Yu.V. Milman

Segregation effects as a possible mechanism for strengthening in metallic glasses

Abstract As a result of examination of the temperature dependences of the mechanical behaviour of iron-based metal-metalloid type metallic glasses (MG), it has been shown that, by analogy with crystalline materials, it is reasonable to introduce for MG the concepts of characteristic deformation temperature T ∗ , thermal and athermal components of flow stress (hardness) and ductile-brittle transition being characterized with two transition temperatures: T db1 , the lowest temperature of macroscopic plasticity emergence, and T db2 ≈ 0.7 T x o ( T x 0 is the initial crystallization temperature) for all alloys tested. It has been found that alloying of MG with chromium and molybdenum leads to an increase of the thermal hardness component (whereas nickel promotes its lowering), the alloy strength and plasticity increase, the value of T db1 is reduced and there is delocalization of the plastic flow. Study of the effects of segregation of MG fracture surfaces allowed one to elucidate the nature of short-range order local disturbances in the sites, where the localization of plastic flow is most intensive, and to suggest the posibility of considering these processes as the basis for a ohenomenological model of strengthening of MG by alloying.

High Strength Aluminum Alloys Reinforced by Nanosize Quasicrystalline Particles for Elevated Temperature Application

Powders and rods from 6 alloys of the group ALMFexCryTizZr6.x.y.z were produced and investigated. Powders were produced by a water atomization process and after degassing consolidated to rods by severe plastic deformation at 350 °C 400 °C without sintering of the powders (by extrusion of powders in the preliminary evacuated and pressurized ampoules). Such a method of producing powders makes it possible to avoid liquation and other non-uniformities in chemical composition, to obtain the metastable quasicrystalline reinforcing particles in nanostructured aluminum matrix. The presence of the quasicrystalline icosahedral phase (the i-phase) in addition to α Al matrix in the produced powders and rods of alloys Al.MFexCryTizZr6-x. y-7, is confirmed by X-ray diffraction analysis and TEM / SEM investigation. The high strength at 300°C (up to 330 MPa) and sufficient plasticity at room temperature (5-8%) were obtained in investigated rods.

Mechanical Behavior of Nanostructured Aluminum Alloys Containing Quasicrystalline Phase

Aluminum-based alloys containing quasicrystalline particles of 50 – 600 nm in diameter as a reinforcing phase were produced in the form of powder or ribbons by water atomization or melt spinning techniques, respectively. Rods were compacted from powders and some ribbons by severe plastic deformation without sintering. Structure and mechanical behavior of alloys are discussed.

The effect of structural state and temperature on mechanical properties and deformation mechanisms of WC-Co hard alloy

The publications reporting systematic investigations of the effect of structural state of WC-Co hard alloys (the cobalt binder content, WC grains size and contiguity) and temperature on mechanical properties and deformation mechanisms have been reviewed and generalized. The ductile-brittle transition, strain hardening, special features of WC-Co alloys deformations in various temperature ranges, and specificity of mechanical properties of the alloys with submicron WC grains have been discussed.

Quasicrystalline Materials. Structure and Mechanical Properties

A brief description of the structure of quasicrystalline materials, their behavior under mechanical load and the mechanism of their high-temperature plastic deformation on the base of literary data are given. Original data about the investigation of the deformation of AlCuFe quasicrystal by a complex of micro- and nanoindentation techniques in a wide temperature interval are presented.

Plasticity determined by indentation and theoretical plasticity of materials

Characterization of the plasticity of materials by the part of plastic strain in the total elastic-plastic strain and application of this characteristic at indentation is considered. The dependence of the new plasticity characteristic on the structure and temperature is discussed. The concept of theoretical plasticity is introduced and the theoretical plasticity is calculated for a number of materials.

Structure and High-Temperature Properties of the Alloyed Quasicrystalline Al-Cu-Fe Powders and Thermal-Sprayed Coatings from Them

A structure and some properties of icosahedral quasicrystalline phase Al-Cu-Fe may be increased by directly alloying. Sc and Cr were selected as the alloying elements. The following composition were investigated: AlMCu2<,Fe12, Al62.73Cu25Fe12Sco.27, Al62.5f,Cu2.,Fe12Sc0.44, Al M > CU| X Fe 8 Cr 8 . The powders were fabricated by melt atomization with high-pressure water. The thermal-sprayed coatings were manufactured from powders of the size fraction of (-63+40) pm. It is established that alloying of the quasicrystalline Al-Cu-Fe alloy with scandium in the amount of 0.265 and 0.44 at. % increases the content of the quasicrystalline icosahedral ψ-phase in powders and coatings. Thus, in the powder of (-63+40) pm size fraction the ψ-phase content increased to 60-65 wt. % compared to 55 wt. % in the non-alloyed powder. The thermal treatment of powders and coatings with scandium provided a reliable possibility to obtain a 100 % ψ-phase content. In Al-Cu-Fe-Sc powders a singlephase ψ-state was obtained by annealing for 1 h at 650°C, whereas in the case of Al-Cu-Fe powders annealing at 700 °C was required. The annealing of AlCu-Fe-Cr powders at 600 °C results in formation of approximant phase (O, -phase) . The thermal-sprayed coating from Al-Cu-Fe powder has microhardness of about 6 GPa at room temperature, which hardly changes at 300 °C, whereas with further heating it gradually falls to a level of about 3 GPa at 600 °C. Alloying with Sc and Cr did not essentially change the temperature dependence of the hardness of coatings from the non-alloyed alloy.

Influence of Scandium on Amorphization of Aluminum Alloys

Structure of Al100−xScx, Al91Ce9−xScx, and Al85Ni10Ce5−xScx alloys manufactured in the form of melt-spun ribbons was investigated in order to establish the influence of scandium on the tendency to amorphization of aluminum alloys alloyed with rare-earth metals. Ribbons structure was compared with their hardness. Thermal stability of ribbon structure was studied.

Structure and mechanical properties of iron subjected to surface severe plastic deformation by friction: I. Structure formation

The severe plastic deformation of armco iron by friction is experimentally studied, and the results obtained are used to show that efficient grain refinement is possible in the temperature ranges of warm and hot deformation. A nanocrystalline structure forms only under dynamic recrystallization conditions during hot deformation, which is ensured by deformation in different directions at a rate higher than 102 s−1.

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)