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Mining processes produce a massive amount of waste which, if not treated properly, can cause significant environmental and social impacts. Recently, some studies have focused on the use of mining waste as an alternative raw material. This work developed new sustainable ceramic formulations based on bentonite mining waste (BMW) for applications in porcelain stoneware. The BMW was incorporated into the ceramic masses in different percentages (0, 2.5, 5, 10, 15, 20, 25, and 40 wt.%), in partial replacement to feldspar and total to quartz. X-ray diffraction (XRD), differential thermal calorimetry (DTA), and thermogravimetry analysis (TGA) techniques were used to characterize bentonite waste. Samples (50 mm × 20 mm × 5 mm) were obtained by uniaxial pressing. Such samples were dried and sintered at 1150, 1200, and 1250 °C. The physical–mechanical properties (apparent porosity, water absorption, linear shrinkage, apparent density, and flexural strength) were evaluated for sintered samples. The phases formed after sintering treatments were characterized by XDR and scanning electron microscopy (SEM). The BMW presented a mineralogical composition suitable for use as ceramic raw material. In summary, our results presented that the new sustainable ceramic formulations sintered at 1250 °C have the potential for use in stoneware and porcelain stoneware.

Efficiency of coin manufacturing is often limited by the service life of the stamping dies, whose degradation by wear results in decreasing the quality of the produced coin engraving. The aim of this work is to explore the ability of the combined application of experimental characterization and numerical simulation of the material elastoplastic forming response, friction effects, and die material wear rate as a tool to contribute to the coin design in order to ultimately increase the number of coins that can be die forged before the use of a worn die compromises the desired quality of the final product. The following aspects have been particularly addressed in this study. First, the influence of two design parameters related with the quality of the coins, i.e., die displacement and depth of engraving, is quantified determining that the die displacement is the most preponderant since the stamping force needed in this process is higher compared with that obtained by varying the depth of engraving. In addition, it is found that the curvature of the coin relief determines the local stress distribution, in some cases even at the opposite die, resulting in a heterogeneous wear evolution. A complementary wear test reveals that, for the involved range of curvatures, the wear mechanism may shift from dominated by plowing/cutting to dominated by fatigue. It is concluded that the numerical simulation allows considering efficiency of the coining process already at the stage of the aesthetic design of a coin.

Deposition of ceramic hard coatings are paramount in surface engineering as a strategy for protecting metallic surfaces of severe wear, many times present in industrial applications. Among the options of materials for this purpose, the transition metal nitrides are some of the most common. Cr-Al-N present interesting mechanical and anti-oxidation properties. Along with the choice of materials, the route of deposition is a major parameter to be taken in consideration and thoroughly studied to optimize the performance of the film solution. In this thesis, Cr-Al-N coatings were deposited over stainless steel substrate using dcMS and HiPIMS and its impact on the properties of the films were investigated. The coatings presented high concentration of N, possibly due to target poisoning during reactive depositions. The samples produced using 70/30 at % target exhibited better mechanical performance as consequence of the larger amount of Al in solid solution. HiPIMS films presented improved properties and densification caused by the higher ionization and consequently higher energy in comparison with dcMS manufactured samples. The nitride coatings were produced using a novel technique in which the substrate is oscillated continuously in front of the target to produce nanostructured coatings by varying the angle of incidence of the sputtered material. This technique named Dynamic Glancing Angle Deposition (DGLAD) was found responsible for creating misorientation gradients along the grains. These features combined with the zigzag shape of grain boundaries contributed to enhancement in hardness and wear resistance, especially when larger oscillatory ranges were used. DGLAD is proved as a technique capable of positively influence microstructure, deposition rate and mechanical performance of the Cr-Al-N coatings. A deposição de recobrimentos cerâmicos duros é fundamental na engenharia de superfícies como uma das estratégias para proteção de superfícies metálicas contra condições de desgaste severo em aplicações industriais. Dentre as opções de materiais disponíveis para essa finalidade, nitretos de metais de transição são algumas das mais comuns. Cr-Al-N apresenta interessantes propriedades mecânicas e de resistência à oxidação, sendo uma opção relevante. Além da escolha do material, a via de deposição é um importante parâmetro a ser levado em consideração e estudado em detalhes quando se desenvolve soluções de recobrimentos. Nesta tese, recobrimentos de Cr-Al-N foram depositados sobre substratos de aço inoxidável fazendo uso das técnicas de HiPIMS e dcMS. O impacto da escolha de técnicas e de seus parâmetros nas propriedades dos filmes foram investigados. Os recobrimentos apresentaram altos teores de N, provavelmente devido ao processo de envenenamento dos alvos ricos em Al durante a pulverização catódica reativa. As amostras produzidas usando alvos precursores com composição atômica de 70/30 % Al/Cr mostram propriedades mecânicas mais relevantes do ponto de vista de dureza e H3 /Er2 devido à adição de maiores quantidades de Al em solução sólida. Os filmes produzidos por HiPIMS apresentaram maior dureza e densificação em comparação aos produzidos por dcMS devido à maior taxa de ionização, e subsequente maior energia de deposição da técnica pulsada. Os nitretos foram fabricados utilizando uma técnica recentemente desenvolvida, em que o substrato é continuamente oscilado na frente do alvo durante a deposição, garantindo a variação constante do ângulo de chegada do fluxo de material proveniente do alvo com relação à superfície da amostra. Esta técnica recebeu o nome de DGLAD (Dynamic Glancing Angle Deposition). A variação no ângulo de incidência do fluxo causa a formação de nanoestruturas ao longo do filme, com grãos apresentando formatos corrugados. Observou-se que estas estruturas geram gradientes de misorientations ao longo dos grãos, e em combinação com a natureza em zigue zague dos contornos de grãos são capazes de aumentar a dureza e a resistência ao desgaste dos recobrimentos, especialmente quando fabricados utilizando-se grandes limites de ângulos de oscilação. A técnica DGLAD se mostrou capaz de controlar positivamente o desempenho e a taxa de deposição dos filmes de Cr-Al-N, posicionando-se como uma importante alternativa para aplicações industriais.

