Alumina Ball Research Articles

Wear performance of antibacterial dental composite with Salvadora persica extract and hydroxyapatite as fillers

AbstractThe characterization of S. persica (Salvadora persica) extract, which involved evaluating its antibacterial activity, demonstrated the extract's strong efficacy. Additionally, incorporating it into PMMA/HA showcased the composite's good antibacterial activity. The objective of this work is to evaluate how the incorporation of S. persica extract affects the wear resistance of the dental composite PMMA/HA, considering the critical importance of wear resistance in dental applications. The wear response of this biocomposite was tested against an Alumina ball using a pin‐on‐disc tribometer. Initially, the hydroxyapatite (HA) micro particles demonstrate a remarkable influence on wear behavior when incorporated at an optimal percentage (10%wt). This optimal inclusion rate not only significantly increases the wear rate but also instigates a shift in the wear mechanism, favoring abrasive wear while minimizing adhesive wear comparing to PMMA. The addition of the extract nanoparticles to the composite PMMA/HA decreases the wear rate except the composite containing 10 wt% of each filler. Additionally, it introduces adhesive wear, in addition to the existing fatigue and abrasion wear. Thus, the composite PMMA/HA could accommodate up to 10 wt% of the S. persica extract as the optimal percentage that provides antibacterial activity to this biocomposite without exhibiting a deterioration in wear performance.Highlights The evaluation of the effect of incorporating S. persica extract, which provides antibacterial activity, on the wear resistance of the PMMA/HA dental composite generally demonstrates a reduction in this property. The addition of S. persica extract introduces adhesive wear in addition to the fatigue and abrasion wear already present in the PMMA/HA composite. The composite PMMA/HA can accommodate up to 10 wt% of S. persica extract without compromising its wear performance.

High Temperature Wear Property of Ta-10W Alloy

This study investigated the high-temperature wear characteristics of Ta-10W alloy, composed of 90% tantalum and 10% tungsten, known for its high melting point, excellent corrosion resistance, and oxidation resistance. Wear tests were conducted using a ball-on-disc method with alumina balls at temperatures of 200°C, 400°C, 600°C, and 700°C. The results indicated that wear loss decreased (increasing wear resistance) from 200°C to 600°C due to the lubrication effect by oxide particles induced by Ta2O5, which enhanced wear resistance. However, at 700°C, a significant increase in wear loss was observed due to excessive oxide formation and the occurrence of cracks. Calculation of the wear rate revealed that it decreased as the temperature increased to 2.12×10-4 mm3· N-1· m-1 at 200 °C, 2.67×10-5 mm3·N-1·m-1 at 400 °C, and 4.21×10-6 mm3· N-1· m-1 at 600 °C. On the other hand, the wear rate increased at 700 °C to 3.87×10-4 mm3· N-1· m-1. The wear track analysis results revealed distinct wear mechanisms at different temperatures. At 200°C, abrasive wear characterized by pits and furrows was dominant. At 400°C, adhesive wear became more prevalent with cleavage worn surfaces compared to the wear pattern at 200°C. At 600°C, fragmented oxides indicating pest oxidation were noted, while at 700°C, deep pits and cracks along with fragmented oxides were prevalent. X-ray diffraction (XRD) analysis results showed the presence of the α-Ta phase at 200°C, 400°C, and 600°C, with peak shifts indicating lattice expansion. In contrast, at 700°C, Ta2O5 peaks were present. Based on the findings, the high-temperature wear mechanism of Ta-10W alloy was also discussed.

