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In this investigation, the microstructure and mechanical properties of AISI420/SAF2507 dissimilar joint produced by TLP process were investigated at different bonding times. For this purpose, TLP process was carried out in a vacuum furnace at 1050 °C using BNi-2 interlayer. The microstructure of different areas of the joint was evaluated by optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Also, the mechanical properties of the bonded samples were studied using microhardness and shear-tensile tests. It was found that isothermal solidification was completed after 60 min of bonding time. The width of DAZ in SAF2507 steel side was greater than that of AISI420 steel side at all bonding times owing to the easier volume diffusion of boron in to the fully austenitic structure of AISI420 steel as compared with dual crystal structure of SAF2507 steel. At bonding time of 60 min, by regarding the more time for diffusion as compared with 1 min, boride compounds dissolved in the base metals and were discontinued. Thus, the aggregation of boride compounds decreased and as a result the microhardness decreased. In fully isothermal solidification sample, due to the lack of eutectic and intermetallic compounds and creating a homogenous joint (γ-Ni phase), the strength increased. In fact, transformation of athermal solidification to isothermal solidification led to the increase of the joint strength. The OM images indicating the base metals and the bonding area and DAZ of the bonded samples at different bonding times at temperature of 1050 °C for TLP bonding of AISI420/BNi-2/SAF2507. [ABSTRACT FROM AUTHOR]

In this research, dissimilar joint properties of pure Cu to AISI304 stainless steel using three different filler metals were studied. In this regard, the welding process was done with gas tungsten arc welding process using ER308L, ER309L, and ERNiCrMo3 filler metals and ERNi1 butter layer. The microstructural evaluations were carried out using optical microscope and scanning electron microscope. The mechanical tests were conducted by microhardness, tensile, bending and impact tests, and the fracture surfaces of impact and tensile tests were studied by scanning electron microscope. The results show that there is no crack or discontinuity in the welded samples. Energy-dispersive spectroscopy analysis revealed that the diffusion of Cu from base metal to butter layer has been occurred during welding. The microhardness profiles indicated the increase of hardness in heat-affected zone and butter layer. The welded sample with ERNiCrMo3 filler metal showed higher microhardness (200 HV) as compared with two other welded samples. The welded sample with ER309L filler metal had lower microhardness of about 150 HV. The tensile test revealed that the welded sample with ER309L filler metal showed maximum (193 MPa) and the welded sample with ER308L showed minimum (147 MPa) of ultimate tensile strength. In bending test of the welded samples with ER308L and ERNiCrMo3 filler metals, the crack and discontinuity were revealed in weld metal and heat-affected zone of Cu, respectively, while in the welded sample with ER309L filler metal no crack and discontinuity were seen. Also the welded sample with ER309L filler metal had highest impact energy of about 90 J as compared to other samples (81 and 88 J for the welded samples with ER308L and ERNiCrMo3 filler metals, respectively). The welded sample with ER309L filler metal showed more ductile fracture surface as compared with other samples. [ABSTRACT FROM AUTHOR]

The AISI 430 stainless steel with ferritic structure is a low cost material for replacing austenitic stainless steel because of its higher yield strength, higher ductility and also better polarisation resistance in harsh environments. The applications of AISI 430 stainless steel are limited due to insignificant ductility and some undesirable changes of magnetic properties of its weld area with different microstructures. In this research, a study has been done to explore the effects of parameters of laser welding process, namely, welding speed, laser lamping current, and pulse duration, on the coercivity of laser welded AISI 430 stainless steel. Vibrating sample magnetometery has been used used to measure the values of magnetic properties. Observation of microstructural changes and also texture analysis were implemented in order to elucidate the change mechanism of magnetic properties in the welded sections. The results indicated that the laser welded samples undergo a considerable change in magnetic properties. These changes were attributed to the significant grain growth which these grains are ideally oriented in the easiest direction of magnetization and also formation of some non-magnetic phases. The main effects of the above-mentioned factors and the interaction effects with other factors were evaluated quantitatively. The analysis considered the effect of lamping current (175-200 A), pulse duration (10-20 ms) and travel speed (2-10 mm/min) on the coercivity of laser welded samples. [ABSTRACT FROM AUTHOR]

