Significant Increase In Microhardness Research Articles

Evaluation of Structural Transition Joints Cu-Al-AlMg3 Used in Galvanizer Hangers

The paper deals with the evaluation of the quality of Cu-Al-AlMg3 structural transition joints (STJ) made by explosion welding proposed for the renovation of galvanizer hangers. The three-layer joint consisted of electrolytic copper with a thickness of 25 mm, 2 mm of aluminium represented by the AW1050 alloy, and 25 mm of the EN AW 575 aluminium alloy. Light microscopy analysis confirmed the wavy pattern of both interfaces of the welded joint and significant plastic deformation in close proximity to the waves. Microhardness measurement revealed a partial strain hardening of the AW5754 copper-aluminium alloy near the interface and a significant increase in microhardness in the vortex zone of waves, reaching a value of up to 863 HV 0.025. Microcracks were also observed in these places. The intermetallic phase Al2Cu was identified in the vortex zones by XRD analysis. As a continuous layer of intermetallic phase was not observed in the interface of the welded joint, it is possible to consider the used welding parameters as appropriate. A semi-quantitative EDX analysis revealed a diversity of chemical composition in the vortex zones, which does not correspond to the phase composition based on the equilibrium binary Al-Cu diagram due to non-equilibrium conditions in the formation of the welded joint interface. The bond strength of three-layer welded joint evaluated by the strength test ranged from 151 to 171 MPa, which represented approximately a two-fold increase in comparison to the ultimate tensile strength of alloy AW1050, while the failure occurred in all samples at the AW1050-AW5754 alloy interface.

Assessment of surface microhardness of enamel surface treated with Nano- HAP serum before and after bleaching

Background: Although bleaching is typically considered a safe procedure, various investigations have found minor negative effects and changes in mineral composition. The aim was to Evaluate and compare the efficacy of using Nanohydroxyapatite serum on surface microhardness of enamel surface before and after bleaching with chemically cured Boost bleaching. Material and methods: ten sound human permanent upper and lower premolar teeth were used and their roots were removed 2 mm apically to the cementoenamel junction, the crowns were sectioned mesiodistally into two halves buccal and lingual/palatal, the buccal surface was further subdivided into two halves. The samples were embeded in an acrylic resin, resulting in 30 specimens divided into 3 groups: Control group: using Boost bleaching and stored in artificial saliva for 14 days, prevention group: nanohydroxyaptite (n-HAP) serum applied 2-3 min once daily for 10 days followed by bleaching then stored for 14 days in artificial saliva and treatment group: in which bleaching used before nanohydroxyapatite serum and stored in artificial saliva for 14 days. The samples were subjected to a Vickers microhardness test measured at 4 times: base line, after nanohydroxyapatitem, after one day of bleaching and after storage in artificial saliva for 14 days in all groups. The data were analyzed statistically using repeated analysis of variance (ANOVA) test followed by Tukey's test. Results: there was a significant increase in microhardness in the prevention group (p<0.05) while there was no significant difference in microhardness readings in control and treatment groups (p> 0.05). Conclusion: n-HAP may enhance the microhardness of a bleached enamel surface when used as a preventive & treatment measure. Suggested that a higher increase in enamel microhardness occurs when n-HAP is used for 2-3 min once daily for 10 days before bleaching and maintaining this increase even after storage for 14 days in artificial saliva.

Study on shot peening strengthening 42CrMoA steel and its fretting wear properties

In order to improve the tribological properties of 42CrMoA steel, it was shot peened using different parameters. The surface morphology, residual stresses, hardness, and micromotor properties of the treated specimens were thoroughly evaluated. The results showed that it led to substantial plastic deformation, increased surface roughness, grain refinement, and introduction of residual compressive stresses. In addition, a significant increase in microhardness and depth of hardened layers on the specimen surfaces was observed. Furthermore, a positive correlation between the effect of the shot peening process and the peening duration was observed. As revealed by the investigation, the shot peening process not only advances the wear resistance of the specimens but also leads to a reduced wear volume compared to untreated specimens. Furthermore, this treatment triggers a shift in the wear mechanism from the predominant occurrence of severe adhesive wear, fatigue wear, and abrasive wear in untreated specimens to a predominant mode of abrasive wear, accompanied by a minor occurrence of adhesive wear.