Experimental study on energy storage characteristics of packed bed using different solid materials

The packed bed energy storage system can solve the mismatch between solar energy supply and demand at a low cost. The physical properties of storage materials have a decisive impact on the performance of storage systems. Different scenarios may require different storage materials. Studying the impact of storage materials on storage characteristics is crucial. However, the comparative analysis and research on different TES materials are focused on characterization and numerical simulation but less on packed bed TES experiments. This paper evaluates the thermal durabilities of three materials, including sintered ore particles, alumina balls, and rock particles, through thermal cycling tests. Through packed bed heat storage experiments, the energy storage characteristics and thermocline evolution characteristics of three beds under different operating conditions are compared and analyzed. The results indicate that all materials exhibit excellent thermal durabilities. A larger bed voidage and smaller bed heat capacity are beneficial for thermal diffusion in the bed. When reverse charging, the natural convection of air in the bed enhances the convective heat transfer effect, resulting in a higher charging power. The existence of natural convection promotes the mixing of cold air and hot air in the tank, increases the irreversibility of the process, and leads to a significantly lower efficiency in reverse flow compared to that in forward flow. When changing the airflow direction, the system overall exergy efficiencies of SOP, alumina, and rock bed decrease from 74.1 %, 72.4 %, and 77.2 % to 47.0 %, 39.9 %, and 45.8 %, respectively. Regardless of the airflow direction, the smaller the bed voidage and the larger the bed heat capacity, the better the maintenance characteristics of the thermocline.

Evaluation of Load on Cervical Disc Prosthesis by Imposing Complex Motion: Multiplanar Motion and Combined Rotational-Translational Motion.

(1) Background: The kinematic characteristics of disc prosthesis undergoing complex motion are not well understood. Therefore, examining complex motion may provide an improved understanding of the post-operative behavior of spinal implants. (2) Methods: The aim of this study was to develop kinematic tests that simulate multiplanar motion and combined rotational-translational motion in a disc prosthesis. In this context, five generic zirconia-toughened alumina (BIOLOX®delta, CeramTec, Germany) ball and socket samples were tested in a 6 DOF spine simulator under displacement control with an axial compressive force of 100 N in five motion modes: (1) flexion-extension (FE = ± 7.5°), (2) lateral bending (LB = ± 6°), (3) combined FE-LB (4) combined FE and anteroposterior translation (AP = 3 mm), and (5) combined LB and lateral motion (3 mm). For combined rotational-translational motion, two scenarios were analyzed: excessive translational movement after sample rotation (scenario 1) and excessive translational movement during rotation (scenario 2). (3) Results: For combined FE-LB, the resultant forces and moments were higher compared to the unidirectional motion modes. For combined rotational-translational motion (scenario 1), subluxation occurred at FE = 7.5° with an incremental increase in AP translation = 1.49 ± 0.18 mm, and LB = 6° with an incremental increase of lateral translation = 2.22 ± 0.16 mm. At the subluxation point, the incremental increase in AP force and lateral force were 30.4 ± 3.14 N and 40.8 ± 2.56 N in FE and LB, respectively, compared to the forces at the same angles during unidirectional motion. For scenario 2, subluxation occurred at FE = 4.93° with an incremental increase in AP translation = 1.75 mm, and LB = 4.52° with an incremental increase in lateral translation = 1.99 mm. At the subluxation point, the incremental increase in AP force and lateral force were 39.17 N and 38.94 N in FE and LB, respectively, compared to the forces in the same angles during the unidirectional motion. (4) Conclusions: The new test protocols improved the understanding of in vivo-like behavior from in vitro testing. Simultaneous translation-rotation motion was shown to provoke subluxation at lower motion extents. Following further validation of the proposed complex motion testing, these new methods can be applied future development and characterization of spinal motion-preserving implants.

Friction and Wear Behavior of Double-Walled Carbon Nanotube-Yttria-Stabilized ZrO2 Nanocomposites Prepared by Spark Plasma Sintering.

