Increase In Surface Microhardness Research Articles

Assessment of the Remineralizing Efficacy of Grape Seed Extract vs Sodium Fluoride on Surface and Subsurface Enamel Lesions: An In Vitro Study

ABSTRACT Background: Dental caries is a prevalent oral health issue, primarily resulting from demineralization of the enamel. Remineralizing agents such as sodium fluoride (NaF) have been widely used to counteract this process. Recent studies suggest that natural extracts, such as grape seed extract (GSE), may also have significant remineralizing properties. This study aims to compare the efficacy of GSE and NaF on surface and subsurface enamel lesions in an in vitro setting. Materials and Methods: In this in vitro study, 60 extracted human premolars were randomly divided into three groups of 20 each: control (no treatment), NaF treatment, and GSE treatment. Artificial enamel lesions were created on the buccal surfaces of all samples. The NaF group was treated with a 5% sodium fluoride solution, while the GSE group received a 6.5% grape seed extract solution. Treatments were applied daily for 10 days. Surface microhardness (SMH) and cross-sectional microhardness (CSMH) were measured before and after treatment to assess remineralization. Results: The NaF group showed a significant increase in SMH (45%) and CSMH (35%) compared to the control group. The GSE group demonstrated a similar trend with a 40% increase in SMH and a 30% increase in CSMH. Both treatments were significantly more effective than the control (P < 0.05), with no significant difference between the NaF and GSE groups (P > 0.05). Conclusion: Grape seed extract exhibits comparable remineralizing efficacy to sodium fluoride on both surface and subsurface enamel lesions in vitro. These findings suggest that GSE could be a viable natural alternative to fluoride for the prevention and treatment of dental caries.

A comparative evaluation of human enamel remineralization ability of biomimetic nacre against casein phosphopeptide-amorphous calcium phosphate: An in vitro study.

This study aimed to assess and compare the efficacy of Nacre and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on the remineralization of enamel using surface microhardness analysis, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. Twenty human maxillary premolars extracted for orthodontic reasons were collected. Under cool water spray, the crowns were sectioned mesiodistally into buccal and palatal halves using a diamond disc. The samples were subsequently mounted in self-cure acrylic resin. The samples were then subjected to Vickers hardness testing and SEM-EDX for baseline. To simulate carious lesions, all of the samples were acid-etched with 37% phosphoric acid for 30 s in a specific area on the enamel samples and subjected to surface microhardness testing and SEM-EDX. The enamel samples were randomly assigned to Group 1: Nacre water-soluble matrix (WSM), Group 2: Nacre varnish, and Group 3: CPP-ACP for remineralization. After 21 days, remineralization assessment of the test samples was done using SMH analysis and SEM-EDX analysis. Data obtained were statistically analyzed using the one-way analysis of variance to reveal the significant differences between the groups. Tukey's test was used for post hoc comparisons. All three groups showed a significant increase in surface microhardness. All three groups showed a significant calcium and phosphorous ratio increase after remineralization. Among the three groups, the highest Ca:P ratio was seen in the Nacre WSM group (0.58) followed by the Nacre Varnish (0.57) and CPP-ACP group (0.57). SEM images of the Nacre surface revealed the presence of extensive interlocking. A layer of packed hydroxyapatite particles was formed on the surface of the nacre through surface reactions. All the groups in the present study showed some extent of remineralizing ability irrespective of the different materials and mechanisms of action. Nacre WSM showed a remarkable hardness spike close to natural enamel after demineralization.

The effect of nano-hydroxyapatite and casein phosphopeptide-amorphous calcium phosphate with and without laser irradiation on the microhardness and surface morphology of demineralized primary enamel: An in vitro experimental study

