Deformation mechanisms in an ultra-fine grained Al alloy

Abstract This work focuses on the deformation behavior of an ultra-fine grained Al-Mg-Si alloy processed by equal channel angular pressing over a wide range of temperatures and strain rates. The effect of temperature and strain rate on the homogeneity of plastic deformation, the evolution of microstructure, the strain rate sensitivity and the underlying deformation mechanisms are investigated. It is demonstrated that the localization of plastic deformation at the micro scale is triggered by grain boundary sliding due to grain boundary diffusion. The contributions of different deformation mechanisms during the plastic deformation of the material are discussed.

Investment casting of nozzle guide vanes from nickel-based superalloys: part I – thermal calibration and porosity prediction

Investment casting is the only commercially used technique for fabrication of nozzle guide vanes (NGVs), which are one of the most important structural parts of gas turbines. Manufacturing of NGVs has always been a challenging task due to their complex shape. This work focuses on development of a simulation tool for investment casting of a new generation NGV from MAR-M247 Ni-based superalloy. A thermal model is developed to predict thermal history during investment casting. Experimental casting trials of the NGV are carried out and the thermal history of metal, mold, and insulation wrap is recorded. Inverse modeling of the casting trials is used to define accurately some thermophysical parameters and boundary conditions of the thermal model. Based on the validated thermal model, another model is developed to predict porosity in the as-cast NGVs. The porosity predictions are in good agreement with the experimental results in the as-cast NGVs. The advantages and shortcomings of the developed modeling tool are discussed.

Effect of Accumulative Roll Bonding on Plastic Flow Properties of Commercially Pure Zirconium

Accumulative roll bonding (ARB) has been considered as one of the promising techniques for fabrication of ultra‐fine grained (UFG) metallic materials. The ARB process consists of several cycles of cutting, stacking, and rolling of metal sheets, so very high strains can be induced in the material resulting in significant grain refinement and in the formation of UFG microstructures. The ARB technique has been applied to a wide range of metallic materials such as Al and Al alloys, Mg, Fe and steels, Zr, Cu, as well as composite materials. UFG metallic materials processed via ARB show increased strength. Despite a significant body of experimental research into the deformation behaviour of the ARB‐processed materials, the fundamentals of their plastic deformation are not fully understood yet. This work focuses on the effect of grain refinement via ARB‐processing on the mechanical behavior and on the strain‐rate sensitivity of commercially pure Zr (99.8% purity). The mechanical properties of the as‐received coa...

Nanostructural engineering of steel

Various analytical rules of mixture are commonly used to take into account heterogeneous features of a material and to derive global properties. But, with such models, one may not be able to fulfil the requirements for separating appropriately the different lengthscales. This might be the case for some issues such as strain localisation, surface effect, or topological distributions. At an intermediate lengthscale, which we refer to as the mesoscopic scale, one can still apply continuum mechanics. So why not perform calculations using the finite element method on volumes of material to obtain the response of Representative Elementary Volumes (R.E.V.). The construction of digital microstructures for such calculations is performed in two steps. First, a series of R.E.V.s with statistics of features of real materials should be defined. Then, finite element meshes should be produced for these R.E.V.s and updated when calculations involve large strains. Powerful automatic three-dimensional mesh generators and remeshing techniques prove necessary for this latter task. This strategy is applied to create digital R.E.V.s which match statistical features of forgings. Measurements provide micromechanical parameters of each subvolume. As an example of calculations, numerical simulations provide the anisotropic fatigue properties of forgings.