Among the third-generation Al-Li alloys, AA2198 stands out for its lower density, formability and increased stiffness, being suitable for use in aircraft fuselage sheets and other inner structures in order to reduce weight and improve performance. An important topic related to damage tolerant structures is the development of techniques to retard fatigue crack propagation, such as the localized heating by a laser source. The aim of the present work was to find the most suitable parameters for the production of laser heating lines in 2198-T851 alloy sheets in order to reduce the fatigue crack growth rate in this material. Laboratory tests using C(T) specimens under two loading conditions (R = 0.1 and 0.5) provided a useful dataset on the laser heated material. The experimental results indicate a 200 W laser beam power at treatment speeds of 1 and 10 mm/s was sufficient to retard crack growth in the current setup. The more expressive results were obtained for 200 W laser power with a speed of 1 mm/s and cyclic loading with stress ratio R = 0.1.

The mechanical properties of age-hardenable aluminum alloys are strongly influenced by the volume fraction, size and spacing of hardening precipitates. In addition, researches have shown that interrupted ageing (T6I4) could benefit the hardening response of these alloys. Interrupted ageing is a term generally used for the microstructural development process of an alloy aged at a reduced temperature after partially aged at a higher temperature. Thus, this process produces a change in the mechanical properties of the alloy. In this study, the precipitate structures and mechanical properties of AA6351 and AA7050 alloys were investigated. Transmission electron microscopy analyses of the hardening precipitates were carried out. Hardness and tensile properties were performed to compare the effect of disrupted ageing on AA6351-T6 / AA6351-T6I4 and AA7050-T7451 / AA7050-T6I4 alloys. AA6351-T6I4 showed a higher volumetric fraction of hardening precipitates with heterogeneous size and resistance lower than AA6351-T6. In addition, AA7050-T6I4 showed a higher volumetric fraction of hardening precipitates with smaller size and similar resistance to AA7050-T7451. However, in both cases, interrupted ageing contributed to increase ductility and toughness.

This work discusses on influence of niobium or molybdenum addition on microstructure and tensile properties of NiCr-based dental alloys. In this regard, the Ni-24Cr-8Nb, Ni-22Cr-10Nb and Ni-20Cr-12Nb (wt. %) alloys produced by arc melting process. To compare the typical Ni-22Cr-10Mo dental alloy was also produced. These ternary alloys were analyzed by chemical analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), thermogravimetric analysis (TG), Vickers hardness and tensile tests. Although the mass losses of the samples during arc melting, the optical emission spectrometry showed that the initial compositions were kept. The Ni-22Cr-10Mo alloy produced a matrix of Ni_ss (ss—solid solution), whereas Ni₃Nb disperse in a Ni_ss matrix was also identified in Ni-Cr-Nb alloys. Excepting for the Ni-22Cr-10Nb alloy with mass gain of 0.23%, the as-cast Ni-Cr alloys presented mass gains close to 0.4% after heating up to 1000 °C under synthetic airflow. The hardness values, the modulus of elasticity, yield strength and ultimate tensile strength have enhanced, whereas the ductility was reduced with increasing niobium addition of up to 12 wt.-%.The Ni-22Cr-10Mo alloy presented an intergranular fracture mechanism containing deep dimples and quasi-cleavage planes, whereas the shallow dimples were identified on fracture surface of the as-cast Nb-richer Ni-Cr alloys due to the presence of higher Ni₃Nb amounts.