Background: Various topical gels, varnishes, and fluoride gels are being used by dentists for the treatment of White spot lesions (WSLs). The remineralizing effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), nano-hydroxyapatite (nHAp), and lasers has been proven earlier. This study was designed to evaluate the remineralizing effect of nHAp and CPP-ACP with and without erbium-doped yttrium aluminum garnet (Er: YAG) laser irradiation on demineralized primary enamel. The aim of this study was to evaluate the effect of CPP-ACP and nHAp with and without Er:YAG laser irradiation on the microhardness and surface morphology of demineralized primary enamel. Materials and Methods: The present study is an experimental in vitro study. Fifty extracted primary incisors were selected for the study. Following cleaning and sectioning, teeth were embedded in acrylic. The tooth models were divided into four groups randomly – Group 1 (CPP-ACP), Group 2 (nHAp), Group 3 (CPP-ACP + laser), and Group 4 (nHAp + laser). The baseline, postdemineralization, and postremineralization Vickers hardness testing was performed. One sample from each group was analyzed by scanning electron microscopy. Descriptive statistics such as frequencies and percentages for categorical data, mean and standard deviation for numerical data were depicted. The normality of numerical data was checked using the Shapiro–Wilk test. The level of significance was kept at 5%. Intergroup comparison (>2 groups) was done using one-way analysis of variance followed by pair-wise comparison using the post hoc test. Results: There was a statistically significant increase in surface microhardness in each group after remineralization. The highest increase in microhardness value was seen in Group 4 (nHAp + laser) followed by Group 3 (CPP-ACP + laser) and the least in Group 1 (CPP-ACP). Similar observations were made in scanning electron microscopic images. This indicated that nHAp has a comparable, if not better ability for remineralization than CPP-ACP. The remineralizing capacity of both the remineralizing agents was seen to be improved in this study when simultaneous laser application was employed. Conclusion: Currently, the evidence supporting the efficacy of nHAp dentifrices and laser in primary teeth is limited. Additional long-term in vivo studies employing standardized protocols and large sample sizes are necessary to draw definitive findings about the effect of remineralizing agents and lasers on primary enamel.

Surface integrity and rolling contact fatigue behavior of 18CrNiMo7-6 steel subjected to ultrasonic surface rolling process

In this study, the effect of ultrasonic surface rolling process (USRP) on the surface integrity and rolling contact fatigue (RCF) behavior of 18CrNiMo7-6 steel have been conducted. The different static loads and ultrasonic amplitudes on surface morphology, surface roughness, microstructure, microhardness, and residual stress were examined. Results revealed that USRP treatment resulted in a remarkably smooth surface with the surface roughness value Ra of 0.035 μm. Moreover, USRP treatment induced the formation of nanocrystalline and ultrafine crystalline structures on the surface layer. Additionally, the sample surface was subjected to a significant layer of residual compressive stress, reaching a maximum value of approximately −1243 MPa and extending to a depth of around 1500 μm. The surface microhardness had been increased to 808 HV0.2. The comprehensive integration of grain refinement, the increase of surface microhardness, and the induction of residual compressive stress led to an improvement in RCF life.

Surface integrity and fatigue behavior of AISI 4340 steel after hybrid laser-ultrasonic assisted ball burnishing process

The final surface modification processes enhance the fatigue strength, wear resistance, and corrosion resistance of the workpiece by improving the surface quality, enhancing the microhardness, generating compressive residual stresses on the surface, and creating favorable changes in the microstructure. In this regard, using processes with different mechanisms is regarded as an optimal method to increase the efficiency of the final surface modification processes. This research seeks to experimentally investigate the hybrid laser-ultrasonic assisted ball burnishing (LUAB) process and its effect on the surface integrity and fatigue strength of 4340 alloy steel. The effect of the process on the sample’s microstructure was evaluated by the images obtained from the optical microscope and SEM. Further, the parameters of mean surface roughness and microhardness, as well as the results of the uniaxial tensile test and fatigue test of the workpiece were evaluated. In the case of using appropriate parameters in the process, the results indicated a 93.38% reduction in mean surface roughness and an increase of surface microhardness by 3.4 times compared to the initial sample. Additionally, the investigation of microstructure revealed the accessibility of homogeneous and refinement martensitic structures without surface melting. The results of uniaxial tensile and fatigue tests indicated a 6.29% increase in tensile strength and a 20.71% increase in the endurance limit of the treated sample (LUAB) compared to the initial sample. Finally, the results also showed a change in the fracture mode in the uniaxial tensile test and a reduction in the final fracture area in the fatigue test.

