Abstract Dental implants are especially susceptible to bacterial adhesion and so microbial contamination. Several techniques have been explored in order to obtain implant surfaces enriched with silver (Ag). The main challenge is to obtain a bactericidal effect keeping the surface biocompatible. In this regard plasma-assisted deposition is a very attractive technique due to its versatility and low environmental impact. Thus, the present work aimed at evaluating the chemical stability, antibacterial activity, and biocompatibility of a commercially pure titanium (cp-Ti) surface containing very low amounts of plasma-deposited Ag. Ag deposition obtained by 10 minutes sputtering was able to promote antibacterial action (around 30%) on a clearly cytocompatible Ti/Ag surface with no apparent impact on biocompatibility. Taken together these results indicate that the proposed deposition process has a great potential for dental implant application with the advantage of using very small amounts of silver to achieve efficacy.

RESUMO Corpos de prova de aço inoxidável austenítico ISO 5832-1(similar ao AISI 316L, para aplicações biomédicas) apresentando camada superficial enrriquecida em nitrogênio (fase S), obtidos pelos processos de nitretação por plasma em baixa temperatura e SHTPN (Solution Heat Treatment after Plasma Nitriding -Tratamento de solubilização após nitretação por plasma), além de amostras não tratadas, foram testadas em ensaio de desgaste microabrasivo do tipo esfera livre. Os resultados mostraram que as superfícies nitretadas por plasma em baixa temperatura apresentam o menor coeficiente de desgaste para menores tempos de ensaio. No entanto, devido à pequena espessura de camada nitretada, com o aumento do tempo de ensaio as amostras processadas via SHTPN passam a apresentar desempenho superior, indicando que, dependendo das solicitações de desgaste, um ou outro processo apresenta o melhor desempenho.

ABSTRACT Samples of the ISO 5832-1 austenitic stainless steel (similar to AISI 316L for biomedical applications) with nitrogen-rich surface layer (S-phase), obtained by plasma nitriding at low temperature and SHTPN (Solution Heat Treatment after Plasma Nitriding) processes, as well as non-treated samples, were tested to evaluate its micro-abrasive wear behavior. The micro-abrasive wear test were performed using the free-ball configuration. The results pointed out that the nitrided surfaces present lower wear coeficient for short measuring time. Nevertheless, since nitrided layers are relatively thin, for prolongated wear tests the SHTPN samples presented lower wear cofiecient, indicating that depending on the apllication one of the processes will present the best behaviour.

Formation of metastable C–, N–, or even Formation of metastable C–, N–, or even C/N– expanded phases can be observed for typical non-equilibrium conditions attained at the plasma assisted thermochemical treatments when temperatures relatively low are used. In present work, kinetics data are considered in a comparative study comprising low-temperature plasma assisted carburizing, nitriding and nitrocarburizing of AISI 420 martensitic stainless steel samples treated at 350, 400, and 450 °C, aiming to put in evidence the main metallurgical differences of the obtained layers. Microstructural characterization and hardness measurement results for untreated and treated sample surfaces show significant difference for the carburized layer growth in relation to that verified for the nitrided and nitrocarburized layers. While the carburized layer is constituted of a thin outer layer and a deep diffusion layer, just the opposite was observed for the other two treatments, id est., formation of thicker outer layers and thinner diffusion layers. Finally, carbide-/nitride-precipitation-free layers were supposedly obtained for samples carburized, nitrided, and nitrocarburized at 350 °C temperature.

Low-temperature plasma assisted nitriding is a very promising technique to improve surface mechanical properties of stainless steels, keeping unaltered or even improving their surface corrosion resistance. During treatment, nitrogen diffuses into the steel surface, increasing its hardness and wear resistance. In the present work the nitriding process of different martensitic stainless steels was studied. As-quenched AISI 410, 410NiMo, 416 and 420 stainless steel samples were plasma nitrided at 300, 350, 400, 450, and 500°C, for 4 h, at 3 Torr, in a gas mixture of 70% N2 + 20% H2 + 10% Ar, and flow rate of 3.33×10–6 Nm3s−1. The study of the nitrogen-rich layer thickness indicates two different activation energies, one for low (<400°C) and another one for high temperature ( ≥400°C), except for the AISI 410NiMo. The surface hardness increases with temperature for all steels between 300 and 450°C. For 500°C, except for the AISI 410NiMo, the surface hardness decreases if compared to that obtained at 450°C. This hardness decrease is related to chromium nitride precipitation, also associated to the treated surface sensitization. Finally, the CrN precipitation in treated surfaces is dependent on the steel composition, with the AISI 410NiMo steel presenting the lower average chromium nitride precipitation rate.

This work reports experimental results on sintered PIM 316L stainless steel low-temperature plasma nitriding. The effect of treatment temperature and time on process kinetics, microstructure and surface characteristics of the nitrided samples were investigated. Nitriding was carried out at temperatures of 350, 380, 410 and 440 ºC , and times of 4, 8 and 16 h, using a gas mixture composed by 60% N2 + 20% H2 + 20% Ar, at a gas flow rate of 5.00 × 10-6 Nm³s-1, and a pressure of 800 Pa. The treated samples were characterized by scanning electron microscopy, X-ray diffractometry and microhardness measurements. Results indicate that low-temperature plasma nitriding is a diffusion controlled process. The calculated activation energy for nitrided layer growth was 111.4 kJmol-1. Apparently precipitation-free layers were produced in this study. It was also observed that the higher the treatment temperature and time the higher is the obtained surface hardness. Hardness up to 1343 HV0.025 was verified for samples nitrided at 440 ºC. Finally, the characterization of the treated surface indicates the formation of cracks, which were observed in regions adjacent to the original pores after the treatment.