Análise comparativa dos métodos MQL, MQL/Água e convencional na retificação cilíndrica do aço ABNT 52100, com rebolo de óxido de alumínio

Pós-graduação em Engenharia Mecânica - FEB

Interaction between recrystallization and strain-induced precipitation in a high Nb- and N-bearing austenitic stainless steel: influence of the interpass time

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Cleaning capacity promoted by motor-driven or manual instrumentation using ProTaper Universal system: Histological analysis

The aim of this study was to assess the cleaning capacity of the Protaper system using motor-driven or manual instrumentation. Materials and Methods: Ten mandibular molars were randomly separated into 2 groups (n = 5) according to the type of instrumentation performed, as follows: Group 1 - instrumentation with rotary nickel-titanium (Ni-Ti) files using ProTaper Universal System (Dentsply/Maillefer); and, Group 2 - instrumentation with Ni-Ti hand files using ProTaper Universal (Dentsply-Maillefer). Afterwards, the teeth were sectioned transversely and submitted to histotechnical processing to obtain histological sections for microscopic evaluation. The images were analyzed by the Corel Photo-Paint X5 program (Corel Corporation) using an integration grid superimposed on the image. Results: Statistical analysis (U-Mann-Whitney - P < 0.05) demonstrated that G1 presented higher cleaning capacity when compared to G2. Conclusions: The rotary technique presented better cleaning results in the apical third of the root canal system when compared to the manual technique.

Effect of polymerization techniques and cleaning solution on flexural resistance of acrylic resin chemically activated

The purpose of this study was to evaluate the impact of different disinfection solutions on flexural resistance of chemically-activated acrylic resin. Test pieces were made of clear acrylic resin using a rectangular mold and employing two techniques: wet polymerization under pressure (n = 20) and dry polymerization under pressure (n = 20). Test pieces were subdivided into four equal groups: distilled water (control), sodium bicarbonate, 1% sodium hypochlorite and effervescent ats. The 30-day cycling technique consisted of immersing the test pieces in 100 ml of solution for 10 min three times a day and placing them in closed containers containing artificial saliva at 37°C. Subsequently, the flexural resistance of samples was tested. Data were analyzed using two-way analysis of variance (ANOVA) with forces serving as the dependent variables and the polymerization technique and cleaning agents as independent variables. Post hoc multiple comparisons were performed using Tukey’s test. There was no statistically significant difference in the flexural strength between the two polymerization techniques. The greatest flexural strength was observed for the effervescent tablets group followed by the control and 1% sodium hypochlorite groups which were statistically similar. Thus, the sodium bicarbonate solution caused the lowest flexural resistance of the test pieces.

Solution heat treatment of plasma nitrided 15-5PH stainless steel - Part I: Improvement of the corrosion resistance

The results of the investigation on Solution Heat Treatment of Plasma Nitrided (SHTPN) precipitation-hardened steel 15-5PH are presented. The layers have been obtained by the plasma nitriding process followed by solution heat treatment at different temperatures. The influence of the solution heat treatment after nitriding on the dissolution process of the nitrided layer has been considered. The nitrided layers were studied by scanning electron microscopy, X-ray microanalysis (EDX), and X-Ray diffraction. Micro-hardness tests of the nitrided layers and solubilized nitrided layers have been carried out and interpreted by considering the processing conditions. It was found that high nitrogen austenitic cases could be obtained after SHTPN of martensitic precipitation-hardened steel (15-5PH). When Solution Heat Treatment (SHT) was performed at 1100 °C, some precipitates were observed. The amount of precipitates significantly reduced when the temperature increased. The EDX microanalysis indicated that the precipitate may be chromium niobium nitride. When the precipitation on the austenite phase occurred in small amount, the corrosion resistance increased in SHTPN specimens and the pit nucleation potential also increased. The best corrosion result occurred for SHT at 1200 °C.

Enhancement of Corrosion Resistance AISI 304 Steel by Plasma Polymerized Thin Films

The purpose of this work is the deposition of films in order to increase the corrosion resistance of AISI 304 steel, which is a material used to construct the reactors for bioethanol production. This deposition inhibits the permeation of corrosive species to the film-metal interface. Thin films were prepared by radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) method using plasmas of hexamethyldisiloxane/argon/oxygen mixtures excited by signals of different powers. The plasma was generated by the application of RF power of 13.56 MHz to the sample holder while keeping grounded the topmost electrode and the chamber walls. The effect of the RF power on the properties of the samples was investigated by perfilometry, X-ray photoelectron spectroscopy (XPS), contact angle, and electrochemical impedance spectroscopy (EIS). The results of the corrosion resistance tests of the AISI 304 steel were interpreted in terms of the energy delivered to the growing layer by plasma excitation power.

Grinding of AISI 4340 steel with interrupted cutting by aluminum oxide grinding wheel

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)