Metallographic Research Articles

Analysis of Fragmentation Phenomenon of Composite Layers of Fe-TiC Type Obtained “in situ” in Steel Casting

A method for fabrication of a composite layer on the surface of a steel casting using coating containing TiC substrates was presented. The reaction of the synthesis of the ceramic phase was based on the SHS method (Self-propagating High-temperature Synthesis) and was triggered by the heat of molten steel. High hardness titanium carbide ceramic phases were obtained, which strengthened the base material improving its performance properties presented in this article. Microstructural examinations carried out by light microscopy (LM) on the in-situ produced composite layers showed that the layers were the products of reaction of the TiC synthesis – the phenomenon called “fragmentation” by the authors of study. The examinations carried out by scanning electron microscopy (SEM) have revealed the presence of spheroidal precipitated and free of impurities. The presence of titanium carbide was twofold increase in hardness in the area of the composite layer as compared to the base alloy which was carbon cast steel.

Buffered Oxide Etch: A Safer, More Effective Etchant for Additively Manufactured Ti-Alloys

Kroll’s reagent is effective for the metallographic etching of traditional Ti-alloys but struggles with the intricate, refined microstructures of newer Ti-alloy compositions like Ti-Cu and Ti-Mo alloys, which are created through additive manufacturing. The presence of fine intermetallic compounds in these alloys results in limited contrast between grains and phases when using Kroll’s reagent, highlighting the need for an alternative etchant. This study systematically investigates the use of buffered oxide etch, a common etchant for micro-electronics, on a range of additively manufactured Ti-alloys. The results show that buffered oxide etch provides superior etching outcomes compared to Kroll’s reagent and ammonium bifluoride, with a clear colour contrast between grains and fine phases. Furthermore, ammonium bifluoride with an F− ion concentration similar to 40% buffered oxide etch (5.60 mmol/ml) is found to reveal microstructural details effectively. These findings suggest that the buffered oxide etch is a reliable tint etchant for additively manufactured Ti-alloys, and could potentially be used to etch other additively manufactured alloy systems for metallographic studies. Both these etchants supply F− ions without the low pH, significantly improving safety by removing the need for HF in the etching process.

Оценка сварочно-технологических свойств электродных покрытий основного типа различных производителей электродов для сварки трубных деталей и сборочных единиц поверхностей теплообмена котлоагрегатов

Introduction. New grades of high-strength steels, machining and repair processes are being introduced in the power industry. At the same time manual arc welding remains the main technological process for equipment repair in conditions of thermal power plants. Welding materials used in equipment repair should provide comparable to the base metal mechanical properties of the weld. The welding industry has long faced the problem of high sensitivity of basic type electrodes to moisture absorption. High susceptibility to cold cracking caused by diffusible hydrogen and hydrogen embrittlement are major obstacles to the wider use of basic-type electrodes for high-strength steels. Hydrogen production during arc welding is the result of the presence of hydrogen in the arc atmosphere, hydrogen-contaminated filler material, or local hydrogen residues on the source material. During welding, molecular hydrogen is dislocated by the arc energy and then easily absorbed by the molten material. Currently, the welding materials market produces electrodes with basic coating of well-known and proven brands, various national and foreign manufacturers. However, in practice there are cases of cold cracks in the weld seam after welding. Purpose of work is to assess the welding and technological properties of basic type electrode coatings of different manufacturers. The work investigates specimens weld overlaid with electrodes TMU-21U, TSU-5 of different manufacturers and the content of diffusion-mobile hydrogen in the weld overlaid metal is determined. The methods of research are mechanical static tensile tests, chemical composition analysis and metallographic studies. Determination of welding-induced hydrogen content can be accomplished by various quantitative elemental analysis methods. All test methods involve welding under defined conditions followed by deep freezing of the test specimens as quickly as possible. In this way, unintended diffusion processes are inhibited and the hydrogen introduced into the weld metal is retained. Subsequently, the diffusing hydrogen is desorbed from the test specimens in a controlled manner. Results and Discussion. An assessment of welding engineering properties of the electrodes revealed unstable arc burning. Mechanical properties of the welded metal of the investigated electrodes are at the minimum permissible level from the requirements of normative documents. The concentration of hydrogen present in the arc weld metal is multifactorially dependent on the welding procedure (process and parameters, consumables used, as well as environmental conditions (e.g. humidity). For qualitative assessment, hydrogen content of more than 15 cm3/100 g is considered high and hydrogen content less than 5 cm3 ml/100 g is considered very low. Presented results. The conducted evaluation of welding engineering properties of electrodes with basic coating showed satisfactory results. Mechanical properties of the welded metal in terms of impact toughness are at the lower permissible limit, relative elongation does not meet the requirements of normative documents. The content of diffusion-mobile hydrogen in the welded metal is higher than the declared indicators by the electrode manufacturers.

