Optical Stereomicroscope Research Articles

Influence of polymerization procedure on marginal leakage of composite resin restorations – an in vitro study

Introduction. Composite materials are currently most commonly used to reconstruct tooth tissues. During the polymerization, it results in marginal leakage between filling and hard dental tissues. Marginal leakage causes bacterial microleakage which leads to the discoloration of restoration margin and secondary caries. Intensive development of new technologies focus on elaborate processes decreasing the risk of microleakage appearance. Aim. The purpose of this in vitro study was to estimate marginal leakage degree in composite restorations which were polymerized with different kinds of lamps. Material and methods. 35 extracted human permanent molars were used in the study. Calibrated cavities on interproximal surfaces (class 2.2 acc. Mount and Hume classification) were prepared. Teeth were divided into 5 groups. Cavities were filled with composite materialaccording to the manufacturer’s instructionsusing different kinds of polymerizationlamps: halogen (floodlight) lamp, high intensity LED lamp and LED lamp with three working modes. Marginal leakage was evaluated by estimating a dye penetration and SEM images registration. Quantitative analysis of marginal gap was also performed. Results. In samples analysis with optical microscope and stereo microscope the dye penetration and marginal gap was not observed. Only scanning electron microscope with back-scatter detector has revealed the marginal leakage. the largest marginal leakage was observed in case of high intensity led lamp– FlashMax(1.60 μm), and the smallest for LED lamp – pulse and increasing modes(0.96 μm and 0.98 μm, respectively). Marginal leakage was not observed in samples polymerized with continuous mode of LED lamp. Conclusions. The results of this study suggest that the increase in light intensity of the polymerization lamp significantly shortens the exposure time, which is clinically advantageous, but excessive light intensity can cause severe systolic tensions leading to a marginal leakage.

Retention force and deformation of an innovative attachment model for mini-implant–retained overdentures

Statement of problemThe gradual loss of retention and the need for periodic replacement of attachment-system components are the most frequent complications in implant-supported overdentures. PurposeThe purpose of this in vitro study was to develop a new attachment system for overdentures with polymeric materials and compare its retention and deformation with a conventional O-ring attachment system. Material and methodsA matrix with 2 mini-implants with ball abutments was used to simulate the mandibular border during a fatigue resistance test. A total of 60 polyacetal (n=20), polytetrafluoroethylene (n=20), and conventional O-ring (n=20) attachments were captured in pairs with acrylic resin and subjected to 3625 insertion and removal cycles, simulating 30 months of overdenture use. The internal and external deformations of the attachments were assessed using an optical stereomicroscope. One-way ANOVA and the Tukey honestly significant difference tests were used for statistical evaluation (α=.05). ResultsThe polyacetal attachment system showed the highest retention (P<.001), followed by the O-ring and polytetrafluoroethylene attachments. The O-ring attachments exhibited the lowest deformation (P<.001), and the polyacetal attachments had the highest internal deformation (P<.001). ConclusionsThe newly developed polyacetal attachment model increased the retention of mini-implant–retained overdentures, and despite the deformation experienced, the retention period appears to be better than that of conventional systems.

Marginal adaptation of CAD-CAM onlays: Influence of preparation design and impression technique

Statement of problemFactors that may affect the marginal adaptation of computer-aided design and computer-aided manufacturing (CAD-CAM) restorations include preparation design, impression technique, and CAD-CAM system. The influence of impression technique and preparation design on CAD-CAM partial coverage restorations has not been fully addressed. PurposeThe purpose of this in vitro study was to investigate the influence of direct and indirect digital scanning techniques and 2 preparation designs on the marginal adaptation of CAD-CAM onlays. Material and methodsTwo mesio-occlusal buccal onlay preparations with reduction of the mesiobuccal cusp were made: conventional preparation (CP) with a 1.2-mm modified shoulder margin and modified preparation (MP) flat cuspal reduction without shoulder. Virtual models were generated from each preparation by using a digital scanner (BlueCam; Dentsply Sirona) from the plastic teeth (direct digital scan) or from the stone dies (indirect digital scan). Onlays were designed using a CAD-CAM system (CEREC 4.0; Dentsply Sirona), and nanoceramic resin blocks (Lava Ultimate Restorative; 3M ESPE) were milled using the CEREC MCX milling machine. Marginal discrepancy was evaluated using an optical stereomicroscope at ×25 magnification in 18 locations distributed along the margins of the preparation. The data were analyzed by using 3-way ANOVA followed by the Tukey HSD test (α=.05). ResultsCP presented a statistically significant reduced average marginal adaptation (59 ±50 μm) than did MP (69 ±58 μm) (P<.001). The Tukey HSD test showed the presence of a significantly larger marginal discrepancy in the mesial and buccal locations of MP when compared with CP. Regarding impression techniques, the buccal location presented the smallest average marginal discrepancy in restorations fabricated with indirect impression when compared with direct impression (42 ±33 μm and 60 ±39 μm) (P<.001). ConclusionsThe results showed that conventional preparation with a modified shoulder margin presented improved marginal adaptation compared with modified preparation with flat cuspal reduction. Direct and indirect digital scanning techniques produced restorations within a clinically acceptable range; however, the indirect scanning technique resulted in the fabrication of restorations with superior marginal adaptation on the buccal location.

