The solidification process of Ti52-xNi38Cu10Nbx alloys was evaluated using the CALPHAD method and microstructural analyses of as-cast alloys with Nb additions of x = 4, 6, 8 and 10 at%. Both in Scheil calculator and structural analyses, the observed phases were TiNi, β-Nb/Ti, and Ti2Ni. TiNi is the matrix phase, and it presented similar amounts of Ti and Ni with varying Nb contents. Enrichments of Ti content and depletion of Ni are expected in the liquid with the solidification of this phase. Formation of Ti2Ni and β-Ti is related to the excess of Ti. Increasing Nb content hinders the formation of Ti2Ni, favoring β-Ti. In turn, Ni depletion and Nb accumulation led to the TiNi/β-Nb eutectic. In the intermetallic phases, coherent ratios were obtained when Cu was considered a substitute for Ni, and Nb, for Ti.

Abstract The crystallographic aspects after air-quenching treatment and the pitting corrosion resistance after single tempering and double tempering treatments of AISI 420 martensitic stainless steel were studied using optical microscopy, Electron Backscatter Diffraction and potentiodynamic polarization tests. The results showed that the observed average orientation relationship (OR) was closer to the Greninger-Troiano (G-T) OR model with a minimum average deviation of 2.66°. The average OR of AISI 420 steel with respect to austenite matrix was φ1 = 3.6°, Φ = 46.0°, φ2 = 6.2° in the area mapped. Blocks showed variant pairs belonging to the same Bain group forming sub-blocks with misorientation 5.51° < 6 ¯ 0 11> (V1/V4 pair), consequently, the AISI 420 martensitic stainless steel showed higher intervariant boundary density for the same Bain group and close-packed plane group. In the same air-quenching condition, the different sizes of prior austenite grain in the microstructure did not influence the variant selection. The air-quenching and single tempering treatments did not impair the pitting corrosion resistance and did not cause significant loss of hardness in relation to the air-quenched treatment. Therefore, the double tempering should be dispensed saving production costs.

Heat treatments and geometries have a significant influence on the mechanical behavior of endodontic files. Finite element analyses were performed to verify the effects due to each of these parameters in NiTi files. Two designs and three NiTi atomic structures (resultant from different heat treatments) were selected for this study. The geometries of the ProTaper Next X1 and ProTaper Universal S2 files, and the structures of fully austenitic (conventional superelastic), austenite treated, and fully R-phased were used. The mechanical responses were evaluated under flexion and torsion loading conditions described by ISO 3630-1 specification. According to the results, the design of the X1 file exhibit higher flexibility in comparison to the S2 model. Under torsional loads, S2 showed higher stiffness. The structures of fully austenitic showed the least flexibility under flexion and the highest torsional stiffness. The stress levels reached for the austenitic condition were uppermost. The treated condition that resulted in a fully R-phase file usually presented a higher level of flexibility with lower stress levels, indicating a longer life in fatigue when compared to the other treatments.

The ToF-SIMS technique was applied to analyze thin ZrO2 coatings deposited on the surface of a Ni-Ti alloy. Due to its nanostructured nature, these films are difficult to characterize by conventional techniques. ZrO2 coatings were deposited on near equiatomic Ni-Ti wires by pulse electrodeposition. Part of the samples was electrolytically polished before the coating process. The coated samples were then analyzed by ToF-SIMS to evaluate the influence of the deposition time and previous surface electropolishing on the structure of the deposited coating. The results indicate that thicker coatings were produced on the electropolished samples, in comparison with the as-received ones. The best uniformity in thickness was achieved when Ni-Ti samples were previously electropolished followed by ZrO2 electrodeposition for 1200 seconds. Moreover, it was possible to observe by this technique that the inclusions in the Ni-Ti matrix were not entirely covered by the coating.

Abstract Objective The aim of this study was to evaluate the influence of torsional preloading on the cyclic flexural fatigue resistance of thermally treated NiTi instruments. Material and Methods Ten new instruments New Hyflex CM (HF 30.06; Coltene/Whaladent Inc.), Typhoon CM (TYP 30.06; Clinician's Choice Dental Products) and Vortex Blue (VB 30.06; Dentsply Tulsa Dental) were chosen, based on geometry and specific characteristics of the manufacturing process. The new instruments of each system were tested in a bench device to determine their fatigue resistance through mean value of number of cycles to failure (Nf) (Control Group – CG). Another group of 10 new HF, TYP and VB instruments were submitted to 20 cycles of torsional straining between 0° and 180° (Experimental Group – EG) and then submitted to fatigue until rupture under the same conditions of the CG. Tested instruments were examined by scanning electron microscopy (SEM). Data were analyzed using one-way analysis of variance and post hoc Tukey’s test (α=.05). Results Higher fatigue resistance was accomplished by HF instruments, followed by VB and TYP (p<0.05). During the torsional preloading, the lowest mean torque value was observed for TYP instruments (p<0.05). The torsional preload caused a significant reduction in the Nf values (p<0.05) of about 20%, 39% and 45% for instruments HF, VB and TYP, respectively. Longitudinal cracks, generated during the torsional preloading, were present in VB files, but were not observed in the CM instruments (HF and TYP). Conclusions In conclusion, the flexural fatigue resistance of thermally treated instruments is diminished after cyclic torsional loading.

