Duplex stainless steels (DSSs) have outstanding mechanical properties and corrosion resistance. However, operating conditions and/or inadequate heat treatments can induce precipitation of deleterious phases or change the proportion of ferrite (alpha) and austenite (gamma) phases. This study evaluates the impact of ageing at 850 and 950 degrees C and solubilization at 1000 and 1150 degrees C treatments on pitting and crevice corrosion of DSS UNS S32205. Cyclic polarization tests revealed that samples with a more balanced alpha/gamma ratio (approximate to 50/50), that is, the base material (BM) and that solubilized at 1000 degrees C, exhibited the lowest corrosion rate (0.044-0.074 mu m/year) and better repassivation capacity (ER approximate to 0.96 V). Conversely, the 1150 degrees C treatment led to reduced corrosion resistance (0.158 +/- 0.009 mu m/year) and is associated with a reduction in the %Cr in alpha. Pitting is present in the aged conditions only. Moreover, the BM and 1000 degrees C samples showed the lowest crevice corrosion susceptibility, presenting the lowest volume loss (1 x 106 mu m3 cm-2) and current densities (approximate to 1000 mu A cm-2), followed by samples treated at 1150, 950, and 850 degrees C. Therefore, the results show that ageing treatments make UNS S32205 susceptible to pitting and crevice corrosion, which is related to the deleterious phase fraction and the alpha/gamma ratio imbalance.

This study presents a comparative analysis of the hardness and intergranular corrosion resistance of two types of martensite: nitrogen-enriched martensite formed in AISI 409 ferritic stainless steel and carbon martensite of AISI 420 martensitic stainless steel. AISI 409 samples are treated by the solution heat treatment after plasma nitriding technique, quenching (1050 degrees C), and tempering (250, 350, 450, and 650 degrees C). AISI 420 samples are quenched and tempered at the same temperatures. Microstructure, hardness, intergranular corrosion resistance, and degree of sensitization (DOS) are evaluated using optical microscopy, Vickers microhardness, and double loop electrochemical potentiokinetic reactivation tests. The results shows a nitrogen martensitic layer whose thickness is over 750 mu m on AISI 409. Concerning hardness, both materials exhibit a decrease as the tempering temperature increases. For the untreated and those tempered at 250 degrees C samples, both steels exhibit similar results. For the other temperatures, AISI 409 shows higher hardness only for the treatment at 450 degrees C. Regarding corrosion, carbon martensite exhibits a higher DOS in samples tempered at 250, 450, and 650 degrees C compared to nitrogen martensite. In the tempering condition at 350 degrees C, both materials shows a similar DOS. The best results are obtained by the AISI 409 tempered at 250 degrees C.

This study explores the effects of anodic, cathodic, and open circuit (OCP) potentials on the tribocorrosion behaviour of the UNS S32205 duplex stainless steel, which is largely used in oil, gas, and cellulose industry. For this purpose, tribocorrosion assays using a contact sphere (Si3N4) against the specimen plane in reciprocating sliding movement in 0.5 M NaCl solution were carried out. For comparison purposes, cathodic polarization or tests without applied potential under distilled water (DW) were used to inhibit corrosion for tribocorrosion tests. Two main distinct behaviours were observed: i) high coefficients of friction and lower wear volumes at the cathodic polarization (CP) for conditions smaller or equal to-0.8 V (vs Ag/AgCl 3 M) as well as in DW; and ii) low coefficients of friction and higher wear volumes for anodic polarization (AP), OCP, and CP for-0.4 V. The tribocorrosion behaviour of both groups was directly related to the chemical characteristics inside the tracks analyzed using SEM-EDS and Raman spectroscopy. All analyzed tracks showed similar oxygen contents and chemical compositions within each group. Finally, this study allowed the determination of the great effect of the potential applied on the tribocorrosion behaviour and the identification of differences between the cathodic protection and distilled water assays as methods to inhibit corrosion.