Roman plasters and mortars from ancient Cosa (Tuscany-Italy). Mineralogical characterisation and construction from domus 10.1 (House with Cryptoporticus)

Between 2005 and 2012, we worked on the project «La ciudad romana de Cosa: arqueología de un enclave comercial mediterráneo» supported by Spanish Goverment. The excavation campaigns carried out since 2005 have made it possible to learn the architect's plan of the House 10.1 (House with Cryptoporticus). The present work aims to provide a study of the construction techniques as well as analytical support to gain knowledge of the plasters and mortars of the main rooms, tablinum and peristylum, of the domus 10.1 of Cosa (House with Cryptoporticus). For the study of the plasters and mortars, two different analytical techniques were used to determine its composition: optical stereo microscope and polarized light microscopy.

Determination on Damage Mechanism of the Planet Gear of Heavy Vehicle Final Drive

The works focus on the investigation of damage mechanism of fractured in the form of spalling of the planet gears from the final drive assembly of 160-ton heavy vehicles. The objective of this work is to clearly understand the mechanism of damage. The work is the first stage of the on-going research on the remaining life estimation of such gears. The understanding of the damage mechanism is critical in order to provide accurate estimate of the gear’s remaining life with observed initial damage. The analysis was performed based on the metallurgy laboratory works, including visual observation, macro-micro fractography by optical stereo and optical microscope and micro-vickers hardness test. From visual observation it was observed pitting that form lining defect at common position, which is at gear flank position. From spalling sample it was observed ratchet mark at the boundary between macro pitting and the edge of fractured parts. Further observation on the cross-section of the samples by optical microscope confirm that initial micro pitting occur without spalling of the case hardened surface. Spalling occur when pitting achieve certain critical size, and occur at multiple initiation site of crack propagation. From the present research it was concluded that pitting was resulted due to repeated contact fatigue. In addition, development of micro to macro pitting as well as spalling occur at certain direction towards the top of the gear teeth.

Comparison of Light-Emitting Diode-Curing Unit and Halogen-Based Light-Curing Unit for the Polymerization of Orthodontic Resins: An In vitro Study.

Aims and Objectives:Conventionally, composites are cured using halogen-based light-curing units (LCUs). However, recently, light-emitting diode (LED) LCUs have been introduced commercially, claiming many advantages, yet producing comparable bond strength even when cured with single LED LCUs. This present study was undertaken to compare the shear bond strength of orthodontic brackets bonded to teeth with conventional halogen LCU (3M ESPE Elipar 2500) and LED LCU (3M ESPE Elipar FreeLight 2) and to determine the site of bond failure.Materials and Methods:Fifty extracted human bicuspid teeth were randomly divided into two groups of 25 each. All the teeth were etched and primed. Then, orthodontic brackets were bonded onto the teeth with the light-cured adhesive (Transbond XT, 3M Unitek), and the adhesive was cured with halogen LCU and LED LCU for Group I and Group II, respectively. The brackets were then subjected to shear stress using a Hounsfield universal testing machine at a crosshead speed of 1 mm/min. The force was recorded in Kgf and converted to MPa. The residual adhesive was scored based on the modified adhesive remnant index (ARI) using an optical stereomicroscope. The data were analyzed using the Student's t-test and the Mann–Whitney test at a significance level of 0.05.Results:The results have shown that there is no significant difference between the shear bond strengths and the ARI scores of both the groups.Conclusion:From this study, it can be concluded that (1) LED LCUs containing even only a single LED can cure the composite as well as a halogen-based LCU; (2) there is no statistically significant difference in the shear bond strengths of the two groups; and (3) the ARI scores show no significant difference.