For the biomedical application of NiTi alloys, an excellent surface finishing process is required to guarantee high corrosion resistance and biocompatibility, eliminating the allergenic and toxic effects associated with the release of nickel ions in the body. Electropolishing is a process that can reduce surface imperfections and form a thin protective layer of TiO2, even in complex-shaped devices. The main objective of our study was to find and report suitable parameters for electrolytic polishing of NiTi wires, in both the superelastic and shape memory states. The results indicate that electropolishing in a 3.5 mol•L-1 methanolic H2SO4 electrolyte at 20ºC can effectively reduce surface roughness, remove superficial nickel-rich layers and improve corrosion resistance for austenitic and martensitic NiTi alloys.

Aluminum is often added to electrical steels since this element causes improvement of the magnetic properties. However the addition of aluminum is usually limited to 0.30 wt%1. Therefore, this work aimed at evaluating the influence of higher levels of aluminum in the magnetic properties of semi-processed steels. To accomplish this, four types of steel were produced in laboratory with different aluminum contents (0.10, 0.30, 0.60 and 1.0 wt%). Carbon, manganese and silicon concentrations were kept constant. It was observed that an increased aluminum content caused reduction of the magnetic core loss, especially of the eddy current component. However, the magnetic permeability virtually wasn't influenced by aluminum concentration.

ABSTRACT Torsional overload is a fracture representative parameter for instruments in single-file techniques. Objective The aim of this study was to assess the influence of clinical use, in vivo, on the torsional behavior of Reciproc and WaveOne instruments considering the possibility that they degraded with use. Material and Methods Diameter at each millimeter, pitch length, and area at 3 mm from the tip were determined for both types of instruments. Twenty-four instruments, size 25, 0.08 taper, of each system were divided into two groups (n=12 each): Control Group (CG), in which new Reciproc (RC) and WaveOne Primary (WO) instruments were tested in torsion until rupture based on ISO 3630-1; and Experimental Group (EG), in which each new instrument was clinically used to clean and shape the root canals of one molar. After clinical use, the instruments were analyzed using optical and scanning electron microscopy and subsequently tested in torsion until fracture. Data were analyzed using one-way analysis of variance at a=.05. Results WO instruments showed significantly higher mean values of cross-sectional area A3 (P=0.000) and smaller pitch lengths than RC instruments with no statistically significant differences in the diameter at D3 (P=0.521). No significant differences in torsional resistance between the RC and WO new instruments (P=0.134) were found. The clinical use resulted in a tendency of reduction in the maximum torque of the analyzed instruments but no statistically significant difference was observed between them (P=0.327). During the preparation of the root canals, two fractured RC instruments and longitudinal and transversal cracks in RC and WO instruments were observed through SEM analysis. Conclusion After clinical use, no statistically significant reduction in the torsional resistance was observed.

Concrete structures must be designed and constructed so as to resist the conditions established in the project design and suffer no deterioration for many years. In highly aggressive environments, in addition to the minimum layer covering the framework, the concrete must receive a protective coating. In this work, the efficiency of acrylic paint as a protective coating, while the concrete was placed in an aggressive environment, was assessed utilizing a profilometric and microstructural characterization. The concrete was dosed using the ACI - American Concrete Institute method. The specimens were prepared with 370 kg.m-3 of cement and the water-binder ratio of 0.50 corresponds to the value established in NBR6118¹ types for concrete subjected to highly aggressive environments. With the use of profilometry, 3D topographical images and surface roughness parameters were generated, which allowed for the identification of the degradation process and the minimization of the effect of this attack on concrete that had received surface protection. The topographic roughness parameters, as well as the images and chemical components identified using SEM/EDS, made it possible to identify the process of deterioration of the concrete under acid attack and to minimize such effect in the coated concrete. The methodology adopted demonstrates that the application of acrylic paint as a protective coating for concrete in an aggressive environment minimizes its surface degradation and increases its durability.