Исследование кинетики формообразования деталей сферического подшипника скольжения из коррозионно-стойких сталей, полученных объемной штамповкой пористых заготовок

Introduction. Spherical powder sliding bearings are widely used in various branches of mechanical engineering. Therefore, the development of a promising method of production of spherical sliding bearing parts from powders of corrosion-resistant steels with specified properties is an urgent task. Purpose of work: is to study the kinetics of forming during cold die forging of spherical sliding bearing parts from stainless steel powder blanks, and to assess the effect of the chemical composition of lubricants and the design of the pressing tool on the structure and properties of the bearing outer ring. Materials from sprayed powders of stainless chromium-nickel steels obtained by cold die forging of sintered blanks coated with lubricants are studied in the work. The following research methods were used: mechanical tensile testing, metallographic studies and cold die forging process simulation. Results and its discussion. It is revealed that the resistance and work of deformation, as well as the kinetics of forming of the outer ring of the spherical sliding bearing are influenced by chemical composition of powders and lubricants, microstructure and mechanical properties of the blank material, configurations of the end surfaces of punches. The top and bottom edges of the outer bearing are most intensively sealed when the punch faces are made with a chamfer angle of 30–40 degrees. With an increase in the relative strain degree by height up to 0.30–0.35 its residual porosity amounted to 0.5–2.0 %. The features of definition of strain state and calculation of strain energy in the implementation of the offered method and the choice of technological parameters of the cold die forging process of sliding bearings parts are shown. A simple method for calculating and experimentally determining the coefficient of contact friction in the process of cold die forging of porous stainless steel blanks is developed, which allows to establish the effect of lubricant composition on the strain resistance at different values of the degree of radial deformation and to develop optimal methods of cold die forging of porous blanks in the production of parts of different complexity.

Influence of pressure and powder characteristics on the properties and microstructure of Colmonoy-5 alloy sintered by spark plasma sintering

This study investigates the microstructure and final properties of Colmonoy-5, a nickel-based hardfacing alloy, consolidated via spark plasma sintering (SPS) as an alternative to traditional welding deposition on stainless steel substrates. Two batches of Colmonoy-5 alloy powders with different particle sizes used for sample processing. Sintering occurred at 900 °C under pressures of either 50 MPa or 60 MPa for 15 min. The evaluation of the sintered samples included density measurement through Archimedes' method, morphology assessment via confocal microscopy, phase composition analysis by X-ray diffraction (XRD), microstructural examination using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and hardness testing by Vickers method. Findings indicate that SPS is an effective technique for producing Colmonoy-5, achieving satisfactory densification. The study also reveals that the initial morphology of the precursor powders can influence the size of phases precipitated within the nickel matrix. Sintering pressure of 50 MPa seems to be the most effective in processing Colmonoy-5 via SPS.

