مجله مواد نوین
سال سوم شماره 3 (پیاپی 11، بهار 1392)

In order to reduce weight and energy, an extensive amount of bake hardening steels are being used in automotive industry. These steels offer good formability during press stamping operations and also provide high final yield strength during paint baking treatments for good dent resistance. The baking operation is usually simulated by a heat treatment at 180˚C for 30 minutes. In this research work, the effect of increasing recrystallization annealing temperature on the bake hardening properties in ultra - low carbon steels, used in the automobile industry, has been investigated. The steel making process was done in an induction furnace. The cast- ingots were hot-forged, hot – rolled and then cold – rolled. Tensile specimens were prepared from the sheets. Box annealing was performed at 750 and 800˚C for 30 minutes. Tensile specimens were pre strained to 8 and 12% along rolling direction, aged at 180˚C for 30 minutes in a silicon oil bath. The results indicate that with increasing annealing temperature, despite the increase in grain size, the BH values increased.

The consolidation of the Al2O3/TiB2 into a dense and high-strength body is difficult because of the high degree of covalent bonding and low self-diffusion coefficient of the constituent elements. Synthesis of fine and homogenous structure in which one phase homogenously dispersed in the other can resolve this problem. Consolidation of Al2O3/TiB2 nano-composite powder derived from two different synthesis methods was investigated. Also the effect of processing condition on the sintering behavior, microstructure, and hardness of the densified samples were evaluated. In the first synthesis method a composite structure containing of an Al2O3 matrix with dispersed TiB2 particles was obtained via mechanical alloying of Al, TiO2 and B2O3 powder mixture. In the second method Al2O3/TiB2 nano-composite powder was prepared from TTIP(titanium tetra iso propoxide) and B2O3 using a sol-gel method followed by mechano-chemical reduction in the presence of Al. For sample which prepared by milling assisted sol-gel method, vickers hardness value of hot pressed sample at 1500°C was measured as 15.3 GPa and indentation fracture toughness was calculated as 10.1 MPa.m1/2; while for mechano-chemically synthesized sample this parameters are 20 GPa and 11.4 MPa.m1/2, respectively. Analysis of the diffraction pattern of samples revealed the presence of Al2O3, TiB2, and Al18B4O33 in the samples. Several factors favors the sintering process of the Al2O3-TiB2 nano-composite particles at low temperature and short time which include; (1) the nanostructured Al2O3-TiB2 particles, (2) the disordered crystal structure of the powder and (3) liquid phase formation of Al18B4O33.

In this short review paper, an attempt has been made to introduce Electron Backscattered Diffraction (EBSD) technique with few of its applications. This technique is a powerful tool for quantitative microstructural analyses. A short history, fundamentals, and capabilities as well as limitations have been discussed. Finally, few applications of EBSD in research and development as well as engineering are briefly described.

Microbial corrosion is a leading deterioration mechanism in concrete wastewater conveyance systems. The aim of this paper is controlling this type of corrosion in steel reinforced concrete sewers by electrodeposition of copper oxide on concrete. Electrodeposition process was tested in two ways: direct and pulse current. Therefore, a pilot study conducted on eight mock pipe specimens and the specimens were characterized by field scanning electron microscopy and atomic absorption tests. The results showed that the percentage of copper deposited in the pores of concrete depends on the type of current and electrolyte solution. Atomic absorption results presented that the percentage of copper oxide deposit in direct current method was more than the pulse current, although the scanning electron microscope images showed that in pulse deposition the size of the particles were smaller than direct mode and the number of holes in concrete is less. Moreover, the effect of beet molasses addition on electrolyte solution was studied and the experimental data revealed that the use of beet molasses could have removed and reduced Cu (II) ions from the electrolyte solution.

Bioactive glass ceramic nanoparticles with 55%SiO2-5%P2O5-40%CaO (%mol) composition were prepared and characterized. Precursors of silicon and calcium were hydrolyzed in acidic solution and gelated in alkaline condition. Fourier transform-infrared spectroscopy (FT-IR) results and the X-ray diffraction (XRD) indicated the presence of glass ceramic. Morphology and particle size of powder was studied by field emission scanning electron microscope (FESEM). its bioactivity was examined in vitro with respect to the ability of hydroxyapatite layer to form on the surface as a result of contact with simulated body fluid (SBF).Bioactivity of nanoparticles was confirmed by SEM, FTIR and XRD Therefore, this nano Bioglass-ceramic composite material with excellent bioactivity is promising for medical applications such as bone substitutes and drug carriers.