Advanced Materials Research Vol. 445

Abstract: ZrNi intermetallic compound is used in several application fields due to its very favorable characteristics for the storage of hydrogen. The hydrogen reactions are important, it is vital to examine the evolution of physico-chemical properties at the surface. X-ray photoelectron spectroscopy, is used to follow the evolution of electronic properties of ZrNi versus the ion sputtering in ultra high vacuum in the range 300-600°C. Morever, the evolution of species concentrations at the surface of ZrNi in the range 100-700°C is followed by means of Auger electron spectroscopy. The present results show that temperature and ion sputtering favor significant changes in surface properties of ZrNi. In situ annealing of ZrNi favors the oxygen decontamination associated with segregation of zirconium metal on the surface. The values of binding energies deduced from the reconstruction of XPS spectra, allowed the identification of species present at the surface. The results indicate that nickel is not contaminated and all the obtained sub-oxides are related to bonding states of oxygen with zirconium (Zr₂O, ZrO, ZrO₂ and Zr₂O₃). The ion sputtering of the surface of ZrNi causes preferential sputtering phenomenon. The later results from the removal of surface layers and from the appearance of zirconium oxide layers initially present on the surface. The results obtained by AES show the segregation of impurities (oxygen and carbon) and of zirconium on the surface of ZrNi. AES observations of Zr segregation start to be important above 300°C and this is in agreement with XPS analysis showing a Zr enrichment of the surface of ZrNi.

Abstract: Grain refinement in medium chromium ferritic stainless steel weld was attempted via elemental (aluminum) powder pre-placement technique prior to melting under a TIG torch. A Box-Behnken experimental design was adopted with current, travel speed and the amount of aluminum powder added as the process factors for producing weld pool. The resolidified weld tracks were characterized using microscopy, microhardness and mechanical testing. The degree of grain refinement achieved was evaluated using a scaling index known as Grain Refinement Index (GRI). The findings showed that the GRI is influenced by the concentration of the aluminum powder introduced into the melt pool. Furthermore, high GRI does not necessarily translate to better mechanical properties relative to the conventional weld. This suggests that the grain size effect might not be the only factor influencing the property of weld metal. However, weld track treated with 0.08mg/mm² of aluminum powder exhibited about 20% improvement in properties relative to the conventional weld made under the same energy conditions.

Abstract: Other than grain coarsening, the loss of corrosion resistance in ferritic stainless steel (FSS) welds due to intergranular precipitation of chromium carbides restricts the use of the alloy for structural application. The use of cryogenic cooling offers dual opportunities for the control of weld geometry and grain structure in FSS. This results in improved mechanical properties but the effect on carbide precipitation was not investigated. In this paper, the effect of heat flux, welding speed and flow rate of cryogenic liquid on carbide precipitation in 16% chromium FSS welds are discussed. The use of cryogenic cooling reduces the size of the sensitized zone but this is not significantly affected by the flow rate of the cryogenic fluid. Compared to the conventional welding, the cryogenic cooling increases the cooling rate and reduces the martensite content in the high temperature heat affected zone (HTHAZ) by about 20%. This results in wider ditched-structure in welds made with flow rates lower than 0.052L/min. Cryogenic cooling produces more ditched weld microstructure revealed by electrolytic etching in oxalic acid; however, the structure is acceptable since no single grain boundary is completely surrounded by ditches.

Abstract: Explosive welding is achieved by the application of pressure, released from explosives, sufficient to cause large plastic deformation at the interface of dissimilar metals being welded. This study addresses the analytical estimation of the weldability domain for Aluminium-Low carbon steel and Copper-Stainless steel combinations. The use of an interlayer is proposed for the control of kinetic energy loss to alleviate the formation of intermetallics at the interface. Welding window the analytical estimation to determine the nature of interface was formulated using empirical relations proposed by various researchers and was verified experimentally. The lower limit of weldability window in three dimensions is developed in this study. Microstructural characterization of interfaces shows a wavy morphology in concurrence with the design expectations.