Improper thermal cycles on duplex stainless steels can lead to the formation of detrimental phases or alter the proportion of ferrite and austenite phases, thus influencing the material’s mechanical properties and corrosion resistance. Therefore, this study aimed to evaluate the effect of aging (at 850 and 950 °C) and solubilization (at 1000 and 1150 °C) thermal treatments on microstructure, indentation hardness, elasticity modulus, and susceptibility to intergranular corrosion of UNS S32205 duplex stainless steel. The sigma phase (σ) formation in the aged samples, with hardness values between 8 and 10 GPa, was confirmed. Furthermore, the pieces treated from 1000 °C upwards showed that increased temperature favored the formation of more equiaxial grains and the ferrite fraction growth. The thermal treatments barely affected the elasticity modulus of austenite and ferrite grains, increasing the hardness of ferrite. The effect of sulfuric acid concentration in the intergranular corrosion was evaluated. Also, the deconvolution of the corrosion curves permits the determination of the influence of the different phases in the corrosion performance. These tests revealed sensitization only at the σ phase grain boundaries in the samples treated at 850 °C in electrolytes containing H2SO4 2.5 mol/L and HCl 1 mol/L. Although the treatment at 950 °C led to the σ phase formation, its higher corrosion resistance was ascribed to the lower volumetric fraction of this phase, its morphology, and its increased Cr mobility compared to the 850 °C treatment. Therefore, it was shown that the σ characteristics and the sulfuric acid concentrations are determining factors in the UNS S32205 intergranular corrosion resistance.

Introduction: Mushroom archwires (MA) were developed to maintain incisor torque during retraction, i.e., control of root position via a generated couple while preserving posterior anchorage. This is achieved through a differential anchorage, either by translation or by controlled movement of the crown and root apex, in cases involving premolar extraction. Although their clinical application has been reported in the literature, the force system resulting from their activation has not yet been demonstrated. The aim of this study was to perform numerical simulations to analyze the force system generated by MA. Materials & Methods: A MA was geometrically modeled using Autodesk Inventor, and finite element analysis (FEA) was performed in ANSYS Workbench to simulate its mechanical behavior. For this simulation, non-linear analysis was used in order to take into account the large displacements effects, which consisted of pre-activation at their posterior extremities by 45° gable bends; restriction of the posterior extremities to mimic the insertion in the molar tubes and spacing between the vertical extremities (legs) 2.5 mm apart. Loops were activated at 4.0 mm and at 5.0 mm. Results: At 4.0 mm and 5.0 mm of activation, the archwire generated forces (Fx) of 184 gf and 251 gf, respectively. The corresponding Mz/Fx ratios were 12.9 mm and 10.6 mm, respectively. Conclusion: MA could be activated up to 5.0 mm for incisor retraction, which may be compatible with the biological limits of tooth movement during incisor retraction.

The tribocorrosion of low-temperature plasma nitrided UNS S32750 super duplex stainless steel was investigated according to procedures for passivating materials. Nitrided and non-treated samples were compared through two reciprocating sliding tests in NaCl solution: the continuous test, without significant passive layer growth, and the intermittent one, with repassivation. Open circuit potential and linear polarization resistance (LPR) characterized the electrochemical response. LPR was successfully introduced to evaluate the polarization resistance evolution during the continuous test. Corrosion and mechanical wear components were quantified. The mechanical wear dominated, and nitrided samples showed lower wear volume loss. After the intermittent test, their values were further reduced. Such improvement was explained by the higher load bearing capacity and repassivation ability of the nitrided surfaces.

