Improved Surface Hardness Research Articles

Microstructural and Passivation Response of Severely Deformed AISI 304 Steel Surface: The Role of Surface Mechanical Attrition Treatment

The present study investigates the microstructural and passivation behavior of surface mechanical attrition treated (SMAT) AISI 304 stainless steel in a 0.6 M NaCl solution at room temperature. SMAT process, which is more advanced than the classical shot-peening, causes 2-3 times improvement in surface hardness of the steel. Ball size, a vital SMAT parameter, plays a significant role in controlling the microstructure and corrosion behavior of the steel. Larger diameter (6 mm) balls induce thicker deformed layer (450 μm), a higher proportion of deformation-induced martensite (~ 50%), a higher density of dislocations and twins, and higher lattice strain. TEM results confirm the presence of {111} twins throughout the deformed layer. SMAT enhances the corrosion properties of the steel. Specimen SMATed with 4-mm-diameter-balls displays the lowest corrosion rate (1.80 × 10−4 mmpy). SMAT increases the pitting resistance of the steel surface. XPS is utilized to understand the passivation mechanism of steel comprehensively. SMAT alters the proportion of Cr2O3, Cr(OH)3, Fe2O3, and FeO compounds in the passive layer. SMAT increases the thickness of the passive layer.

Impact of CO2 curing on the microhardness and strength of 0.35 w/c cement paste: Comparative study of internal/surface layers

The aim of this paper is to investigate the effect of carbonation on the microhardness and mechanical-related properties of carbonated and uncarbonated layers of cement pastes. The microhardness and mechanical property changes were examined 1 day after demolding and then 3, 7, 14, and 28 days with further CO2 and water curing. CO2 treatment yielded substantial impacts on the microstructure and densification of the surface layer of the paste by consuming calcium hydroxide and forming calcium carbonates. The maximum carbonation depth of 5 mm was recorded at 28 days, and the microhardness of the surface layer was significantly enhanced compared to the internal layer as well as uncarbonated paste samples. However, despite improved surface hardness, the overall compressive strength of carbonated sample was lower than that of water-cured samples, probably due to the non-preconditioning (to remove excess water for carbonation) of the carbonated samples and better hydration in the internal layer of the samples cured in water. In addition, the thin denser surface layer of the carbonated samples could decrease the cement hydration process. However, the denser and lower surface water absorption relation to CO2 treatment could facilitate long-term durability performance of concrete structures.

A self-cured glass-ionomer cement with improved antibacterial function and hardness.

A novel antimicrobial dental self-cured glass-ionomer cement has been developed and evaluated. Alumina filler particles were covalently coated with an antibacterial polymer and blended into a self-cured glass-ionomer cement formulation. Surface hardness and bacterial viability were used to evaluate the modified cements. Results showed that the modified cements exhibited a significantly enhanced antibacterial activity along with improved surface hardness. Effects of antibacterial moiety content, alumina particle size and loading, and total filler content were investigated. It was found that increasing antibacterial moiety content, particle size and loading, and total filler content generally increased surface hardness. Increasing antibacterial moiety, filler loading and total filler content increased antibacterial activity. On the other hand, increasing particle size showed a negative impact on antibacterial activity. The leaching tests indicate no cytotoxicity produced from the modified cements to both bacteria and 3T3 mouse fibroblast cells.

Influence of Nitrocarburizing and Post-Oxidation on Surface Characteristics, Fatigue, and Corrosion Fatigue Behaviour of AISI 4330V Steel

In the present work, gaseous nitrocarburizing followed by water spray oxidation in vacuum was carried out on 4330V steel. The X-ray diffraction analysis showed that the thermochemically modified surface layer mainly consisted of e-Fe2-3(N,C), γ′-Fe4(N,C), and magnetite (Fe3O4). To quantify the residual stress generated due to surface treatment, the Sin2ψ method was used. Residual stress of compressive nature up to a depth of 1 mm was observed, and its maximum value was 383 MPa. Nitrocarburizing followed by oxidation not only increased the surface hardness but also decreased the wear loss. The synergistic effect of corrosion-resistant phases formed after surface treatment improved surface hardness and compressive residual stress which resulted in the enhancement of corrosion fatigue life.