Double-walled carbon nanotube-yttria-stabilized ZrO2 nanocomposites are prepared by a mixing route followed by Spark Plasma Sintering. The double-walled carbon nanotubes (DWCNTs) have been previously subjected to a covalent functionalization. The nanocomposites present a high densification and show a homogenous dispersion of DWCNTs into a matrix about 100 nm in size. The DWCNTs are well distributed at the matrix grain boundaries but form larger bundles upon the increase in carbon content. The Vickers microhardness of the nanocomposites decreases regularly upon the increase in carbon content. Incorporation of carbon at contents higher than 2 wt.% results in significantly lower friction coefficients, both against alumina and steel balls, possibly because of the elastic deformation of the DWCNTs at the surface of the sample. Their presence also favors a reduction of the steel/ceramic contacts and reduces the wear of the steel ball at high loads. DWCNTs improve wear resistance and reduce friction without incurring any severe damage, contrary to multi-walled carbon nanotubes.

Duplex surface engineering of cold spray Ti coatings and physical vapor-deposited TiN and AlTiN thin films

The feasibility of a duplex coating based on cold spray technology and magnetron sputtering was evaluated for repair applications requiring a ‘thin-on-thick’ layered structure. Commercially pure angular-shaped Ti grade 4 particles are fed to a cold spray gun and accelerated toward a Ti alloy substrate to deposit thick coatings (∼4.5 mm). TiN and AlTiN thin films are deposited on polished cold spray coatings using a four-source closed-field unbalanced magnetron sputtering (CFUBMS) system. Microstructure was characterized using focused ion beam (FIB) lift-out, scanning electron microscopy (SEM), and electron channeling contrast imaging (ECCI). The nanoindentation technique was used to evaluate the mechanical properties of coatings. The H/E ratios and H3/E2 ratios for TiN films were found to be 0.098 and 0.26 GPa, respectively, while those for AlTiN films were measured at 0.066 and 0.052 GPa, respectively, suggesting higher capacity of TiN films to withstand both elastic and plastic deformation. Using scratch testing, the adhesion of TiN and AlTiN thin films to cold spray Ti was investigated, with TiN-Ti duplex coatings exhibiting better performance compared to AlTiN-Ti coatings. Tribological testing was performed on duplex coatings using a reciprocating tribometer equipped with an alumina ball counterface. The wear rate for AlTiN-Ti coatings after 2000 sliding cycles was found to be (1.0 × 10−3 ± 0.1 × 10−3 mm3/Nm), three orders of magnitudes higher than that for TiN-Ti (8 × 10−6 ± 2 × 10−6 mm3/Nm. SEM was used to reveal worn surface morphologies and cross-sectional analysis of the wear track. Subsurface microstructural changes due to wear were examined using focused ion beam cross-sectioning, revealing bending cracks and tribofilm formation.

Synthesis and tribological characterization of cold-sprayed Ni-based composite coatings containing Ag, MoS2 and h-BN

The tribo components often fail to perform in a desired way due to absence of adequate lubrication in severe conditions and may cause loss of material. Even under room temperature (RT), it is desirable to maintain the proper lubrication for efficient functioning. In recent years, many efforts have been made to develop a coating material which can facilitate low friction and wear properties in diverse working conditions. The proper use of the solid lubricants can deliver utmost lubricity and, therefore, minimize the loss of materials. Solid lubricating coatings have found various industrial applications in harsh environmental conditions, such as in internal combustion engine, gas turbine and aircraft. As far as development of coating is concerned, cold spray (CS) technology has been observed to develop the coatings at relatively low temperature (avoids decomposition) as compared to conventional thermal spray technologies (plasma spray & high velocity oxy fuel). In the current investigation, synergistic response of the participating solid lubricants viz. silver (Ag), molybdenum disulfide (MoS2) and hexagonal boron nitride (h-BN) on the tribological properties of the developed coatings were studied in various working regime of loads. The tribological characteristics of different composite coatings, such as NiAl-MoS2-Ag (NB0), NiAl-MoS2-Ag-5 wt. % hBN (NB5), NiAl-MoS2-Ag-7.5 wt % hBN (NB7.5) and NiAl-MoS2-Ag-10 wt % hBN (NB10) against alumina ball were explored at various loads (6, 11, 16 and 21 N) and at a fixed speed of 0.3 m/s under room temperature (RT). The fixed concentration of Ag and MoS2 with varying weight percentage of h-BN (0, 5, 7.5 and 10 wt %) were introduced as solid lubricants for evaluating the lubricating potential of h-BN. During the tests, coefficient of friction (COF) and wear rate were observed to lessen as the load increased from 6 to 16 N. However, increased COF and wear rate were noticed for all the participating coatings at higher load (21 N). The ideal content of hBN in the deposited coatings was ascertained in order to get the utmost favourable lubricating conditions. It was observed that NB7.5 coating exhibited the enhanced tribological characteristics under the aforesaid operating conditions. Coating NB7.5 shows the best friction and wear characteristics during each testing load and reached a COF (0.19) and wear rate (2.1 × 10−5 mm3/Nm) at 16 N load. The observed wear mechanisms were analysed on the basis of the synergy shown by Ag, MoS2, and hBN as well as the optimal hBN level in the coating (NB7.5) which helped in attaining the improved tribological properties.