Materials chemistry and physics 276, 125388 (2022). doi:10.1016/j.matchemphys.2021.125388, Microstructural and crystallographic aspects arising from thermomechanical processing of a Ti���6Al���4V alloy in ��and ��+�� phase fields were studied by electron backscatter diffraction and both conventional and high energysynchrotron X-ray diffraction. The impact of deformation in the single �� field on the final microstructure has beenacknowledged by an increase of the retained �� phase content and decrease of martensitic c/a ratio with thereduction of strain rate, although no significant influence of strain rate on the well-defined fiber texture of ����� hasbeen observed. During deformation in the ��+�� field, texture weakening has been observed, and misorientationangle/axis distribution analysis has evidenced randomization and loss of the Burgers orientation relationshipbetween �� and �� upon globularization. The behavior of deformed �� lamellae in the ��+�� field was also evaluatedin terms of internal misorientation spread and lattice rotation around the deformation axis, corroborating thatglobularization takes place through dynamic recrystallization, boundary splitting and shearing. Globularizedgrain size was shown to be exponentially proportional to strain rate decrease. Lower strain rates in the ��+�� fieldalso increase the �� phase fraction and decrease the c/a ratio of the �� phase, leading to values closer to the idealone for titanium. However, an excessive amount of �� causes its instability during quenching, resulting in itsdecomposition into secondary �� during cooling., Published by Elsevier, New York, NY [u.a.]

The development of alternatives for wear protection in surface engineering can be responsible for a significant decrease in energy waste as a large amount of the energy produced in the world is lost due to tribological contact. Dynamic Glancing Angle Deposition has been recently evaluated as a route to produce coatings with improved wear performance. In this technique, the substrate oscillates along with a determined range in front of the sputtering target during the growth of the film. In this study, five oscillatory ranges (0, ±5°, ±10°, ±15°, ±20°) were probed to manufacture nanostructured Cr-Al-N coatings using direct current magnetron sputtering, and their impact was investigated on the grain morphology, phase formation, chemical composition, and performance of the coatings. FEG-SEM revealed the formation of multilayer-like architecture across the grains of the coatings. The deposition rate and hardness improved, and a more than 2-fold decrease in the material loss was observed in a comparison between the stationary-deposited conventional coating and the sample produced under ±10° oscillatory range. This indicated the potential use of this technique in future surface engineering applications.

In this work, the electrochemical behavior and morphological characterization of a system consisting of a cerium conversion layer, a hybrid sol-gel coating, and the two coatings applied sequentially (duplex) have been evaluated for the corrosion protection of WE43 Mg alloy. The different characterization techniques showed that the surface coverage by the hybrid coating was improved by the previous application of the conversion coating. The fitting of the impedance diagrams with electrical equivalent circuits allowed to propose a physical model for the coating, evidencing its interaction with the porous Mg oxide/hydroxide layer. Self-healing properties of the duplex coating were also disclosed. This study was funded in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors would like to thank the SMM/EESC-USP for the use of the laboratory facilities and EMBRAER for providing the material. O.M. Prada Ramirez is thankful to CAPES Proc. 88887.388129/2019-00. Haroldo C. Pinto is a CNPq fellow. HG de Melo is thankful to Fundação de Amparo à Pesquisa do Estado de São Paulo - Brazil (FAPESP) Proc. 2018/01096-5 and Proc. 2013/13235-6.