A dental filling composite resin restorative with improved antibacterial function and hardness

A novel antimicrobial dental composite resin has been developed and evaluated. Alumina filler particles were covalently coated with an antibacterial resin and blended into a composite resin formulation. Surface hardness and bacterial viability were used to evaluate the modified composite resin. Results showed that almost all the modified composite resins exhibited higher antibacterial activity along with improved surface hardness, as compared to unmodified one. Effects of antibacterial moiety content on the modified fillers, modified alumina particle size and loading, and total filler content were investigated. It was found that increasing antibacterial moiety content, particle size and loading of the modified filler, and total filler content generally increased surface hardness. Increasing antibacterial moiety, filler loading and total filler content increased antibacterial activity. On the other hand, increasing particle size showed a negative impact on antibacterial activity. The leaching tests indicate that the modified experimental composite resin showed no leachable antibacterial component to bacteria and 3T3 mouse fibroblasts.

Optimization of anti-wear and anti-bacterial properties of beta TiNb alloy via controlling duty cycle in open-air laser nitriding

A multifunctional beta TiNb surface, featuring wear-resistant and antibacterial properties, was successfully created by means of open-air fibre laser nitriding. Beta TiNb alloy was selected in this study as it has low Young's modulus, is highly biocompatible, and thus can be a promising prosthetic joint material. It is, however, necessary to overcome intrinsically weak mechanical properties and poor wear resistance of beta TiNb in order to cover the range of applications to load-bearing and/or shearing parts. To this end, open-air laser nitriding technique was employed. A control of single processing parameter, namely duty cycle (between 5% and 100%), led to substantially different structural and functional properties of the processed beta TiNb surfaces as analyzed by an array of analytical tools. The TiNb samples nitrided at the DC condition of 60% showed a most enhanced performance in terms of improving surface hardness, anti-friction, anti-wear and anti-bacterial properties in comparison with other conditions. These findings are expected to be highly important and useful when TiNb alloys are considered as materials for hip/knee articular joint implants.

Plasma-immersion ion implantation surface oxidation on a cobalt-chromium alloy for biomedical applications.

Co-Cr alloys such as L605 are widely applied for the manufacture of medical devices, including tiny cardiovascular stents. The presence of potentially toxic and allergenic release of Ni, Co, and Cr ions from these devices remains an unsolved concern. Surface modification by oxygen plasma immersion implantation (PIII) could be an excellent technique to create a dense and thin passive oxide layer on a relatively complex shape of a tiny device, such as a stent, thus reducing the potential release of metallic ions. The effect of oxygen PIII was investigated on L605 alloy specimens, from 5 to 50 mTorr gas pressures, and under pulsed bias voltages from -0.1 to -10 kV. The surface chemistry was investigated by x-ray photoelectron spectroscopy, while its morphology and surface energy were evaluated, respectively, by atomic force microscopy and scanning electron microscopy and by a sessile drop static contact angle. Electrochemical characterization was performed by potentiodynamic tests in the saline solution. Mechanical properties of the modified surface layer, specifically film adhesion and hardness (H), were assessed by scratch and nanoindentation tests. Results shown that the oxidized layers were composed of a mixture of Co and Cr oxides and hydroxides and were rich in Co. The corrosion rate was considerably reduced after O PIII, even for treatments using low bias voltage (-0.1 kV) and with consequent low oxygen implantation depth. Moreover, O PIII also improved surface hardness. The oxidized layers were found to have good adhesion and to be scratch resistant.

Nanoscratch self-healing characteristics of polyvinyl polymer thin films embedded with Al2O3 nanoparticles with thermal and UV energy reactivity

Self-healing materials can partially or completely heal the damage done to them, and it is expected that their original function will be thereby restored. Herein, we report a novel self-healing polyvinyl (Sh-PV) containing functional polymer that reacts to thermal and ultraviolet (UV) energy. The structure of Sh-PV was characterized by fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (1H NMR). In addition, aluminum oxide (Al2O3) inorganic nanoparticles (NPs) were added and hybridized to improve their poor self-healing efficiency and surface hardness of the coated thin film. Mechanical nanoscratch testing and scanning probe microscopy (SPM) imaging of surface using a nanoindenter were performed to investigate the healing ability of self-healing thin films. The organic–inorganic hybrid self-healing polymer thin film exhibited a 10 % improvement in surface hardness as well as 100 % healing against nanoscale damage compared to virgin self-healing polymers. Here, we discuss and evaluate the optimized method and mechanism of the self-healing system based on the results of self-healing materials and physical recovery methods for healing surface damage.

