HIGH STRAIN RATE BEHAVIOUR OF AN AZ31 + 0.5 Ca MAGNESIUM ALLOY

<em>The paper reports behaviour of magnesium alloy AZ31 (nominal composition 3 % Al - 1 % Zn – balance Mg) with an addition of 0.5 wt. % Ca at high strain rates. Samples were prepared by the squeeze cast technology. Dynamic compression Hopkinson tests were performed at room temperature with impact velocities ranging from 11.2 to 21.9 m.s^-1. A rapid increase of the flow stress and the strain rate sensitivity was observed at high strain rates. Transmission electron microscopy showed extremely high dislocation density and mechanical twins of two types. Adiabatic shear banding is discussed as the reason for the observed behaviour at high strain rates.</em><span> </span

CYCLIC PLASTIC BEHAVIOUR OF UFG COPPER UNDER CONTROLLED STRESS AND STRAIN LOADING

<em>The influence of stress- and strain-controlled loading on microstructure and cyclic plastic behaviour of ultrafine-grained copper prepared by equal channel angular pressing was examined. The stability of microstructure is a characteristic feature for stress-controlled test whereas grain coarsening and development of bimodal structure was observed after plastic strain-controlled tests. An attempt to explain the observed behaviour was made.</em

THE ANALYSIS OF CAUSES OF LORRY PISTON COMBUSTION ENGINE DAMAGE

<div><p>The article deals with analysis of causes of lorry piston combustion engine damage. For docummentation and analysis of causes was used macroscopical, microscopical and scanning electron microscopy. The analysis showed that the reason of fatal damage resides in production process of lorry combustion pistons which proved in implication of fatigue damage and subsequent burnout in two piston place.<em> </em></p> <p><em> </em></p></div

SOLUTION TREATMENT EFFECT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AUTOMOTIVE CAST ALLOY

The contribution describes influence of the heat treatment (solution treatment at temperature 545°C and 565°C with different holding time 2, 4, 8, 16 and 32 hours; than water quenching at 40°C and natural aging at room temperature during 24 hours) on mechanical properties (tensile strength and Brinell hardness) and microstructure of the secondary AlSi12Cu1Fe automotive cast alloy. Mechanical properties were measured in line with EN ISO. A combination of different analytical techniques (light microscopy, scanning electron microscopy (SEM)) were therefore been used for study of microstructure. Solution treatment led to changes in microstructure includes the spheroidization and coarsening of eutectic silicon. The dissolution of precipitates and the precipitation of finer hardening phase further increase the hardness and tensile strength of the alloy. Optimal solution treatment (545°C/4 hours) most improves mechanical properties and there mechanical properties are comparable with mechanical properties of primary AlSi12Cu1Fe alloy. Solution treatment at 565 °C caused testing samples distortion, local melting process and is not applicable for this secondary alloy with 12.5 % Si

EXPERIMENTAL INVESTIGATION OF EROSIVE WEAR ON THE HIGH CHROME CAST IRON IMPELLER OF SLURRY DISPOSAL PUMP USING RESPONSE SURFACE METHODOLOGY

Erosive wear occurs on the impeller and volute casing of the slurry disposal pump due to the impact of the ash particles on the impeller with a high velocity. Due to erosive wear, pump life become very short. The service life of centrifugal pump, handling slurry can be increased by reducing the erosive wear. In the present work, the experimental investigation of erosive wear has been carried out on the high speed slurry erosion tester to understand the effects of the ash concentration in slurry, rotational speed of the pump impeller and ash particle size on erosive wear. The erosive wear behaviour of high chrome cast iron was investigated by Response surface methodology (RSM). Analysis of variance (ANOVA) was used for statistical analysis and the modeled values for the response were obtained with the help of modeled equation. The result shows that the ash concentration in slurry and kinetic energy of the moving particles highly contributes to erosive wear of pump impeller as compared to the ash particle size

The influence of heat treatment on properties of lead-free solders

The article is focused on the analysis of degradation of properties of two eutectic lead-free solders SnCu0.7 and SnAg3.5Cu0.7. The microstructures of the intermetallic compound (IMC) layers at the copper substrate - solder interface were examined before and after heat treatment at 150°C for 50, 200, 500 and 1000 hours. The thickness of IMC layers of the Cu6Sn5 phase was growing with the increasing time of annealing and shown the typical scallops. For the heat treatment times of 200 hours and longer, the Cu3Sn IMC layers located near the Cu substrate were also observed. The experiments showed there is a link between the thickness of IMC layers and decrease of the shear strength of solder joints. In general, the joints made of the ternary solder showed higher shear strength before and after heat treatment in comparison to joints from solder SnCu0.7