Effects of Lasers and Fluoride Varnish on Microhardness and Calcium and Phosphorus Content of Demineralized Enamel.

Objectives: This study assessed the effects of blue and Er:YAG lasers, fluoride varnish, and their combination on microhardness, and calcium and phosphorus content of demineralized enamel. Materials and Methods: The primary Vickers microhardness of 28 third molars was measured and their enamel calcium and phosphorous content was quantified by energy-dispersive X-ray spectroscopy. They were then randomly assigned to five groups of 5% sodium fluoride (NaF) varnish, 445nm blue laser, Er:YAG laser, 5% NaF + 445nm blue laser, and 5% NaF + Er:YAG laser. The teeth then underwent pH-cycling to induce caries-like lesions. The surface microhardness of the teeth and the calcium and phosphorous content of demineralized enamel were measured again. Data were analyzed by one-way ANOVA and Tukey's test (alpha=0.05). Results: NaF, NaF-diode laser, and NaF-Er:YAG laser groups experienced a significant increase in microhardness of demineralized enamel close to the baseline value (P<0.05). The efficacy of NaF-blue laser and NaF-Er:YAG laser was higher than NaF . In blue and Er:YAG laser groups, the mean final microhardness was significantly lower than the baseline microhardness. The percentage of phosphorus in all groups was similar to that of sound enamel. The percentage of calcium in NaF group was significantly lower than that of sound enamel and all other groups. The calcium content in other groups was similar to that of sound enamel. Conclusion: Fluoride varnish had a synergistic effect with Er:YAG and blue lasers to increase the demineralized enamel microhardness; blue and Er:YAG lasers alone were less effective.

Structure and properties of alloys based on electroerosive brass powder LS58-3 obtained in distilled water

The purpose of this work was to study the microstructure and physico-mechanical properties of alloy blanks based on electroerosive powder brass of the LS58-3 brand obtained in distilled water. Methods. To carry out the planned research, waste of the LS58-3 alloy was selected. Distilled water was used as the working fluid. In an experimental patented installation for producing powders, waste LS58-3 alloy was dispersed in distilled water with a load mass of 300 g. The following modes were used: capacitor capacity 45–65 μF; voltage at the electrodes from 150–200 V; pulse repetition rate 50–100 Hz. The preparation of new alloy blanks was carried out using an SPS 25-10 electric spark plasma sintering installation (ThermalTechnology, USA). The microstructure of new alloy workpieces was studied using an electron-ion scanning (raster) microscope QUANTA 600 FEG (Netherlands). The study of the porosity of workpieces of new alloys was carried out using an optical inverted microscope OLYMPUS GX51 (Japan). The study of microhardness of workpieces of new alloys was carried out using an automated microhardness tester AFFRI DM-8 (Vickers). Results. Analysis of the microstructure showed that the sample has a fine-grained structure and a homogeneous surface. According to the obtained porosity analysis results, the sample has less than 1% pores, which is achieved thanks to the technology of spark plasma sintering of the powder. Analysis of the microhardness of the sample showed a significant increase in microhardness, which is explained by the presence of high-hard particles formed during quenching of metal vapor in the working fluid during dispersion. Conclusion. The use of spark plasma sintering technology for electroerosive brass makes it possible to obtain blanks of new alloys with a practically non-porous structure, which leads to an increase in the hardness of the resulting blanks. The results of the conducted studies make it possible to recommend the use of the resulting powder as a starting material for the production of alloy blanks and to expand the scope of their practical application.

