Search Results (430)

The TC4 alloy is widely used in aerospace and marine engineering due to its excellent mechanical properties and corrosion resistance. However, titanium alloys often face fretting wear problems during use, which affect their long-term stability and service life. This study investigates the effects of surface mechanical attrition treatment (SMAT) time on the surface morphology, microstructure, stress distribution, and fretting wear properties of TC4 alloy. Characterization was performed using white light interferometry, EBSD, SEM, XRD, and microhardness measurements. The results show that SMAT significantly changes the surface and wear properties of TC4 alloy. With the increase in SMAT time from 0 to 240 min, the surface roughness (Ra), hardness, deformation depth, and stress gradually increase while the grain size decreases. After 240 min of SMAT, the TC4 alloy exhibited optimal fretting wear resistance, achieving a wear depth of 14.27 μm, a wear volume of 2.48 × 10⁶ μm³, and a wear rate of 1.24 × 10³ μm³/s. This represents a significant improvement, corresponding to an approximate 32.8% reduction in wear depth and a ~48% reduction in both wear volume and wear rate compared to the untreated sample. Full article

This study aimed to evaluate the effect of experimental bleaching gels containing chitosan and theobromine and compare their performance in terms of tooth surface roughness, microhardness, and colour change with the bleaching gels BioWhiten ProHome and FGM Whiteness Perfect. One hundred and forty-four upper central incisors were used for microhardness, surface roughness, and colour change analyses (n = 12). Prior to bleaching, surface roughness was measured using a profilometer, microhardness was analysed using a Vickers hardness test, and colour was measured using a spectrophotometer. For Group 1, the treatment consisted of an experimental gel containing chitosan–theobromine (16% CP); for Group 2, it was an experimental gel containing chitosan–theobromine (6% HP); for Group 3, it consisted of BioWhiten ProHome (6% HP); and for Group 4, it consisted of FGM Whiteness Perfect (16% CP). Microhardness and surface roughness tests were performed under the same conditions before bleaching, after bleaching, and 14 days after the initial treatment. Colour analysis was performed before the bleaching, during the application, 24 h after bleaching, and at 7 and 14 days after treatment. p < 0.05 was considered significant. No statistically significant increase in microhardness values after bleaching was detected in any group (p > 0.05), effective bleaching was detected in all groups, and the highest efficacy was observed in Group 4 (p < 0.05). The experimental gels containing theobromine and chitosan resulted in effective bleaching and did not exert any negative effects regarding surface roughness or microhardness. Full article

This study investigates the substitution of fossil-based isocyanates with bio-based alternatives in polyurethane resin (PU) coatings and polyurethane dispersion (PUD) coatings, focusing on mechanical and thermal performance. The coatings were formulated using bio-based pentamethylene diisocyanate (PDI) and a range of fossil-based hexamethylene diisocyanate (HDI) trimers, combined with either a polyester polyol or a polyacrylate polyol. Differential-scanning calorimetry analysis revealed that PDI-based coatings exhibit higher reactivity during crosslinking, resulting in higher glass transition temperatures. Thermogravimetric analysis showed lower thermal stability compared to HDI-based polyurethanes, indicating increased rigidity but reduced thermal resilience. Mechanical testing of the coatings on wood showed superior microhardness, scratch resistance, and wear resistance for PDI-based coatings, particularly when combined with polyester polyols. Microscopic surface evaluation and roughness analysis confirmed smoother morphologies and lower crack densities in PDI-polyester coatings. Gloss and water contact angle measurements further demonstrated improved surface uniformity and hydrophobicity for PDI-based coatings. The FTIR spectroscopy validated the chemical integrity and more intense hydrogen bonding for PDI-based coatings. The post-wear spectra indicated chemical oxidation and surface rearrangements in PDI-based systems and mechanical degradation with chain scission for HDI-based coatings. Overall, the study highlights that bio-based PDI trimers can effectively replace fossil-based HDI trimers in PU and PUD coatings without compromising mechanical performance, especially when paired with polyester polyols. These findings support the development of more sustainable polyurethane coatings with enhanced durability and environmental compatibility. Full article