Mechanically tailored surface of titanium based alloy (Ti6Al4V) by laser surface treatment

In this study, laser surface treatment (LST) of Ti6Al4V carried out by melting within a narrow regime of optimum process parameters for the formation of a surface with improved wear and tribo-corrosion resistance is presented. The effect of applied power and shrouding gas on the microstructure, phase, surface hardness, residual stress, dry wear (against tungsten carbide, WC) and tribocorrosion resistance (against ZrO2 in Hank's solution) is established. LST in argon atmosphere leads to the formation of a composite structure consisting of acicular α’ martensite and α. LST in nitrogen atmosphere causes the formation of titanium nitride (TiN and Ti2N) dispersed in α matrix. Due to LST, there is an increase in surface microhardness both under argon (435–630 VHN) and nitrogen atmosphere (839–1327 VHN) when compared to untreated Ti6Al4V (278 VHN). There is a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17–5.81 × 10−3 mm3/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91–4.94 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.93 × 10−3 mm3/Nm). The mechanism of wear is established. On the other hand, the tribo-corrosion rate is found to decrease for laser surface melting (3.5–4.8 × 10−3 mm3/Nm) and nitriding (1.3–3.2 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.7 × 10−3 mm3/Nm). Bioactivity in terms of calcium phosphate deposition followed by dipping in Hank's solution was found to increase due to both melting and nitriding, though nitriding offered a marginally higher bioactivity than only melting.

In vitro remineralization of adjacent interproximal enamel carious lesions in primary molars using a bioactive bulk-fill composite

BackgroundSurface remineralization is recommended for the management of active non-cavitated interproximal carious lesions in primary teeth. According to the American Academy of Pediatric Dentistry, a recently recognized category of materials called bioactive restorative materials can be used for remineralization. This study aimed to evaluate the release of fluoride (F), calcium (Ca) and phosphate (P) ions from Predicta® Bioactive Bulk-fill composite compared with EQUIA Forte® and Filtek™ Z350 and to determine the remineralization effect of these 3 restorative materials on adjacent initial interproximal enamel carious lesions.MethodsThe release of F, Ca and P ions from 3 groups ((n = 10/group) (Group 1- Predicta®, Group 2- EQUIA Forte® and Group 3- Filtek™ Z350)) was determined at 1st, 4th, 7th and 14th days. After creating artificial carious lesions, human enamel samples were randomly assigned into 3 groups (n = 13/group) which were placed in contact with occluso-proximal restorative materials and exposed to a 14-day pH cycling period. Surface microhardness was determined using a Knoop microhardness assay at baseline, after artificial carious lesions formation and after pH cycling. The difference in the percentage of surface microhardness recovery (%SMHR) among groups was compared. Mineral deposition was analyzed with energy-dispersive x-ray spectroscopy (EDS) and the enamel surface morphology was evaluated with scanning electron microscopy (SEM). Kruskal-Wallis’s test with Dunn’s post hoc test and one-way ANOVA with Tukey’s post hoc test were used for data analysis.ResultsEQUIA Forte® released the highest cumulative amount of F and P ions, followed by Predicta® and Filtek™ Z350. Predicta® released higher amount of Ca ions than EQUIA Forte® and Filtek™ Z350. Predicta® demonstrated the highest %SMHR, followed by EQUIA Forte® and Filtek™ Z350. There was a significant difference in the %SMHR between Predicta® and Filtek™ Z350 (p < 0.05). However, EQUIA Forte® demonstrated the highest fluoride content, followed by Predicta® and Filtek™ Z350. The SEM images of EQUIA Forte® and Predicta® revealed the greater mineral deposition.ConclusionPredicta® demonstrated a marked increase in surface microhardness and fluoride content of adjacent initial interproximal enamel carious lesions in primary molars compared with Filtek™ Z350. Predicta® is an alternative restorative material to remineralize adjacent initial interproximal enamel carious lesions in primary molars, especially in high-risk caries patients.