Pb-Co anodes have been considered an attractive candidate for oxygen evolution reaction (OER) applications due to their low overpotential to catalyze the OER and its low cost. Despite these characteristics, their efficiency to produce oxygen at high current densities is low. In this work, we report a Pb-Co-Sn film with enhanced efficiency and improved electrocatalytic properties. Pulsed cathodic electrodeposition was used to develop Pb-Co-Sn films at different deposition times among 2 and 10 min. Polarization curves were recorded to determine the deposition parameters. Morphological studies showed that the films grown for 6 min exhibited a well-covered and homogeneous surface. Structural analyses were recorded employing X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) that showed a nanostructured film composed by Pb and CoSn2 nanocrystallites. The electrochemical behavior of the developed Pb-Co-Sn films was measured by polarization curves in a sulfuric acid solution demonstrating a great ability to catalyze the OER: a reduction of the overpotential by 55% and 8.5% versus a Pb-Ca-Sn anode and Pb-Co film, respectively, accompanied by a strong increase in the current density. Thus, the addition of tin to the anode has a positive effect on the electrocatalytic performance of the film.

Mg-Zn-Zr (ZK) alloys exhibit notably high mechanical strength amongst all magnesium alloy grades. However, due to the formation of low melting point Mg3Zn7-precipitates, these alloys are susceptible to hot cracking, thus compromising their metallurgical processing. The addition of rare earths to ZK alloys is an alternative to form higher melting point intermetallic compounds, speed up dynamic recrystallization, refine grain size, enhance corrosion resistance and extend the service temperature due to improved creep resistance. This work deals with the effect of Ce-base mischmetal addition on the hot rolling behaviour of as-cast ZK60 alloy. The microstructure investigation conducted using electron microscopy and X-Ray diffraction shows that precipitation of Mg7Zn3 intermetallics occur during hot rolling, whereas no further precipitation is observed for the ZK60-Mm alloys. The fragmentation of the intermetallic compounds occur during hot rolling and finer particles of Mg7Zn3 are observed for the ZK60, whereas Mg7Zn3 and MgZn2Ce intermetallics are formed in the alloy modified with mischmetal addition. A higher fraction of dynamically recrystallized grains is observed for the ZK60-Mm in comparison to the ZK60. Continuous recrystallization takes place in ZK60 with the formation of sub-grains near to the intermetallics and the addition of mischmetal promotes the occurrence of discontinuous recrystallization with the nucleation of new grains close to the precipitates. The mechanical strength and, in particular, the ductility of the hot-rolled alloys are notably improved when compared to the same alloys in the as-cast condition. The mechanical strength is, however, higher for the ZK60 alloy. Less solid solution strengthening, softer MgZn2Ce intermetallics and more extensive recrystallization contribute to reduce the mechanical strength of ZK60-Mm. Failure in both alloys are initiated at coarse intermetallics and propagate through intermetallic-rich regions.

Multilayer-like CrN and Cr1&minus, xAlxN coatings with different Al contents were deposited onto a stainless steel substrate using dynamic glancing angle deposition direct current magnetron sputtering (DGLAD dcMS) in a N rich atmosphere to understand the role of Al on the growth of the films and mechanical properties of the nitrides with a multilayer architecture. Chemical analysis by means of energy dispersive analysis (EDS) and glow discharge optical emission spectroscopy (GDOES) depth profiling revealed that while CrN samples were close to stoichiometric, the Cr1&minus, xAlxN coatings presented excess N between 70 and 80% at. An expressive change in texture was observed as the CrN coating changed its preferred orientation from (111) to (200) with the addition of Al, followed by a modification in morphology from grains with faceted pyramidal tops in CrN to dome-shaped grains in Cr1&minus, xAlxN coatings. Multilayer-like nanostructures of corrugated grains were produced with a periodicity of approximately 30 nm using dynamic glancing angle deposition. The deposition rate was drastically reduced with an increase of Al, meanwhile, the best mechanical performance was achieved for the coating with a higher content of Al, with hardness up to 27 GPa and a higher value of maximum resistance to plastic deformation.

Aiming to decrease friction coefficient () during the forming of magnesium alloy sheets, nine (9) tools with different hole geometries in their surface (flat, elliptical, and circular) were manufactured from steel Boehler W400 VMR (as known as DIN 1.2343).. Tribological investigations were accomplished on a strip drawing machine at 288 &deg, C without lubricants. When compared with a standard tool (surface flat), on average, tools with circular geometries in their surface showed the smallest friction coefficient, while tools with elliptical geometries shown higher. The friction coefficient also was confronted with the ratio between area occupied by holes in the surface of the tool and the total tool surface (i.e., factor f (%)), hole diameter (&Oslash, ), and the distance between circle centers (d(c,c)). Principal Component Analysis (PCA) complemented the experimental approach. In summary, both approaches (experimental and theoretical) indicated that the manufactured tool with circular geometries on its surface presented lower friction coefficient values on the forming processes of the magnesium AZ31 sheets.

