This paper is a contribution to the study of the microstructure in welded joint of INC 738 LC. It presents the microstructures obtained after real welding and also after thermal cycle simulation of welding by rapid heating and cooling treatments in specific simulation equipment. We were focusing on the temperature range [900°C, 1100°C] which is the temperature range of main phases occurrence, as coarse γ’primary, fine γ’ secondary and carbides. Optical microscopy and microhardness measurements were used as characterization techniques. We have found that the obtained microstructures by thermal cycle simulation of welding correspond to those observed in the same zone of the real welded joint performed by real welding.

Purpose The Ni-base superalloy INC738LC is a precipitation strengthened alloy and is widely used in hot sections of gas turbine engines owing to its excellent high-temperature strength and high hot corrosion resistance. The purpose of this study is to determine the appropriate welding current of Ni-base superalloy INC738LC after two passes of applying the tungsten inert gas (TIG) welding technique. Design/methodology/approach Ni-base superalloy INC738LC plates were joined by TIG welding technique by varying the welding current (30, 40 and 50 A). Welded specimens were investigated using optical microscopy, tensile tests, Vickers’s micro-hardness tests and X-ray diffraction (XRD). Optical microscopy was used to characterize fusion zone, heat-affected zone and base metal. Tensile test was conducted to characterize weld strength by determining ultimate tensile strength. Scanning electron microscopy was used to investigate the fracture surfaces after tensile tests. Micro-hardness test was conducted to characterize the welded joint. XRD was applied to determine precipitates formed after welding. Findings The ultimate tensile strength results show that the optimum weld current out of the three weld currents was found to be 40 A, which is the closest to that of the base metal. Originality/value Many researchers have worked to optimize welding parameters such as current and speed from the microstructural observations and mechanical properties of welded joints. The optimum weld current out of the three weld currents was found to be 40 A.

Purpose The purpose of this paper is to present the effect of the aging at 200°C on creep and hardening behavior of hardenable 6101 aluminum alloy manufactured by an industrial wiredrawing process used for construction of self-supporting overhead aerial power line conductors. Design/methodology/approach The creep tests were carried out under applied constant stress 100 MPa and constant temperature 150°C. Hardness measurements were also used to investigate the mechanical behavior of the aged alloy. Micrographs of the fractured wires by creep tests were performed by scanning electron microscope. Electrical resistivity of the aged alloy was measured at different time of the aging treatment. Findings The authors have found the relationship between the precipitation sequence, the mechanical properties and the electrical resistivity of aged 6101 aluminum alloy. Originality/value The optimum properties were also deduced.

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