Variations in enamel damage after debonding of two different bracket base designs: An in vitro study.

Background. Bracket base design is a factor influencing shear bond strength. High shear bond strength leads to enamel crack formation during debonding. The aim of this study was to compare enamel damage variations, including the number and length of enamel cracks after debonding of two different base designs. Methods. Eighty-eight extracted human premolars were randomly divided into2 groups (n=44). The teeth in each group were bonded by two types of brackets with different base designs: 80-gauge mesh design versus anchor pylon design with pylons for adhesive retention. The number and length of enamel cracks before bonding and after debonding were evaluated under an optical stereomicroscope ×40 in both groups. Mann-Whitney U test was used to compare the number of cracks between the two groups. ANCOVA was used for comparison of crack lengths after and before debonding in each group and between the two groups. Results. There was a significant increase in enamel crack length and numbers in each group after debonding. There was no significant difference in enamel crack numbers after debonding between the two groups, whereas the length of enamel cracks was significantly greater in anchor pylon base design after debonding. Conclusion. Bracket bases with pylon design for adhesive retention caused more iatrogenic debonding damage to enamel surface.

Microstructural properties of a dissimilar friction stir welded thick aluminum aa6082-t6 and aa7075-t6 alloy

Friction stir welding is a severe plastic deformation process. This solid state welding procedure has recently received a general acceptance in the aerospace industry for joining difficult to weld aluminum alloy using the conventional method. A 10mm thick AA6082 and AA7075 in tempered form (T6) were friction stir welded in butt configuration as against the previous research on 4mm, 6mm and 8mm thicknesses respectively. The response of the stir zone (SZ) microstructure to processing parameters was evaluated using optical microscope (OM), Stereo microscope (SM) and scanning electron microscope (SEM) respectively. The magnitude forge force (kN) at the tool shoulder directly affect the flow of the extruded materials through the tool probe. The distribution of thermal energy, dissolution, precipitation and re-precipitation of solute influences the materials flow and properties evolution. Hence, equiaxed grain structures observed were due to the dynamic recrystallization mechanism at the weld nugget. Some microstructure imperfection were observed at the weld nugget when AA6082 aluminum plates were clamped on the retreating side to the backing plate. However, the material flow and mixing was not sufficient to establish good bonding and quality welds due to deviation in the positioning of the aluminum plates.

An Evaluation of Shear Bond Strength of Admira (Ormocer) as an Alternative Material for Bonding Orthodontic Brackets: An In vitro Study.

Objective:To evaluate shear bond strength (SBS) of Ormocer-bonded orthodontic brackets with self-etching primer (SEP) and conventional adhesive system and also to assess the amount of adhesive remaining on the tooth surface after debonding using adhesive remnant index (ARI).Materials and Methods:The study was done on 90 extracted human upper first permanent maxillary premolars. The study sample was categorized into three groups of 30 each to assess the SBS using three adhesives, Ormocer, SEP, and conventional adhesive system. Following debonding, the surfaces of teeth were examined for residual adhesive remaining by means of the optical stereomicroscope at ×50 magnification. ARI (Artun and Bergland) was used to classify the amount of residual adhesive. Obtained data were expressed as mean ± standard deviation, and obtained data was expressed as mean ± standard deviation (SD) and statistical analysis was done using one way ANOVA and Mann-Whitney U-test [SPSS version 17 statistical package (SPSS Inc., Chicago, IL)].Results:The mean SBS was maximum in Group I followed by Group II and Group III. The difference in the mean SBS among Group I (8.67 ± 1.84 Mpa), Group II (7.72 ± 1.82 MPa) and Group III (6.42 ± 1.55 MPa) was statistically significant. ARI was maximum in Group I followed by Group II and minimum Group III.Conclusion:Ormocer may be utilized as a substitute to generally used bisphenol A-glycidyl methacrylate-based adhesives; however, its effectiveness should be determined clinically by in vivo studies.