The low carbon martensitic stainless AWS 410NiMo steel has in its chemical composition 13% chromium, 4% nickel, and 0.4% molybdenum (wt.%) and is used in turbine recovery, rotors, and high-pressure steam pump housings due to its resistance to impact at low temperatures, as well as to corrosion and cavitation. Those applications of the AWS 410NiMo steel frequently demand repair, which is performed by welding or cladding. Arc welding is a well-established technique for joining materials and presents several parameters that influence the mechanical performance of the weld bead. Although numerous welding processes exist, optimizing welding parameters for specific applications and materials is always challenging. The present work deals with a systematic study to verify the correlation between the pulsed fluxed core arc welding (FCAW) parameters, namely pulse current and frequency, welding speed, and contact tip work distance (CTWD), and the bead morphology, microstructure formation, residual stress, and hardness of the martensitic clad. The substrate used was the AISI 1020 steel, and the AWS 410NiMo steel was the filler metal for clad deposition. From the initial nine (9) samples, three (3) were selected for in-depth characterization. Lower heat input resulted in lower dilution, more elevated hardness, and lower compressive residual stresses. Therefore, the results highlight the need for selecting the proper heat input, even when using a pulsed FCAW procedure, to achieve the desired performance of the clad. In the present case, a higher heat input appears to be more advantageous owing to the lower convexity index, smooth hardness transition between fusion and heat-affected zones in addition to more elevated compressive stresses.

Magnesium alloys are important alternatives for structural weight reduction due to their low density and good specific mechanical strength. Among the magnesium alloys, the ZK type exhibits the highest mechanical strength. However, it has limitations on hot working or welding owing to the presence of intermetallics with low melting point and consequently susceptibility to hot crack formation. The addition of rare earths tends to form intermetallics with higher melting points, thus inhibiting the formation of hot cracks, as well as building up thin and dense surface films that improve corrosion resistance. This work studies the addition of 1.5% wt. of mischmetal (Mm) to the ZK60 alloy, and then demonstrates the effects of the casting process with mechanical mixing in the semi-solid state. The alloys produced were: ZK60 and ZK60–1.5 wt%Mm manufactured by conventional casting and rheocast ZK60–1.5 wt%Mm produced with mechanical mixing in the semi-solid state. The casting and cooling methods result in defect-free and chemically homogeneous materials, and the mechanical mixing provides a homogeneous microstructure with globular grains. The mechanical strength was though higher for the ZK60 alloy due to its increased solute content within the Mg-matrix and the smaller quantity of intermetallics that builds up an intermittent network. The Mg7Zn3 intermetallic, which is the main precipitate for ZK60 alloy, has hardness 20% higher than the MgZn2Ce intermetallic that is precipitated with the mischmetal addition and partly removes solute from the Mg-solid solution.

The cladding welding analysis with pulsed flux cored arc welding (FCAW) process, were carried over a AISI 1020 base metal (thickness 12,7 mm, width 63,5 and length 185mm) with an CA6NM steel wire with diameter of 1.2mm. Was performed only one weld cord in the flat position. For experimental design was used the method of Taguchi L9 to determinate the parameter to be analyzed through the application of the analysis of variance (ANOVA) method. The response signals in RMS (Root Mean Square) analyzed were the voltage, current and acceleration. The procedure is based on a non-parametric domain-selective ANOVA for functional data, which results in the selection of the intervals of the domain presenting the most statistically significant effects of each factor over the selected response signals. The statistical results presented by ANOVA show that not all the selected variables have influenced the results. The best results for the cladding welding were obtained from the current average of230amperes, and statistically the average current was the variable that significantly affected the results, however, the welding speed only affected the yield of the process.

Glass-ceramics foams (GCs foams) were manufactured with the aid of the replica method and from cheap and sustainable raw materials (waste glass bottle, bentonite, and alumina). In order to evaluate the Al2O3 effect on the microstructure and physico-chemical properties of the GCs foams, the precursor aqueous solutions were prepared with different contents of the waste glass bottles (30 wt% and 35 wt%), alumina (0 wt%, 2 wt%, 5 wt%, and 8 wt%), and sintered at temperatures 750 °C and 800 °C. The amorphous/crystalline nature of the GCs foams was investigated by XRD, and the calcium sodium silicate (Na2Ca3Si6O16), cristobalite, and corundum were the main crystalline phases identified. In general, the addition of alumina increased porosity and water absorption with a consequent reduction in flexural strength. The manufactured glass-ceramic foams showed average pore sizes in the range of 240–360 μm, porosity between 52% and 85%, and flexural strength between 0.2 MPa and 3.7 MPa.

In this study, a commercial Mg-based ZK60 alloy was modified with 2.5 wt% mischmetal (ZK60-2.5 wt%Mm) and further processed by cold rolling followed by manual filing. The chips obtained by manual filing process were collected from the as cast (AC) and the cold rolled (CR) materials. The hydrogen storage properties were evaluated by kinetics measurements at 350 °C. A full microstructural characterization including optical, scanning and transmission electron microscopy (MO, MEV and TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) was performed in the samples. For the first absorption of both filed samples the H storage capacity showed a value around 6.0 wt% after 1 h while for the CR sample it was close to 1.25 wt% after the same time. The manual filing produced samples with higher hydrogenation kinetics compared with that of the CR sample. Besides, their hydrogen storage capacity was maintained close to the theoretical value (6.75 wt%). The breakage and pulverization of the intermetallic phases gave the chips from the CR alloy the faster hydrogenation kinetics, especially for H-desorption.

