Alexandra Byakova

DEVELOPMENT OF LIGHTWEIGHT AL ALLOY AND TECHNIQUE

Abstract A most promising lightweight material termed cellular metal is of growing interest to industry because of its combination of strength and energy absorption. A new foaming agent, calcium carbonate, along with an appropriate technique are suggested to improve the metal structure and control the foaming process. An applied coating enhances wetting of the agent particles and improves the homogeneity of the foam. Structure and mechanical properties of the foams obtained were also studied. The results showed that calcium carbonate ensured an aluminum foam with comparable density and smaller pores than with the conventional foaming agent, titanium hydride. The present study confirmed that calcium carbonate and the described technique have good applicability for foamed metal production. Un matériel léger très prometteur qu’on appelle métal cellulaire est d’un intérêt croissant dans l’industrie grâce à sa combinaison de force et de capacité d’absorption d’énergie. On suggère un nouvel agent moussant, le carbonate de calcium, ainsi qu’une technique appropriée, pour améliorer la structure du métal et pour contrôler l’opération de moussage. L’application d’un revêtement favorise le mouillage des particules de l’agent et améliore l’homogénéité de la mousse. On a également étudié la structure et les propriétés mécaniques des mousses ainsi obtenues. Les résultats ont montré que le carbonate permettait l’obtention d’une mousse d’aluminium de densité comparable et avec de plus petits pores qu’avec l’agent de moussage conventionnel, l’hydrure de titane. La présente étude a confirmé que le carbonate de calcium, ainsi que la technique décrite, s’appliquait à la production de métal cellulaire.

The role of foaming agent and processing route in mechanical performance of fabricated aluminum foams

The results of this study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affects the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have been produced with pure Al/Al-alloys by the Alporas like melt process, all performed with and without Ca additive and processed either with conventional TiH2 foaming agent or CaCO3 as an alternative one. Damage behavior of contaminations was believed to affect the micromechanism of foam deformation, favoring either plastic buckling or brittle failure of cell walls. No discrepancy between experimental values of compressive strengths for Al-foams comprising ductile cell wall constituents and those prescribed by theoretical models for closed-cell structure was found while the presence of low ductile and/or brittle eutectic domains and contaminations including particles/layers of Al3Ti, residues of partially reacted TiH2, and Ca bearing compounds, results in reducing the compressive strength to values close to or even below those of open-cell foams of the same relative density.

Improvement of Structure and Deformation Behaviour of High Strength Al-Zn-Mg Foam

Metal foams based on high-strength Al-Zn-Mg alloy are promising material for energy absorption application. The performance of coated calcium carbonate (CaCO3) as foaming agent for Alporas like route is studied in the present paper by comparison with the conventional titanium hydride (TiH2). Compressive response of the foams was examined and microstructure of cell wall was investigated. The advantages of CaCO3–foam are shown and discussed.

Cold-sprayed Coatings based on High Strength Aluminium Alloys Reinforced By Quasicrystalline Particles: Microstructure and Key Properties

This study presents significant advantages of coldspraying in performance of coatings based on Al matrix reinforced by metastable nanoand submicrosized quasicrystalline particles as compared to those processed by thermal spraying and, in particular, by high velocity oxy-fuel (HVOF) spraying technique. Two kinds of feedstock powders with nominal compositions Al^J^C^ and Al94Fe2.5Cr2.5Ti1 were employed in spraying the coatings on cold rolled steel substrate. Microstructure and key mechanical characteristics of feedstock powders and coatings performed by coldspraying and HVOF process were studied and discussed. The main benefit of cold-spraying as opposed to HVOF spraying was that the composite quasicrystalline structure of initial feedstock powders is retained in the interior of flattened particles heavily deformed under impact in solid state. Strain hardening of coating and substrate is resulted from impact during cold-spraying. The results showed that unlike to HVOF sprayed coatings important advantage of cold-sprayed quasicrystalline coatings is referred to combination of increased hardness with ductility indicated by plasticity characteristic just about critical value δΗ « 0.9, which is quite enough for preventing brittle failure of material during particle impact onto substrate or previously deposited particles. E-mail: maximkiz@gmail.com (M.M. Kiz)

Mechanical Behaviour of Nanostructured Iron Fabricated by Severe Plastic Deformation under Diffusion Flow of Nitrogen

Specific features of mechanical behaviour of ultra fine grained iron subjected to friction treatment with nitriding (FN) were clarified by comparison with that induced by friction treatment (FT) with air. Mechanical parameters such as Young’s modulus, nanohardness, and plasticity characteristic δA were found to be of high sensitive both to the scale of grain structure and to iron modification by nitrogen. Young’s modulus tends to decrease and Hall-Petch low fails to describe correlation between grain structure and hardness for submicro-grained and nanocrystalline iron. Hall-Petch coefficient, ky, decreases as grain size decreases within submicro-grained and, then, nano grained sections and it takes even negative value in nano grained section modified by nitrogen. Parameter δA is found to be dependent on combination of hardness and Young’s modulus, resulting in its variation with decreasing the grain size. The presence of secondary nanocrystalline Fe4N phase fundamentally changes mechanical behaviour of nanocrystalline iron, leading to strengthening the grain boundaries and triple junctions.