Evaluation of the effect of strontium and tungsten carbide on the microstructure evolution, tribological and mechanical behaviour of Al-Zn-Mg-Cu-5Sr-WC metal matrix composite

The present study focused on the experimental investigation of the metallurgical, tribological, and mechanical behavior of the developed Al-Zn-Mg-Cu-Sr-WC (Al7075-Sr-WC) metal matrix composite. The effect of the reinforcements such as strontium and tungsten carbide (WC) along with a 2 wt% magnesium as the wetting agent during the stir casting of the synthesized aluminum metal matrix composite (MMC) was investigated by varying the weight percentages. The microstructure examination was characterized using field emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) techniques. Wear analysis and mechanical testing were conducted to study the effect of WC particles in the matrix phase by examining their wear rate, tensile strength, proof strength, and hardness values. From the mechanical and tribological tests, it was observed that there was an increase of 55% in hardness and 43% in tensile strength, along with a 31% reduction in wear rate. The secondary phases revealed from XRD analysis lead to more hardness along the refined grain boundaries. The tensile strength of the composite initially increased with a 3 wt% of WC and 5 wt% strontium due to hindrance to the dislocation movement but decreased with more reinforcement particles caused by brittleness. The hard WC particles presence has reduced the wear rate significantly due to its resistance towards abrasive wear and lubricating effect. The unique combination of a grain refiner and a binder helped develop a novel composite with superior characteristics that could replace many aerospace components made up of Al7075 alloy.

Morphological variation and expressed sequence tags-simple sequence repeats-based genetic diversity of Aspergillus cristatus in Chinese dark tea.

Aspergillus cristatus is a homothallic fungus that is used in the natural fermentation process of Chinese Fuzhuan tea and has been linked to the production of bioactive components. However, not much is known about the variations present in the fungus. To understand the variation of the dominant microorganism, A. cristatus, within dark tea, the present study investigated the genetic and morphological diversity of 70 A. cristatus collected across six provinces of China. Expressed sequence tags-simple sequence repeats (EST-SSR) loci for A. cristatus were identified and corresponding primers were developed. Subsequently, 15 specimens were selected for PCR amplification. The phylogenetic tree obtained revealed four distinct clusters with a genetic similarity coefficient of 0.983, corresponding to previously identified morphological groups. Five strains (A1, A11, B1, D1, and JH1805) with considerable differences in EST-SSR results were selected for further physiological variation investigation. Microstructural examinations revealed no apparent differentiation among the representative strains. However, colony morphology under a range of culture media varied substantially between strains, as did the extracellular enzymatic activity (cellulase, pectinase, protease, and polyphenol oxidase); the data indicate that there are differences in physiological metabolic capacity among A. cristatus strains. Notably, JH1805, B1, and A11 exhibited higher enzymatic activity, indicating their potential application in the production of genetically improved strains. The findings provide valuable insights into species identification, genetic diversity determination, and marker-assisted breeding strategies for A. cristatus.

Study on temperature field in the process of induction heat treatment with current assisted weld double side method

At present, in the process of weld induction heat treatment, the common method is to carry out centralized induction heating in the weld area, which will lead to large radial temperature difference of the weld, poor controllability of temperature distribution and easy to cause the defects of residual stress concentration in the weld area. To solve the above problems, this paper adopts the two-sided method to conduct induction heating on both sides of the weld, and at the same time, the auxiliary pulse current is passed into the weld to improve the quality of the weld. ANSYS finite element software is used to establish a multi-field coupling prediction model of electric-magnetic-thermal structure, and explore the distribution law of the auxiliary pulse current and the temperature field of the weld. Finally, an experimental study of pulsed current assisted two-sided induction heating is carried out. Temperature test and metallographic test were carried out respectively to verify the effectiveness of pulsed current assisted induction heating technology.