Surface hardening of structural steels ShKh15 and 40KhN2MA by pulsed plasma flows

The article is devoted to an innovative method of surface hardening of steels 40KhN2МА and ShKh15 by pulsed plasma flows. The treatment was carried out in a wide range of absorbed energy density from 20 to 100 J/cm2, with a plasma exposure duration of 1 ms. The results of a study of the structure, phase composition and morphology of the modified surface layer, as well as such characteristics as thickness, microhardness, surface roughness, and level of residual stresses are presented. The modified layer of steel contains several structural components with distinctive characteristics. The maximum thickness of the modified hardened layer was 125 µm. The conducted research made it possible to establish optimal treatment modes, characterized by an increase in surface microhardness by 3—4 times, a decrease in roughness by up to 35 % and the presence of compressive residual stresses, which opens up prospects for the development of highly effective technology for strengthening critical products.

Remineralization effect of Er;Cr:YSGG laser irradiation with or without acidulated phosphate fluoride application on deciduous teeth enamel surface with induced white spot lesion. An in vitro study.

This study aims to assess the efficacy of Er; Cr: YSGG laser operating under sub-ablative settings for the remineralization of artificially induced white spot lesions on the enamel of primary teeth, both as a standalone treatment and in conjunction with 1.23% acidulated phosphate fluoride (APF) gel. Eighty primary posterior teeth were used to induce white spot lesions and were randomly divided into eight groups. The groups consisted of a negative control group (G1), a 0.75W laser irradiation group (G2), a 0.5W laser irradiation group (G3), a 0.25W laser irradiation group (G4), a positive control group with APF gel application (G5), and three groups that received laser irradiation of 0.75W, 0.5W, and 0.25W followed by APF gel application (G6, G7, and G8) respectively. Surface microhardness, SEM, and X-RD were used to evaluate the remineralization effect. There was a notable enhancement in surface microhardness post-treatment with the laser, APF gel, and their combination compared to the negative control group. The most pronounced increase in surface microhardness was observed in the combination treatment groups (G6, G7, and G8). SEM analysis showed increased surface roughness in groups treated with 0.75W and 0.5W laser power. X-RD assessments indicated an augmentation in crystal intensity within groups G6 and G8. The combined application of Er; Cr: YSGG laser under sub-ablative parameters and APF gel demonstrated a superior potential for remineralizing primary teeth enamel affected by white spot lesions. Key words:Er;Cr:YSGG laser. Sub-ablative irradiation. Remineralization. White spot lesion. APF gel. SEM. X-RD.

Formation of expanded phases in ferritic stainless steel nitrided at low temperatures

Nitriding treatments at low temperatures (<450 °C) are receiving increasing interest for the surface engineering of stainless steels due to the possibility of producing supersaturated solid solutions of nitrogen in the iron-based lattices, known as “expanded” phases. In this study this treatment was applied to AISI 430 ferritic stainless steel with the aim of clarifying the characteristics of the modified surface layer, and in particular the microstructure and phase composition. The formation of expanded ferrite caused high compressive stresses, so that local plastic deformation phenomena occurred, observable as microstructural changes (slip lines, grain swelling) both at the surface and in the section of the samples. Moreover, the formation of a nitrogen-containing hexagonal close-packed phase, dissimilar to ε-nitride, was reported for the first time for low-temperature nitrided ferritic stainless steels. It is suggested that this phase might be a N-rich expanded ε′-martensite, which formed from expanded ferrite due to a bcc-to-hcp displacive transformation and it remained in the microstructure owing to the residual compressive stresses and nitrogen and chromium solubilization. The presence of this phase contributed to the increase of surface microhardness together with expanded ferrite. The assessment of the corrosion behaviour in 3.5 wt% NaCl aerated solution by means of electrochemical impedance spectroscopy analysis and potentiodynamic measurements showed that, when the modified surface layer consisted only of expanded ferrite, impedance values and corrosion potential had a marked increase and corrosion current density decreased, as compared to those of the untreated steel, suggesting an enhancement of the resistance to general corrosion. On the contrary, when a heterogeneous modified layer formed (expanded ferrite and N-rich expanded ε′-martensite), a worsening of corrosion resistance was observed.