Aftermarket additives are used to enhance the performance of internal combustion engines in specific aspects such as reducing wear, increasing power, and improving fuel economy. Despite their advantages, they can sometimes cause corrosion-related problems. This research evaluated the corrosiveness of four aftermarket additives on the corrosion of a high-leaded tin bronze alloy over 28 days at 80 °C in immersion tests. Among the evaluated products, three showed corrosive effects ranging from intermediate to severe. Notably, the visual appearance of the surfaces often did not indicate the underlying corrosive damage. Therefore, the assessment of corrosiveness was based on chemical characterizations conducted on both the drained oils and the bronze surfaces. The study found minimal oil degradation under the testing conditions, indicating that the primary cause of corrosion was the interaction between the specific additives and the metal elements of the alloy, rather than oil degradation itself. A direct correlation was observed between the dissolution of lead and copper and the adsorption of S and Cl-containing additives on the surfaces, respectively. The corrosive impact of Cl-containing additives in aftermarket formulations was significantly reduced when mixed with engine oil SAE 10W-30 (at a 25:1 ratio), suggesting a mitigated effect in combined formulations, which is the recommended usage for engines.

RESUMO: Aços inoxidáveis duplex (AID's) apresentam uma combinação de alta resistência à corrosão e boas propriedades mecânicas, tendo aplicações nas indústrias petroquímicas ou de celulose.Entretanto, tratamentos térmicos em determinadas temperaturas acarretam a precipitação de fases intermetálicas como sigma e chi que degradam propriedades mecânicas e químicas.Assim, torna-se importante identificar a influência dos parâmetros de ciclos térmicos nos AID's.Desse modo, visando estudar um tratamento térmico apropriado ao aço duplex UNS S32205, tem-se como objetivo avaliar a variação da porcentagem volumétrica das fases a partir de distintas temperaturas de tratamento de envelhecimento entre 800 e 950°C, bem como de solubilização entre 1000 e 1150°C, com tempo de encharque de 30 minutos seguido de resfriamento em água.Os resultados revelaram que entre 800 e 950°C ocorre a precipitação da fase sigma, com maior incidência na temperatura de 850°C (8%).Adicionalmente, para os tratamentos acima de 1000°C, tem-se somente a presença das fases ferrita e austenita, com a obtenção de maiores porcentagens da fase ferrita para as maiores temperaturas de tratamento térmico.Ademais, observou-se que a precipitação da fase sigma aumentou substancialmente a dureza

RESUMO: Os aços inoxidáveis duplex possuem excelentes propriedades mecânicas combinadas a alta resistência à corrosão.Entretanto, ciclos térmicos inadequados podem induzir precipitações de fases intermetálicas como sigma e chi, que podem prejudicar as propriedades mecânicas e de corrosão.Nesse sentido, o presente artigo tem como objetivo avaliar a tribocorrosão em duas condições de tratamento térmico distintas: envelhecidas na temperatura com maior cinética de precipitação da fase sigma (850°C), bem como em condição solubilizada (1000°C) com ausência de fases deletérias.O material utilizado foi o UNS S32205 submetido ao encharque de 30 minutos seguido de resfriamento em água.Foram realizados ensaios eletroquímicos concomitantemente ao desgaste (Resistência a Polarização Linear (RPL) e Potencial de Circuito aberto (PCA

The existence and formation of expanded austenite in ferritic stainless steels remains a subject of debate. This research article aims to provide comprehensive insights into the formation and decomposition of expanded austenite through in situ structure analyses during thermal treatments of ferritic steels. To achieve this objective, we employed the Plasma Immersion Ion Implantation (PIII) technique for nitriding in conjunction with in situ synchrotron X-ray diffraction (ISS-XRD) for microstructural analyses during the thermal treatment of the samples. The PIII was carried out at a low temperature (300–400 °C) to promote the formation of metastable phases. The ISS-XRD analyses were carried out at 450 °C, which is in the working temperature range of the ferritic steel UNS S44400, which has applications, for instance, in the coating of petroleum distillation towers. Nitrogen-expanded ferrite (αN) and nitrogen-expanded austenite (γN) metastable phases were formed by nitriding in the modified layers. The production of the αN or γN phase in a ferritic matrix during nitriding has a direct relationship with the nitrogen concentration attained on the treated surfaces, which depends on the ion fluence imposed during the PIII treatment. During the thermal evolution of crystallographic phase analyses by ISS-XRD, after nitriding, structure evolution occurs mainly by nitrogen diffusion. In the nitrided samples prepared under the highest ion fluences—longer treatment times and frequencies (PIII 300 °C 6 h and PIII 400 °C 3 h) containing a significant amount of γN—a transition from the γN phase to the α and CrN phases and the formation of oxides occurred.