Ni/ZrO₂ composite coatings are increasingly employed, yet the influence of organic additives under a pulse current regime on their electrodeposition remains insufficiently addressed. This study investigates the combined effect of pulse frequency (0.01–100 Hz) and coumarin concentration (0–2 mmol L⁻¹) on the co-deposition behavior, microstructure, and properties of Ni/ZrO₂ coatings electrodeposited from a Watts-type bath. The structural, morphological, and compositional features were analyzed through SEM/EDS, FE-SEM, and XRD, while microhardness and surface roughness were determined to establish processing–structure–property correlations. The results revealed that coumarin acts as an effective levelling agent, promoting smoother and finer-grained coatings while modifying ZrO₂ incorporation and Ni crystallographic orientation. Increasing coumarin concentration led to a notable refinement of nickel crystallites and a rise in hardness, reaching values close to 650 HV under optimal PC conditions. Pulse frequency was found to strongly influence the microstructural characteristics and particle co-deposition rates, particularly at low frequencies, where a balance between additive adsorption and current modulation favored particle incorporation and enhanced the microhardness. It was demonstrated that the synergistic control of pulse parameters and coumarin concentration enables the design of Ni/ZrO₂ composite coatings with tailored microstructure, low roughness, and superior hardness for demanding applications. Full article

To meet the surface polishing requirements of aluminum nitride (AlN) ceramics, this study developed a multi-objective optimization experimental model based on response surface methodology (RSM), with surface roughness as the key optimization target. A systematic series of femtosecond laser polishing experiments were conducted. Polishing effectiveness and the evolution of material properties under different process parameters were comprehensively evaluated through surface morphology characterization, microhardness testing, friction and wear experiments, and energy-dispersive X-ray spectroscopy (EDS) analysis. The experimental results indicated that the optimal combination of process parameters, as determined by RSM optimization, was identified as a laser power of 17.43 W, pulse frequency of 292.29 kHz, and scanning speed of 1004.82 mm/s. Under these parameters, femtosecond laser polishing significantly reduced the surface roughness of the AlN ceramic, with the initial Ra value decreasing from 2.513 μm to 0.538 μm, a reduction of 78.57%. Compared to CO₂ laser polishing (R_a = 0.817 μm), femtosecond laser polishing demonstrated superior performance in enhancing surface quality. Analysis of the microstructural mechanisms revealed that the femtosecond laser, due to its ultra-short pulse characteristics, effectively suppressed the expansion of the heat-affected zone. It passivated surface microcracks through a photothermal ablation effect and reduced the thickness of the subsurface damage layer. Furthermore, the friction coefficient and wear rate of the polished samples decreased, indicating a significant improvement in wear resistance. On the numerical simulation front, a multi-physics model describing the interaction between the femtosecond laser and AlN ceramic was established based on the non-equilibrium two-temperature model (NTTM) coupled with solid mechanics. The key innovation of our model is the full coupling of heat transfer and solid mechanics, which allows for an accurate revelation of the material morphology evolution mechanism during femtosecond laser ablation. The model’s accuracy is confirmed by the excellent agreement with experimental results, showing relative errors of only 3.23% and 12.5% for the melt pool width and depth, respectively. Full article

The present study demonstrates the roller burnishing process of aluminum alloy 6061-T6 by using a combination of aluminum oxide and vegetable oil as a lubricant. Machining parameters were explored, varying speed (v) (range 100–300 rpm), feed (f) (range 0.1–0.3 mm), and number of passes (nop) (range 1 to 3). However, performance was measured in terms of surface roughness, microhardness, and roundness. According to the results obtained from experiments, it was found that lubrication had a significant impact on performance in terms of surface roughness, mmicrohardness and roundness. Under lubricated conditions, surface roughness ranged from 0.012 µm to 1.7 µm. However, an increase in mimicrohardnessrom 92 HV to 96 HV and an improvement in roundness from 0.07 mm up to 0.05 mm were observed. Additionally, the findings indicated that high speeds with low feed rates yielded the best results: for instance, at a feed of 0.1 mm/rev, speed (v) of 300 rpm, and number of passes of three, a surface roughness of about 0.8 µm, microhardness of approximately 94 HV, and roundness of about 0.02 mm were recorded when applying lubrication. This study demonstrates how minimal lubrication techniques can be used to improve the roller burnishing process, thereby achieving better mechanical properties and surface finishes while extending the lifespan of the burnishing tool. The study has brought about a conclusion that optimizing v and f during burnishing while including relevant lubricant helps manufacturers to realize significant product quality improvements and enhance production efficiency. Full article