Electron-beam nitriding of carbon steel alloy in the forevacuum pressure range

We have explored the ion nitriding of AISI 5135 carbon steel alloy. Nitriding was performed in the plasma formed by an electron beam at the forevacuum pressure of 5 Pa. The beam was generated using a forevacuum-pressure plasma-cathode electron source. We report the results of SEM and X-ray diffraction pattern analysis of the surface of nitrided samples, as well as results of measured micro hardness, surface wear rate, coefficient of friction, roughness, and nitrogen penetration depth. We find that the sample temperature during nitriding affects the surface morphology and phase composition of surface layers. A threefold increase in surface micro hardness was achieved. The surface micro hardness increases with increasing nitriding duration. Samples nitrided at temperatures up to 500°С for a time of no less than 2 h show the greatest abrasive wear resistance. The nitrogen penetration depth is greater than 200 μm for all experimental conditions, with maximum of 450 μm.

Surface nanocrystallization and mechanical properties of mold steel induced via scanning electron beam treatment

Improving the comprehensive mechanical properties of the surface of 5CrNiMo mold steel and prolonging the service life of the mold are important tasks of mold development. Hence, 5CrNiMo mold steel was irradiated by scanning electron beam to improve the property. It is indicated that during the electron beam irradiation process, the carbide nano-grains appeared in material surface, leading to a significant increase in surface microhardness by more than twofold to reach 845.6 HV. Additionally, the wear resistance of the specimen increased 7 times while its wear loss decreased to 0.2 mg from 1.4 mg. The surface roughness of the irradiated sample also decreased from 1.9 μm to 0.9 μm. The relationship between the comprehensive mechanical properties of the surface nanocrystallization is uncovered, which provides a dawn for producing 5CrNiMo mold steel with extraordinary properties.

Estimation of the Efficacy of Remineralizing Agents on the Microhardness of Deciduous Teeth Demineralized Using Pediatric Formulations.

This study aimed to evaluate the demineralizing effect of commonly used pediatric syrup formulations on primary teeth and the efficacy of two readily available remineralizing agents in treating this effect. Ninety primary teeth were used for sample preparation and divided into three groups: antibiotic syrup (group A), cough syrup (group B), and control (group C) groups. These groups were further categorized into intragroups according to the treatment with remineralizing agents: groups A1, B1, and C1 received GC Tooth Mousse (casein phosphopeptide-amorphous calcium phosphate, CPP-ACP paste) and groups A2, B2, and C2 received Clinpro Tooth Crème. The samples were subjected to a series of demineralization cycles for 14 days, and remineralization cycles until 30 days were performed using two remineralizing agents, that is, GC Tooth Mousse (CPP-ACP paste) and Clinpro Tooth Crème and were evaluated using Vicker's microhardness test. Antibiotic syrup (group A) and cough syrup (group B) showed a significant decrease in surface microhardness compared with control (group C). All intragroups showed an increase in surface microhardness after treatment with remineralizing agents, which was significantly higher in intragroups A1, B1, and C1 treated with GC Tooth Mousse (CPP-ACP paste). Oral liquid medications showed definite demineralization potential. CPP-ACP paste was found to be better than Clinpro Tooth Crème for demineralized teeth. The use of over-the-counter drugs has increased among the average Indian population, especially for the treatment of fever, cold, and cough. Unwise use of medications by the present population without proper medical guidance will lead to irreparable changes in future generations.

Strengthening of friction surfaces by using geomodifiers based on serpentines from the Dashukivka deposit