Temperature-induced wear micro-mechanism transition in additively deposited nickel alloys with different solid lubricants

Additive manufacturing of self-lubricating alloys plays a crucial role in the production of complex wear-resistant components and in expanding repair capabilities, especially for intricate wear parts with low tolerances (e.g. with cooling channels). Herein, we report a novel approach providing nickel-based alloy with an excellent tribological performance in dry sliding contacts. Laser-deposited self-lubricating nickel alloys, infused with anti-wear additives of molybdenum disulfide, nickel sulfide, copper sulfide, or bismuth sulfide, were subjected to dry sliding wear tests against an alumina ball counterbody at a temperature range of up to 800 °C. The self-lubricating alloys exhibited a significant decline in friction (43 %) and wear (45 %) at room temperature, 400 °C (friction 40 %, wear rate 55 %), and 600 °C (MoS2-based, friction 58 %, wear rate 75 %). The MoS2-based alloy coating demonstrated excellent performance characteristics up to 800 °C (friction coefficient ⁓0.25, wear rate 11 × 10−6 mm3 N−1 m−1) due to the formation of a ‘glazed’ tribolayer. Wear mapping allowed to identification of a critical condition for self-lubricating alloys where positive transitions in wear mechanisms led to a synergistic lubrication mode involving the formation of tribologically induced new lubricious phases such as silver molybdate or nickel-bismuth intermetallic. This work provides a comparative evaluation of the micromechanisms, surface transitions, and tribochemistry of solid lubricants at a wide temperature range and a variety of applications.

Exploring the Interplay between Tribocorrosion and Surface Chemistry of the ASTM F139 Surgical Stainless Steel in Phosphate-Buffered Saline Solution.

Surgical ASTM F139 stainless steel is used for temporary fixtures in the biomedical field. Tribocorrosion is a major concern in this application. The aim of the present work was to study the interplay between tribocorrosion behavior and the surface chemistry of the ASTM F139 stainless steel in phosphate-buffered saline solution (PBS). Sliding wear tests were conducted against alumina balls at different electrochemical potentials: open circuit potential (OCP), cathodic potential (-100 mV versus the OCP), and anodic potentials (+200 mVAg/AgCl and +700 mVAg/AgCl). The normal load was 20 N. The wear volume was estimated based on micrographs obtained from the wear tracks using confocal laser scanning microscopy. Moreover, the wear tracks were also examined by scanning electron microscopy (SEM). The surface chemistry of the ASTM F139 specimens was analyzed by X-ray photoelectron spectroscopy (XPS). The wear volume was dependent on the electrochemical potential, being maximized at +700 mVAg/AgCl. Delamination areas and grooves were observed in the wear tracks. Detailed assessment of the surface chemistry inside the wear tracks allowed identification of the main chemical species and their relative quantities, thus enabling correlation of the passive film composition with the observed tribocorrosion behavior.