The effect of different powder mixtures used in the boriding process on the surface properties of AISI 304 stainless steel material

AISI 304 stainless steel, which is used in many areas such as chemistry, petrochemistry, storage tanks and food storage, attracts attention in terms of surface hardness and wear resistance, especially when its industrial applications are evaluated. In this study, it was aimed to improve the surface properties of the AISI 304 stainless steel material used as the substrate material. To develop the best surface properties, boriding layers of varying percentages were created. In order to create these layers, B4C, KBF4, SiC and graphite powders were compared using variable ratios. Microhardness and wear tests were performed on the borided samples and microstructure examinations were carried out using optical, SEM, XRD and EDX. It has been determined that the B4C used as boron source should not be less than 20% for the formation of the boriding layer and the double phase FeB/Fe2B. The powder mixture ratio with the highest thickness and hardness value of the boriding layer formed is the powder mixture with 20% B4C, 50% KBF4, 10% SiC and 20% graphite content. It was observed that the layer thickness increased by 63% and the hardness value increased by 11%. It was observed that this powder mixture gave the lowest wear rate compared to the other powder mixtures in the study. The difference between the highest and lowest wear rate is more than 3 times greater.

Optimizing friction stir welding of AA7075 and AA8090 aluminum alloys: a desirability-driven investigation into mechanical and microstructural enhancement

This research explores the multifaceted analysis of a friction-welded joint, employing Central Composite Design of Response Surface Methodology. The study integrates microstructural investigations and fracture analyses to explain the effect of process parameters on mechanical properties. The optimum settings for Friction Stir Welding of AA7075 and AA8090 were determined by assessing desirability indices. These settings comprised a tool rotation speed of 1927.7 rpm, a tool travel speed of 35 mm min−1, and a tool tilt angle of 0.9°. This specific combination yielded a noteworthy combined desirability index of 0.79, considering both Ultimate Tensile Strength (UTS) and Tensile Elongation (TE). Microstructural examinations revealed distinct characteristics in the Heat-Affected Zone (HAZ), Thermo-Mechanically Affected Zone (TMAZ), and Nugget Zone (NZ). Notably, fine grain structure in the NZ was attributed to the stirring effect created by the tool pin. Fracture analyses indicated ductile fractures, with dimple size variation correlating to tensile strength. Lower dimple density in low-strength joints suggested insufficient material mixing during welding. The maximum tensile strength sample exhibited a high dimple density. These findings contribute to a comprehensive understanding of the welding process’s influence on microstructure and fracture characteristics, providing valuable insights for optimizing mechanical properties in friction-welded joints.

Microstructural and Mechanical Characteristics Examination of Ultrasonically Welded Joints Using Orthogonal Experimentation

Microstructural and Mechanical Characteristics Examination of Ultrasonically Welded Joints Using Orthogonal Experimentation

Investigating the wear resistance of AISI 410/AISI 2205 hybrid weld cladding on annealed EN 8 medium carbon steel

A new multi-layer and multi-material hybrid configuration of weld cladding an annealed EN 8 substrate has been developed and investigated. The AISI 410 martensitic stainless steel is used as the bottom and top clad layers and the AISI 2205 duplex stainless steel is used as the middle weld cladding layer which creates a composite multi-material clad structure with distinct interfacial characteristics. Examination of microstructure unveiled lamellar morphology of the top layer with martensitic-austenitic constituents with maximum hardness, whereas the intermediate layer exhibited ferritic-austenitic morphology with lower hardness. The bottom layer exhibited a tempered martensite structure with a relatively smaller grain size and exhibited intermediate hardness. The bottom-substrate interface displaying the highest interfacial hardness, followed by the middle-bottom interface and the top-middle interface in descending order. Incorporation of AISI 2205 in the intermediate contributed to an increased toughness of 30 MPa√m. During the ball-on-flat sliding wear test, the coefficient of friction displayed an intriguing pattern after a critical load threshold. Higher applied loads led to decreased absorbed energy and a reduction in wear track dimensions. Elevated heat levels promoted tribofilm formation, contributing to lower wear rates, with the optimum condition observed at 7 N, displaying the lowest volumetric loss and wear rate. The primary wear mechanism predominantly involved plastic deformation and plowing, with no apparent indications of brittle fracture.