Novel approach to enhancing remineralization of tooth surface by magnetic field exposure

Modern dentistry is directed toward overcoming dental caries progression in the early stages with the aid of remineralizing agents. Long-established remineralizing agents have very slow kinetics to be applicable, and the need for an external cofactor is a must. In the present work, the authors improved the kinetics of dentin/enamel remineralization by magnetic field exposure whereby calcium (Ca2+) and phosphate (PO4 3−) elements are supplied from an external source. Gels made of casein phosphopeptide–amorphous calcium phosphate mixed with nanochitosan were used as an external source and combined with exposure of the tooth surface to a magnetic field of 1.8 mT for 20 min. The treated tooth samples were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Vickers microhardness test and X-ray diffraction. The obtained tooth characteristics confirmed the improvement of tooth surface integrity, mineralization, hardness and crystallinity under the application of the magnetic field. Unexpectedly, the results indicated the highest tooth surface remineralization for samples exposed to magnetic fields and treated with casein phosphopeptide–amorphous calcium phosphate gel only without nanochitosan. In conclusion, the resulting advantages here are the ease of use, safety and applicability of this novel combination of casein phosphopeptide–amorphous calcium phosphate gel with magnetic field exposure.

Optimization of Shot Peening Effective Parameters on Surface Hardness Improvement

Shot peening is well-known process for mechanical properties integrity in metallic materials. In present study influences of different shot peening treatments on the surface hardness of different carbon steels were investigated experimentally and then alternative approach by using artificial neural network is presented for hardness prediction of the shot peened surface. After modeling a comprehensive parametric investigations and sensitivity analysis were applied according to the influence of the related effective parameters on surface hardness improvements.

Effects of ultrasonic nanocrystal surface modification on the surface integrity, microstructure, and wear resistance of 300M martensitic ultra-high strength steel

Abstract In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment on the surface integrity, microstructures and wear resistance of 300M ultra-high strength steel (300M steel) were investigated. The results showed that surface roughness of 300M steels after UNSM processing was significantly decreased with a lower scanning speed even though the surface roughness values were higher than that of mechanically polished control samples. In addition, the surface hardness of 300M steel was significantly enhanced as the static load increased. It was found that using a static load of 50 N and a scanning speed of 250 mm/min in the UNSM process can significantly improve surface hardness (797 HV) while slightly increasing the surface roughness. With these parameters, the resulting microstructure of UNSM-processed samples have three layers: the layer of severe plastic deformation, the layer with gradual plastic deformation, and the unaffected layer. Due to the plastic deformation, greater and deeper compressive residual stresses were induced in the UNSM-processed samples. In addition, the wear resistance of UNSM-processed samples was significantly improved, which was attributed to the refined martensite laths, work hardening and compressive residual stress.

Microstructure and mechanical properties of CoCrFeMnNi high entropy alloy with ultrasonic nanocrystal surface modification process

In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification (UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and 60 N provided a severe plastic deformation, which produced a gradient structure. The near-surface area exhibited a high number of dislocation densities and deformation twin interaction, leading to a surface strengthening and hardness improvement of up to 112% than the deformation-free interior region. Increment of dislocation densities and deformation twin formation on the surface also enhanced the yield and ultimate tensile strength of the UNSM-treated specimens. Furthermore, the combination of hard nanocrystallites layer on the surface and ductile coarse grain in the specimen interior as a result of the UNSM treatment successfully maintained the strength–ductility balance of the CoCrFeMnNi.

Optimization of the Burnishing Process for Energy Responses and Surface Properties

In the current work, the optimal factors are selected to achieve the improvements in the energy consumption (EB), power factor (PB), decreased roughness (DR) and improved surface hardness (IH) for the roller burnishing operation. The process inputs are the burnishing speed (V), the feed (f), and the depth (d). A hybrid approach comprising the principal component analysis and Technique for Order of Preference by Similarity to Ideal Solution was used to explore the weight values of burnishing performances and select the optimum parameters. Moreover, another optimization technique employing the response surface method and archive-based micro-genetic algorithm was adopted to identify the optimal outcomes in the continuous domain. The main findings showed the performances measured are primarily affected by the burnishing feed, depth and speed, respectively. The energy consumption and roughness are approximately decreased by 31.46% and 7.41%, while the power factor and hardness are improved by 17.47% and 43.09%, respectively, as compared to the general process. The outcomes and findings of the investigated work can be used for further research in sustainable design and manufacturing as well as directly used in the knowledge-based and expert systems for burnishing applications in industrial practices.