Micro-arc and thermal oxidized titanium matrix composites for tribocorrosion-resistant biomedical implants

Superior tribocorrosion resistance is offered by titanium matrix composites (TMCs) compared to their unreinforced matrix metal, but bioactivity concerns are raised for biomedical applications. Simple methods such as micro-arc oxidation (MAO) and thermal oxidation (TO) are employed to enhance the bioactivity and degradation resistance of Ti. However, the impact of those surface treatments on TMC surfaces is poorly understood. Therefore, the present work aimed to explore the influence of MAO and TO treatments on the surfaces of in-situ Ti-TiB-TiC and ex-situ Ti-B4C composites, and to assess their corrosion and tribocorrosion performance. Corrosion and tribocorrosion tests were conducted in phosphate-buffered saline solution (PBS) at body temperature. Electrochemical assays were performed by means of potentiodynamic polarization scans while additional potentiostatic tests were performed for the untreated ex-situ composites. Tribo-electrochemical assays were conducted under open circuit potential (OCP) and under normal loads of 0.5 and 10 N against a 10 mm diameter alumina ball in a reciprocating ball-on-plate tribometer. Results revealed reinforcement detachments in ex-situ composites after both treatments. This was primarily attributed to oxide layer growth at the reinforcement/reaction zone interface. Hence, the use of MAO and TO on ex-situ Ti-B4C composites may not be appropriate for biomedical applications, mainly because the B4C particles tend to detach during the treatment. In contrast, TO-treated in-situ composites displayed excellent combination of corrosion and tribocorrosion performance, even under elevated applied loads, mainly due to the existence of the oxygen diffusion zone (ODZ) beneath the oxide surface produced by TO, together with the more stable electrochemical properties observed during steady-state conditions.

Surface Depassivation via B-O Dative Bonds Affects the Friction Performance of B-Doped Carbon Coatings.

Boron doping of diamond-like carbon coatings has multiple effects on their tribological properties. While boron typically reduces wear in cutting applications, some B-doped coatings show poor tribological performance compared with undoped films. This is the case of the tribological tests presented in this work in which an alumina ball is placed in frictional contact with different undoped and B-doped amorphous carbon coatings in humid air. With B-doped coatings, a higher friction coefficient at a steady state with respect to their undoped counterparts was observed. Estimates of the average contact shear stress based on experimental friction coefficients, surface topographies, and Persson's contact theory suggest that the increased friction is compatible with the formation of a sparse network of interfacial ether bonds leading to a mild cold-welding friction regime, as documented in the literature. Tight binding and density functional theory simulations were performed to investigate the chemical effect of B-doping on the interfacial properties of the carbon coatings. The results reveal that OH groups that normally passivate carbon surfaces in humid environments can be activated by boron and form B-O dative bonds across the tribological interfaces, leading to a mild cold-welding friction regime. Simulations performed on different tribological pairs suggest that this mechanism could be valid for B-doped carbon surfaces in contact with a variety of materials. In general, this study highlights the impact that subtle modifications in surface and interface chemistry caused by the presence of impurities can have on macroscopic properties, such as friction and wear.

High-Temperature Tribology of Selective Laser-Melted Titanium Alloys: Role of Adhesive Wear

Abstract Titanium alloys (Ti6Al4V) are emerging materials used in many engineering applications, especially aerospace, due to their strength-to-weight ratio, corrosion resistance, and high specific strength. The selective laser melting (SLM) process is vividly used to fabricate components with minimum material usage, which reduces the total weight of the product. The hard particles in the atmosphere repeatedly hit the aircraft turbine blades in a rotary motion during aircraft operations. Due to significant sliding action between articulating surfaces, these turbine blades need good wear resistance. With this motivation, rotary wear tests were performed under high vacuum at three different temperatures: room temperature, 400 °C, and 850 °C on as-built and heat-treated titanium alloy fabricated by the SLM process. The parameters like the speed, number of cycles, time, and high vacuum were considered to be constant while performing these high-temperature tribology experiments. As-built and heat-treated samples against the alumina ball resulted in lower coefficient of friction (COF) values at high temperatures compared to room temperature. In addition, adhesive wear was found to be the dominant wear mechanism at high temperatures. From the morphological studies, plowing strips, plowing ridges, and shallow grooves were significantly noticed on the worn-out surfaces of the heat-treated samples. Although low COF values were obtained at high temperatures on tested samples, higher specific wear-rates were seen in these samples due to the continuous removal of soft material.