Abstract: The feasibility of nanocrystalline NbAl3 intermetallic synthesis by mechanical alloying, and its formation kinetics were investigated. The structural changes of powder particles during milling were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques and the reaction mechanism and activation energy (E α ) for the formation of NbAl3 compound were determined under nonisothermal conditions using differential thermal analysis (DTA). DTA results of the specimens mechanically treated for 3h showed a temperature decrease from 933°C to 454°C for the formation of NbAl3 and suitable thermal stability of nanostructured NbAl3. Two isoconversional methods, of Starink and Friedman (FR) were used to determine the activation energy, E α , for NbAl3 formation reaction and its variation with conversion degree (α). The results showed that Starink method lead to values of E α which are comparable to the results obtained by FR method. [Copyright &y& Elsevier]

Abstract: The present study was carried out to synthesize NbAl3/Al2O3 intermetallic matrix nanocomposite by mechanical alloying (MA) using Nb2O5 and Al as raw materials. This nanocomposite was produced through a mechanochemical reaction between Nb2O5 and Al. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry and scanning electron microscopy techniques. It was found that the reaction between Al and Nb2O5 takes place in an explosive mode after about 450min of milling time. The milled powder had a microstructure consisting of nanocrystalline NbAl3 base adjacent to Al2O3 particles with a nanoscale grain size. At longer milling times, no changes were observed, except peaks broadening due to the decreasing in crystallite size and increasing in lattice strain. After 15h of milling time, average crystallite size of NbAl3 and Al2O3 were about 8 and 13nm, respectively. Heat treatment of powder mixture milled for 15h showed a good thermal stability for this nanocomposite. [Copyright &y& Elsevier]

Abstract: In this study, Al2O3/Nb ceramic matrix nanocomposite was synthesized by mechanical alloying, through mechanochemical reaction between Nb2O5 and Al. Structural and phase evolution during mechanical alloying was studied by employing X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques. It was found that the reaction between Al and Nb2O5 takes place in an explosive mode after 170min of milling time. The milled powder had a microstructure consisting of nanocrystalline Al2O3 base adjacent to Nb particles with a nanoscale grain size. At longer milling times, the intensity of Al2O3 and Nb peaks decreased and became considerably broader due to the decreasing in crystallite size. After 15h of milling time, crystallite sizes of Nb and Al2O3 were about 8 and 10nm, respectively. From DTA results, it was revealed that milling for 2h decreases the temperature of reaction between Nb2O5 and Al from 910°C to 492°C. [Copyright &y& Elsevier]

Friction stir welding (FSW) and friction stir processing (FSP) are two of the most widely used solid-state welding techniques for magnesium (Mg) and magnesium alloys. Mg-based alloys are widely used in the railway, aerospace, nuclear, and marine industries, among others. Their primary advantage is their high strength-to-weight ratio and usefulness as a structural material. Due to their properties, it is difficult to weld using traditional gas- or electric-based processes; however, FSW and FSP work very well for Mg and its alloys. Recently, extensive studies have been carried out on FSW and FSP of Mg-based alloys. This paper reviews the context of future areas and existing constraints for FSW/FSP. In addition, in this review article, in connection with the FSW and FSP of Mg alloys, research advancement; the influencing parameters and their influence on weld characteristics; applications; and evolution related to the microstructure, substructure, texture and phase formations as well as mechanical properties were considered. The mechanisms underlying the joining and grain refinement during FSW/FSP of Mg alloys-based alloys are discussed. Moreover, this review paper can provide valuable and vital information regarding the FSW and FSP of these alloys for different sectors of relevant industries.