The Role of Technological Process in Structural Performances of Quasi-Crystalline Al–Fe–Cr Alloy

The present study emphasizes the role of processing strategy in terms of its effect on structural performances, heat-treatment response, and mechanical behaviour of quasi-crystalline Al–Fe–Cr-based alloy with nominal composition Al94Fe3Cr3. Several kinds of semi-products and bulk-shaped materials, all processed with Al94Fe3Cr3 alloy, have been produced using rapid solidification by melt spinning, powder atomization, hot extrusion, and cold-spraying, respectively. All kinds of semi-products and bulk-shaped materials comprised nanosize quasi-crystalline particles of i-phase, all embedded in α-Al matrix, although fraction volume of quasi-crystals and other structural parameters were rather different and dependent on processing route. In particular, cold-spraying technique was believed to give essential advantage in retaining quasi-crystalline particles contained by feedstock powder as compared to currently employed hot extrusion. Crucial role of nanosize quasi-crystalline particles in structural performances and superior combination of high strength and sufficient ductility of ternary Al–Fe–Cr alloy was justified over evolution of mechanical properties under heating. In this aim, evolution of the structure and mechanical properties of each kind of Al94Fe3Cr3 alloy in response to heat treatment was examined and discussed by considering the classical strengthening mechanisms. A set of mechanical characteristics including microhardness, HV, yield stress, σy, Young’s modulus, E, and plasticity characteristic δH/δA was determined by indentation technique and used in consideration. Strength properties (HV, σy, E) and plasticity characteristic (δH/δA) of cold-sprayed Al94Fe3Cr3 alloy were revealed to be much higher than those provided by currently employed hot extrusion. The important point concerns the fact that cold-sprayed Al94Fe3Cr3 alloy kept almost stable values of mechanical properties at least up to 350 °C, suggesting potential application of this material in engineering practice under intermediate temperature.

PLASTICITY CHARACTERISTICS OBTAINED THROUGH INSTRUMENTAL INDENTATION

The nanohardness and microhardness testing of crystalline materials with different types of interatomic bonds and different crystal structures was performed with Berkovich indenter.The plasticity characteristics for crystalline materials with different types of interatomic bonds and different crystalline structures were determined by microindentation and by nanoindentation. The relation between these characteristics and parameters of material (Meyer hardness, Young's modulus and Poisson's ratio) was assigned. Plasticity characteristic may be used for characterization of mechanical behavior of materials which are brittle at standard mechanical tests and for coatings.

A nanoindentation study of magnetron co-sputtered nanocrystalline ternary nitride coatings

Nanoindentation testing was used to determine the hardness, elastic modulus and plasticity parameter of three newly developed ternary nitride coatings with nano-sized grains. With decreasing nitrogen deposition pressure, grain diameter of the coatings decreases that leads to both higher nanohardness and elastic modulus with conservation of satisfactory values of plasticity characteristic.

Application of the plasticity characteristic determined by the indentation technique for evaluation of mechanical properties of coatings: I. specific features of the test method procedure

Specific features of the test method procedure capable for determining the plasticity characteristic dH by indentation of inhomogeneous coatings affected by residual stress was clarified. When the value of the plasticity characteristic for coating was found to be as great as dH > 0.5 a simplified model was found to be reasonably adequate, while a modified model assumed compressibility of the deformation core beneath indentation. The advantage of the modified approach compared to the simplified one was grounded experimentally only if the elastic deformation for coating becomes greater than ?e ? 3.5%, resulting in the decrease of plasticity characteristic dH < 0.5. To overcome non accuracy caused by the effect of the scale factor on measurement results a comparison of different coatings was suggested using stabilized values of the plasticity characteristic dH determined under loads higher than critical, P ? Pc, ensuring week dependence of micro hardness values on the indentation load.