EVOLUTION OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ULTRA-FINE-GRAINED INTERSTITIAL-FREE STEEL PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING

Equal channel angular pressing (ECAP) is one of the severe plastic deformation techniques which is widely used for producing metals with ultra-fine-grained microstructures. In the present work the influence of number of pressing by route BC on grain size, evolution of microstructure and mechanical properties of interstitial-free (IF) steel has been investigated by means of optical microscopy, electron back-scattering diffraction (EBSD) and tensile tests. It has been found, that the grain size decreases with increasing number of passes. Simultaneously tensile strength increases. The thermal stability of ECAP-processed microstructures has been also examined. It was found that the degradation of mechanical properties occurs only above 600 ˚C and 700 ˚C

Damage Characterization during Compression in a Perlite-Aluminum Syntactic Foam

Aluminum matrix (Al99.5) syntactic foam containing expanded perlite particles was produced using the pressure infiltration technique. The dominant deformation mechanisms during compression of this foam were determined by sequential k-means analysis of the acoustic emission data. Since the different deformation mechanisms were concurrently active even at small strains, successive unloading and reloading measurement was proposed for cluster identification. The repetitive unloading and reloading allowed us to identify two mechanical parameters, namely the unloading modulus and the loss for unloading-reloading cycles. Based on the correlations among the strain localization within the specimen, the acoustic emission results, the changes in these mechanical parameters, and the transition from quasi-elastic deformation to plasticity were revealed in this material

Monitoring the failure mechanisms in metal matrix syntactic foams during compression by acoustic emission

Syntactic foam containing hollow ceramic spheres with an average outer diameter of 1.45 mm and wall thickness of 58 µm was produced using the pressure infiltration technique. This paper presents the analysis of the compressive deformation mechanisms of these syntactic foams using the acoustic emission (AE) technique. The active deformation mechanisms are determined by sequential k-means analysis of the AE data. The analysis revealed three dominant deformation mechanisms: plastic deformation of the cell walls, sphere fracture, and cell wall collapse. The AE results obtained are in good correlation with the findings of the visual inspection of the surface of the specimen, suggesting that the active deformation mechanisms in the whole volume of the specimen can be determined by this technique

The Effect of Matrix Composition on the Deformation and Failure Mechanisms in Metal Matrix Syntactic Foams during Compression

The influence of the matrix material on the deformation and failure mechanisms in metal matrix syntactic foams was investigated in this study. Samples with commercially pure Al (Al) and Al-12 wt % Si (AlSi12) eutectic aluminum matrix, reinforced by hollow ceramic spheres, were compressed at room temperature. Concurrently, the acoustic emission response and the strain field development on the surface were monitored in-situ. The results indicate that the plastic deformation of the cell walls is the governing mechanism in the early stage of straining for both types of foams. At large stresses, deformation bands form both in the Al and AlSi12 foam. In Al foam, cell walls collapse in a large volume. In contrast, the AlSi12 foam is more brittle; therefore, the fracture of precipitates and the crushing of the matrix take place within a distinctive deformation band, along with an occurrence of a significant stress drop. The onset stress of ceramic sphere failure was shown to be not influenced by the matrix material. The in-situ methods provided complementary data which further support these results

Characterization of Deformation Mechanisms in Mg Alloys by Advanced Acoustic Emission Methods

Adaptive sequential k-means (ASK) analysis of acoustic emission (AE) data was used to analyze the sources of AE during compression of three AZ31 magnesium samples with different initial texture. The results were compared to the classical hit-based approach. Observation of the deformed microstructure shows that the ASK analysis can distinguish very well between the signal originating in deformation twinning and dislocation slip. Moreover, together with microstructural analysis, the ASK algorithm revealed another source of AE for one of the samples, which was shown to be the double twinning

The Role of LPSO Structures in Corrosion Resistance of Mg-Y-Zn Alloys

The growing interest in improving Mg-based alloys’ corrosion properties stimulates the development of Mg-Y-Zn alloys with long-period stacking-ordered (LPSO) structures. In this work, to describe the corrosion performance of Mg-LPSO alloys, a set of experiments, including microstructure observations and corrosion testing in media containing various concentrations of chloride ions, were carried out. It was shown that the main corrosion mechanism occurring on the alloys was not only related to the volume of LPSO structures in the Mg matrix but was also dependent on their distribution. In the chloride-containing solutions, pitting was the predominant corrosion mechanism, and with the increasing chloride concentration, microgalvanic corrosion was accelerated

Elastoplastic deformations of layered structures

We formulate a large-strain model of single-slip crystal elastoplasticity in the framework of energetic solutions. Numerical performance of the model is compared with lab experiments on the compression of a stack of note papers

Micro-Tensile Behavior of Mg-Al-Zn Alloy Processed by Equal Channel Angular Pressing (ECAP)

Commercially available AZ31 magnesium alloy was four times extruded in an equal rectangular channel using three different routes (A, B, and C). Micro tensile deformation tests were performed at room temperature with the aim to reveal any plastic anisotropy developed during the extrusion. Samples for micro tensile experiments were cut from extruded billets in different orientations with respect to the pressing direction. Information about the microstructure of samples was obtained using the electron back-scatter diffraction (EBSD) technique. Deformation characteristics (yield stress, ultimate tensile stress and uniform elongation) exhibited significant anisotropy as a consequence of different orientations between the stress direction and texture and thus different deformation mechanisms