How taphonomic alteration affects the detection and imaging of striations in stab wounds

Stabbing with a kitchen knife is a common method of homicide in Europe. Serrated knives may leave tool markings (striations) in tissues. Documentation of striations is necessary for their use as forensic evidence. Traditional methods (physical casting and photography) have significant limitations, and micro-computed tomography (micro-CT) has been trialled in cartilage to “virtually cast” wounds. Previous research has shown the proportion of striations in cartilage falls following decomposition. This project has investigated the effects of taphonomic alteration and documentation methods of striations in porcine skin. Fresh, decomposed, mummified, burnt and waterlogged stab wounds in a porcine analogue were excised and imaged using photography, stereo-optical microscopy and micro-CT. The proportion of striations in each taphonomic group was determined from the images by independent analysts. Striations were observed more frequently in serrated blade wounds, although they were also identified in non-serrated blade wounds. The proportion of wounds showing striations declined following decomposition. An inversely proportional linear correlation between advancing decomposition and proportion of striations existed. Dehydration (mummification and burning) rendered serrated and non-serrated blade wounds indistinguishable. Water composition affected the preservation of striations. Identification of striations gradually declined after decomposition in tap water, but persisted to a point when left in brackish water. All three techniques imaged striations; however, the optimum technique was stereo-optical microscopy due to practical advantages and specific limitations affecting photography and micro-CT. This study demonstrates the effects of taphonomic alteration on striations and suggests stereo-optical microscopy is the optimum method for their documentation.

Surface and Thermal Characteristics of Single-Use Electrosurgical Pencils After Clinical Reuse and In-Hospital Reprocessing

Safety and efficacy issues are associated with reprocessing of single-use electrosurgical pencils (EPs), requiring methods for assessing the reprocessing protocol before clinical reuse. This study aimed at monitoring the surface characteristics of single-use EPs subjected to multiple clinical use and in-hospital reprocessing. A total of 24 single-use-labeled EPs were divided in five test groups and one control group. The test groups were subjected to a different number of clinical uses, ranging from one to five. A multitechnique approach based on optical stereomicroscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) was applied. The silicon coating of the tip was significantly reduced, and foreign bodies were occasionally found on reprocessed EPs. The amount of biological debris and chemical residuals increased with the number of reprocessing cycles in critical areas. The degradation temperature of the EP handle polymer showed a progressive significant reduction. Cable cord showed no modification after reprocessing. EP tip could undergo major surface modifications that can affect functionality. The efficacy of the reprocessing protocol in removing debris from the EP handle should be carefully assessed. Surface and thermal characteristics have to be considered for validating a reprocessing protocol of single-use labeled EP.

Laboratory evaluation of the effect of unfilled resin after the use of self-etch and total-etch dentin adhesives on the Shear Bond Strength of composite to dentin.

BackgroundBased on the frequent application of composite resins as tooth-colored fillings, this method is considered a viable alternative to dental amalgam. However, this method has the low bond strength of the composite to dentin. To solve this issue, various dental adhesive systems with different characteristics have been developed by dentistry experts.AimTo assess the effect of an additional layer of unfilled resin in self-etch and total-etch dentin adhesives on the shear bond strength (SBS) of composite to dentin. Moreover, we assessed the effects of sample storage in artificial saliva on the SBS of composite to dentin.MethodsMethods: This experimental study was conducted on 160 freshly extracted human first or second premolar teeth, which were randomly divided into 16 groups. The teeth were prepared from Mashhad University of Medical Sciences, Mashhad, Iran (2008–2009). Scotchbond Multi-purpose (SBMP), single bond (SB), Clearfil SE Bond, and Clearfil S3 Bond were applied to dentin surface with or without the placement of hydrophobic resin (Margin Bond) in accordance with the instructions of the manufacturers. To expose the coronal dentin, the teeth were abraded with 600 grit SiC paper. Immediately after restoration, half of the samples were tested in terms of SBS, while the other samples were evaluated in terms of SBS after three months of storage in artificial saliva. SBS rates of dental composites evaluated by universal testing machine and samples were studied by optical stereomicroscopy to verify the failure type. Data analysis was performed in SPSS V.16 using Kolmogorov-Smirnov test, independent-samples t-test, ANOVA, and Duncan’s logistic regression test.ResultsIn this study, a significant reduction was observed in the SBS rates of SB and S3 bond adhesive systems after storage with and without hydrophobic resin (p>0.000). Without storage in normal saline, a significant increase was observed in the SBS rate of the SE bond (p=0.013). In addition, SBS rate of SBMP significantly increased after storage with hydrophobic resin (p=0.001). Finally, the highest and lowest rates of SBS were observed in the SE and S3 bonds in all the experimental groups, respectively.ConclusionThe effects of using a hydrophobic resin layer on shear bond strength values seem to be effective. The mild self-etch adhesive exhibited the best resin-dentine bond strength after aging