Remelting of In Situ Fe‐xTiC Metal Matrix Composites by the Sessile Drop Method: Characteristic Temperatures and Microstructural Analysis

The remelting of Fe‐xTiC metal matrix composites (MMCs) is studied using the sessile drop method. This is to determine the conditions needed for the complete dissolution of TiC precipitates in the Fe‐based melt. Samples with different amounts of TiC (2, 3.5, and 5 wt%) are analyzed in a hot‐stage microscope (HSM), capturing the softening and melting temperatures. A Cr‐alloyed steel is selected as a matrix. Consequently, the presence of TiC elevates the melting initiation temperature above the melting point of pure iron (e.g., 1659 ± 10 °C for Fe‐5TiC). Furthermore, samples with higher TiC amounts exhibit higher melting initiation temperatures. This trend is confirmed by differential scanning calorimetry measurements, conducted on the representative Fe‐xTiC samples. Microstructural examinations of the solidified (HSM) samples identify two distinct TiC precipitate morphologies: primary blocky/cubic and secondary eutectic plate like. For instance, the Fe‐5TiC sample contains numerous blocky/cubic precipitates (7.5 ± 3.1 μm) clustered at the upper cross‐ section, while secondary plate‐like precipitates (20.4 ± 11.8 μm) are uniformly distributed in eutectic assemblies with the matrix. This study provides meaningful insights for optimizing the production of as‐cast and as‐atomized Fe‐TiC MMCs, particularly in selecting reinforcement levels and homogenization temperatures for complete TiC dissolution.

Flange joining using friction stir welding and tungsten inert gas welding of AA6082: A comparison based on joint performance

Expanding the use of 6xx aluminum alloy series in various industries is challenging due to the need for cost-effective welding processes and optimal settings to ensure high-quality joints. The present research focused on the comparison of joint performance of the pipes and plates using tungsten inert gas (TIG) and friction stir welding (FSW) The AA6082 alloy material is used for pipes and plates used in the study. Various techniques were utilized, including hardness and tensile tests, and microstructural examinations. Using a scanning electron microscope (SEM), the surface fracture of the specimens that failed under tensile tension was also examined. The present research also included the economic impact on the welding processes used. Results demonstrated that the weld obtained using FSW was defects free whereas, internal flaws were seen in TIG welded samples. The hardness value increased over the base material (BM) for the FSW and TIG by 31–35% and 46-40%, respectively. The FSW joint was welded at a maximum UTS of 3 mm/min and a rotational speed of 3000 rpm. FSW can create the AA60682 flange joints more efficiently and effectively than fusion welding procedures like TIG processes in pipeline applications. For AA6082 flange joints, overall total cost comparisons between FSW and TIG were also made.

Estimation of optimal process parameters for minimum wear in the application of SiC/RHA reinforced Al7075 hybrid composites using ANN, ANFIS, and GA

Increasing demand for high-performance materials has led to the exploration of composite materials for enhanced mechanical properties. In this study, a composite of silicon carbide particulate and rice husk ash (RHA) in varying proportions was utilized to reinforce an aluminum alloy (Al7075) hybrid composite fabricated through the stir casting technique. Microstructure examination via an optical microscope ensured the homogeneous distribution of reinforced particles. Wear was evaluated using a pin-on-disc apparatus, considering material factors (% of SiC and % of RHA) and mechanical wear factors (load applied, speed of rotation, and sliding distance). Experimental data were used to develop artificial neural network and adaptive neural fuzzy inference system models, which demonstrated high predictive accuracy. An objective function, formulated to minimize wear via regression analysis, guided the application of a genetic algorithm to determine optimal process parameters. The optimal combination, resulting in a minimum wear of 34.5 µm, comprised 12% SiC, 7% RHA, a sliding speed of 1.9 m/s, an applied load of 11.5 N, and a sliding distance of 715 mm. This study concludes with recommendations for further research and implications for composite material design and optimization.

