Sergio Ruben Gonzaga-Segura

Aluminum metal matrix composites (AMMCs) were obtained using the stir-casting method, adding 0.15, 0.25, and 0.50 in vol.% of ZrO₂. Microstructural observations made using scanning electron microscopy (SEM) indicated that oxide addition modified grain size. X-ray diffraction analyses revealed that mainly ZrAl₃ and Al₂O₃ phases had formed. Hardness evaluation indicated a maximum value of 63 HV for the zirconia-reinforced samples, representing an increase of approximately 70% compared with pure aluminum. This hardness increase was mainly attributed to the zirconia distribution in the aluminum matrix promoting lattice distortion, which promoted the inhibition of dislocation mobility. Wear tests indicated that the samples with 0.50 vol.% of ZrO₂ added presented the lowest wear rate because of the hardness they acquired. The results are discussed considering composite strengthening due to ZrO₂ addition and the thermal treatment applied (cooling rate).

AISI 316L austenitic stainless steel superficially modified by the solid nitriding technique was investigated at different nitriding times (2, 4, 6, 8, 12 and 24 h) and at 450 °C. The microstructural characterization was conducted using scanning electron microscopy (SEM) analysis and X-ray diffraction analyses, finding the presence of Fe2–3N, Fe4N and Cr2N, among others. The mechanical behavior of the modified surfaces was carried out by developing hardness profiles and relating it with the nitride layer thickness evaluated using scanning electron microscopy (SEM), obtaining layers up to 70 µm wide. The nitrogen diffusion produced species above and below the surface sample with a transformation from the austenitic phase to an expanded austenite (γN) phase, which is responsible for producing an increase in hardness of up to 1200 HV in the samples treated at 24 h, which is four times higher than the untreated steels. Wear evaluations of the obtained layers were performed using a pin-on-disk system under zero lubrication, indicating that the samples with 12 and 24 h of treatment present the best wear resistance promoted by an oxidative–adhesive mechanism. The obtained results are positively comparable with those of the ion nitriding technique but with a lower implementation cost.

In the present work, the powder metallurgy (PM) technique was used to synthesize biocompatible alloys Mg95–Zn5, Mg90–Zn10, and Mg85–Zn15 (wt %) under an argon atmosphere that employed stainless-steel vessels and spheres with a milling treatment of 360 rpm during 15 h. The obtained powder was consolidated through a sintering process for subsequent ion nitriding treatment to increase its corrosion resistance and hardness. The synthesized alloys analyzed by Scanning electron microscopy (SEM) images showed a reduction in particle size with increasing grinding time. The X-ray diffraction (XRD) results showed the formation of a MgZn intermetallic phase and, furthermore, that no impurities were found during the grinding process. The surface-modified Mg–Zn alloys showed some improvement in terms of corrosion (Ecorr 26% and Icorr 13%) and microhardness (HV 40%) compared to Mg. Cytotoxicity evaluation was conducted via an MTT ((3-(4,5-DIMETHYLTHIAZOL-2-YL)-2,5-DIPHENYLTETRAZOLIUM BROMIDE)) assay, which revealed that the Mg–Zn alloys and nitrided samples did not exhibit cytotoxicity towards fibroblast cells after 96 h.

The biocompatibility and biodegradability of magnesium (Mg), along with its lightness, make magnesium-based materials promising for use in the biomedical industry. In this work, ternary Mg–Zn–Ca alloys were manufactured for biomedical applications using mechanical alloying (MA). The objective of this work was to study the effect of milling time on the produced ternary alloys Mg65–Zn30–Ca5 and Mg70–Zn25–Ca5 (percentages by weight), the degradation of the alloys in synthetic human fluids, and their generated cytotoxicity. The Mg-based alloys were synthesized in a planetary ball mill under an argon atmosphere using stainless-steel containers and balls with a milling regimen of 400 rpm for 2, 5, 10, 15, and 20 h. The powders obtained after MA were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), which verified that ternary Mg–Zn–Ca alloys can be obtained using MA. The XRD refinement analysis of the samples showed the presence of a MgZn intermetallic phase. Electrochemical tests showed that the corrosion resistance and corrosion current density of Mg65–Zn30–Ca5 and Mg70–Zn25–Ca5 alloys improved compared to those of pure Mg. Cytotoxicity testing was conducted using the Sulforhodamine B (SRB) assay, which revealed that the alloys did not exhibit cytotoxicity toward human fibroblast cells. Mg65–Zn30–Ca5 and Mg70–Zn25–Ca5 alloys show good potential to be used in biomedical applications.