Corrosion Failure Study in an Oil Cooler Heat Exchanger in Marine Diesel Engine

In this article, the failure of a heat exchanger during its operation in the marine environment has been analyzed. This heat exchanger was used for cooling the oil in a marine diesel engine. Based on the existing failure history, damages in engine components were observed after 89 hours of engine working due to the leakage of the sea water to the oil. For the objective of the failure analysis, each component was investigated under the stereo optical microscopy and the scanning electron microscopy (SEM). The diameter of pits was also recorded as 8 micrometer. Besides, the chemical composition of corrosion products on the surface and in pits was additionally analyzed with the energy dispersive X-ray spectroscopy (EDAX). Results indicated that two corrosion mechanisms were failure root causes of leakages, including the crevice corrosion and the pitting corrosion. In such situation, in the engine, the oil and the sea water in tubes of the heat exchanger mixed and decreased the oil viscosity and damaged the oil film on crankshaft bearings, and finally caused damages of the engine.

Gahnite From the São João Del Rei Pegmatitic Province, Minas Gerais, Brazil: Chemical Composition and Genetic Implications

Abstract A swarm of pegmatitic bodies occurs in the central portion of the Mineiro Belt at the meridional border of the Sao Francisco craton (Brazil), forming the Sao Joao del Rei Pegmatitic Province. These bodies are genetically related to one common source, the granitic magmatism precursor to the Ritapolis granitoid, whose age of 2121 ± 7 Ma marks the last pulse of paleoproterozoic plutonism in the Mineiro Belt. A selected group of gahnite crystals from several pegmatite bodies hosted in the Brumado metadiorite, Ritapolis metagranitoid, and Rio das Mortes amphibolites and phyllites has been analyzed by optical stereomicroscopy, Raman spectroscopy, SEM/EDS, and EMPA/WDS. The gahnites have compositions defined by the ranges Ghn 65.52–85.38 Spl 0–2.16 Hc 13.71–31.92 Jac 0–0.92 Mfr 0–1.22 Glx 0–1.11 (in mol.%), plot almost exclusively on the gahnite–hercynite axis, and fall into the granitic pegmatite field in the gahnite–spinel–hercynite ternary diagram. The composition of gahnite varies depending on the country rock the pegmatite cuts, and the interaction between the pegmatite and host rocks is more evident in grains found in pegmatite bodies associated with amphibolites due to higher Fe and Mg in these rocks. These compositions also indicate a higher degree of fractionation of the pegmatites hosted by the Brumado metadiorite in comparison to those hosted by the Rio das Mortes metavolcano-sedimentary sequence (amphibolites and phyllites) and the Ritapolis metagranitoid, reflecting different crustal levels of emplacement of these pegmatitic bodies.

Porosity and swelling properties of novel polyurethane–ascorbic acid scaffolds prepared by different procedures for potential use in bone tissue engineering

In this work, a novel polyurethane (PU) system based on poly(ethylene-butylene) adipate diol, 1,6-hexamethylene diisocyanate, 1,4-butanediol, and ascorbic acid was used to prepare scaffolds with potential applications in bone tissue engineering. Two fabrication methods to obtain porous materials were chosen: phase separation (PS)/salt particle leaching (PL) and solvent casting (SC)/salt PL. The calculated porosity demonstrated that scaffolds with a higher porosity were obtained (76–86%) using the PS/PL method. The morphology of pores was examined with the use of optical stereomicroscope and scanning electron microscope. The appropriate porosity, pore morphology, and swelling properties for bone tissue scaffolds were obtained for our novel PU system by the PS/PL method using 15 wt% solution of PU in the mixture of dimethylformamide (DMF)/tetrahydrofuran solvents and by SC/PL method from 20 wt% from DMF. The distilled water and saline water swelling for those samples was also appropriate for bone tissue scaffold application.

Hidden surface microstructures on Carboniferous insect Brodioptera sinensis (Megasecoptera) enlighten functional morphology and sensorial perception.

Megasecoptera are insects with haustellate mouthparts and petiolate wings closely related to Palaeodictyoptera and one of the few insect groups that didn’t survive the Permian-Triassic mass extinction. Recent discovery of Brodioptera sinensis in early Pennsylvanian deposits at Xiaheyan in northern China has increased our knowledge of its external morphology using conventional optical stereomicroscopy. Environmental scanning electron microscopy (ESEM) of structures, such as antennae, mouthparts, wing surfaces, external copulatory organs and cerci have shed light on their micromorphology and supposed function. A comparative study has shown an unexpected dense pattern of setae on the wing membrane of B. sinensis. In addition, unlike the results obtained by stereomicroscopy it revealed that the male and female external genitalia clearly differ in their fine structure and setation. Therefore, the present study resulted in a closer examination of the microstructure and function of previously poorly studied parts of the body of Paleozoic insects and a comparison with homologous structures occurring in other Palaeodictyopteroida, Odonatoptera and Ephemerida. This indicates, that the role and presumptive function of these integumental protuberances is likely to have been a sensory one in the coordination of mouthparts and manipulation of stylets, escape from predators, enhancement of aerodynamic properties and copulatory behaviour.

