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The present work aims to investigate the microstructure evolution along the length of a directionally solidified Al–8wt.%Ni hypereutectic alloy with a view to tailoring the range of microstructural parameters providing the best balance among tensile, wear, and corrosion properties. A macrostructure columnar region is shown to be associated with solidification cooling rates ( T ˙ ) > 4.8 °C/s, having a microstructure typified by eutectic colonies (EC) of Al3Ni fibers + α-Al matrix. Differently, for T ˙ < 4.8 °C/s, equiaxed grains prevailed consisting of the primary Al3Ni phase distributed in the EC matrix boundaries. A single diagram is proposed to relate experimental values of tensile, wear, and corrosion properties to each kind of microstructure (EC and Al3Ni + EC), exhibiting distinct behaviors, i.e., the Al–8wt.%Ni alloy with an EC microstructure is shown to provide higher tensile and wear resistances, whereas the best corrosion resistance and medium wear resistance can be assigned to the Al–8wt.%Ni alloy with an Al3Ni + EC microstructure. [ABSTRACT FROM AUTHOR]

This article studies the effect of silicon (Si) on ultrahigh-strength AISI 4340 steels in connection with the thermal treatment, as well as the influence of this element on nitriding and, consequently, abrasive wear. Four alloys with different Si contents were nitrided at 350 °C (4 and 8 h) and 500 and 550 °C (2 and 4 h) in a gas mixture of 80 vol. % H2 and 20 vol. % N2. The nitrided layers were characterized by microhardness and pin-on-disk tests, optical microscopy, scanning electron microscopy with energy-dispersive x-ray spectrometry, and x-ray diffraction (XRD). The increase in Si enhanced the tempering resistance of the steels and also improved considerably the hardness of the nitrided layers. The increase in Si produced thinner compound layers with better hardness quality and high abrasive wear resistance. XRD analysis detected a mixture of nitrides in the layers γ′-Fe4N, ε-Fe2-3N, CrN, MoN, and Si3S4 with their proportions varying with the nitriding conditions. [ABSTRACT FROM AUTHOR]

The effect of silicon content on the tempering behaviour and ion nitriding of ultrahigh strength AISI 4340 steels has been investigated. Four alloys with varying silicon contents were quenched and tempered for 1, 3, and 5 h, and ion nitrided at different temperature and time conditions. The nitrided layers were characterised by microhardness tests, optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). An increase in silicon content enhanced tempering resistance of the steels and also significantly improved the hardness of the nitrided layers. The increase in silicon content produced thinner compound layers with better hardness. XRD analysis indicated a mixture of nitrides in these layers, γ-Fe4N, ε-Fe2-3N, CrN, MoN, and Si3N4, with their proportions varying with nitriding conditions. [ABSTRACT FROM AUTHOR]

Several studies have shown that austenitic stainless steels are suitable for use in the final phases of orthodontic treatments, such as finishing and retention. These steels demonstrate appropriate mechanical properties, such as high ultimate tensile strength and good corrosion resistance. A new class of materials, the austenic-ferritic stainless steels, is substituting for austenitic stainless steels in several industrial applications where these properties are necessary. This work supports the hypothesis that orthodontic wires of austenic-ferritic stainless steels can replace austenitic stainless steels. The advantages are cost reduction and decrease of the nickel hypersensitivity effect in patients undergoing orthodontic treatments. The object of this study was to evaluate wires of austenitic-ferritic stainless steel SEW 410 Nr. 14517 (Cr26Ni6Mo3Cu3) produced by cold working through rolling and drawing processes. Tests were performed to evaluate the ultimate tensile strength, hardness, ductility, and formability. In accordance with technical standards the wires exhibited ultimate tensile strength and ductility suitable for orthodontic clinical applications. These austenitic-ferritic wires can be an alternative to substitute the common commercial wires of austenic stainless steels with the advantage of decreasing the nickel content. [ABSTRACT FROM AUTHOR]