Materials characterization 165(110400), 1-10 (2020). doi:10.1016/j.matchar.2020.110400, The aging behavior of a Ti-6Al-4V alloy with different starting microstructures was evaluated by means ofsynchrotron X-ray diffraction, scanning-transmission electron microscopy and micro-hardness measurements.Initial microstructures were produced by thermal and thermomechanical treatments and comprised differentmorphologies of �� phase (martensitic, lamellar, bimodal and globular), as well as the presence or absence of the�� phase. Results show that one or more of the following phenomena can take place during aging and contributeto the hardening of the alloy: �� decomposition into fine secondary �� laths; transformation of the metastablemartensitic ����� into the equilibrium �� phase; and precipitation of the intermetallic Ti$_3$Al. The composition anddistribution of the �� phase was shown to affect the precipitation of secondary �� during aging, while the compositionof the �� phase plays a key role on the formation of Ti$_3$Al. In situ X-ray diffraction studies of the earlystages of aging show the kinetics of the ���������� conversion by the reduction in FWHM of XRD reflections, indicatethe contribution to hardening by the increase of the c/a ratio and the consequent limitation of active slip systemsand depict the chemical homogenization and decomposition of the �� phase., Published by Science Direct, New York, NY

Recently, there has been growing interest in multi-principal element alloys for hydrogen storage. However, most of the papers published so far report compositions based only on transition metal elements, which limit the gravimetric storage capacities due to their densities. Since Mg is a low-density element promising for hydrogen storage, the study of Mg-containing multi-principal element compositions is opportune. In the present work, we report for the first time the structural characterization and hydrogen storage properties of the A2B type MgTiNbCr0.5Mn0.5Ni0.5 alloy and its derivative Mg0.68TiNbNi0.55 alloy. These Mg-containing multi-principal element alloys form major BCC phase (W-type, Im 3 ¯ m) and major FCC hydride (MH2 with CaF2-type structure) when synthesized by mechanical alloying (MA) and reactive milling (RM), respectively. Hydrogen is desorbed from both RM samples in two steps, with some overlap, from different hydrides formed during synthesis. The microstructure of the Mg0.68TiNbNi0.55 composition is more homogeneous (less secondary phases), but both alloys present a total gravimetric capacity of around 1.6 wt% H2.

Thermal treatments are the main route to achieve improvements in mechanical properties of &beta, metastable titanium alloys developed for structural applications in automotive and aerospace industries. Therefore, it is of vital importance to determine phase transformation kinetics and mechanisms of nucleation and precipitation during heat treatment of these alloys. In this context, the present paper focuses on the assessment of solid-state transformations in a &beta, water-quenched Ti-5Al-5Mo-5V-3Cr-1Zr alloy during the early stages of ageing treatment at 500 &deg, C. In situ tracking of transformations was performed using high-energy synchrotron X-ray diffraction. The transformation sequence &beta, + &omega, &rarr, &alpha, + &alpha, &rdquo, iso + &beta, is proposed to take place during this stage. Results show that isothermal &alpha, phase precipitates from &omega, and from spinodal decomposition domains of the &beta, phase, whereas &alpha, nucleates from &omega, &beta, and also from &alpha, with different morphologies. Isothermal &alpha, is considered to be the regulator of transformation kinetics. Hardness measurements confirm the presence of &omega, although this phase was not detected by X-ray diffraction during the in situ treatment.

The impact of starting microstructure on the isothermal behavior of β-metastable Ti–5Al–5Mo–5V–3Cr alloy during aging at 400 °C for 8 h was studied by means of in situ synchrotron X-ray diffraction. Results show that prior deformation does not accelerate phase precipitation during heating, but has an influence on secondary α precipitation during aging, and that the composition of the β matrix, which is affected by the amount of primary α formed depending on the preliminary processing route applied, plays a major role. At this aging temperature, α" phase tends to form from the β matrix in high quantities without the presence of primary α phase or with a low fraction of this phase, and the conversion of α" into α is sluggish, being faster in the β-heat-treated condition, whereas a continuous β → α transformation occurs, with no reliable evidence of α" precipitation, in the α+β-heat-treated condition. Isothermal precipitation was enough to promote a significant hardness increase in the alloy. Observation of the behavior of α" based on its atomic y-coordinate and orthorhombicity helped to elucidate its transformation pathway.