Ti-6Al-4V, a popular biomedical alloy, is increasingly fabricated by additive manufacturing methods, like laser powder bed fusion (LPBF). However, rapid thermal cycling and steep temperature gradients often induce mechanical degradation, corrosion, and wear. To address these challenges, laser surface modification is explored. This study investigates the microstructure and corrosion behaviour (simulated body fluid, 37 °C) of LPBF and wrought Ti-6Al-4V after laser surface melting (LSM) treatment. LSM produced modified layers of 1250–1350 µm (LPBF) and 1530–1600 µm (wrought), with gradients from remelted dendrites to acicular martensite. Microhardness in the layers increased to 655–680 HV due to lattice expansion, crystallite refinement, and higher dislocation density. However, LSM-treated alloys showed higher corrosion rates and weaker passive films, attributed to increased surface roughness, martensite formation, residual stresses, and microstructural inhomogeneity. Aluminium silicate surface films/residues further compromised passivity. Nevertheless, both LSM-LPBF and LSM-wrought specimens displayed low corrosion current densities (10⁻⁴ mA/cm²), true passivity (10⁻³–10⁻⁴ mA/cm²), and high resistance to localised corrosion. After cyclic polarisation, rutile-rich TiO₂ surface films with aluminium silicate hydrates were observed. LSM-LPBF specimens showed slightly inferior general corrosion resistance compared to LSM-wrought counterparts, due to pronounced surface texture variations, phase/composition differences, higher microstrains and dislocation density. Full article

Ti65 high-temperature titanium alloy, known for its exceptional high-temperature mechanical properties and oxidation resistance, demonstrates considerable potential for aerospace applications. Nevertheless, conventional manufacturing techniques are often inadequate for achieving high design freedom and fabricating complex geometries. This study presents a systematic investigation into the process optimization, microstructure characterization, and mechanical performance of Ti65 alloy produced by laser powder bed fusion (LPBF). Via meticulously designed single-track, multi-track, and bulk sample experiments, the influences of laser power (P), scanning speed (V), and hatch spacing (h) on molten pool behavior, defect formation, microstructural evolution, and surface roughness were thoroughly examined. The results indicate that under optimized parameters, the specimens attain ultra-high dimensional accuracy, with a near-full density (>99.99%) and reduced surface roughness (Ra = 3.9 ± 1.3 μm). Inadequate energy input (low P or high V) led to lack-of-fusion defects, whereas excessive energy (high P or low V) resulted in keyhole porosity. Microstructural analysis revealed that the rapid solidification inherent to LPBF promotes the formation of fine acicular α′-phase (0.236–0.274 μm), while elevated laser power or reduced scanning speed facilitated the development of coarse lamellar α′-martensite (0.525–0.645 μm). Tensile tests demonstrated that samples produced under the optimized parameters exhibit high ultimate tensile strength (1489 ± 7.5 MPa), yield strength (1278 ± 5.2 MPa), and satisfactory elongation (5.7 ± 0.15%), alongside elevated microhardness (446.7 ± 1.7 HV_0.2). The optimized microstructure thereby enables the simultaneous achievement of high density and superior mechanical properties. The fundamental mechanism is attributed to precise control over volumetric energy density, which governs melt pool mode, defect generation, and solidification kinetics, thereby tailoring the resultant microstructure. This study offers valuable insights into defect suppression, microstructure control, and process optimization for LPBF-fabricated Ti65 alloy, facilitating its application in high-temperature structural components. Full article