A comparative study on the mechanical properties, scratch resistance, and localized corrosion (pitting and crevice) of plasma-nitrided Inconel alloy 718 (UNS NO7718: IN 718) was carried out. Thermochemical treatment was performed at low temperatures (400 and 450 °C) for 4 h. The treatment formed layers with thicknesses of 7.17 ± 0.89 µm (400 °C) and 7.96 ± 0.48 µm (450 °C). The XRD and nanohardness analyses indicated the formation of a hard layer composed of the expanded austenite phase (γN), CrN at 400 °C, and CrN + γ at 450 °C, with a maximum indentation hardness of 12 and 12.5 GPa, respectively, when compared to the 5 GPa substrate hardness. The scratching tests (2–8 N) showed that with increasing load, the nitrided surfaces had a transition from 100% microcutting to a combination of microplowing/cutting, with the presence of cracks. The critical load of the nitrided surfaces was 3 N for 400 °C and 4 N for 450 °C. The untreated condition maintained a crack-free combined mechanism regardless of the load. For the same load, the nitrided surfaces held lower coefficient of friction values and higher scratch resistance values, which were more pronounced at 450 °C. The linear polarization tests (3.56 wt.% NaCl) showed pitting corrosion in all samples, with the 450 °C condition being less resistant. Nitriding at 400 °C increased the crevice corrosion resistance of Inconel, while at 450 °C, it severely damaged it. Nitriding at 400 °C brought concomitant gains in hardness and scratch and crevice corrosion resistance when compared to the as-received IN 718.

This study aimed at the mechanical characterization, on a nanometric scale, of the constituents obtained for different fractions in duplex stainless-steel plates subjected to 850, 950, 1000, and 1150 °C heating treatments via hardness measurements and determining their influences on the fretting wear behavior of the studied steel. The obtained ferrite (α)-, austenite (γ)-, and sigma (σ)-phase fractions were determined using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. The mechanical characterization was carried out using hardness measurement and fretting wear techniques via nanoindentation. For comparison purposes, the Vickers microhardness was also characterized to determine the effect of the σ phase, which eventually formed, on the obtained microstructure properties as a whole. Two distinct behaviors were observed, depending on the eventual formation of σ phase as a function of the treatment temperature: (i) specimens treated at 850 and 950 °C showed a hardening effect (HV0.5 values of 333 ± 15 and 264 ± 13, respectively) due to σ-phase precipitation (hereafter termed ‘as-aged’), and (ii) specimens treated at 1000 and 1150 °C (with HV0.5 values of 240 ± 13 and 249 ± 4, respectively) showed no σ-phase precipitation (hereafter termed ‘as-solubilized’). The increases in the microhardness values for the as-aged specimens were attributed to the hardness of the σ-phase precipitates (which showed nanohardness values varying in the 8.0–8.5 GPa range), which was approximately twice that of the austenite and ferrite grains (both phases showed nanohardness values in the 3.6–4.1 GPa range, on average). When formed (for fractions on the order of 8% and 3% at 850 and 950 °C, respectively), σ phase was mainly observed at the α/γ grain interfaces or boundaries. Fretting wear tests, using a diamond sphere with a radius of 10 μm as the counter body and a load of 20 mN, revealed the same wear mechanisms in the α/γ matrix for all studied conditions. However, as-solubilized specimens (heat-treated at 1000 and 1150 °C) displayed higher resistance to fretting micro-wear in the austenitic grains compared to the ferritic grains, indicating lower plastic deformation in the respective wear scars on the obtained tracks. In particular, as-aged specimens (heat-treated at 850 and 950 °C) exhibited lower coefficients of friction due to their higher surface resistances. The localized wear at σ-phase grains was much less pronounced than at ferrite and austenite grains. Overall, this study provides valuable insights into the mechanical behavior of microstructural changes in duplex steel at the nanometric scale.