Hydrated Calcium Silicate in Resin Composites for Prevention of Secondary Caries

Introduction and aimsThe gaps at the margins of restorative composite resin can increase as the carious process occurs underneath the materials, causing further demineralization along the tooth cavity wall. The aim of this study was to evaluate the effects of restorative resin composite containing hydrated calcium silicate (hCS) filler on enamel protection against demineralization by simulating microleakage between the test material and teeth in a cariogenic environment. MethodsThe experimental resin composites were composed of 70 wt.% filler, which was mixed with a glass filler and hCS in a weight ratio of 70.0% glass (hCS 0), 17.5% hCS + 52.5% glass (hCS 17.5), 35.0% hCS + 35.0% glass (hCS 35.0), and 52.5% hCS + 17.5% glass (hCS 52.5). A light-cured experimental resin composite disk was positioned over a polished bovine enamel disk, separated by a 30-µm gap, and immersed in artificial saliva with pH 4.0 for 15, 30, and 60 days. After the immersion period, the enamel disk was separated from the resin composite disk and evaluated using a microhardness tester, atomic force microscopy, and polarized light microscopy. The opposing sides of the enamel and resin composite disks were observed using scanning electron microscopy/energy dispersive X-ray spectrometry. ResultsThe enamel surface showed a significant increase in microhardness, decreased roughness, and remineralization layer as the proportion of hCS increased (P < .05). In the scanning electron microscopy image, the enamel surface with hCS 35.0 and 52.5 after all experimental immersion periods, showed a pattern similar to that of a sound tooth. ConclusionsThe results demonstrated that increasing the hCS filler level of restorative resin composites significantly decreased enamel demineralization. Clinical relevanceHydrated calcium silicate laced restorative resin composites may be a promising dental biomaterial for protecting teeth against demineralization and preventing secondary caries around restorations.

Effect of Interlayer Machining Interventions on the Geometric and Mechanical Properties of Wire Arc Directed Energy Deposition Parts

Abstract Wire Arc Directed Energy Deposition (Wire Arc DED) has become a popular metal additive manufacturing technique for its capability to print large metal parts at a high deposition rate while being economically efficient. However, the Wire Arc DED process exhibits geometric inaccuracies resulting from the variability in the bead geometry and demonstrates heterogeneity in microstructure and mechanical properties. This study investigates the use of tailored periodic machining interventions during the Wire Arc DED process to address these shortcomings. The as-built geometry and surface finish, microstructure, and microhardness of multi-layer wall structures produced with and without machining interventions carried out at different temperatures are compared. The machining interventions are found to reduce the uncertainty in bead geometry evolution and significantly improve the surface roughness of the as-built walls, thus reducing the need for further post-processing of the wall surfaces. Although the microstructure constituents of the as-built wall structures with and without machining interventions are similar, the machining interventions result in finer grains in the interior of the part. Machining interventions are found to yield a statistically significant increase in microhardness, indicating increased strength compared to Wire Arc DED alone. In addition, the spread of the microhardness distribution is reduced in Hybrid-Wire Arc DED, indicating improved homogeneity of the grain size distribution compared to Wire Arc DED alone. The study shows that the proposed hybrid manufacturing technique has the potential to control and improve the geometric and mechanical properties of additively manufactured metal components.

Study on preparation and properties of silver alloy for Mongolian medicine acupuncture

The Mongolian medical silver needles often encounter issues of bending, fracturing, and blunting in clinical applications. Similarly, Mongolian warm needles can cause burns on patients due to inaccurate temperature control. In this study, we developed an Ag85Cu15 alloy specifically for acupuncture needles based on material preparation. By incorporating appropriate amounts of Mn and Ti elements, we were able to enhance the mechanical properties and biocompatibility of the acupuncture needles. Compared to commercially available silver needles, this alloy exhibited a significant increase in microhardness up to 210.2 Hv0.2 and an improved tensile strength of 880.2 MPa. Furthermore, we designed a thermoelectric effect-based temperature measurement model for precise control of the warm needle's temperature, enhancing the therapeutic effectiveness of the treatment.

Evaluation of the Remineralization Capacity of Water-based Silver Fluoride

Silver diamine fluoride, which can arrest dental caries, is alkaline and may cause mild soft tissue irritation. Water-based silver fluoride has a neutral pH, which is closer to the physiological range, and is biocompatible for use in the oral environment. This study aimed to evaluate the effect of water-based silver fluoride on remineralizing early enamel lesions by comparing it with other fluoride agents through microhardness and quantitative light-induced fluorescence measurements. An in vitro study with intact bovine incisors was performed. Artificial enamel lesions were induced and subjected to microhardness and quantitative light-induced fluorescence testing. Specimens were randomly divided into 4 groups for treatment. The specimens in group I were treated with water-based silver fluoride and potassium iodide, group II with silver diamine fluoride and potassium iodide, group III with sodium fluoride varnish, and group IV with distilled water. After 8 days of pH cycling, the specimens were subjected to microhardness and quantitative light-induced fluorescence testing. Water-based silver fluoride and silver diamine fluoride showed the greatest increases in microhardness and quantitative light-induced fluorescence, with no significant differences between the two. Sodium fluoride varnish also exhibited a significant increase in microhardness and quantitative light-induced fluorescence, but the differences were smaller than those for water-based silver fluoride and silver diamine fluoride. Water-based silver fluoride is considered useful in a clinical setting for remineralizing enamel lesions, with the advantages of no risk of tissue burn and improved taste and smell.