Active screen plasma nitriding of Al–Si eutectic alloy and evaluation of compound coatings

Active screen plasma nitriding (ASPN) of steel has been extensively studied during the past few years. ASPN is a new technique with many advantages and can be used for treating non-electrical conducting materials like oxides and polymers. Recently, ASPN technique has been used for aluminum and aluminum alloys for surface treatment. The current study reports the growth and characterization of the compound aluminum and iron nitride coating on aluminum–silicon (Al–11Si) eutectic alloy using the active screen plasma nitriding setup to improve the surface properties of the alloy. After treatment in low-pressure plasma environment for five-hours, samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), atomic force microscopy, and Vickers's Micro Hardness testing to investigate the changes in surface morphology, elemental composition, and mechanical properties before and after the plasma treatment. XRD peaks (111), (200), (220), (311) of AlN were observed while that of FeXN peaks were also observed. Spherical, highly crystalline, agglomerated aluminum, and iron nitrides were observed in SEM micrographs. Elemental analysis using EDS and laser-induced breakdown spectroscopy confirmed the presence of nitrogen at the surface of the low pressure plasma treated sample. The presence of nitrides on the surface of the alloy resulted in improvement of the hardness as observed from the Vickers' hardness testing. It is concluded that ASPN is a useful technique for the improvement of surface hardness of Al–11Si alloy.

Highly robust and transparent flexible cover window films based on UV‐curable polysilsesquioxane nano sol

AbstractFlexible cover window films based on the ultraviolet‐curable polysilsesquioxane are prepared to have enhanced mechanical, optical properties, and bending performance. To figure out the factors determining those properties, post–treatment conditions are varied into the light source, temperature, and relative humidity. Then, the effect of such variables is examined in respect of surface hardness, yellow index (YI), and bending cycle reliability of flexible hard coating. Also, the effect of photoinitiator type in terms of their chemical structure is also investigated. Notably, the relative humidity and thermal treatment are more effective to enhance the mechanical properties rather than light exposure. Indeed, compared to that of reference condition, the cover windows treated with 99% relative humidity and thermal aging at 85°C exhibit improved surface hardness by 24.4 and 19.5%, respectively. However, only the relative humidity is rather effective to enhance the optical properties such as the YI by lowering to the most 2.6. The YI is also improved by varying the chemical structure of the photoinitiator. By virtue of post–treatment and a different photoinitiator, we could achieve flexible cover window films with bending reliability at bending radius of 3 mm for 100,000 cycles, showing good mechanical and optical properties simultaneously.

Effects of Surface Modification by Means of Low-Temperature Plasma Nitriding on Wetting and Corrosion Behavior of Austenitic Stainless Steel

Low-temperature nitriding of austenitic stainless steels produces modified surface layers, consisting mainly of the S phase, which improve surface hardness and corrosion resistance. Because of the localized plastic deformations, owing to modified layer formation, and ion bombardment occurring during the process itself, this treatment produces also modifications of surface morphology and roughness, which can affect wettability and corrosion behavior. In this study the effects of plasma nitriding, performed using different treatment conditions, on the surface morphology and roughness, and thus on wettability and corrosion resistance, of AISI 202 specimens with different initial finishings (2D and polished finishing) were investigated. Different probe liquids, having both high (bi-distilled water and solution of 3.5% NaCl) and low (ethanol and rapeseed oil) surface tension, were employed for assessing the wetting behavior with the sessile drop method. The contact angle values for water increased markedly when nitriding was performed on polished samples, while this increase was smaller for 2D samples, and on selected specimens a hydrophobic behavior was observed. Very low contact angle values were registered using low surface tension liquids, suggesting an oleophilic behavior. Corrosion resistance in a 5% NaCl solution was assessed, and it depended on the characteristics of the nitrided specimens.

