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Fatigue is the main cause of mechanical failure in aircraft structures, in which aluminum alloys are employed in approximately 70% of their structural components. Among the microstructural characteristics of aluminum alloys, the hardening precipitates provided by the ageing heat treatment have an important influence in their mechanical properties. In this context, current studies have shown that the two-step ageing heat treatment (T6I4) improves the mechanical properties of 6xxx and 7xxx aluminum alloys. This investigation presents a study of high cycle fatigue behavior of aluminum alloys AA 6351 (T6 and T6I4) and AA 7050 (T7451 and T6I4) as well the influence of microstructural characteristics and two-step ageing heat treatment in the fatigue properties of these alloys. Fatigue tests were performed on smooth and notched specimens.

The medium carbon steel and low alloy SAE 4340 has undergone several changes in this development process came 300M steel, from this ultra-high strength steel. With similar resistance and higher ductility to the steel 300M, the maraging steel can replace conventional steels in various applications. This study aims to evaluate and compare the microstructure and mechanical strength of SAE 4340 steel, 300M and Maraging 18Ni 300, underwent the procedure of autogenous laser welding.

The aim of this paper is to study of oxidation effects in creep of the Ti-6Al-4V alloy, in different atmospheres (air, nitrogen and argon). The samples were treated during 24 hours at 600°C in different atmospheres The samples treated during 24 hours at 600°C and the oxidation behavior in each atmosphere was observed. The oxidation was more aggressive in air atmosphere, forming TiO2 film in the surface. The alloy was tested in creep at 600°C in argon, nitrogen and air atmospheres using 250 MPa. The behavior of creep curves shows that useful life is better in atmospheres not so oxidant.

The objective of this work was to evaluate the creep behavior of the Ti-6Al-4V alloy focusing on the determination of the experimental parameters related to the primary and secondary creep stages. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates. Constant load creep tests were conducted with Ti-6Al-4V alloy in air for coated and uncoated samples and in nitrogen atmosphere for uncoated samples at 500°C to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Results indicated the creep resistance of the coated alloy was greater than uncoated in air, but nitrogen atmosphere was more efficient in oxidation protection.