Effect of grain size on tribological behavior of hot‐pressed boron carbide sliding against alumina balls

AbstractBoron carbide ceramics (B4C) have extraordinary hardness and well‐abrasive resistance, while the tribological behavior of ceramic materials is complicated, which are affected by microstructures, mechanical properties, and surface characteristics, and so on. In this paper, the effect of grain size on the mechanical properties especially the wear resistance of hot‐pressed B4C was investigated. The average coefficient of friction of the B4C/Al2O3 friction pair ranges from .41 to .66. The sample with the minimum grain size possesses the lowest wear rate of about 2.15 × 10−6–7.66 × 10−6 mm3∙N−1∙m−1. The analysis of the wear rate (WR) and grain size (G) indicates that the wear resistance (WR−1) and the reciprocal of the square root of grain size (G−1/2) are in line with the Hall–Petch relation. Fracture and the resulting abrasive wear are the main wear mechanisms of B4C in the dry sliding process. This success provides a theoretical basis and a design approach of microstructure to improve the tribological behavior of ceramic materials.

High-temperature dry sliding wear behavior of additively manufactured austenitic stainless steel (316L)

Austenitic steels are commonly used in aero-engine components owing to their higher thermal resistance to wear and corrosion. This study investigates the high-temperature dry sliding wear behavior of direct metal laser-sintered (DMLS) austenitic stainless steel (SS 316L) up to 400°C. A dry sliding reciprocating wear test conducted on a high-frequency tribometer with a ball-on-flat setup. High-hardness chrome steel (900 HV0.5) and alumina (1165 HV0.5) balls of 6 mm diameter were used as the steel and ceramic counterbodies against 316L specimen (320 ± 5 HV0.5). When tested against the chrome steel, the initial average coefficient of friction (CoF) decreased to a lower value (0.45) during the initial running-in period. However, with rising temperatures, the CoF also increased, stabilizing at 0.6 under steady-state conditions. A similar CoF pattern was observed in experiments with the alumina counterbody. Wear resistance declined at 100°C, followed by an increase at 200°C due to the development of an oxide glaze on the surface. Subsequently, wear resistance decreased as the temperature continued to rise. Up to 200°C , the wear mechanism was characterized by a combination of abrasive and oxide debris wear, transitioning to adhesive wear with plastic deformation at higher temperatures (400°C). Diffraction (XRD) analysis revealed the formation of oxide layers and martensite phase at higher temperatures, contributing to the observed improved wear resistance around 200°C . However, these oxide layers were progressively removed from the surface at 400°C, leading to an increased wear. The measured wear rates are two times lower, up to 200°C, compared to the reported values for conventional 316L due to the fine microstructure and higher hardness of DMLS SS 316L. This results in potentially rendering it suitable for applications where high-temperature (up to 200°C) wear-resistant SS is needed. This study provides further insights into the importance of post-treatment of DMLS parts for temperature beyond 400°C.

Enhancing wear performance: A comparative study of traditional vs. additive manufacturing techniques for 17–4pH SS