Due to their applicability for manufacturing dense, hard and stable coatings, Physical Vapor Deposition (PVD) techniques, such as High Power Impulse Magnetron Sputtering (HiPIMS), are currently used to deposit transition metal nitrides for tribological applications. Cr-Al-N is one of the most promising ceramic coating systems owing to its remarkable mechanical and tribological properties along with excellent corrosion resistance and high-temperature stability. This work explores the possibility of further improving Cr-Al-N coatings by modulation of its microstructure. Multilayer-like Cr1−xAlxN single films were manufactured using the angular oscillation of the substrate surface during HiPIMS. The sputtering process was accomplished using pulse frequencies ranging from 200 to 500 Hz and the resulting films were evaluated with respect to their hardness, Young’s modulus, residual stresses, deposition rate, crystallite size, crystallographic texture, coating morphology, chemical composition, and surface roughness. The multilayer-like structure, with periodicities ranging from 250 to 550 nm, were found associated with misorientation gradients and small-angle grain boundaries along the columnar grains, rather than mesoscopic chemical modulation of the microstructure. This minute modification of microstructure along with associated compressive residual stresses are concluded to explain the increased hardness ranging from 25 to 30 GPa, which is at least 20% over that expected for a film of the same chemical composition grown by a conventional PVD processing route.

The modified ASTM A297 Gr. HH austenitic stainless steels are a group of refractory alloys designed for high temperature applications that required elevated mechanical strength, such as those found in petrochemical furnace structures and in the steel industry. This study examines the overall microstructural features and cyclic oxidation behaviour of modified HH steels with 0.09%Nb and 0.77%Nb additions. The investigations involved thermodynamic simulations and microstructure analyses conducted by optical and scanning electron microscopy of the substrate materials in the as-cast and aged conditions. The cyclic oxidation tests were performed at 900 °C in atmospheric conditions with oxidation times up to 960h. The resulting oxide scales were analyzed by X-ray diffraction and scanning electron microscopy. The thermodynamic simulations and microstructure analyses of the as-cast steels revealed larger amounts of niobium carbides in the 0.77%Nb steel than in the 0.09%Nb steel, in connection with larger amounts of chromium in solution. Despite this precipitation difference, no significant changes were noticed in the long-term oxidation behaviour of the tested materials.

The stress behavior and the associated microstructure evolution of industrial Ti(C,N)/α-Al2O3 coatings subjected to thermal cycling are investigated by in situ energy dispersive synchrotron X-ray diffraction and transmission electron microscopy. Temperature-dependent stresses and changes in microstructural parameters (domain size and microstrain) are analyzed by in situ measurements at different temperatures between 25 and 800 °C, both in the heating up and cooling down step, including several thermal cycles. Transmission electron microscopy is used to evaluate defects before and after the thermal treatment. The introduction of high compressive stresses in α-Al2O3 by top-blasting is connected to a high defect density at the basal planes of the alumina layer. The stress relaxation of the alumina layer at high temperatures is associated with a successive annihilation of defects until a reversible temperature-dependent stress condition is set. Top-blasting does not change the initial microstructure and residual stress of the Ti(C,N) layer. Ti(C,N) shows a cyclic stress behavior associated with the heat treatment and an elastic deformation behavior in the temperature range investigated.

Phase transformations in a lamellar Ti–5Al–5Mo–5V–3Cr–1Zr (Ti-55531) alloy upon heating at continuous rates of 5, 20 and 100 °C/min has been studied by in situ high energy X-ray diffraction (HEXRD), aided by scanning and transmission electron microscopy, atom probe tomography and hardness measurements. During slow heating, the β phase has shown a behavior suggestive of additional transformations other than the continuous α → β decomposition observed at higher heating rates. Such behavior has been attributed to the precipitation of an embryonic isothermal ω phase. APT analyses have shown that no elemental partitioning occurs between the β matrix and the lamellar α phase, but it does between β and grain boundary α, suggesting that ω phase precipitates with solute rejection in regions outside lamellar colonies embedded in an enriched matrix. Above 500 °C, diffusion becomes significantly enhanced and α decomposition takes place.

Solution treatments (T4) at 380 °C for 16 h and 500 °C for 8 h were performed for ZK60 magnesium alloys modified with addition of 0.5, 1.5 and 2.5 wt% of mischmetal (combination of rare-earth (RE) elements). The compression behaviour was investigated at room temperature and at 300 °C correlated with the microstructure and differential scanning calorimetry (DSC) data. The as-cast microstructure is formed by a-Mg matrix with globular grains reinforced by a semi continuous network of Mg-Zn, Mg-Zn-RE and Mg-RE intermetallic particles. Solution-treated alloys show lower yield strengths due to partial dissolution of precipitates. Work hardening was not observed for the alloys compressed at 300°C with the compression speed of 10-3 s-1, whereas it was observed for the compression speed of 10-2 s-1 for the all as-cast, ZK60-1.5RE-T4 at 380 °C and ZK60-1.5RE-T4 at 380 °C.

