نشریه مهندسی متالورژی و مواد
سال بیست و چهارم شماره 1 (بهار و تابستان 1392)

Forming limit diagram (FLD) is an important diagram by which the formability of sheet metals is studied. Strain rate is a very effective parameter influencing the FLD which is، in turn، influenced by the forming velocity. In this work، forming limit diagram for St14 was investigated both experimentally and numerically. In addition، the effect of forming velocity was studied and the experiments were conducted at three different velocities، i. e. 10، 100 and 200 mm/min. In numerical simulation، bifurcation theory was used to determine the necking time. The experimental results were compared with the numerical results and it was shown that the forming limit is increased as the forming velocity increases

In this study، the microstructure and properties of foam glass obtained as a result of the interaction of the waste glass with SiC as the foaming agent and Fe2O3 as the oxidizing agent have been investigated using scanning electron microscopy (SEM)، as well as three-point bending and pycnometery tests. First، the temperature and optimized amount of SiC for making foam glass was determined. The results showed that the sample with 4% SiC is changed into a foam at 850˚C with the highest percentage porosity (90%) and bending strength of 0. 57 MPa، although the size of pores was relatively large and their distribution was heterogeneous. Then، the effect of Fe2O3 addition on the amount of porosity، microstructure and bending strength was taken into consideration، and the samples with smaller pores and homogenous pore distribution were obtained. Moreover، the bending strength increased considerably in such a way that foam glasses with 61. 4-73. 2% porosity and 4. 12-7. 05 MPa bending strength were produced. These properties showed an enhancement when compared with those of the commercial samples

In this study، the microstructure and properties of foam glass obtained as a result of the interaction of the waste glass with SiC as the foaming agent and Fe2O3 as the oxidizing agent have been investigated using scanning electron microscopy (SEM)، as well as three-point bending and pycnometery tests. First، the temperature and optimized amount of SiC for making foam glass was determined. The results showed that the sample with 4% SiC is changed into a foam at 850˚C with the highest percentage porosity (90%) and bending strength of 0. 57 MPa، although the size of pores was relatively large and their distribution was heterogeneous. Then، the effect of Fe2O3 addition on the amount of porosity، microstructure and bending strength was taken into consideration، and the samples with smaller pores and homogenous pore distribution were obtained. Moreover، the bending strength increased considerably in such a way that foam glasses with 61. 4-73. 2% porosity and 4. 12-7. 05 MPa bending strength were produced. These properties showed an enhancement when compared with those of the commercial samples.

In this research، Taguchi method with the orthogonal array of L9 (34) was used in order to optimize the parameters of pulsed TIG welding for obtaining the optimum mechanical properties (UTS) in AZ31 Magnesium alloy Weldments. For this reason، the main parameters of pulsed TIG welding including the peak current (80-120 A)، the base current (20-40 A)، the pulse ferequency (1. 6-5 Hz)، and the welding speed (200-300 mm/min) were investigated in three levels with the same duty cycle. Then، the effect of each parameter on the ultimate tensile strength (UTS) of the alloy was evaluated. In addition، in order to choose a proper set of parameters، the results were examined by varience analysis method (ANOVA). Exprements were conducted to confirm the results. The results were found to have a good agreement with the predicted results. Microstructures of all the welds were studied، and their relations with the mechanical properties were evaluated.

The present research aims to synthesize the HA/YSZ composite and to formulate HA/YSZ-GIC for improving the fluoride release of the set cement. Experiments were performed by mixture design (MD) method، and data analysis was carried out by mini- tab 14 software. The results showed that the combination of 25. 891wt. % HA، 70. 246wt. % ZrO2 and 3. 86wt. % Y2O3 has desirable fluoride release profile. Combination of HA/YSZ-GIC in the optimized formulation improved the fluoride release from 7 ppm to 18 ppm after immesrsion for 56 days.

As a high temperature structural ceramic، cermets exhibit less brittleness than ceramic-ceramic composites or monolithic ceramics owing to the presence of a ductile metal second phase in their microstructure. These cermets can، therefore، be used in applications where the abrasive، creep and thermo-mechanical resistance are required. In the present study، aluminum-alumina cermets with different amounts of aluminum were fabricated at different heat treatment temperatures. In order to evaluate the optimum manufacturing conditions، specimens with different aluminum contents were subjected to DTA and TGA analyses. In addition، microscopic observations، phase analyses، and toughness، strength and hardness measurements were performed using SEM، XRD، three-point bending testing and Vickers hardness testing methods، respectively. The results of DTA and XRD analyses showed that for the oxidizing atmosphere and high amounts of aluminum، there is an exothermic peak corresponding to the oxidation of aluminum and an endothermic peak corresponding to the phase transformation of Al2O3. Higher amounts of aluminum in starting materials caused an increase in the density and toughness، and a decrease in the hardness of the cermet specimens sintered at 1550°C، however، their strength increased when up to 20% aluminum was added. In addition، for the case of 30%Al-Al2O3 cermet، the strength and density increased as the temperature increased up to 1500 ºC، while the toughness increased up to 1550 °C. The oxidation of aluminum phase was also found to be of great importance، hence، it was concluded that the optimized properties may only be obtained using an argon atmosphere.