Plasma immersion ion implantation and shot peening influence on the fatigue strength of AA 7050-T7451 aluminum alloy

The 7xxx aluminum alloy series is applied in aircraft components that demand high specific mechanical strength and fatigue resistance. The corrosive environment and friction forces imposed on those components reduce the service life. Therefore, anodizing is frequently used to enhance resistance against corrosion and wear. However, anodizing decreases the fatigue life of aluminum alloys. Plasma immersion ion implantation (PIII) is an alternative surface treatment that has been used to improve surface hardness, corrosion resistance and reduce wear damage. The PIII treatment consists of accelerating positive ions towards a sample by applying negative high voltage pulses in plasma. The shot peening (SP) process is a surface treatment that can be used with other surface treatments to improve the fatigue strength. The present work aimed at investigating the fatigue behavior of AA 7050-T451 aluminum alloy treated with SP, PIII, and a combination of both SP and PIII surface treatments. The combination of SP and PIII treatments (SP + PIII) improved the fatigue performance with respect to the base material and was more efficient than PIII in improving the fatigue strength for high-cycle fatigue regime. The fatigue strength improvement is related to the induced compressive residual stresses at the surface layers, which was responsible for delaying the nucleation and early fatigue crack propagation periods. The residual stress at the surface changed from −62 MPa to −130 MPa and −210 MPa for the SP and SP + PIII conditions, respectively. Compared to chromic anodizing, the SP + PIII condition increased the fatigue life in about 4 times at a maximum stress level of 281 MPa. The combination of SP and PIII treatments tested in this work is more advantageous regarding fatigue behavior than chromic anodizing, which reduces the fatigue strength of the material.

Surface modification of M2 steel by combination of cathodic cage plasma deposition and magnetron sputtered MoS2-TiN multilayer coatings

Titanium nitride (TiN) is a good choice for the improvement in surface hardness of high-speed steel. Unfortunately, it has low adhesion with substrate and exhibits high friction coefficient; as a result it does not provide sufficient protection against sliding wear in metal-to-metal contact. The adhesion problem can be removed by nitriding process, whereas friction coefficient can be reduced by solid lubrication coating. In this study, an attempt is made to synthesize TiN hard coating as well as solid lubrication coating of molybdenum disulfide (MoS2) using magnetron sputtering, along with substrate pre-treatment by cathodic cage plasma deposition using titanium cathodic cage. The cathodic cage plasma nitrided sample exhibits significantly higher surface hardness, which reduced by solid lubrication coating. The nitrided sample depicts the presence of iron nitrides, TiN and nitrogen diffused martensite phases, whereas coated samples shows the presence of MoS2 and TiN phases. The friction coefficient and machining temperature are dramatically reduced by lubrication coating. This study recommends that the use of cathodic cage plasma nitriding using titanium cathodic cage is beneficial for improved surface hardness, and addition of solid lubrication coating is beneficial for reducing the coefficient of friction and machining temperature by scarifying hardness. As, both the systems are already proven to be appropriate for industrial-scale uses, thus results from this study can be applied for industrial-scale application.

Improvement of Surface Hardness and Wear Resistance of Medical CoCr Alloy by Laser Peening

Improvement of Surface Hardness and Wear Resistance of Medical CoCr Alloy by Laser Peening

Nano-porous oxide deposition on titanium alloy (grade-5) to enhance its biocompatibility along with tribological and mechanical analysis

The aim of this paper is to explicate the results concerning the surface modification of titanium grade-5 via anodisation in a sulphuric acid electrolyte. Fabrication of nanoporous oxide film structure over titanium substrate is the key requirement of this study and after anodisation realised remarkable wear-resisting strength along with improved surface hardness as compared to the untreated metal substrate. The consequence of anodising parameters for instance voltage, time, electrolytic concentration, anodic current density are monitored to determine their optimum values. Phase analysis and morphological survey of the anodised surface has been performed by XRD and SEM respectively. A nanoporous structure appeared at 0.4 M whereas XRD analysis exposed that a phase transformation from anatase to rutile occurs at 0.5 M of H2SO4. A pin-on-disc type wear test practiced to determine the wear-resisting strength of the oxide surface and showed accumulated oxide layer significantly enhance wear-resisting strength, especially abrasive wear. SEM analysis performed after wear test evident that fracture on a larger scale occurs and that large flakes are removed from the surface. Performed work raises the chances for utilisation of the nanostructured titania and make it more reliable and adaptable for further engineering as well as biomedical applications.