The microstructure and mechanical properties of dissimilar butt-joints between a high-strength low alloyed (HSLA) grade and an austenitic high Mn TRIP steel were investigated. The tool rotation and the tool offset toward the TRIP steel were varied between 300–500 rpm and 1–2 mm, respectively. Tool advancing speed amounted to 100 mm/min. Maximum tension stress was observed for the butt-joint welded with 300 rpm and 2 mm offset. The lowest increase in hardness within the stirred zone also occurred for this FSW condition, indicating that this tool rotation is more promising for welding dissimilar joints of commercial HSLA and high Mn TRIP steels. The weld microstructure consisted mainly of a stirred zone, and neither significant HAZ nor TMAZ are observed. However, two main lobular regions are observed, one at the bottom and another one at the top side of the welds. Besides, the HSLA develops a multiphase microstructure consisting of bainite, martensite and retained austenite phases, whereas no e/a martensite is found in the stirred zone of the austenitic high-Mn TRIP steel.

The role of thermally grown α-Fe2O3 on the nucleation of α-Al2O3 during oxidation of binary Fe–Al alloys with 15 and 26 at.%Al at 700 °C was investigated. Surface morphology of the oxide scales indicated direct nucleation of α-Al2O3 preferentially instead of conversion from metastable Al2O3 polymorphs. Oxide scale development over time was also monitored by use of synchrotron X-ray diffraction and Raman spectroscopy. The results showed that the α-Fe2O3 crystal lattice decreases in volume as oxidation progresses, which was found to be consistent with an Al3+ enrichment of α-Fe2O3 as confirmed by the change in relative intensity of α-Fe2O3 Raman peaks.

Reliable high temperature operation of refractory metals depends on the mechanical integrity of the protective oxide formed on the material surface. The residual stress state in oxide layers developed on two modified Nb-alloyed ASTM A297 HH austenitic stainless steels, thermal expansion analysis of the substrate, steel microstructure, oxide layers morphology and phases composition were analyzed. The experimental analyses revealed that larger Nb additions increased NbC precipitates, which was connected to lower thermal expansion coefficient of the substrate. Despite similarities in the oxide scales, the higher Nb-alloyed samples exhibited lower magnitude residual stress values and larger spallation after long-term oxidation.

Made available in DSpace on 2019-10-06T15:55:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Laboratório Nacional de Nanotecnologia Petrobras Friction stir welding is a solid-state joining method conducted under large stress and strain conditions at low peak temperatures when compared to arc welding. Friction stir welding produces a large variety of microstructures and a M-shaped residual stress line profile along the cross-section of the welds. In this work, we present the use of magnetic Barkhausen noise to qualitatively assess the residual stress profile along the transverse direction of a two-pass friction stir welding butt joint on a X80 pipeline steel. Results were compared and correlated to X-ray diffraction, microstructural and hardness characterization. The peak position and the root mean square profiles of the magnetic Barkhausen noise reproduced the residual stress profile obtained by X-ray diffraction and the hardness profile, respectively. These results can be used for developing a qualitative quality control method for friction stir welding joints in other steels. São Paulo State University (UNESP), Campus of São João da Boa Vista, Av. Profª Isette Corrêa Fontão, 505, Jardim das Flores Department of Materials Engineering São Carlos School of Engineering (EESC) University of São Paulo (USP), Av. Joao Dagnone, 1100 Jd. Sta Angelina EIA University, Km 2 + 200 Vía al Aeropuerto José María Córdova School of Mechanical Engineering University of Campinas (UNICAMP), Rua Mendeleyev 200 São Paulo State University (UNESP), Campus of São João da Boa Vista, Av. Profª Isette Corrêa Fontão, 505, Jardim das Flores CNPq: 150215/2016-9

Austempered ductile irons exhibit an interesting combination of properties such as low cost, elevated strength, fatigue and wear resistance. In the present contribution, the influence of shot-peening on the dry-sliding wear behavior of as-cast and austempered ductile irons was evaluated. Specimens from a casting with an initial ferritic-pearlitic matrix were submitted to austempering at 320 °C for 60 min after which an ausferritic microstructure with 40 HRC and approximately 30% retained austenite was obtained. The wear and friction behaviors were assessed by applying ball-on-disc tests using a hard metal (WC) counter-body on as-cast and austempered materials before and after shot-peening and after removal of the rough surface layer created by the shot-peening process. The microstructure of the tested materials was evaluated by X-ray diffraction, optical and scanning electron microscopy. After shot-peening, the austempered samples experienced an elevated increase in surface hardness because of the formation of strain-induced martensite, but a reduction in wear resistance caused by the increase in surface roughness. By removing 20 μm from the surface of the shot-peened samples, it was possible to reduce roughness while preserving the hardened layer, which was found to improve wear resistance.