This study investigates the microstructural, mechanical, and tribological characteristics of 17–4 PH stainless steel specimens produced through Additive Manufacturing (AM) techniques, namely Selective Laser Melting (SLM) and Fused Filament Fabrication (FFF), in comparison to conventionally wrought steel (W). The wear test carried out on the samples were pin-on-disk, ball-on-plate and lubricated pin-on-disk. The counter part was an alumina ball with a diameter of 3 mm. The wear scar was less pronounced on lubrication test than in dry conditions for all samples. The coefficients of friction (COFs) were higher in dry conditions (in the order of 10−1) than in lubrication conditions (in the order of 10−2). Moreover, the wear rate had a significant reduction under lubrication conditions (in dry tests are in the order of 10−7, while lubrication conditions led to results in the order of 10−9). Additionally, FFF and SLM exhibited remarkably low wear rates in comparison to the wrought sample showing a superior dry and lubricated wear behaviour. AM allows for comparable or improved properties, despite slightly lower hardness due to retained austenite/delta ferrite and reduced precipitates. That significant improvement enhances the appeal of AM for high-performance components, particularly for small production runs and complex geometries being a promising and efficient technology for diverse industries.

Wear behavior at high temperature of ZrO2–Y2O3 (YSZ) plasma-sprayed coatings

The wear behavior of two plasma-sprayed zirconia–yttria coatings was studied at high temperatures. Agglomerated and sintered, as well as fused and crushed zirconia–yttria feedstock powders were used to manufacture bimodal and monomodal coatings by atmospheric plasma spraying onto an INCONEL 718 substrate previously coated with a NiCrAlY bond coat. The structure of the coatings was analyzed by SEM on their cross section and surface. The samples were subjected to wear conditions by sliding contact through a ball-on-disk test up to 1000 °C, using an alumina ball 6 mm in diameter as the counterbody, on which a load of 5 N was applied. The samples were rotated during 20000 cycles, reaching a speed of 0.10 m·s−1 at the contact area with the counterbody. The porosity, phase, and mechanical properties were determined before and after wear tests. The results indicate that at 25 °C, both coatings have enough mechanical resistance to withstand the tribological conditions they were exposed to. Therefore, low wear rates were produced by ductile deformation. The tribological conditions became more aggressive as the thermal stresses increased with the test temperature, producing cracking, and detaching particles in the coatings tested at 500 and 750 °C. Consequently, high wear rates related to brittle deformation were obtained. However, the transformation of the amorphous phase to the t′-zirconia phase, produced at 1000 °C, increased the hardness of both coatings and, consequently, their wear resistance; thus, the predominant mechanism of damage was ductile deformation, with wear rates similar to those obtained when the coatings were tested at 25 °C.

Investigation of the wear behavior of FeNi36 alloy cut by WEDM method under different loads

PurposeFeNi36 (Invar-36) alloy is widely used in the fabrication of molding tools in aerospace industries but there remains a need to improve its wear and friction performance due to its relatively low hardness. The formation of a heat affected zone (HAZ) on the surface of Invar-36 cut by wire electric discharge machining (WEDM) is promising to enhance its tribological properties. This study aims to investigate the tribological performance of WEDM-treated Invar-36 via a ball-on-disk tribometer in dry-sliding conditions.Design/methodology/approachThe untreated and WEDM-treated Invar-36 surfaces were reciprocated against an alumina ball at a sliding velocity of 40 mm/s, a stroke length of 10 mm and a sliding duration of 125 min under loads of 5, 10 and 20 N. The worn surfaces were characterized using a 2D profilometry and a scanning electron microscope equipped with energy-dispersive spectroscopy.FindingsThe results showed that the WEDM-treated surface had a superior friction coefficient and wear resistance in comparison to the untreated surface, due to the grown HAZ. There was found to be a 9.3%–11.4% decrease in the friction coefficient and a 47%–57% reduction in the wear volume after the WEDM treatment. Both the untreated and WEDM-treated Invar-36 surfaces found abrasion and plastic deformation as the dominant wear mechanisms.Originality/valuePrevious works have not focused on the tribological performance of the WEDM-treated Invar-36 extensively used for molding tools in aerospace industries. Our findings provide compelling evidence that the WEDM treatment improved the wear and friction performance of Invar-36 alloy because of the grown HAZ.

