Iranian Journal of Materials science and Engineering
Volume:10 Issue: 3, Sep 2013

Precipitation behaviour of wrought Al-6Mg alloys with ternary scandium and quaternary zirconium and titanium has been studied. Hardness measurements and resistivity studies are employed to assess the precipitation behaviour of scandium doped Al-6Mg alloy without or with quaternary additions of zirconium and titanium. Further, the kinetics of precipitations are studied by differential scanning calorimetric technique. Scandium has been observed to form fine coherent Al3Sc precipitates during ageing and these are responsible for strengthening of the alloys. The precipitation kinetics of Al3Sc depends on the diffusion of scandium in aluminium. Presence of fine coherent precipitates of Al3Sc impedes the migration of dislocations and increase the recovery temperature. The kinetics of recrystallisation is also delayed.

In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN738LC base metal then, the YSZ (ZrO2-8% Y2O3) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na2SO4-55% V2O5 and mixed salts environment at 900°C up to 15 hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO2 and formation of YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior

The wear mechanism of plasma electrolytic nitrocarburised (PEN/C) 316L stainless steel samples was studied after a pin on disc wear test. The surface morphology of samples after application of PEN/C process was studied using scanning electron microscope technique. The sliding tracks resulting from the wear tests on the treated specimens indicated no signs of plastic deformation and adhesive wear, but the slider wear particles were trapped in the micro-craters of the counterface. The results showed that this mechanism may further improve the tribological performance of the system by increasing the wear resistance and lowering friction. PEN/C treated surfaces are therefore believed to have the potential to limit metal-to-metal wear mechanisms on a microscale, if contact pressures are sufficiently low

Ni and Cu elemental powder mixtures containing 25, 50, and 75% at Cu were subjected to mechanical alloying in a planetary ball mill under various milling times. Structural evolution was analyzed by means of X-ray diffraction and scanning electron microscopy. Experimental results indicated that nanostructured solid solution alloy powders having homogeneous distribution of Ni and Cu were formed by milling-induced interdiffusion of the elements. Average crystallite size of the as-milled powders was decreased with increasing Ni content and milling duration, and found to be in the order of 15-40 nm after 30 h of milling for all powder compositions. Moreover, lattice parameter and lattice strain of solid solutions were increased with the time of MA, which was more intense for nickel-rich alloys

The microstructure and mechanical properties of 7075 wrought aluminum alloy produced by strain induced melt activation (SIMA) route were investigated.Also liquid volume fraction measurement was studied by three procedures. Remelting process was carried out in the range of 560 to 610 °C for 20 min holding. The microstructure in the semi-solid state consists of fine spherical solid grains surrounded byliquid.The mechanical properties of the alloy vary with the grain size and weak mechanical properties of globular samples would appear if an alloy reheated at a high temperature. Thermodynamic simulation is a fast and efficient tool for the selection of alloys suitable for semi-solid processing

In order to evaluate the sintering behavior of lithium meta titanate (Li2TiO3) powder, the shrinkage of powder compact was measured under constant rates of heating. Densification curves for Li2TiO3 have been constructed with the help of shrinkage powder measured at different heating rates. The activation energy at the initial stage of sintering was determined by analyzing the densification curves and the value of Q=377 kJ/mol was obtained. The diffusion mechanism at the initial sintering stage was determined by the analytical method applied to the constant rates of heating data. This analysis exhibited that the dominant mechanism for initial sintering stage of Li2TiO3 is volume diffusion from grain boundary and surfaces.

The influences of age hardening and HIP (Hot Isostatic Pressing) on the mechanical properties of A356 (Al 7Si 0.6 Mg) casting alloys were studied. Cast bars were homogenized, heated and maintained at a temperature of 540°C for a duration of 2 hours, followed by rapid cooling in a polymeric solution. The castings were age hardened at 180°C for a duration of 4 hours before being subjected to HIP process at pressure of 104 MPa for 2 hours. The results indicated that the age hardening process used improved the tensile properties of A356. The HIP process removed the internal surface-connected porosities and improved the ductility of the samples significantly. Additionally, HIP reduced scattering in the tensile test data