Efficacy of Three Remineralizing Agents on Erosion of Root Dentin by Cola Drink: An In Vitro Study

Abstract Objective The aim of the study was to investigate the effects of silver diamine fluoride (38% SDF), sodium fluoride (NaF) varnish, and casein phosphopeptide-amorphous calcium phosphate fluoride (CPP-ACPF) on cola-eroded root dentin microhardness and mineral alteration in vitro. Materials and Methods Forty human root dentin slabs were exposed to alternating 10 cycles of cola drink and artificial saliva, repeated 3 times at 6-hour intervals. Specimens were randomly assigned to four groups: control (deionized water), 38% SDF, NaF varnish, and CPP-ACPF. All specimens underwent the second erosion process. Microhardness was measured at baseline (KHN0), pretreatment (KHN1), and posttreatment (KHN2). The mean difference of microhardness (ΔKHN2-1) was analyzed using one-way analysis of variance (ANOVA) and Tukey's post hoc tests (α = 0.05). The chemical composition and surface morphology were assessed using energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). Results All experimental groups exhibited dentinal tubule occlusion. Both 38% SDF and NaF varnish demonstrated a statistically significant increase in microhardness compared to CPP-ACPF. However, CPP-ACPF was comparable to the control group. EDS analysis showed an increase in weight percentage of fluorine in all groups. Furthermore, silver and chlorine were detected in the 38% SDF group. Conclusion All treatments enhanced eroded root dentin microhardness, with 38% SDF and NaF varnish demonstrating superior acid resistance and preventing morphological changes induced by cola re-immersion.

Влияние ионной имплантации на свойства чугуна, используемого в конструкциях горнодобывающих машин и аппаратов

Introduction. Cast iron is a widely used material in mechanical engineering, mining and other industries. Modification of the surface properties of cast iron by ion implantation is of great interest. Research methods and materials. Samples of cast iron before and after implantation with C+, B+, N+ ions with dose D = 1017 ions/cm2 and energy of 40 keVwere taken for research. All samples were tested for wear resistance; microhardness was also measured and X-ray analysis was performed. Research results. It is shown that cast iron samples after ion implantation had higher wear resistance and microhardness in comparison with the initial state. The increase in hardness of all samples is apparently associated with the presence of a large number of specific radiation defects and the formation of dispersed phases (nitrides, borides, carbides). Discussion of the research results. The study of micro-hardness was carried out to determine the depth of the hardened layer after ion implantation with C+ , B+ , and N+ ions. The highest micro-hardness was detected at the surface of the sample after irradiation with N + ions. The lowest micro-hardness was obtained by B+ ions. X-ray analysis of cast iron samples after implantation by C+ , B+ , and N+ ions with dose D = 1017 ions/cm2 was the fine structure are observed. Conclusion. Ion implantation of cast iron with C+, B+, N+ ions has shown that irradiation leads to: Increased wear resistance of the material; A significant increase in micro-hardness; Changes in the fine structure of the implanted cast iron (mosaic block size and average dislocation density) and the formation of carbides, borides, and nitrides. Resume. The results of the research show that ion implantation of cast iron can significantly increase the wear resistance of various units of machines (parts) and other mining equipment, which ultimately increases their service life. Suggestions for practical application and direction of future research. The shown results allow us to propose the method of ion implantation as a hardening treatment of parts made of cast iron used, in particular, in the mining industry. In order to develop ion implantation as one of the hardening technologies, it would be advisable to continue studying various physical and chemical properties (for example, corrosion resistance) after exposure to ion implantation.