Replacing Toxic Hard Chrome Coatings: Exploring the Tribocorrosion Behaviour of Electroless Nickel-Boron Coatings

Electroless nickel-boron coatings present outstanding properties such as high hardness, excellent wear resistance and uniform coating, and thus they are considered to be alternative to toxic hard chrome coatings. However, they contain lead that is toxic and used as stabilizer in the plating bath. This study aims to investigate the tribocorrosion behaviour of lead-free electroless nickel-boron coatings. In the present research, several tests were carried out to investigate the behaviour of these coatings under both dry and tribocorrosion reciprocating sliding wear against alumina balls, at room temperature. The open circuit potential (OCP) method was used to determine the degradation mechanism of the coatings. The results of the tribocorrosion and dry wear tests showed that the performance of coatings was very different from each other. A steady state for the coefficient of friction (COF) is achieved during the tribocorrosion test, whereas the constant production of debris and their presence in the contact implied an increase in COF with distance during the dry wear test. The wear mechanisms of these coatings also presented variations in these tests. It was found that the wear area calculated from tribocorrosion is lower (56 µm2) than the one from dry sliding test (86 µm2).

Integrated Process for High Phenol Removal from Wastewater Employing a ZnO Nanocatalyst in an Ozonation Reaction in a Packed Bubble Column Reactor

The use of an ozonized bubble column reactor (OBCR) in wastewater treatment is advantageous due to its efficient mixing and mass transfer characteristics. Among all high-performance features, the ozonation reaction in a BCR undergoes a low dissolution of O3 in the reactor with a limited reaction rate. In this study, the ozonation reaction of phenol in an OBCR was tested using a ZnO nanocatalyst and alumina balls as packing material. Three concentrations of O3 were evaluated (i.e., 10, 15, and 20 ppm), and 20 ppm was found to be the optimum concentration for phenol degradation. Also, two doses (i.e., 0.05 and 0.1 g/L) of ZnO nanocatalysts were applied in the reaction mixture, with the optimal dose found to be 0.1 g/L. Accordingly, three phenol concentrations were investigated in the OBCR (i.e., 15, 20, and 25 ppm) using four treatment methods (i.e., O3 alone, O3/Al2O3, O3/ZnO nanocatalyst, and O3/Al2O3/ZnO nanocatalyst). At a contact time of 60 min and phenol concentration of 15 ppm, the removal rate was 66.2, 73.1, 74.5, and 86.8% for each treatment method, respectively. The treatment experiment that applied the O3/Al2O3/ZnO nanocatalyst produced the highest phenol conversion into CO2 and H2O in the shortest contact time for all phenol concentrations. Thus, the OBCR employed with a ZnO nanocatalyst plus packing material is a promising technology for the rapid and active removal of phenol because it enhances the number of hydroxyl radicals (•OH) generated, which ultimately increases the oxidation activity in the OBCR. Also, the results showed efficient flow characteristics in the OBCR, with channeling problems averted due to appropriate gas movement resulting from the use of packing materials. Finally, it was found that the ozonation process in an OBCR is an efficient method for phenol conversion with good economic feasibility.

Structure, mechanical and tribological properties of Ta-xN coatings deposited by reactive HiTUS

This work investigates the structure, mechanical, and tribological properties of Ta-xN coatings deposited using reactive High Target Utilization Sputtering (HiTUS) with a focus on the role of tribological layers formed in the sliding contacts. The scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy observations revealed that the gradual increase of nitrogen flow results in the transition from textured fcc Ta structure (without nitrogen) toward mixed sub-stoichiometric Ta-Ny/Ta2N/amorphous structures up to near-stoichiometric fcc TaN coatings. The highest hardness HIT ∼37 GPa and indentation modulus EIT ∼375 GPa as well as the lowest coefficients of friction (COF) in the range 0.16–0.36 and wear rates around 3 × 10−7 mm2/N·m were obtained in the layer with Ta2N structure. The unique combination of low COF and high wear resistance combined with high hardness and stiffness were attributed to the shear sliding between Ta2O5-based transfer film in the wear track and pure alumina ball.