Abstract: NiTi shape memory alloys have attracted significant interest due to their unique superelasticity and high damping performance. In this work, the effect of SiC particle size on both physical and mechanical properties of NiTi matrix composite was investigated. Ni and Ti powders with particle sizes of 40 µm were used with the SiC addition with varying particle sizes of 20 µm and 40 µm, respectively. Composites of NiTi with 1wt. % SiC were fabricated by powder metallurgy technique. The effects of SiCp addition on hardness, relative density and wear behavior of NiTi composites have been investigated. The samples were examined by scanning electron microscope, for microstructural studies and phase development. The results showed that the distribution of the reinforced particle was uniform. Moreover, as the SiC particle size decreases, hardness and wear resistance increase. It was demonstrated that SiC particle size significantly enhanced the wear resistance of NiTi composite.
Abstract: The paper introduces the possibility to replace the “wet alloy”, used for sprinkler-triggering within automatic fire protection systems, with a shape memory alloy (SMA) type. The idea of the present application is based on the thermoelastic reversible martensitic transformation, governing SMA functioning, which has completely reversible character, and enables the occurrence of two-way shape memory effect (TWSME) after the application of a thermomechanical treatment called “training”. For this purpose a commercial NiTi rod, which was martensitic at room temperature, was subjected to thermal analysis tests, performed by differential scanning calorimetry (DSC) and dilatometry. Martensite (M) reversion to parent phase (A), during heating, was emphasized by an endothermic peak on the DSC thermogram and by a length shrinkage, on the dilatogram. The capacity to develop TWSME was revealed by the change in displacement-temperature variation, with increasing the number of training cycles. This stabilized fully reversible behavior recommends NiTi rods as executive elements of a new concept of resettable sprinkler for fire protection.
Abstract: Samples of VT23 β-metastable titanium alloy quenched from temperatures in a range between critical and β-transus were studied in situ during heating on X-ray diffractometer. The anisotropy of orthorhombic martensite lattice was investigated. Abnormal behavior of «b» lattice spacing, which demonstrated a negative value of thermal expansion, has been revealed.
Abstract: Perovskite compounds have received keen interest from academic research due to their unique properties such as ferroelectric, pyroelectric, piezoelectric, and dielectric properties. Nano sized oxides of strontium doped barium zirconate of general formula Ba1-xSrxZrO3 (x= 0.2, 0.4, 0.6, 0.8) have been prepared by a solid-state procedure. The surface morphology, microstructure, and phase analysis, of the sintered ceramics were characterized by field emission scanning electron microscopy (FE-SEM). Scanning electron microscopic studies showed the formation of cubic and hexagonal nanoparticles with an average grain size of 1.6μm±0.47 and 0.82±0.35μm. Dielectric studies were carried out as a function of frequency to explore the electrical properties of Sr-doped BaZrO3.
Abstract: Tensile specimens, with the chemical composition Fe-28Mn-6Si-5Cr (mass. %), were obtained by ingot metallurgy, hot rolling, solution treatment (1100°C/ 5 min/ water) and spark erosion cutting. Tensile tests were performed to failure and to prescribed strains, by loading-unloading. Ultimate strain and strength increased up to 80.8 % and 1033 MPa, respectively, with decreasing the cross section of specimens’ gauge down to 2 mm2. The specimens were pre-strained by static tensile loading-unloading tests, to permanent strains as high as 60 %. This procedure aimed to stress-induce martensite, which was further analyzed, on the gauges of pre-strained specimens, by optical and scanning electron microscopy (SEM) as well as X-ray diffraction (XRD). Thermally induced reversion to austenite, of stress-induced martensite, was emphasized, during heating, by differential scanning calorimetry (DSC).
Abstract: The most widely used equation for analytical description of the transformation kinetics of the metastable solid solutions (the steel austenite in particular) is Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation . However the practical analysis of the experimental isothermal bainite transformation kinetics often gives significant deviation from the conventional theory . This problem can be solved by the derivation of an analytical function which would provide the best fit of the experimental results. Two analytical approaches describing the kinetics of bainite transformation in steels 300M and D6AC are proposed. The first one is based on an approximation of the experimental ln (-ln (1-Р)) vs. ln τ dependence by a second order polynomial function. The second approach is based on the solution of the differential equation y(x) = ay’(x)+b, where x= ln τ, y(x) = ln(-ln(1-P)). A comparison between the proposed approaches and Kolmogorov - Johnson - Mehl – Avrami equation is conducted. The adequacy of the two analytical models is estimated using Fisher ratio test.
Abstract: Several ceramic materials with a perovskite structure often exhibit interesting electronic properties and, therefore, are often called “electroceramics”. Electroceramics with high dielectric constants are used in capacitors and superconductors. The effect on calcination temperatures (1000°C–1400°C) and the changing of ions in A and B sites on the phase formation and microstructure of barium strontium zirconate (Ba1-xSrxZr)O3, BSZ, x = 0.2 and 0.4 ceramics were investigated. The BSZ powders were prepared using the solid state reaction method. The phase purity, crystal structure and microstructure of samples were examined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD). We found out that the percentage phase purity of perovskite increases with an increase in the calcination temperatures as expected and it was found that BSZ powders adopts a perovskite structure with a cubic () unit cell as well. The purity of perovskite powders was obtained above 1300°C and the purity phase of ceramics was detected in all samples.
Abstract: Effect of the alloy initial structure before remelting on the melt viscosity, its state prior to crystallization, and on processes occurring in the alloy in solid state during its subsequent treatment was investigated using EK77 alloy. The study was performed by means of torsional oscillation of the melt with crucible, scanning electron microscopy, and optical metallography.
Abstract: In this paper, austempering heat treatment was applied to a new generation high silicon GJS 600-10 grade ductile iron with an initial ferritic matrix. Different austempering temperatures of 270, 330 and 390°C were applied after austenitizing at 975°C for 120 min. Depending on the austempering temperatures, lower and upper ausferritic microstructures were obtained. Results showed that volume fraction of the retained austenite in the ausferritic microstructures, which was estimated by VSM technique is well correlated with those estimated by XRD technique.