Objective: To perform an experimental-numerical analysis to study the influence of the interbracket distance (IBD) on the spring’s mechanical behavior and on the resulting force system during space closure in the segmented arch technique (SAT). Material and Methods: Twenty delta springs (DSs) made of beta-titanium alloy, [Formula: see text] inch, were tested on a platform transducer. A Young’s modulus ([Formula: see text] of 69 GPa ([Formula: see text] psi) and Yield’s strength ([Formula: see text] of 1240 MPa ([Formula: see text] psi) were used. The springs were activated considering different IBDs. The spring was modeled in autodesk Inventor software and its behavior was simulated using the finite element (FE) code Ansys Workbench. Results: The ANOVA showed a significant difference in the studied variables with a reliability of over 95% (only for the activation variable there was an effect upon the horizontal forces (Fx). The Tukey HSD and the Games–Howell post hoc multiple comparisons tests were applied to identify differences between the treatments for heterogeneous variances. Conclusions: The IBDs do not significantly affect the force system during space closure, even though there was an increase in the Mz/Fx ratio as spring deactivates. Activation can cause a statistically significant effect on the force system even though the force showed safe levels. At 4[Formula: see text]mm activation (19[Formula: see text]mm IBD), the spring wire starts yielding, i.e. plastic deformation occurs near the anterior attachment due to the shorter IBD.

Metal conditioners (MC) are added to lubricants to enhance their friction and wear in friction pairs, mainly in engines, gearboxes, and rolling bearings. Its growth in the Brazilian market is primarily focused on internal combustion engines. The effect of mixing MC with commercial engine oil (SAE 5W-30 API SN) was studied regarding the rheological and thermal properties. Also, the tribological performance of steel–steel contact was investigated. The rheological and thermal properties were determined by flow curves (at 20, 40, and 100 °C) and differential scanning calorimetry (DSC), respectively. Reciprocating fully-lubricated tests were performed at 40 °C and 80 °C (Po = 1.7 GPa, 5 Hz). Differences in the chemical composition between SAE 5W-30 and its mixture with MC were identified by infrared spectroscopy and related to their tribological performance. The coefficient of friction remained within the range of 0.09–0.1 for all conditions, typical of lubricated steel–steel contacts under boundary and mixed lubrication regimes. However, the mixture improved the wear resistance by around 33% when lubricated at 80 °C compared to the wear resistance offered by 5W-30. The formation of tribofilms with different chemical compositions was confirmed by SEM-EDS for all conditions. At both temperatures, the tribological performance reveals beneficial synergy between the metal conditioner and fully formulated oil additives. The tests lubricated with the mixture at 40 °C showed a less severe wear mechanism when compared to the tests lubricated with neat 5W-30. The study demonstrated that the mixture maintained the physicochemical properties of the commercial oil with a substantial anti-wear action at 80 °C.

Introduction: To verify the literature concerning the mechanical properties, measuring methods and the resultant force system developed by closing loops (CL). The effectiveness of a certain CL is related to its geometry and the nature of the wire material. To obtain the necessary performance CL must work in the elastic range and be geometrically configured to express an adequate force system, which is the result of compensatory gable bends and preactivation. It was performed a literature search in MEDLINE from 1974 to 2014 using search for “orthodontic AND retraction AND springs” and “orthodontic AND closing AND loops”. From the 147 papers resulted from Pubmed, 50 were chosen. Overall, many works seek not only improve the knowledge about the force system, but also a better understanding of their mechanical behavior. FEM, Holographic and Photoelastic studies, are tests commonly used before testing them experimentally. Wire material and the cross-section show a great influence in the choice of the geometric variables because the modulus of elasticity (E), modulus of resiliency (R) and the moment of inertia (I). Experimental tests should be preceded by numerical methods because the latter idealize a particular setting, and allows modifying variables.