CHARACTERIZATION AND PERFORMANCE OF DUPLEX-COATINGS ON Cr-V COLD WORK TOOL STEEL

Specimens made of Vanadis 6 steel were heat treated, plasma nitrided and coated with Cr2N. The microstructure, phase constitution and mechanical properties of plasma nitrided areas and duplex-coatings have been investigated using the light microscopy, scanning electron microscopy, X-ray diffraction and microhardness measurements. The adhesion of the coatings and the wear performance were studied using the scratch test and ring-on-plate tribological testing. Worn surfaces were examined by scanning electron microscopy. Nitrided areas formed at lower temperature were free of compound “white” layer while hose developed at higher temperatures contained as the white layer so the nitrided network. Significant increase in substrate hardness was detected due to the nitriding. Beneficial effect of the nitriding on the adhesion of Cr2N coatings was clearly determined whereas the extent in improvement of the adhesion depends on the presence/no presence of “white” layer on the surface. The extent of beneficial effect of plasma nitriding on the wear performance follows the impact of the constitution of nitrided areas on the adhesion. The amelioration of wear performance of Cr2N coatings can be attributed to the supporting effect of hard nitrided intermediate region, which provides excellent resistance of the substrate against plastic deformation, under heavy loading in particular. Practical testing demonstrated many times prolonged service-time of duplex-treated tools for sheet metal working.

Influence of processing on microstructure and mechanical properties of magnesium alloy AZ91

This paper deals with differences of mechanical characteristics and fracture surface morphology of AZ91 magnesium alloy in extruded state and after subsequent equal channel angular pressing (ECAP). According to the results, the tensile properties were not controlled by grain size only as values of the tensile strength and 0.2 proof stress were similar for both alloys despite having average grain size 15.9 μm for the extruded alloy and 1.2 μm for the ECAPed alloy. In contrast, microhardness seemed to be dependnt solely on the grain size. Fractographic analysis has shown changes in the damage mode from quasi-cleavage fracture in extruded state to rather ductile fracture with dimple morphology in exECAPed state during tensile loading.

INTERACTION OF SUB-ZERO PROCESSED Cr-V LEDEBURITIC STEEL WITH ALUMINA, 100Cr6-STEEL AND BRONZE IN DRY SLIDING

The interaction of the Vanadis 6 steel, processed without/with an application of sub-zero treatment, with alumina (hard counterface), 100Cr6-ball bearing steel (counterface of an intermediate hardness) and CuSn6 (soft counterface) has been examined. Obtained results infer that the wear performance against alumina is the best for no-SZT material quenched from higher austenitizing temperature (highest hardness). In dry sliding against 100 Cr6 ball bearing steel, the best wear resistance has been achieved for the material after SZT at -196 oC/10 h. The interaction of Vanadis 6 steel with CuSn6 results in a considerable counterpart material transfer to the samples of Vanadis 6-steel whereas the extent of the transfer is rather independent on both the austenitizing temperature and the SZT parameters, within the range of parameters used for the investigations

ELECTROCHEMICAL METHODS TO IMPROVE THE WEAR RESISTANCE OF COATING DEPOSITED ON THE METAL SURFACE

It was established that existing methods show low accuracy when assessing the durability of coatings. Furthermore, they don’t allow assessment of the contribution into durability of structural components and fillers for thermodiffusion and polymer-composite coatings, respectively. A method to evaluate durability of thermal diffusion chrome coatings on carbon steel and gray cast irons has been developed - the speed υp of destruction of the structural components of the coating. In addition, the destruction of each structural component is characterized by a constant value of destruction speed υp and potential φ, and their sharp vibrations are in complete destruction of the coating and the beginning of the destruction of the base metal. From the start of the test until the abrupt change in the rate of destruction υp, which is found on the curve υp - τ is the assessment of durability coating t¶ hat is specified with the curve φ - τ. Accuracy of the durability decreases from ± 30 min to ± 2 min. Developed as a way to assess the durability fillers polymer composite coatings, along with the finding that the rate of destruction υp of the time includes total disability coverage t3aƧ and time breakdown cover τn which are fixed on the curve φ - τ.