Microstructure and texture evolution in AZX311 Mg alloy during in-plane shear deformation

The current study examined the deformation mechanisms, microstructure, and texture evolution in AZX311 Mg alloy sheets subjected to in-plane shear (IPS) deformation. Different levels of shear strains, with values 0.05, 0.10, and 0.15, were applied along the rolling direction (RD) using a specialized in-plane shear testing jig. The strain measurement for the applied shear deformation was conducted utilizing the digital image correlation (DIC) technique. The strain distribution was found to be nearly homogeneous over sufficiently large areas, thereby allowing the microstructural measurements to yield relevant statistical data. A thorough microstructural examination across the thickness using electron back-scattered diffraction (EBSD) revealed that the application of IPS strain led to the formation of a significant number of tensile twins (TTWs) in the sheet. This was evidenced by the emergence of two satellite peaks at the periphery of the pole figures. As the shear strain increased, the proportion of TTWs in the material also increased, encompassing the entire parent grain and leading to the formation of what has been termed as “all-twinned microstructure”. The microstructural and texture investigation after IPS deformation revealed that TTWs were the dominant deformation mechanism that defined the microstructure and texture under IPS deformation, while dislocation slip activity was dominated by prismatic slip, as evidenced by the resolved shear stress analysis in this study. Consequently, this research highlights the effect of IPS deformation on the microstructure and texture evolution throughout the thickness of an Mg alloy sheet and elucidates the underlying mechanisms.

Effects of stress relief annealing in NGO steels

The effect of stress relief annealing (SRA) has been investigated on two classes of non-grain oriented (NGO) steels and with different sheet thickness. Magnetic properties were measured on mechanically sheared and water jet cut Epstein strips before and after SRA treatment at 800 °C in a nitrogen gas atmosphere. Significant improvement in power loss was achieved for the steel with lower aluminium content after SRA but the effect was much smaller for steel with the higher aluminium level, especially for thinner sheets where the SRA treatment was actually deleterious. No change in steel chemistry after SRA was found that could explain these differences. Microstructural examination showed residual dislocation substructures due to shearing before SRA and recrystallisation along the sheared edges together with recovery of the dislocation structures afterwards.A completely new finding was the presence of dislocation loops after SRA in the steel with higher aluminium content. These were not present previously but were created during the heat treatment. The presence of these dislocation loops is proposed as the reason for the weak or adverse effect of SRA on power loss. Detailed electron microscopy revealed that there are two families of dislocation loops having either Burgers’ vectors of a 〈100〉 lying on {100} planes or a√3/2 〈111〉 on {111 planes}. A model is presented whereby oxidation which occurs at the sheet surfaces causes a concentration gradient within which the Al atoms diffuse. This process necessitates a balancing flux of vacancies diffusing into the interior. When the content of vacancies exceeds the equilibrium content they agglomerate and ‘precipitate’ out as vacancy dislocation loops.

Identification of structural defects and their impact on the magnetic memory, static and cyclic strength of VNS9-SH thin sheet trip-steel

Identification of microstructure defects, which are stress concentrators (SC) during the operation of mechanical engineering products, is an important scientific and practical task relevant for manufacturing enterprises. This problem becomes especially urgent and difficult for critical helicopter parts made of sheet TRIP steel VNS9-Sh (23Kh15N5AM3-Sh) and operating under cyclic loads due to the complex microstructure of the steel and small thickness of strips and sheets. To assess the impact of structural defects on the cyclic strength of products made of the steel under study, the specimens were preliminary sorted proceeding from the results of their testing using the method of metal magnetic memory (MMM) and metallographic studies. The MMM method is a structure-sensitive procedure which provides information about the presence of structural defects that arise during the manufacture. Magnetic anomalies in the form of sharp local changes in the intrinsic stray magnetic field (SSMF) (H) and its gradient |ΔH| along the length of the controlled section Δx, were identified on the surface of sheets cut from five different batches. A conventional classification of the identified anomalies was made according to the magnitude of the magnetic field gradient. The specimens of two types were cut in zones of magnetic anomalies and outside them: type 1 — for cyclic tests and type 2 — for metallographic studies. The geometric parameters and field gradient values of magnetic anomalies on specimens of type 1 and type 2 were the same. Metallographic studies in zones of maximum magnetic field gradient on type 2 specimens revealed defects in the form of a strip at the boundary of different structures, which is a structural stress concentrator (SSC) and a source of the inhomogeneity and changes in the magnetic properties. Type 1 specimens with similar magnetic anomalies and Type 1 specimens cut from sheets outside zones of magnetic anomalies were then selected for cyclic testing. Comparative tests for cyclic strength of the specimens with and without specified SSC were carried out. It is shown that the presence of SSC zones in the specimens reduces the number of cycles to failure during cyclic tests by 1 – 2 orders of magnitude compared to the specimens free of SSC. Based on cyclic tensile tests of specimens, a limiting value of the magnetic field gradient was determined that corresponds to the acceptable level of stress concentration on structural defects. This value is recommended for use as a rejection criterion when examining a new tape by the MMM method.

