Grain refiners play a critical role in changing characteristics and properties of casting aluminum alloys. The Al-Si alloy (A332) is one of the most popular hypoeutectic alloys with a large range of industrial applications. It has a varied phase and morphology; however, it features problems with acicular-shaped eutectic phase, and generally exhibits dendritic cast grain type. To change this situation, the Sr element acts as a modifier of eutectic, which, along with a grain refiner may increase mechanical properties. In this work, two different grain refiners (Al5Ti1B, Al5Ti2B) were applied to the A332 alloy modified with Sr, and analyzed in relation to grain size, hardness, corrosion resistance, and wear behavior. Corrosion tests in 3.5 wt.% NaCl solution, nanoindentations, and Heyn’s method to analyze grain size and microhardness as optical and SEM images were made to examine the changes caused by grain refiners. A reduction in grain size was achieved, and the influence in size and hardness of the β-Fe phase was verified in the wear and corrosion analyses.

The existence and formation of expanded austenite in ferritic stainless steels remains a subject of debate. This research article aims to provide comprehensive insights into the formation and decomposition of expanded austenite through in situ structure analyses during thermal treatments of ferritic steels. To achieve this objective, we employed the Plasma Immersion Ion Implantation (PIII) technique for nitriding in conjunction with in situ synchrotron X-ray diffraction (ISS-XRD) for microstructural analyses during the thermal treatment of the samples. The PIII was carried out at a low temperature (300–400 °C) to promote the formation of metastable phases. The ISS-XRD analyses were carried out at 450 °C, which is in the working temperature range of the ferritic steel UNS S44400, which has applications, for instance, in the coating of petroleum distillation towers. Nitrogen-expanded ferrite (α_N) and nitrogen-expanded austenite (γ_N) metastable phases were formed by nitriding in the modified layers. The production of the α_N or γ_N phase in a ferritic matrix during nitriding has a direct relationship with the nitrogen concentration attained on the treated surfaces, which depends on the ion fluence imposed during the PIII treatment. During the thermal evolution of crystallographic phase analyses by ISS-XRD, after nitriding, structure evolution occurs mainly by nitrogen diffusion. In the nitrided samples prepared under the highest ion fluences—longer treatment times and frequencies (PIII 300 °C 6 h and PIII 400 °C 3 h) containing a significant amount of γ_N—a transition from the γ_N phase to the α and CrN phases and the formation of oxides occurred.

Adequate mechanical responses are decisive features for novel superconductor materials, ideally enabling their machinability and conformability capacities to produce practical devices. The recently developed polycrystalline Bi ₄ O ₄ S ₃ superconductor was prepared following a two-step solid state reaction. Grains consisted of lamellae, ∼5 μ m in the planar orientation and 100–500 nm thick, presenting a tetragonal crystalline structure. The mechanical and tribological properties of the millimeter-size samples were investigated at the nanoscale using varied testing routines. Indentation hardness was about 1.6 GPa, whereas elastic modulus was 50–53 GPa. At the nanometer scale, cracks were visible through all the surface, possibly due to the structural inherent features of the material. On the other hand, it disclosed ductile-like plastic deformation features under normal loading and scratch tests up to 100 mN, as predicted by the index of plasticity H / E * ≈ 0.3. In these tests, the BiS ₂ -based material presented some limited strain hardening, but with the absence of load-induced fractures.