The object of research is the process of improving the tribological characteristics of friction joints, in particular anti-wear and anti-burr properties. There is a practice of using serpentines, so-called "friction geomodifiers" (FGM), as special repair and restoration additives. Their use leads to a decrease in the coefficient of friction and temperatures in the contact zone; an increase in the mass of parts is observed, which indicates the restoration of worn surfaces. The mechanism of formation of new structures is still unclear. There are hypotheses that severe friction conditions initiate micrometallurgical processes at the atomic-crystalline level, as a result of which modified layers with unique tribological characteristics are formed on the surfaces. A comparative analysis of the main indicators of serpentines of the Dashukivka deposit in terms of chemical composition and structure showed their correspondence to widely known analogs but they were never used in such a capacity. According to the results of the tests, the additives have shown their effectiveness as geomodifiers of friction. Addition of 4 % serpentine to the lubricating composition based on I-20 A oil reduced the wear rate by 2–3 times, the friction moment by 15 %, compared to I-20 A without additives. An increase in surface microhardness was observed, from 6 GPa for the basic variant to 10 GPa, for the variant with FGM additives. It has been established that the use is most effective for heavily loaded friction pairs (ship fittings, hatch closures, etc.) as it increases the clamping load (from 600 to 1400 N for a pair of steel 45/ShKh15); with increasing load, the coefficient of friction and the rate of wear decrease. The results confirm the need to expand research into this area to solve the complex problem of increasing the reliability of tribojunctions. Keywords: repair and restoration technologies, friction geomodifiers, serpentine, heavily loaded friction pairs

Enhancing surface properties and corrosion resistance of API 5L X52 steel through orthogonal ball burnishing

Surface engineering involves using various technologies to modify the surface and near-surface areas of a material to enable it to perform different functions from the bulk of the material. Two primary methods of surface engineering are surface coatings and surface modification. Orthogonal ball burnishing is a process that improves certain surface integrity properties of materials through superficial plastic deformation. This study focuses on the effect of this treatment and the influence of its parameters on the physico-geometric surface characteristics of API 5L X52 steel. Burnishing tests were conducted with four main parameters: burnishing force (Py), feed rate (f), spindle speed (N), and number of passes (i). The analysis revealed an appropriate combination of burnishing parameters that led to a 98% reduction in surface roughness and a 42% increase in surface microhardness. A multi-objective optimization of roughness and microhardness after burnishing yielded optimal parameters. Furthermore, a multifactorial experimental design demonstrated that corrosion resistance increased by 318%.

Effect of split sleeve cold expansion on microstructure and fatigue performance of 7075-T6 aluminum alloy holes

7075-T6 aluminum alloy is widely used in the manufacture of various structural parts of aircraft, most of which are joined and assembled through hole structures. However, stress concentration will occur around the hole during the service process of the part, which is easy to cause fatigue failure. It is significant to improve the fatigue performance of the hole structure. In this work, surface strengthening of 7075-T6 aluminum alloy holes induced by split sleeve cold expansion (SCE) was studied regarding surface microstructure, microhardness, and residual stress profiles. The effects of SCE process on the fatigue properties in different stress levels were finally discussed. The results show that the surface of the SCE sample undergoes severe plastic deformation and forms a gradient grain structure with a layer of nanocrystals in the outermost layer. This process lead to an increase of surface microhardness by about 14.3% and a compressive residual stress of up to 255 MPa. Dislocation slip is dominant deformation mechanism in the expansion process. During expansion, more dislocation tangles, dislocation walls and dislocation cells appear, which induces the formation of sub-grain boundaries and refines the grains. In the SCE samples, the high-strength nanocrystals on the surface of holes, the excellent resistance to strain localization of the gradient structure and the high compressive residual stress can effectively hinder the initiation of fatigue cracks and increase the high-cycle fatigue life by 9 times.

Enhanced Biotribological and Anticorrosion Properties and Bioactivity of Ti6Al4V Alloys with Laser Texturing.

The poor biotribological properties and bioinertness of Ti6Al4V have restricted its application in biomedical materials. In this study, microgrooves of different widths were prepared on the surface of a Ti6Al4V alloy by laser treatment. The tribological properties under dry lubrication and simulated body fluid (SBF) lubrication conditions, the electrochemical corrosion properties in SBF solution, and the bone marrow mesenchymal stem cell (BMSC) behavior on the surfaces were systematically tested. The corresponding mechanisms were discussed. The results showed that Ti6Al4V with a microgroove width of 45 μm (Ti64-45) exhibited excellent wear resistance with decreasing wear rates of 89.79 and 85.43% under dry friction and SBF lubrication compared to the Ti64 sample, which might be due to the increase of surface microhardness. Moreover, the excellent anticorrosion performance of Ti64-45 was attributed to the grain refinement on the titanium alloy surface with a lower volume fraction ratio of β phase to α phase. In addition, the microgrooves with a width of 45 μm are more conducive to BMSC proliferation and adhesion, related to promoting cell signal transduction due to cell extrusion. These studies imply that the microgroove structures are potential for application in the medical field.