This study systematically investigates the surface nanocrystallization of 35CrMo steel induced by Ultrasonic Surface Rolling Processing (USRP). It reveals the formation of a gradient nanostructure, where martensite lath fragmentation under high-frequency impacts leads to a surface layer of equiaxed nanocrystals and high-density dislocations. This novel microstructure yields exceptional surface integrity: roughness is minimized to 0.029 μm due to plastic flow, residual stress is transformed into high compressive stress, and surface microhardness is significantly enhanced by 32.3%, primarily governed by grain refinement and dislocation strengthening. Consequently, the treated material exhibits a 28.9% reduction in wear mass loss, which is directly attributed to the combined effects of the strengthened gradient layer’s improved load-bearing capacity and the effective suppression of crack initiation by compressive residual stresses. Our findings not only provide direct microstructural evidence for classic strengthening theories but also offer a practical guide for optimizing the surface performance of high-strength alloy components. Full article

The study investigates the effect of plasma-electrolytic polishing on the structure and wear resistance of 30KhGSA steel after plasma-electrolytic boriding. Plasma-electrolytic boriding was carried out in a boron-containing electrolyte at a temperature of 900 °C, which ensured the formation of a hardened modified layer consisting of a surface oxide layer, a subsequent zone composed of boride phases FeB and Fe₂B, as well as a transitional martensitic zone. To remove brittle oxide phases and reduce surface roughness, plasma-electrolytic polishing in an alkaline solution was applied, which made it possible to form a smoother and more stable surface. The results showed that plasma-electrolytic boriding increases the microhardness up to 1500–1600 HV_0.1, which is 5–6 times higher compared to untreated steel, and reduces the friction coefficient and wear rate. However, the borided layers exhibit brittleness and surface roughness. Subsequent plasma-electrolytic polishing made it possible to reduce surface roughness by nearly an order of magnitude, decrease the friction coefficient by more than 30%, and almost halve the wear rate. The obtained results confirm the high potential of this combined technology for strengthening structural steel components operating under high loads and severe wear conditions. Full article

This publication presents the performance properties of 30HGSA steel after various surface treatments involving hybrid graphene coating, shot peening, and graphene oxide coating, and of the material in its delivery state used in aerospace structures. Performance tests were carried out on the structure, measuring surface roughness, microhardness, corrosion, residual stresses and bending strength for all surface treatments. It has been demonstrated that hybrid graphitization results in increased surface roughness, increased compressive stress and a beneficial increase in the bending strength of the sample compared to other research groups. A new method of strengthening steel surfaces by hybrid graphitization, consisting of coating the steel surface with graphene oxide and shot peening, has been described. The mechanism of hybrid graphitization affecting the increase in the performance properties of 30HGSA steel, including a 43% increase in maximum bending strength compared to BM, has been presented. Full article

A Ti-6Al-4V titanium alloy exhibits low hardness and poor wear resistance under sliding contact. This study evaluates the effect of low-pressure gas oxynitriding (LPON) followed by low-temperature oxidation on its microstructure and tribological performance. Specimens were nitrided at 1000 °C for 100 min, then oxidized at 450–600 °C for 120 min. Microstructural and phase changes were characterized by SEM and XRD; surface roughness, hardness, and wear were assessed using 3D laser scanning microscopy, microhardness profiling, and pin-on-disk tests under 2 N and 4 N loads. XRD revealed TiN, Ti₂N, Ti₂AlN, and TiO₂ phases, with oxidation temperature governing TiN grain growth and nitride-to-oxide transformation. Oxidation at 500–550 °C formed a dense TiO₂-rich layer over a stable TiN/Ti₂N substrate, achieving hardness up to ~670 HV_0.025 and the lowest wear volume. At low load (2 N), nitriding alone provided the highest wear resistance, while at higher load (4 N), oxidation yielded only slight improvement due to oxide embrittlement. Excessive oxidation at 600 °C increased roughness, induced spallation, and reduced wear resistance. The optimal condition (550 °C) offered synergistic protection from nitrides and stable oxides, enhancing load-bearing capacity. Overall, duplex nitriding–oxidation is most effective for low-to-moderate load applications, with potential use in biomedical implants, aerospace fasteners, and precision components. Full article