Bond strengths of brackets bonded to enamel surfaces conditioned with femtosecond and Er:YAG laser systems.

The aim of this study was to compare femtosecond and Er:YAG laser systems with regard to enamel demineralization and bracket bond strength. Human-extracted premolars were randomized to three groups (n = 17) depending on the conditioning treatment used for the buccal surfaces: 37% orthophosphoric acid, Er:YAG laser etching (MSP mode 120mJ, 10Hz, 1.2W), and femtosecond laser etching (0.4W, 800nm, 90fs/pulse, 1kHz). Metal brackets were bonded with Transbond XT to the conditioned surfaces and light cured for 20s. The samples were thermocycled (5000cycles, 5-55°C) and subjected to shear bond strength (SBS) testing using a universal testing machine. Failure types were analyzed under an optical stereomicroscope and SEM. The adhesive remnant index (ARI) was evaluated to assess residual adhesive on the enamel surface. The results revealed no significant differences in SBS between the Er:YAG laser (7.2 ± 3.3MPa) and acid etching groups (7.3 ± 2.7MPa; p < 0.05), whereas a significant difference was observed between the femtosecond laser etching group (3.3 ± 1.2MPa) and the other two groups (p < 0.01). ARI scores were significantly different among the three groups. The results of our study suggest that laser conditioning with an Er:YAG system results in successful etching, similar to that obtained with acid. The sole use of a femtosecond laser system may not provide an adequate bond strength at the bracket-enamel interface.

Shape memory composite (SMC) self-healing coatings for corrosion protection

Abstract A shape memory composite (SMC) coating with a self-healing ability was prepared by a facile method based on a thermoresponsive shape memory polymer (SMP) that utilized carnauba wax microparticles as the healing agent. Damages to the SMC coating was healed via heating, which triggered a two-step healing mechanism consisting of defect closure through a shape memory effect at 65 °C and then defect sealing by molten wax at 90 °C. The surface morphologies of the scratched and healed coatings as well as a wax-free SMP coating were first studied by optical stereomicroscopy and scanning electron microscopy (SEM). To assess the recovery of the coating’s barrier properties, macroscopic and localized information was obtained by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM), respectively. The healing performance was also evaluated by comparing the macroscopic morphologies of the intact, damaged and healed coatings after long-term immersion. The results from both tests were in agreement and confirmed the key roles of carnauba wax microparticles in the complete recovery of the barrier properties of initially damaged coatings upon thermally assisted self-healing.

The Mechanical Properties and Wear Resistance of HVOF Sprayed WC-Co Coatings

In this work, the Woka 5810 powders (88% tungsten carbide–12% cobalt) were used to produce coating by high velocity oxy-fuel spraying. WC–Co is widely used as a tribological coating material providing a combination of high toughness, high hardness, and good strength. The treated samples were characterized by using optical micrograph, stereo microscope and scanning electron microscopy, X-ray diffractometry, and microhardness tests. Also the wear performance of the coatings was investigated. The results indicated that the coating shows slight higher microhardness and better abrasive wear resistance than the conventional counterpart. The friction coefficient of coating was low. The scanning electron microscopy and energy dispersive spectroscopy analyses were applied to worn surfaces.

Characterization of microstructure, chemical composition, and toughness of a multipass welded joint of austenitic stainless steel AISI316L

In this study, AISI 316 types of austenitic stainless steels were welded by FCAW (flux-cored arc welding) using E316LT1-1/4 flux-cored wire under various shielding gas mixtures containing CO2 at different ratios. Effects of mixed ratio of Ar and CO2 in the in the shielding gas on the microstructure, impact toughness, and microhardness of welded materials were studied. Stereo optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), and TEM/mapping analysis techniques were used for microstructural characterizations. The impact toughness values of the weldments were decreased as a result of the formation and growth of inclusions in the microstructure due to the increases amount of CO2 in the shielding gas. The hardness values and δ-ferrite amount in the weld metal were affected by depending on of the shielding gas mixtures.