f. nematzadeh

Stent placement has been a unique treatment for peripheral arteries illnesses in the recent years. Intelligent alloy stents can be used for peripheral arteries by reducing problems such as insufficient radial strength, low torsional capability and poor dynamic behavior compared to other stents. The application of the stent develops twofold chief objectivesundersized duration influence which avoids the effects of intimal division and the flexible shrinking and extended duration consequence which avoids restenosis due to the neointimal hyperplasia. Additionally, the other advantages of stent applications can be shortened as monitors: operative contour-capability to attain a satisfactory obsession to the vessel’s wall; adequate resistance contrary to the flexible shrinking; fatigue asset due to the pulsatile current and physique’s kinematics; a much smaller device to facilitate the percutaneous technique; small thrombogenicity; and height biocompatibility. In this study, metallurgical and mechanical behaviors of two types of intelligent alloys stent were studied by finite element method during the crushing process (axial loading) according to the standard. The intelligent stent material’ model used to describe the material and mechanical behavior were based on the free thermodynamic energy of Helmholtz and the free thermodynamic energy of Gibbs. with varying the Af temperature from 293 to 303 ° K (about 10 ° K), the difference between the upper and lower plateau stresses was about 40 MPa (equivalent to about 12%).The results showed favorable mechanical and clinical behavior of the stent with high Af temperature. Intelligent stents with high Af temperature is shown to have the best mechanical performance for clinical applications owing to lower Chronic Outward Force (COF), higher Radial Resistive Force (RRF), and more suitable superelastic behavior. Model calculations showed that a high Af temperature of Intelligent stent could exert a substantial effect on practical performance of the stent. This finite element model can provide a convenient way for evaluation of biomechanical properties of stents given to effects of intelligent alloys stents used in peripheral artery with respect to the effects of metallurgical, mechanical and clinical performance.

In this research, microstructure and mechanical properties of laser welded joints between 2304 duplex stainless steel and Inconel 718 nickel-based super alloy were investigated. Microstructural evolution in the various areas of welded joints and also the effect of welding parameters on the mechanical properties of dissimilar joints were studied. Response surface methodology based on the central composite design was used in order to find the optimum welding parameters. Effective parameters of the welding process including laser power, travel speed and defocusing distance were set in the range of 1000 to 1900 W, 1 to 5 mm/s and -1 to 1 mm, respectively. Uniaxial tensile test was used to evaluate the fracture force of weld joints. The microstructural observations and phase evolutions were studied using optical microscope. It was found that the fracture force of the weld joints firstly increased by travel speed and defocusing distance and then decreased by further increase. The maximum fracture force was obtained when laser power, travel speed and defocusing distance were 1900 W, 3 mm/s and 0 mm, respectively. The center line of weld metal was mainly consisted of equiaxed grains where, columnar grains were formed in the fusion line. The obtained results from the hardness measurement showed that the hardness of Inconel 718 was decreased due to dissolution of TiC and NbC particles.

In this research, dissimilar joint between AISI 430 ferritic stainless steel and AISI 2304 duplex stainless steel was made by Nd:YAG laser welding process. At first, microstructural and phase evolutions and also changes in mechanical properties due to the welding process were investigated. Hence, mechanical properties of weld joints were optimized using statistical methods. For this purpose, response surface methodology based on central composite design was used in order to find the optimum values of laser power, welding speed and defocusing distance and to obtain the maximum value of fracture force of joints. Uniaxial tensile test and optical microscopy were used to study the mechanical properties and structural features of weld joints, respectively. It was found that the fracture force of weld joints increases by decrease in welding speed and laser power and the maximum fracture force reached to 3587 N. Regarding microstructural evolutions studies, grain growth and presence of dispersed carbides in the fusion zone were observed. Finally, the effect of heat input on the hardness profile was evaluated and discussed. According to the result, the maximum hardness was obtained in the weld metal of the sample with low heat input and it was measured at about 332 vickers.