Made available in DSpace on 2019-10-06T15:24:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 The thermal cycles associated to friction stir welding and processing produce a wide range of microstructures, resulting in different mechanical behaviors along the weld. Most research efforts have focused on the development of welding parameters to obtain sound welds, yet there is still an opportunity for performance improvement based on the understanding of how microstructures are produced. This work explored the different microstructures obtained after physical simulation of an X80 pipeline steel, as a function of the cooling rate and the isothermal transformation temperature. The aim was to study the development of complex mixed microstructures under controlled conditions, in order to compare them to the ones obtained after friction stir processing. As result of the continuous cooling and isothermal thermal simulations, intermediated and high cooling rates, the microstructures matched with those found at the processed plates. These results might help developing a better cooling control after welding. UNESP São Paulo State University Campus of Sao Joao da Boa Vista, Av. Profa Isette Correa Fontao, 505, Jardim das Flores School of Mechanical Engineering University of Campinas, Rua Mendeleyev 200 Department of Mechanical Engineering EIA University University of Sao Paulo (USP) São Carlos School of Engineering, Av. João Dagnone, 1100, Jd. Sta Angelina Ohio State University, 1248 Arthur E. Adams Drive UNESP São Paulo State University Campus of Sao Joao da Boa Vista, Av. Profa Isette Correa Fontao, 505, Jardim das Flores

Ion peening with noble gas is typically used to generate lattice imperfections and a nanostructure within the bombarded metal surfaces. This might have therefore an impact on subsequent plasma nitriding, thus allowing for enhancing the adhesion and wear resistance of hard ceramic coatings deposited onto steel surfaces. In this work, the influence of pre-treating a 100Cr6 steel surface by Xe+ ion bombardment and pulsed plasma nitriding was investigated with respect to surface roughness, wear resistance and residual stresses of thin TiN coatings deposited by reactive ion beam assisted deposition.Xe+ ion bombardment was carried out using a 400 eV acceleration energy produced by a broad Kaufman cell and subsequent thermo-chemical nitrogen diffusion was accomplished at 520 °C. The results show that Xe+ ion bombardment intensifies nitrogen diffusion without inducing significant changes in the substrate topography. The combined pre-treatment with Xe+ ion bombardment and subsequent pulsed plasma nitriding leads to a reduction of compressive stresses in the TiN coatings. The presence of porosity in the white layer diminished the wear resistance.

Microstructural features resulting from thermomechanical treatment of the β-metastable Ti-5Al-5Mo-5V-3Cr (Ti-5553) alloy were studied by means of electron backscatter diffraction and X-ray diffraction. The alloy was deformed at 950 °C (β field) and 800 °C (α + β field) with strain rates of 0.001 s−1 and 0.1 s−1 in compression mode up to a compression ratio of 0.5 (true ratio = 0.7). It was concluded that β phase undergoes dynamic recovery both above and below its β-transus temperature, and recovery is more dominant at lower strain rates, which was corroborated by EBSD misorientation measurements. Meanwhile, α phase undergoes not only a process of breakage and globularization, but also decomposition, which contributes to flow softening. The increase in strain rate caused non-uniform recovery at 950 °C and a more intense refinement of α precipitates at 800 °C. Macrotexture evaluation after deformation indicates that β's texture is much stronger than that of α, with its (200) component being the strongest one.

As-cast ZK40 alloys, modified with the addition of CaO, Gd, Nd and Y were investigated. Solution heat treatments were performed based on differential thermal analysis results. The unmodified ZK40 alloy exhibited microstructure with nearly no intermetallic compound but with precipitates formed during the solution treatment. The modified ZK40 alloys exhibited a semi-dissolved network of intermetallic compounds along the grain boundaries and zones of intermetallic compounds within the grains. Interestingly, no precipitates were observed immediately next to the grain boundaries. The energy dispersive X-ray spectroscopy line scans showed an enrichment of Zn and Zr in the regions where the precipitates are found, suggesting that they are Zn-Zr precipitates. The ageing behaviour was compared between the as-cast and the solution treated materials and it was found that apart from the ZK40-Gd, ZK40-Nd and ZK40-Y aged at 200 °C after solution treatment, there is no notable ageing response for the investigated alloys.

Hard coatings are a suitable solution for increasing the lifetime of tools and components employed in different industrial applications. Coatings of transition metal nitrides have great use for tribological applications due to due to their unique mechanical properties. Although widely employed, current deposition methods such as cathodic arc evaporation produce coatings with many defects, which in turn reduce the resistance to wear, especially under severe conditions. High Power Impulse Magnetron Sputtering is a novel physical vapor deposition technique that produces homogeneous coatings. In this study, CrN and CrAlN monolayer coatings were deposited on AISI 304 stainless steel substrates using HiPIMS. X-Ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy were used to evaluate the microstructure, phase composition, morphology and chemical composition of the coating. Results showed that HiPIMS is a promising technique to deposit CrN and CrAlN homogeneous coatings with high hardness and good adhesion to the substrate.