Iranian Journal of Materials Science and Engineering

Temperature Distribution of Particles in a Laser Beam

D. Schitz

This article studies the particle temperature distribution depending on the laser radiation power and the particle’s trajectory and velocity. The uneven heating of particles moving in the laser radiation field is identified. The regimes of laser heating without melting, with partial melting, and with complete particle melting are considered.

Comprehensive Analysis on the Effect of Deep Cryogenic Treatment on The Mechanical Behaviour of Martensitic Valve steel

M. Arockia Jaswin

The behaviour of the cryogenically treated En52 martensitic valve steel has been experimentally analyzed in this paper. Material samples are subjected to deep cryogenic treatment after completing the regular heat treatment. The critical properties of the valve steel like wear resistance, hardness, tensile strength and impact strength are evaluated for the cryo treated En52 valve steel samples as per the ASTM standards. The microstructural changes and the mechanism behind the enhancement of the properties are examined and reported. The precipitation of fine carbides, transformation of retained austenite and refinement of carbides were the reasons behind the improvement of the mechanical properties. Deep cryogenic treatment process parameters are optimized for better wear resistance, hardness and tensile strength using grey Taguchi technique. Deep cryogenic treatment process greatly influences the wear resistance, a maximum enhancement of 54% is observed

Effect of P2O5 on Crystallization Behavior and Chemical Resistance of Dental Glasses in the Li2O-SiO2-ZrO2 System

B. Eftekhari Yekta

Commercial dental lithium disilicate based glass-ceramics containing various amounts of P₂O₅ were synthesized. Regarding the crystallization behavior and physico-chemical properties of the glasses, the optimum percent of P₂O₅ was determined.as 8 %wt.
Crystallization behavior of the glasses was investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA). The micro-hardness and chemical resistance of both glass and glass-ceramic searies were also determined.
According to our results, lithium phosphate was precipitated prior to crystallization of the main phases, i.e lithium meta silicate and lithium disilicate. This early precipitation led to evacuation of residual glass phase from lithium ions, which caused increasing the viscosity of glass and so shifting of crystallization to higher temperatures.
In addition, increasing in P₂O₅ amounts and consequently increasing in Li₃PO₄, led to significant decrease in the crystallite size and aspect ratio of crystals.
Furthermore, while the chemical resistance of the glasses was decreased with P₂O₅, it was increased with P₂O₅ after heat treatment process.
The chemical solubility of these three glass-ceramics was between 2080~1188 μg/cm².

Determination of Optical Properties in Germanium Carbon Coatings Deposited by Plasma Enhanced Chemical Vapor Deposition

F. Sousani

In this research, Germanium-carbon coatings were deposited on ZnS substrates by plasma enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ precursors. Optical parameters of the Ge_1-xC_x coating such as refractive index, Absorption coefficient, extinction coefficient and band gap were measured by the Swanepoel method based on the transmittance spectrum. The results showed that the refractive index of the Ge₁_−xC_x coatings at the band of 2 to 2.2 µm decreased from 3.767 to 3.715 and the optical gap increased from 0.66 to 0.72 eV as CH₄:GeH₄increases from 10:1 to 20:1.

Effect of Equal Channel Angular Pressing and Annealing Treatment on the Evolution of Microstructure in AlMg0.7Si Aluminum Alloy

A. Eivani

In this research, samples of AlMg0.7Si aluminum alloy are deformed up to three passes using equal channel angular pressing (ECAP). Formation of a sub-micron structure after three passes of ECAP is demonstrated. Microstructural stability of the samples is investigated at temperatures of 300-500 °C. At 300 °C, fine recrystallized structure forms after 10 min which remains stable when the annealing proceeds up to 18 hrs. However, at 350 °C and higher, the microstructure is quite unstable. Even by 10 sec annealing, the samples exhibit recrystallized structure which turned to abnormal grain growth when temperature enhances to 500 °C and time up to 300 sec.

Finite Element Studies on Friction Stir Welding Processes of Polyethylene Plates

A. Ghasemi

One of the interesting state-of-the-art approaches to welding is the process of friction stir welding (FSW). In comparison with the fusion processes, FSW is an advantageous method as it is suitable for the non-fusion weldable alloys and polymeric materials joining. Regarding the materials pure solid state joining, it also provides joints with less distortion and enhanced mechanical properties. In the present work, a three-dimensional (3D) model based on finite element analysis was applied to study the thermal history and thermomechanical procedure in friction stir welding of high density polyethylene plate. The technique includes the tool mechanical reaction and the weld material thermomechanical procedure. The considered heat source in the model, includes the friction among three items: the material, the probe and the shoulder. Finally, the model was validated by measuring actual temperatures near the weld nugget using thermocouples, and good agreement was obtained for studied materials and conditions.

Microstructure and Crystallographic Texture Characterization of Friction Stir Welded Thin AA2024 Aluminum Alloy

E. Borhani

Friction stir welding (FSW) is a promising technique to join aluminum alloys without having problems encountered during fusion welding processes. In the present work, the evolution of microstructure and texture in friction stir welded thin AA2024 aluminum alloy are examined by electron backscattered diffraction (EBSD) technique. The sheets with 0.8 mm thickness were successfully welded by friction stir welding at the tool rotational speeds of 500, 750, and 1000 rpm with a constant traverse speed of 160 mm/min. EBSD revealed that stir zones exhibited equiaxed recrystallized grains and the grain size increased with increasing the tool rotation rate. The fraction of high angle grain boundaries and mean misorientation angle of the boundaries in the FSW joints at 500 rpm were 63.6% and 24.96°, respectively, which were higher than those of the sample welded at 1000 rpm (53.6% and 17.37°). Crystallographic texture results indicated that the Cube {001}<100> and S {123}<634> textures in base metal gradually transformed in to Copper {112}<111> shear texture. It was found that with increasing the tool rotation rate, the intensity of Cube {001}<100>, Y {111}<112>, S {123}<634>, and Dillamore {4 4 11}<11 11 8> texture orientations increased and the intensity of Brass {011}<211> texture orientation decreased.

On the Characteristics of Friction Stir Welding Lap Joint of Magnesium and Aluminum

M. Divandari

Lap joints of commercially pure magnesium plates to aluminium plates (Magnesium plate on the top, and Aluminium plate, grade 1100, on the bottom side) were conducted by friction stir welding using various traveling and rotation speeds of the tool to investigate the effects of the welding parameters on the joint characteristics and strength. Defect-free lap joints were obtained in the welding traveling speed range of 40-80 mm/min, and rotational speed range of 1200-1600 rpm. The shear tensile strength of Mg/Al joints increased as a result of decreasing the welding speed from 120 to 40 mm/min at constant rotation speed of 1600 rpm. Defects such as surface grooves, excessive flash, tunnels, and voids were observed if the joints prepared out of the mentioned range. The effects of the welding parameters are discussed metallographically based on observations with optical and scanning electron microscopes.