Comparative analysis of microstructure,mechanical,and corrosion properties of biodegradable Mg-3Y alloy prepared by selective laser melting and spark plasma sintering

This work explored possibilities of biodegradable magnesium alloy Mg-3Y preparation by two modern powder metallurgy techniques–spark plasma sintering(SPS)and selective laser melting(SLM).The powder material was consolidated by both methods utilising optimised parameters,which led to very low porosity(∼0.3%)in the SLM material and unmeasurably low porosity in the SPS material.The main aim of the study was the thorough microstructure characterisation and interrelation between the microstructure and the functional properties,such as mechanical strength,deformability,and corrosion resistance.Both materials showed comparable strength of∼110 MPa in tension and compression and relatively good deformability of∼9%and∼21%for the SLM and SPS materials,respectively.The corrosion resistance of the SPS material in 0.1 M NaCl solution was superior to the SLM one and comparable to the conventional extruded material.The digital image correlation during loading and the cross-section analysis of the corrosion layers revealed that the residual porosity and large strained grains have the dominant negative effect on the functional properties of the SLM material.On the other hand,one of the primary outcomes of this study is that the SPS consolidation method is very effective in the preparation of the W3 biodegradable alloy,resulting in material with convenient mechanical and degradation properties that might find practical applications.

NANOCOMPOSITE COATINGS WITH ENHANCED HARDNESS

The article reviews the present state of the art in the magnetron sputtering of hart and superhard nanocomposite coatings. It is shown that there are (1) two gr oups of hard and superhard nanocomposites: (i) nc-MN/hard phase and (ii) nc-MN/s oft phase, (2) three possible origins of the enhanced hardness: (i) dislocation- dominated plastic deformation, (ii) cohesive forces between atoms and (iii) nano structure of materials, and (3) huge differences in the microstructure of single - and two-phase films. A main attention is devoted to the formation of nanocryst alline and/or X-ray amorphous films. Such films are created in a vicinity of tra nsitions between (i) crystalline and amorphous phases, (ii) two crystalline phas es of different chemical composition or (iii) two different preferred orientatio ns of grains of the same material from which the coating is composed. The existe nce of the last transition makes it possible to explain the enhanced hardness in single-phase films. The thermal stability and oxidation resistance of hard nano composite films is also shortly discussed.

Structure,Adhesion Strength and Corrosion Resistance of Vacuum Arc Multi-Period NbN/Cu Coatings

resistance,and adhesive strength of vacuum-arc multi-period NbN/Cu coatings is studied.It was found that in thin layers(about 8 nm,in a constant rotation mode),regardless of the change in the pressure of the nitrogen atmosphere,a metastableδ-NbN phase forms(cubic crystal lattice of the NaCl type).At a layer thickness of^40 nm or more,a phase composition changes from the metastableδ-NbN to the equilibriumε-NbN phase with a hexagonal crystal lattice.In the presence of theε-NbN phase in the niobium nitride layers,the highest adhesive strength is achieved with a value of LС5=96.5 N.Corrosion resistance tests have shown that for all the studied samples the corrosion process has mainly an anodic reaction.The highest corrosion resistance was shown by coatings obtained at a pressure of 7·10-4 Torr,with the smallest bias potential of-50 V and the smallest layer thickness;with a thickness of such a coating of about 10 microns,its service life in the environment of the formation of chloride ions is about a year.

Prediction of Dynamic and Aerodynamic Characteristics of the Centrifugal Fan with Forward Curved Blades

The main aim of this paper is determine the centrifugal fan with forward curved blades aerodynamic characteristics based on numerical modeling. Three variants of geometry were investigated. The first, basic "A" variant contains 12 blades. The geometry of second "B" variant contains 12 blades and 12 semi-blades with optimal length[1]. The third, control variant "C" contains 24 blades without semi-blades. Numerical calculations were performed by CFD Ansys. Another aim of this paper is to compare results of the numerical simulation with results of approximate numerical procedure. Applied approximate numerical procedure [2] is designated to determine characteristics of the turbulent flow in the bladed space of a centrifugal-flow fan impeller. This numerical method is an extension of the hydro-dynamical cascade theory for incompressible and inviscid fluid flow. Paper also partially compares results from the numerical simulation and results from the experimental investigation. Acoustic phenomena observed during experiment, during numerical simulation manifested as deterioration of the calculation stability, residuals oscillation and thus also as a flow field oscillation. Pressure pulsations are evaluated by using frequency analysis for each variant and working condition.