Este estudo avaliou protocolos de irrigação sônica e a vácuo em relação à capacidade de remoção de debris do sistema de canais radiculares. Trinta primeiros molares mandibulares tiveram seus canais radiculares preparados pela utilização do Sistema ProTaper Universal. Os dentes foram divididos em dois grupos experimentais (n=15): Grupo 1: protocolo de irrigação sônica, e Grupo 2: protocolo de irrigação a vácuo. Posteriormente, as raízes mesiais foram seccionadas e observadas em lupa estereoscópica e microscopia eletrônica de varredura. Três examinadores independentes avaliaram as imagens do terço apical de acordo com as seguintes pontuações: 1. pequena presença de debris; 2: moderada presença de debris; e 3. densa presença de debris. Os dados foram analisados pelos testes estatísticos ANOVA e Kruskal-Wallis (α=0,05). A comparação entre os grupos revelou que, no terço apical, as hemissecções radiculares do Grupo 1 apresentaram debris remanescentes de forma significativamente menor (p=0,002) do que as do Grupo 2. No entanto, a 2 mm do comprimento de trabalho, as amostras do Grupo 2 mostraram menos debris remanescentes em aproximadamente 75% dos canais radiculares analisados. Considerando todo o terço apical, o protocolo de irrigação sônica removeu significativamente mais debris do que o protocolo de irrigação a vácuo. No entanto, na região a 2 mm do comprimento de trabalho, o segundo método de irrigação demonstrou um melhor desempenho

This study evaluated the protocols of sonic and vacuum irrigation regarding the capacity of debris removal from root canal systems. Canal preparations were carried out on 30 mandibular first molars using the ProTaper Universal System. Teeth were divided into two experimental groups (n=15): Group 1: sonic irrigation and Group 2: vacuum irrigation protocol. Subsequently, the mesial roots were sectioned and observed by stereomicroscopy and scanning electron microscopy. Three independent examiners evaluated images of the apical thirds according to the following scores: 1= small presence of debris, 2= moderate presence of debris, and 3= dense presence of debris. Data were analyzed with ANOVA and Kruskal-Wallis tests (α=0.05). Comparison among the groups revealed that at the apical third, the root halves of Group 1 had significantly less surface debris (p=0.002) than those of Group 2. However, at 2 mm from the working length, Group 2's specimens showed less remaining debris in approximately 75% of the analyzed root canals. At the whole apical third, the sonic irrigation protocol removed significantly more debris than the vacuum protocol. However, in the region at 2 mm from the working length, the second irrigation method demonstrated a better performance.

OBJECTIVE: This study identified which regions of ProTaper instruments work during curved root canal instrumentation. MATERIAL AND METHODS: Twelve ProTaper instruments of each type, S1, S2, F1, and F2, were assessed morphometrically by measuring tip angle, tip length, tip diameter, length of each pitch along the cutting blades, and instrument diameter at each millimeter from the tip. Curved canals in resin blocks were explored with manual stainless steel files and prepared with ProTaper instruments until the apical end following four distinct sequences of instrumentation: S1; S1 and S2; S1, S2, and F1; S1, S2, F1, and F2. Image analysis was employed for measuring canal diameters. The diameters of the canals and diameters of the instruments were compared. Data were analyzed by one-way ANOVA and Tukey's test. RESULTS: No statistically significant difference was found between the canals and instrument diameters (p>0.05). The largest diameters in the end-point of the instrumented canals were obtained with F1 and F2 instruments and in the initial and middle thirds with S1 and S2 instruments. CONCLUSIONS: All instruments worked at the tip and along their cutting blades, being susceptible to fail by torsion, fatigue, or the combination of these two mechanisms.

The aim of this work was to characterize thin interference films grown on the surface of AISI 304 stainless steel for decorative purposes. Films were grown in a sulphochromic solution at room temperature by an alternating pulse current method. The morphology and chemical state of the elements in the films were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), glow discharge optical emission spectrometry (GDOES), and infrared Fourier transform spectroscopy (FTIR). Depth-sensing indentation (DSI) experiments and wear abrasion tests were employed to assess the mechanical resistance of the films. The coloration process resulted in porous thin films which increased the surface roughness of the substrate. The interference films mainly consisted of hydrated chromium oxide containing iron. Increasing film thickness produced different colors and affected the mechanical properties of the coating-substrate system. Thicker films, such as those producing gold and green colors, were softer but more abrasion resistant.

The aim of this work was to evaluate the adhesiveness of uncoated and zinc-electrogalvanized steel sheets used in the automotive industry. Three types of adhesives, one acrylic and two epoxy resins, were employed to join low carbon cold rolled steels, one uncoated and another electrogalvanized, both previously degreased or chemically pickled. Mechanical strength of the joints was evaluated by the T-peel and tensile strength tests. Steel grade, surface condition and heating below the cure temperatures did not influence the joints' mechanical strength. However, their shear strength decreased drastically as the test temperature increased. The exposure of the joints to an atmosphere with 90% relative humidity at 40 °C caused reduction of their shear strength. Epoxy adhesives showed higher mechanical strength, but exhibited higher degradation by humidity.