Aluminum–lithium alloys, as promising next-generation aerospace materials, exhibit outstanding properties, such as high strength, low density, excellent cryogenic performance, and superior corrosion resistance. In this study, aluminum–lithium alloy powders were processed via selective laser melting to systematically investigate the effects of processing parameters on manufacturing quality, microstructure, microhardness, residual stress, and tensile properties, with a particular emphasis on crack initiation and evolution. The results demonstrate that increasing laser power significantly improves specimen densification and reduces surface roughness. Moreover, the number of cracks decreases while their average length increases with elevated laser power. The maximum microhardness of 106.8 HV was achieved at the highest laser power, which also corresponded to the optimal tensile performance. These findings provide valuable insights into the relationship between laser parameters, microstructural evolution, and mechanical behavior, offering practical guidance for optimizing process parameters in the SLM fabrication of Al-Li alloy components for aerospace applications. Full article

Objective: The purpose of this study was to compare the flexural strength, flexural modulus, hardness, and surface roughness of one brand each of 3D-printed and heat-cured acrylic resin materials after they were immersed in various disinfection solutions. Methods: The study included 160 specimens, consisting of 80 heat-cured and 80 3D-printed specimens. Forty specimens of each resin material type were prepared for flexural testing, while an additional forty specimens were designated for hardness and surface roughness assessments. Each collection of 40 specimens was subsequently randomized into four subgroups (n = 10) for immersion in either distilled water (control), 1% sodium hypochlorite, Superdent, or Kin Oro denture cleansers. Flexural test, hardness, and surface roughness assessments were performed. Data analysis was conducted using SPSS, with a level of significance set at p < 0.05. Results: Flexural strength and surface roughness did not differ significantly between the two resin types. Flexural modulus was significantly higher in the heat-cured resin among all the disinfectants (p = 0.000). The heat-cured resin had significantly higher microhardness than the 3D-printed resin among the disinfectants except for the Kin Oro group, and both resins showed a significant reduction in hardness after immersion in disinfectants compared to distilled water (p < 0.05). Conclusions: The heat-cured resin demonstrated higher flexural modulus and surface hardness compared to the 3D-printed resin. Flexural strength and surface roughness were comparable between the two materials. Both resins had their highest mechanical properties in distilled water. Full article

The surface properties of composite resin restorative materials are critical for the esthetics and longevity of restorations. This in vitro study evaluated the microhardness change and surface roughness change in four resin composites recommended for anterior restorations after two aging simulations: thermal cycling (10,000 cycles) and one year of water storage. Ten specimens (n = 10) were prepared for each material. After baseline measurements, samples were subjected to one of the aging procedures, and surface properties were reassessed. For microhardness change (∆H), significant differences were observed among materials under both thermal cycling (p = 0.001) and water storage (p = 0.001). Omnichroma–thermal cycling showed a greater decrease than G-ænial Anterior (p = 0.028) and Clearfil Majesty ES-2 (p = 0.001), while Optishade–thermal cycling decreased more than Clearfil Majesty ES-2 (p = 0.015). In water storage, Omnichroma exhibited a greater decrease than Optishade (p = 0.042) and Clearfil Majesty ES-2 (p = 0.001), and G-ænial Anterior decreased more than Clearfil Majesty ES-2 (p = 0.026). Optishade and Clearfil Majesty ES-2 showed significantly greater decreases after thermal cycling than water storage, while Omnichroma and G-ænial Anterior showed no difference. For the change in surface roughness (∆R), significant differences were also found (p = 0.001). In thermal cycling, Optishade exhibited the lowest increase, while G-ænial Anterior showed the highest. In water storage, G-ænial Anterior again had the highest increase, significantly greater than all others (p = 0.001). For all materials, ∆R values were significantly higher after thermal cycling compared with those in water storage (p = 0.001). These results demonstrate that both composite type and aging method influence long-term surface properties. Overall, thermal cycling exerted more detrimental effects than water storage. Full article