Accelerated corrosion tests of a contact pair austenitic stainless steel – titanium alloy

The results of accelerated corrosion tests of a pair of austenitic stainless steel — titanium alloy under conditions of elevated temperatures and high concentrations of corrosive agents are presented, conditions for the developing the mechanism of local corrosion being the same. The proposed approach included provoking the appearance of microstress concentrators by three-point loading of test samples with subsequent forced development of local types of corrosion through simultaneous exposure to an increased concentration of corrosive agents and temperatures at a fixed exposure in an autoclave. The results of modeling the corrosion process in a titanium alloy being in contact with stainless steel are assessed proceeding from the data obtained from metallographic studies of the state of surface layers of the metal and the morphology of corrosion products on prepared sections of the surface of templates cut from the samples under study. We considred a pair of steel 08Kh18N10T — titanium alloy VT-5. It is shown that the contact of samples under conditions of accelerated corrosion tests does not lead to a significant development of local types of corrosion of the titanium alloy. On the contrary, analysis of the state of the surface layers of the samples of stainless steel revealed the presence of deep corrosion pits, triggering the intergranular corrosion. In this case, corrosion of austenitic steel, both in the presence and in the absence of contact with titanium, proceeded in three stages: the initiation and fusion of pitting; formation of knife corrosion ulcers; propagation of intergranular cracks into the depth of steel. The proposed methodology of corrosion testing can be used to predict the possible nature of the development of metal corrosion under operating conditions that form local zones of static stresses in structural materials, and for prompt response to extend the design life of the equipment at thermal and nuclear power facilities.

Geopolymer mortars having glassy materials considering mechanical and microstructural features

In comparison with ordinary Portland cements, geopolymer-based cements are now gaining prominence as an eco-friendly substitute to decline CO2 emissions in the course of OPC manufacturing. In this study, mechanical/microstructural features of geopolymers under different curing heats using 12 M NaOH as alkaline activator, obsidian and waste glass powder as binder at different dosages (0 %, 25 %, 50 %, 75 % and 100 %) were investigated. The mixture calculations of 5 different series of geopolymer mortars were produced, as stated by ASTM C109. Samples were cured for 4 different temperatures (75, 90, 105 and 120 °C) for 72 h and then kept in ziplock bags at room conditions until the mechanical tests after curing of up to 90-day. At 7-90-day, samples' flexural/compressive strengths were detected, as stated by ASTM C348/349 standards, respectively. Microstructural examinations of mortar samples were also made by ensuing practices: XRD, SEM-EDS and FTIR. Laboratory findings disclosed that an ideal compressive/flexural strength of 52.6/13.75 MPa was obtained from mortars with waste glass and obsidian binder subjected to a curing temperature of 75 and 90 °C. In addition, one can clearly observe that it exists a substantial link between microstructure images obtained from SEM analysis and compressive/flexural strength results. From existing investigation, one could conclude that substitution of obsidian joining high reactive content into waste glass rose mortars’ flexural/compressive strengths. Considering mechanical/microstructural features obtained from the present investigation, it is seen that obsidian, an inert material, and waste glass, a waste material, could be employed separately or together to create a new geopolymer product.