Evolution of manufacturing parameters in Al/Ni3Al composite powder formation using blending and mechanical milling processes

Aluminu–matrix composites produced by Ni₃Al intermetallic particles are increasingly used in aerospace and structural applications because of their outstanding properties. In manufacturing of metal–matrix composites using powder metallurgy blending and milling are important factors. They control the final distribution of reinforcement particles and porosity in green compacts which in turn, strongly affect the mechanical properties of the produced PM materials. This paper studies different conditions for producing composite powders with uniform dispersion of Ni₃Al particles in aluminum powders and improved physical and mechanical properties. The results indicated that an intermediate milling time for fabrication of composite powder, better than prolonged and shortened ones, causes better microstructure and properties. It was shown that addition of 5 vol.% Ni₃Al particles, produced by 15 h mechanical alloying to aluminum powders, and then 12 h blending operation provides an appropriate condition for producing Al–Ni₃Al composite powder.     

Classification of Hydrogels Based on Their Source: A Review and Application in Stem Cell Regulation

Stem cells are recognized by their self-renewal ability and can give rise to specialized progeny. Hydrogels are an established class of biomaterials with the ability to control stem cell fate via mechanotransduction. They can mimic various physiological conditions to influence the fate of stem cells and are an ideal platform to support stem cell regulation. This review article provides a summary of recent advances in the application of different classes of hydrogels based on their source (e.g., natural, synthetic, or hybrid). This classification is important because the chemistry of substrate affects stem cell differentiation and proliferation. Natural and synthetic hydrogels have been widely used in stem cell regulation. Nevertheless, they have limitations that necessitate a new class of material. Hybrid hydrogels obtained by manipulation of the natural and synthetic ones can potentially overcome these limitations and shape the future of research in application of hydrogels in stem cell regulation.     

Relationship between pore coarsening and mass loss during supersolidus liquid phase sintering of alpha brass

ABSTRACT

The effect of sintering variables on the zinc loss during sintering of brass was investigated. Zinc loss, evident through mass change, starts during heating of the powder at approximately 700°C. By supersolidus liquid phase sintering of the cold-pressed brass powder, the maximum amount of zinc loss occurred at lower temperatures and prolonged sintering times. At higher temperatures, especially near the zinc boiling point, the rate of zinc loss from the surface is surprisingly moderate since closing of the pores causes zinc to be trapped in the samples. At lower temperatures, in contrast, when the pores in the surface are open and there is also a lower volume fraction of liquid phase, zinc can easily escape from the samples. Generally, it was thus concluded that during sintering, zinc loss depends more strongly on the pore connectivity and the specific surface than just on the nominal vapour pressure.     

Effect of Intermediate Annealing Temperature on Response of Repressing to Densification of Pre-Alloyed Cr-Mo Steel

 Increasing density is one of the important factors for producing high quality powder metallurgy (PM) parts, which has beneficial effect on mechanical properties. One of the common techniques for achieving this goal is double compacting, which seems to be a potentially attractive method in PM route, also for Cr-Mo alloyed-steels. The objective of this research was to investigate the effect of first compacting pressure and intermediate annealing temperature on attaining higher densities and minimum interconnected porosity for Cr-Mo pre-alloyed steel. The effect of mentioned parameters was studied by measuring density, transverse rupture strength and macrohardness of repressed samples. The results show that for each first compacting pressure, the density range of repressed samples increases with the increasing annealing temperature up to a certain limit, due to C dissolution which causes free porosity and further densification. Annealing temperatures higher than optimum one should be avoided, since too much carbon dissolution results in harder and less deformable compacts. On the other hand, with regard to repressed density and other resulted properties, the amount of first compacting pressure offers considerable advantage in obtaining higher level of density and consequently improved mechanical properties.     

Study on an elaborated method to improve corrosion resistance of zinc phosphate coating

Coating with dense and fine particles containing fewer cracks and lower porosity shows more improved protective properties due to limiting pathways between the environment and base metal. The main aim of present research is to introduce an innovative method that is called rephosphating to achieve this morphology. The outstanding point of the present investigation is to highlight the significant effect of surface pretreatment by secondary grinding of phosphated surface and then rephosphating of this surface to obtain a coating with appropriate properties. The SEM observations showed that this method has an obvious influence on the formation of a very uniform zinc phosphate coating on the plain carbon steel compared with the traditional method of phosphating. Furthermore, the protecting properties of phosphated and rephosphated samples were described and compared using the neutral salt spray and the electrochemical polarization tests. The results showed that rephosphating method had a beneficial effect on improving the corrosion resistance. As well, improved paint adhesion of rephosphated sample was observed compared with that of the phosphated sample. Finally, it was concluded that when rephosphating method can be used to repair damaged phosphated areas, the coating with more compact morphology and improved properties can be achieved.     

Effect of TiB2 content on the characteristics of spark plasma sintered Ti–TiBw composites

Spark plasma sintering (SPS) was employed to fabricate monolithic titanium and in-situ formed TiB whisker (TiB_w) reinforced titanium matrix composites (TMCs) by adding different amounts of TiB₂ as boron source. The sintering process was completed at 1050 °C for 5 min under 50 MPa. The influences of TiB₂ content (0.6–9.6 wt. %) on microstructural evolution and mechanical properties of TMCs were investigated. Thermodynamics, XRD analysis and microstructural investigations confirmed the in-situ formation of TiB_w in the composite samples. However, some semi-reacted TiB₂ phases, surrounded by TiB coronas, were remained in the microstructure due to the unfinished chemical reaction between the components during a short-time sintering process. The results showed that all samples were appropriately densified by SPS process into the almost dense parts with relative density no less than 97.5%. While bending strength decreased and hardness increased with increasing TiB₂ content, the sample with 4.8 wt. % TiB₂ had the maximum tensile strength. Fractographical assessments showed that the addition of TiB₂ hindered the grain growth of titanium matrix. With increasing TiB₂ content, fracture mode changed from a multiple pattern to a predominantly transgranular and brittle state.     

Liquid–Liquid Equilibria in Biodiesel Production

During biodiesel production, the product is contaminated with impurities such as some non-reacted alcohol, glycerol, and catalyst. In order to comply with product requirements, these impurities must be removed, for example, by washing with water. Knowledge of the extent of water solubility in biodiesel is required to design the drying system and determine fuel quality. In the present work, the solubilities of water in biodiesels produced from sunflower and canola oils were measured within the temperature range of 24–60 °C. The solubility of water increased with increasing temperature and biodiesel unsaturation. The liquid–liquid equilibria of ternary systems of glycerol, methanol, and the above-mentioned biodiesels were investigated experimentally at 20, 30, and 40 °C. The binodal curves were determined by using the cloud point titration method and the tie lines were measured by evaporating the methanol. Both binary and ternary data were modeled using the UNIQUAC model. The model showed good agreement with the data. Othmer-Tobias correlations were applied and the corresponding constants were obtained. The results validated the consistency of the tie-line data obtained experimentally.     

Effect of Chemical Composition of Tetraethoxysilane and Trimethoxy(Propyl)Silane Hybrid Sol on Hydrophobicity and Corrosion Resistance of Anodized Aluminum

Silicon - The current study indicates the application of three different range of hybrid sols on substrates. The aim was to achieve an optimum chemical composition on the silane- treated surface in...