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Hazratinezhad M.,Islamic Azad University at Gachsaran | Mostafa Arab N.B.,Shahid Rajaee Teacher Training University | Sufizadeh A.R.,Falat Pejvak Co | Torkamany M.J.,Iranian National Center for Laser Science and Technology
Materials and Design | Year: 2012

In this paper, the effect of energy input pattern in pulsed neodymium-doped yttrium aluminum garnet laser welding on mechanical and metallurgical characteristics of a 0.19% carbon dual phase steel is studied. The experimental results showed that the energy input pattern to the fusion zone had a significant effect on the ultimate tensile strength of the welded samples. The longitudinally and transversely tested weld specimens showed higher and lower strength than the base metal respectively. Increase in effective peak power density increased the volume of fusion zone which in turn caused an increase in the strength of the welded specimens. Microstructural studies showed coarse grains in the heat affected zone of welded samples especially at higher levels of pulse duration. Fracture studies showed presence of dimples on the fractured surfaces of the heat affected zone indicating that a ductile fracture had occurred. © 2011 Elsevier Ltd.

Mojaver R.,Tarbiat Modares University | Mojtahedi F.,Tarbiat Modares University | Shahverdi H.R.,Tarbiat Modares University | Torkamany M.J.,Iranian National Center for Laser Science and Technology
Applied Surface Science | Year: 2013

This work aims to investigate whether an amorphous surface layer can be obtained when as-cast Fe49Cr18Mo7B 16C4Nb3 alloy is submitted to pulsed Nd:YAG laser surface melting. The experiments were conducted in the various laser scanning speeds. The microstructures of laser treated zones were investigated by X-ray diffraction XRD and Field Emission Scanning Electron Microscope (FESEM) and their microhardness were measured, too. The chemical composition of different points of each sample was analyzed by energy-dispersive X-ray spectroscopy EDS. Although the estimated cooling rates in surface layers were higher than the required cooling rate to achieve full amorphization, but the present experiments were unable to retain complete glassy microstructure on surface and a mixture of amorphous (low volume fraction) and ultrafine grained phases were produced in surface of samples. Based on the findings, it was understood that the overlapping of successive pulses and element redistributions occurred in pulsed laser melting could severely restrict amorphization. The influence of laser scan speed and laser power on heat input, melting ratio, compositional changes and cracking in laser treated zone were discussed separately. It is suggested that the limited range of laser variables in pulsed Nd:YAG laser melting may help to produce a sound amorphous phase of as-cast Fe49Cr18Mo7B16C4Nb 3 alloy. © 2012 Elsevier B.V. All rights reserved.

Tahamtan S.,University of Tehran | Halvaee A.,University of Tehran | Emamy M.,University of Tehran | Zabihi M.S.,Iranian National Center for Laser Science and Technology
Materials and Design | Year: 2013

Al206/5vol.%Al2O3p cast composites were fabricated by the injection of reinforcing particles into molten Al alloy in two different forms, i.e. as Al2O3 particles and milled particulates of alumina with Al and Mg powders. The resultant milled powders (Master Metal Matrix Composite (MMMC)) were then added into the molten Al alloy both in semi-solid state and above liquidus temperature. Effects of powder addition technique, reinforcement particle size and casting temperature on distribution and incorporation of reinforcing particles into molten Al alloy were investigated. Morphology evolution of powders during milling, microscopic examinations of composite and matrix alloy were studied by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was also used to determine the possible interaction between powders after ball milling process. Results showed that injection of powders in the form of MMMC leads to considerable improvement in incorporation and distribution of Al2O3p in the Al206 matrix alloy leading to the improvement in tensile properties. Improvement in tensile properties is attributed to the better wetting of Al2O3p by melt as well as removing microchannels and roughness on alumina particles as a consequence of ball milling process. © 2013 Elsevier Ltd.

Farnia A.,Tarbiat Modares University | Malek Ghaini F.,Tarbiat Modares University | Sabbaghzadeh J.,Iranian National Center for Laser Science and Technology
Optics and Lasers in Engineering | Year: 2013

Melting ratio is known as a suitable factor to illustrate the effects of process parameters on the clad profile in order to provide a proper process design. However, the definition of melting ratio based on continuous irradiation of energy does not accommodate for pulse parameters. Hence, in order to study the effects of pulse parameters, such as pulse duration and overlapping factor, the definition of melting ratio is restated for pulsed laser process based on energy density concept. Carbon steel was cladded with Stellite 6 by scanning a 400 W pulsed Nd:YAG laser over a preplaced layer of powder paste. The results show that the trends of clad profiles variations can be explained using the restated definition. The results also show two different ranges for the effects of pulse duration and overlapping factor on melting ratio. © 2012 Elsevier Ltd.

Hadi I.,Iranian National Center for Laser Science and Technology
Journal of Applied Physics | Year: 2012

A one-dimensional mathematical model based on the front tracking method was developed to predict the melt depth as a function of internal and external parameters of laser spot remelting process in conduction mode. Power density, pulse duration, and thermophysical properties of material including thermal diffusivity, melting point, latent heat, and absorption coefficient have been taken into account in the model of this article. By comparing the theoretical results and experimental welding data of commercial pure nickel and titanium plates, the validity of the developed model was examined. Comparison shows a reasonably good agreement between the theory and experiment. For the sake of simplicity, a graphical technique was presented to obtain the melt depth of various materials at any arbitrary amount of power density and pulse duration. In the graphical technique, two dimensionless constants including the Stefan number (Ste) and an introduced constant named laser power factor (LPF) are used. Indeed, all of the internal and external parameters have been gathered in LPF. The effect of power density and pulse duration on the variation of melt depth for different materials such as aluminum, copper, and stainless steel were investigated. Additionally, appropriate expressions were extracted to describe the minimum power density and time to reach melting point in terms of process parameters. A simple expression is also extracted to estimate the thickness of mushy zone for alloys. © 2012 American Institute of Physics.

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