Abstract: Explosive cladding produces a strong weld between two dissimilar metals using explosive energy. The influence of material properties in achieving strong AluminiumSteel, CopperSteel explosive clad is discussed in this study. The solidification microstructure is determined by the nature of the competitive growth between adjacent columnar grains and, therefore, has a significant influence in the final characteristics of fusion zone. A compatible interlayer can significantly reduce the solidification time resulting in an intermetallics free interface. The influence of interlayer in the lower limit of weldability window is also discussed.

Abstract: To achieve a defect-free butt joint of dissimilar metals by friction stir welding procedure, there are some major parameters, such as tool material and geometry, tool rotational speed, feed rate and tilt angel. This research is focused on dissimilar metals welding, namely 1100 Al alloy and 1045 carbon steel. In this paper, the effect of tool rotation speed and feed rate are experimentally investigated on surface appearance, microstructure and micro hardness of the friction stir welded plates. Optimum values of tool rotation speed and feed rate have been achieved experimentally by the quality of the butt joint.

Abstract: In this research, effect of tool material and tool offset on tool erosion and metallurgical and mechanical properties of dissimilar friction stir welding of Al alloy to carbon steel are investigated. As the tool erosion is one of the important parameters on the defect-free friction stir welding, especially in butt joint of Al alloy to steel. In present work, different tool material and offset are used in friction stir welding at Al alloy to carbon steel with a constant tool speed and feed rate named as 710 rpm and 28 mm/min respectively. The result of experimental observation is shown better performance by tungsten carbide (WC) tool material with 1 mm offset on Al alloy area.

Abstract: The effect of tool traverse and rotation speeds on the microstructures and mechanical properties are quantified for welds between non-age-hardening Al5083 and age hardening Al2024 and compared to single alloy joints made from each of the two constituents. In this paper, we report the results of microstructural, mechanical property investigations of Al5186Al2024 friction stir welds produced using various rotations and traveling speeds of the tool to investigate the effects of the welding parameters on the joint strength. Metallographic studies by optical microscopy, electron probe microscopy, and the utilization of the X-ray diffraction technique have been conducted. It was found that the weld properties were dominated by the thermal input rather than the mechanical deformation by the tool. In particular the larger stresses under the weld tool on the AA5186 side compared to the AA2024 side are related to a transient reduction in yield stress due to dissolution of the hardening precipitates during welding prior to natural aging after welding.

Abstract: In this study the wettability, microstructure and mechanical properties of joining between cemented carbide and CK35 steel which brazed with two filler metals, L-Ag40Cd and L-Ag34Cd, were investigated. Wettability test shows that with increase of brazing time, the contact angle decreases and the best situation was resulted in the 20 minute brazing. Microscopic investigation of the brazed area with both filler metal shows that there is a copper enriched primary phase and eutectic microstructure in the silver enriched matrix which composed of copper enriched particles. The amount and the dispersion of precipitates are depended upon type of filler metal and brazing temperature. The results show that brazing with L-Ag34Cd filler metal at 800 °C exhibit superior shear strength in the level of 108 MPa.

Abstract: With the increasing growth of engineering plastics, the demand for reliable, rapid, high productivity and cost effective joining methods (similar to those used in the case of metals) is an undeniable requirement [. Furthermore, the need to produce larger and more complex parts from polymers has created an increased demand for joining, particularly in thermoplastic materials. In the case of creating a joint with high efficiency (the ratio of joint strength to base material strength) between currently available joining methods, welding is the best option [2,3]. Plastic welding processes can be divided into two groups: (1) Processes involving mechanical movement to produce heating (ultrasonic welding, friction welding, vibration welding) (2) processes involving external heating (hot plate welding, hot gas welding and resistive and implant welding) [. The welding method presented in this study utilizes both mechanical movement and external heating to produce heat.