Structure and wear characteristics of cast iron after laser surface modification

The paper presents the results of studies of macro- and microstructure of alloyed chromium-vanadium cast iron after laser treatment (LT) in air using a continuous laser source with a variation in its power from 60 to 100 W and scanning speed of the laser beam varying from 5 to 17 mm/s. Metallography and durometry methods were used to determine composition and structure of the laser exposure zones (LEZ). It is shown that LT with a slight melting of the surface leads to a significant increase in microhardness in LEZ. In this case, martensite is the main structure in the near-surface layer of LEZ in the melting zone, and ledeburite structure prevails in the quenching zone. For the studied LT modes, LEZ depth is 220 – 310 μm. At the same time, microhardness is more than 2.5 – 4.2 times higher than microhardness of the base metal and reaches 820 HV0.1, that is a significant factor in increasing the wear resistance of the material. On the contrary, no significant structural changes were found in the case of LT without melting the surface. In order to identify the role of LT in wear of cast iron, sliding friction tests were carried out according to the “disk – finger” scheme at a pressure in the contact zone of 12.5 MPa and indenter rotation speed of 580 rpm. According to the test data, a significant decrease in linear wear and the wear intensity after the surface melting was found. The wear intensity is reduced by more than 100 times, and linear wear – by more than 50 times. The characteristics of LEZ surface cause a decrease in the friction coefficient by 30 % relative to the untreated surface.

Study of the influence of alphoning on the structure and properties of the alloy BT6

The paper considers the influence of two technologies of alfing (oxidation) on the structure and properties of the deformable titanium alloy BT6, which is used, in particular, in the aviation and space industries. The application of oxide coating by methods of chemical-thermal treatment (CTO) allows to compensate for the main drawback of the alloy – low wear resistance of the surface. The initial set of properties increases. The objects of research are titanium alloy BT6 and its oxide coatings. Two samples of the part with oxide coatings obtained by different technologies were compared. The first technology is alfing in fine-grained graphite, the second is alfafing in a vacuum. The aim of the work is to find out the influence of two technologies of alfing on the structure and properties of the BT6 alloy. Alfalfing was carried out: 1) in fine-grained graphite at a temperature of 800 ± 10 ° C with exposure for 8 hours; 2) in an electric furnace at a temperature of 760–780 ° C in a vacuum of 10-1 – 10-3 mm Hg. art. for 1.5–2 hours. A study of the microstructure (light and electron microscopy) was performed. We used a microscope type Carl Zeiss Axio Observer A1m using a digital camera, adapter devices for converting an optical signal, a computer. Statistical processing was carried out according to the SIAMS700 program. Electron microscopic studies were performed using a scanning electron microscope (SEM) EVO 50 with an energy-dispersive microanalyzer INCA Energ 350. X-ray phase analysis was carried out using an X-ray diffractometer Shimadzu XRD7000, Japan (CuKa radiation, monochromator), in the following mode: range from 5 to 70 ° on a scale of 2θ, increments of 0.03°, scanning speed of 1.5 ° / min. Powders obtained from two types of coatings were investigated. The microhardness of the samples was measured on the DM8 microhardometer according to GOST 9450–76. The wear resistance of the alloy was assessed at a special laboratory installation. The phase composition and structure of the BT6 alloy after alphoning were clarified. In the diffusion layer, the following were detected: after alphonation in graphite – TiO2 phases; Ti3O; TiN. After carbonation in vacuum – TiO2; Ti6O11. In the alphad layer, after processing in graphite, grains of α – solid solution, intermetallics Ti–Al-V, Ti–V and Ti–Al were detected; the alphied layer contains more titanium after treatment in vacuum, and areas with 100% (at.) titanium have also been identified; the region of solid solution (α) and the intermetallics Ti–Al-V, Ti–V and Ti–Al are visible. The thickness of the oxidized layer is on average 103.6 μm (graphite), and in a vacuum - 66.8 μm. The average grain size in the layer is 17.2 μm (graphite); 6.0 μm (vacuum). It has been established that chemical-thermal treatment (alfing) contributes to a significant increase in microhardness in the diffusion layer. The hardness of HV580 (vacuum) and HV724 (graphite) was obtained on the surface. Alfalfing in graphite and in vacuum ensures the wear resistance of the product, but the best result is obtained after alfafing in a vacuum. Both technologies improve the properties, but it is more profitable to carry out alfing in a vacuum, since in this case the process is carried out within 2 hours instead of 8 hours in graphite. Alfing (oxidation) provides wear resistance of the BT6 alloy, which contributes to the reliable operation of the product during operation.