Effect of quench-tempering and laser quenching on the microstructure and properties of high-chromium cast iron

In this paper, quench-tempering (QT) and laser quenching (LQ) treatments were performed on the high-chromium cast iron to obtain better microstructure and mechanical properties. The changes in microhardness, microstructure, retained austenite (RA) content, grain size, phase and elemental content of the QT and LQ samples were compared and analyzed. The results showed that the RA content of the untreated samples was 77.02% and the was 26.8 nm. The QT samples showed an increase in carbide dissolution, gradual rounding from sharp angles, transformation of austenite into martensite, reduction of RA content to 28.48%, average grain size (AGS) of 35.8 nm, increase in surface microhardness by 16.6%, and the friction coefficient was reduced by 6.9%. The LQ samples showed a large amount of fine martensite, daisy-like eutectic carbides and diffusely distributed secondary carbides, and the RA content was reduced to 17.72%, with an AGS of 29.9 nm. Compared with the QT samples, the LQ samples showed a 25.1% reduction in AGS, a 16.5% increase in surface microhardness, and a 9.7% decrease in friction coefficient, which was more wear resistant. However, the hard and brittle surface layer of the LQ samples tended to be a source of cracks during impact, resulting in a final reduction of 8.4% in impact toughness compared to the QT samples.

Surface Microstructure and Performance of Anodized TZ30 Alloy in SBF Solution

Anodization is performed on the Ti-30Zr-5Al-3V (TZ30) alloy to improve its surface performance. X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Olympus microscope are used to determine the phase constitution, morphology, and thickness of the anodization film (AOF). Tribological tests and electrochemical corrosion experiments are carried out to measure, respectively, the wear behavior and corrosion resistance of AOFs in simulated body fluid (SBF) solution. The microstructure characteristic of the AOF anodized at low voltage (20 V) is composed of compact and loose regions. As the applied voltage increases to 60 V, the compact regions transform progressively into loose regions, and then grow into nanotube regions. Besides, an increase in thickness of the AOF from 8.6 ± 4.61 μm to 20.7 ± 2.18 μm, and a gradual increase in surface microhardness from 364.6 ± 14.4 HV to 818.4 ± 19.3 HV, are also exhibited as the applied voltage increases from 20 V to 60 V. Specimens anodized at 40 V and 60 V have a low friction coefficient (~0.15) and wear rate (~2.2 mg/N/m) in the SBF solution. The enhanced wearability originates from the high hardness and various wear mechanisms. Potentiodynamic polarization curves suggest that the corrosion resistance in the SBF solution of all anodized specimens is greatly improved, thanks to the protection from the anodized TiO2 film.

Plasma duplex treatment influence on the tribological properties of the UNS S32760 stainless steel

Super duplex stainless steels are widely used in harsh environments due to their high corrosion resistance. However, the improvement of their tribological properties can contribute to a better performance of these materials in service. In this regard, this study aimed to evaluate the application influence of duplex treatment on the tribological properties of the UNS S32760 super duplex stainless steel. Two treatment times, 2 h and 4 h, were studied for both the nitriding step and the cathodic cage plasma deposition step. The results showed that the combination of the nitrided layer and the TiN film, confirmed with the application of Rietveld refinement on the XRD data, contributes to the wear volume decrease by up to 9.41 times. This behaviour was associated with the increase in surface microhardness and the excellent adhesion conditions (HF1) presented by the film deposited over the nitrided layer. The film provided a change in the wear mechanism, evidenced by the reduction in the tendency to wear by scratches. Additionally, was observed the presence of lower oxygen content in the wear region of the treated samples, that can be associated a lower heating of the samples during the test. Thus, the duplex treatment has a great application potential for improving the wear resistance of UNS S32760 steel.