Low-temperature micromechanical properties of polyolephin/graphene oxide nanocomposites with low weight percent filler

The effect of small impurities of reduced graphene oxide (rGO) on microhardness of polyethylene (PЕ) and polypropylene (PP) matrices and the reaction of these nanocomposites and initial polymers on the influence of localized load in the temperature range of 77–295 K were studied. When rGO was introduced, PE practically did not change its properties, whereas the introduction of 0.3 wt% rGO into the PP matrix was accompanied by a significant increase in microhardness, especially in the room temperature range (by approximately 70%). A transition to reversible deformation was detected when the indenter impressions applied in liquid and gaseous nitrogen at temperatures below the threshold (T &amp;lt; 174.5 K for PP and T &amp;lt; 226.5 K for nanocomposite PP + 0.3 wt% rGO) were not fixed on the surface of the samples after their heating in the measuring device to room temperature.

Influence of Natural Aging on Microstructure and Mechanical Properties of Gravity Casting Al-Cu-Mg Alloy

For the Al-5.0Cu-0.8Mg alloy fabricated by gravity casting, the 12h natural aging was added between the solution and artificial aging to study its influence on the microstructure and mechanical properties. The transitional phases form during the natural aging following the solution, leading to a significant increase in microhardness. Meanwhile, this microstructure variation accelerates the formation and growth of stable strengthening phases in the same artificial aging. Unfortunately, the 12 h natural aging added in this work excessively coarsens the precipitation, which results in the mechanical properties reduction including ultimate stress from 332 MPa to 302 MPa, especially the elongation from 8.1% to 3.7%. The results indicate that exploring the favorable match of natural and artificial aging is significant to further finely control the precipitation characteristic, which contributes to better mechanical properties of the Al-Cu-Mg alloy.

Remineralization effects of Er,Cr:YSGG and/or bioactive glass on human enamel after radiotherapy-an in vitro study.

The aim was to evaluate the effects of Er,Cr:YSGG and/or bioactive glass 45S5 (BG) on the chemical and physical properties of enamel after radiotherapy. Third molar crowns were cut in half (buccal-lingually), and the mid part of the labial/oral surface was subjected to different protocols. All samples were treated with standard 70Gy. After radiotherapy, enamel was treated with either Er,Cr:YSGG (2780nm; pulse 60μs) and BG or only BG, and control samples were kept in deionized water. Vickers microhardness, scanning electron microscopy (SEM), and characteristic X-ray spectroscopy (EDS) were performed before, after radiotherapy, and after treatment. Analysis of variance (ANOVA) was used. A significant drop in enamel microhardness was observed after radiotherapy (p < 0.001). After Er,Cr:YSGG and BG or BG alone, there was a significant increase in microhardness (p < 0.001), which was on average significantly higher compared to the initial measurements for Er,Cr:YSGG with BG (p < 0.001), but not observed in BG alone (p = 0.331). After radiotherapy, SEM showed increased surface roughness with eroded prisms. Er,Cr:YSGG and BG or BG alone both showed disorderly packed glass particles on the enamel surface. Radiotherapy noticeably reduced the concentrations of calcium and phosphorus. Er,Cr:YSGG and BG treatment increased the concentrations of calcium, sodium, phosphorus, and silicate. BG treatment alone increased the concetration of calcium and phosphorus. Directly induced radiotherapy led to potential damage of enamel, but afterwards treatment with Er,Cr:YSGG laser and BG resulted in a higher increase of enamel microhardness compared to BG alone, reflecting in a possible better remineralization effect.

Influence of Ionizing Radiation on Fluoride-Releasing Dental Restorative Materials.

This study aimed to investigate the effects of radiotherapy on the mechanical, chemical, and surface properties of two recently introduced restorative dental materials (a glass hybrid and an alkasite), while two conventional restorative materials served as references. Material specimens of the experimental groups (irradiated) were compared to the specimens of the control groups that underwent the same preparation procedure but without irradiation. The experimental groups of restorative material specimens were irradiated with a total of 70 Gy over 35 days (2 Gy/day × 35 days), while the control groups received no treatment. The following properties were evaluated: surface microhardness (Vickers), surface roughness, color change, flexural strength, flexural modulus, material reliability, and infrared spectra. For the experimental groups, measurements were performed 24 h after specimen preparation, i.e., before radiotherapy and after the completion of the irradiation protocol. For the control groups, measurements were performed after the corresponding periods of no treatment. A statistically significant increase in microhardness (p = 0.001-0.004) and surface roughness (p = 0.013) was observed as a result of material aging/maturation in both the control and experimental groups. However, the only statistically significant difference between the control and experimental groups was observed in the discoloration of the conventional reference material (p < 0.001). In conclusion, no statistically significant negative effects of a therapeutic dose of radiotherapy on any of the tested properties of the alkasite and glass hybrid materials were observed, whereas only a minor negative effect of radiotherapy in terms of discoloration was found for a conventional resin composite that was used as a reference material.

Characterization of Boride Coatings on AISI 8620 Steels without and with Hydrogen Permeation

The present work studied the characterization of boriding coatings without and with exposed hydrogen permeation on AISI 8620 through microstructure and mechanical behavior. A dehydrated paste pack process was carried out for the formation of boride coatings on AISI 8620 at 1173, 1223, and 1273 K for 6 h of exposure time for each temperature. After boronizing, hydrogen was introduced into the borided steels by in situ cathodic charging using an H2SO4 acid electrolyte. Specimens borided without and with hydrogen were characterized by scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The experimental techniques of the Vickers microhardness and three-point bending were used. As a result, the hydrogen diffusion on steel AISI 8620 borided shows a significant increase in microhardness. Furthermore, three-point bend tests showed an increased strength on 8620 steel borided. However, the ductility and strength value on 8620 steel borided surfaces presented a drastic reduction due to hydrogen permeation. The results revealed that the borided coatings provided strength and reduced the hydrogen embrittlement index on AISI 8620 borided.

Development of cryogenic assisted machining strategy to reduce the burr formation during micro-milling of ductile material

Micro-milling is an inevitable machining process for the fabrication of products with complex shapes and high dimensional accuracy. However, this process usually needs post-processing operations to remove the burrs formed from the ductile materials. This research work focuses on the development of a micro-milling strategy to suppress the formation of burrs during machining and hence avoid post-processing operations, consequently reducing the cost of the products. During micro-milling, a LN2 jet was positioned ahead of the tool movement loci resulting in a change of microstructure at the top layer of the workpiece surface, enhancing its mechanical properties with the subsequent reduction of excessive plastic flow during the shearing process. Micro-hardness tests were performed below the top layer to conform the speculation and evaluate the effect of cryogenic treatment and a significant increase in micro-hardness was found. The experimental results reveal a significant decrease in the burrs formation due to the cryogenic treatment with an enhanced machining quality in terms of cutting forces, chip morphology and surface roughness.

RELATIONSHIP BETWEEN MICROSTRUCTURE, MECHANICAL PROPERTIES AND WEAR BEHAVIOR OF FRICTION STIR PROCESSED AZ31B ALLOY UNDER VARIOUS MEDIUM

Plates of AZ31B were friction stir processed in three different environments, such as liquid nitrogen, water and air with a rotational speed of 1200[Formula: see text]rpm and feed rate of 90[Formula: see text]mm/min. Microstructural studies were carried out using optical and electron microscopes, phase identification was performed using X-ray diffraction, and all specimens were tested for hardness, tensile and wear. An examination of wear debris morphology was carried out. Under cryogenic, water and air mediums, grain refinement was achieved at 1.89, 2.23 and 18.23[Formula: see text]μm, respectively. The specimen using cryogenic medium displayed greater tensile strength and elongation than the water medium. Dissolution of consistently refined grains and secondary Mg17 Al12 particles was observed after FSP underwater and cryogenic medium, resulting in a significant increase in microhardness. This surface hardening produced a significant benefit for the friction and wear behavior of the magnesium as measured by pin-on-disc configuration using a universal tribometer. With a cryogenic cooling medium, the friction coefficient is reduced by approximately 23% and the wear rate is reduced by 8% in comparison to AFSP.