Narrow Results

This study is focused on improving the mechanical properties and slurry erosion resistance of traditional Ni–20Al₂O₃ and Ni–20Cr₂O₃ thermal spray coatings by reducing the 5% of Al₂O₃ and Cr₂O₃, respectively, and addition of 5% TiO₂ feedstock in both coatings. Thermal sprayed powders were thermally sprayed on SS-420 substrates with high-velocity oxy-fuel (HVOF) method. A lab-scale pot tester was used to conduct the wear testing at low rotating speeds of 750, 1000, 1250, and 1500 rpm. To create severe accelerated conditions, a high mass flux (35–50 wt.%) of fly ash particles was used. Multi-sized fly ash slurries ranging from $<53$$\mu$m to 250$\mu$m were used during the experiments to evaluate the impact of particle size fraction on the erosion over a 30–120 min time-period. Coatings’ surface characterization was done to examine more about their composition. According to the findings, the addition of 5% TiO₂ powder to both Ni–15%Al₂O₃ and Ni–15%Cr₂O₃ coatings significantly improved their wear resistance of SS-420. This occurred because of the enhancement of hardness as well as brittleness by 5% TiO₂ in matrix of Ni–15%Cr₂O₃ and Ni–15%Al₂O₃ coatings. Moreover, TiO₂ particles aid in strengthening of Cr₂O₃ and Al₂O₃ reinforcements and the binding with matrix. Also, the results showed that Ni–15Cr₂O₃–5TiO₂ coating showed superior wear resistance compared to Ni–15Al₂O₃–5TiO₂ coating.

In this paper, a novel support vector machine (SVM) learning approach has been used to predict the silt erosion of coatings sprayed by the high-velocity oxy-fuel (HVOF) process. The silt erosion resistance of HVOF-coated Co- and Ni-alloys is studied using an erosion tester. Both of these spraying powders were deposited on the 18Cr-12Ni-2Mo austenitic steel substrate. For the erosion experiments, the fixtures were developed to test the erosion characteristics at different impingement conditions (i.e. $30^{\circ }$, $45^{\circ }$, and $60^{\circ }$). The image processing technique enables an understanding of the erosion mechanisms of coatings. The support vector regression is more effective than the traditional regression models. The proposed model employs support vector regression with parameter tuning. The ideal parameters are selected with the help of the grid search method. The model is trained by supplying 70% data and validated with 15% data. Afterward, the remaining 15% is given to the prepared model as testing data. The dataset obtained is employed for building an effective support vector regression model. The predicted results are compared against the original experimental values. The developed model is also compared with other state-of-the-art machine learning techniques for showing the preciseness of the proposed model. The Ni-based HVOF coating showed superior performance ($\sim 17\%$) better than the Co-based HVOF coating under similar experimental conditions. An SVM model was successfully developed to predict the erosion of coated and uncoated 18Cr-12Ni-2Mo austenitic steel. The precision performance of the SVM model was calculated in terms of $R^2$, RMSE, $R$, and MAE as 0.99, $1.12\times 10^{-6}$, 0.99, and $9.13\times 10^{-7}$, respectively.

Aluminum metal matrix composites (AMMCs) are currently widely engaged in industrial sectors. No other monolithic material can match the characteristics of AMMCs. AMMCs are stronger than traditional materials and have a wide range of industrial uses. This research work aims to study the tribological properties of AA8079/Zirconium boride (ZrB₂) composite manufactured via the stir casting (SC) process. The different combinations of composites are AA8079/0wt.% ZrB₂, AA8079/5wt.% ZrB₂, AA8079/10wt.% ZrB₂, and AA8079/15wt.% ZrB₂. The parameters are reinforcement wt.% [A], load [B], sliding velocity [C], and sliding distance [D]. When designing experiments using the Taguchi method, an L${}_{16}$ orthogonal array was used. In order to determine which process parameter had the biggest influence on the output variables, wear rate (WR), coefficient of friction (COF), and analysis of variance (ANOVA) were applied. Successful fabrication of different weight fractions of ZrB₂ was synthesized with AA8079 matrix through the SC process. The microstructural investigations revealed the dispersion of ZrB₂ particles over the surface of the base AA8079. The response table clearly depicts that the combinations of A and C are the more dominant factor for WR, while the combinations of B and C are the more interacting parameters for COF. From the ANOVA results, it is clear that A with a 55.26% contribution, is the most predominant parameter in attaining the least WR, and for COF, B with a 31.39% contribution, is the major influencing parameter.

Rheological properties of Cholesteryl n-valerate, Cholesteryl decanoate and Cholesteryl myristate which are esters of cholesterol have been studied. Phase transition temperatures and rheological parameters such as viscosity, elastic modulus G${}^{\prime }$, loss modulus G${}^{″}$ as functions of temperature, shear rate and time are investigated. In frequency sweep test, a higher transition crossover region has occurred for Cholesteryl myristate, whereas for Cholesteryl n-valerate a frequency-independent plateau prevailed for both the moduli. The occurrence of blue phase in Cholesteryl decanoate during temperature sweep measurements is an indication for the rheological support. The results for steady state have informed that cholesteric esters are having non-Newtonian flow behavior in their respective cholesteric phases. The power-law model has explained well the shear rate dependence of shear stress. A few practical applications of these esters as lubricant additives are discussed, too.

In order to satisfy the requirements of precise components with tidiness, low power and high stability in the field of biological engineering, medical equipment and semiconductors etc. a pre-stress acoustic transport prototype without horn was proposed in this paper. The mechanism of levitation and transport which is driven by orthogonal waves was revealed by the analysis of waveform and squeeze film characteristics in high-frequency exciting condition; also, the electric, solid and acoustic coupled finite element method (FEM) was established to investigate the effect of pre-stress and acoustic pressure distribution in the near field. The levitation and driving capacity of near field acoustic levitation (NFAL) transport platform without horns can be proved in this experiment and further to achieve the goal of parameters optimization. The theoretical and experimental results indicate that the pre-stress has a significant effect on resonant frequency and levitating stability, the pre-stress are determined by the DC voltage offset which is related to the system working point so that we cannot increase the offset and exciting voltage unlimitedly to improve the stability. At the same time, the calculated pressure distribution of acoustic radiation can generally reflect the regional bearing capacity in near and far field for levitation. These achievements can partly solve the problem of accuracy design of prototype and thickness of gas film, supporting for accuracy close loop control of levitating height.

Analysis of wear debris carried by a lubricant in an oil-wetted system provides important information about the condition of a machine. This paper describes the analysis of microscopic metal particles generated by wear using computer vision and image processing. The aim is to classify these particles according to their morphology and surface texture and by using the information obtained, to predict wear failure modes in engines and other machinery. This approach obviates the need for specialists and reliance on human visual inspection techniques. The procedure reported in this paper, is used to classify surface features of the wear particles by using artificial neural networks. A visual comparison between cooccurrence matrices representing five different texture classes is described. Based on these comparisons, matrices of reduced sizes are utilized to train a feed-forward neural classifier in order to distinguish between the various texture classes.

Nanoscale frictional phenomena at solid–solid surfaces with lubricants are studied numerically using a lattice model which consists of two rigid substrates and a monolayer of lubricant molecules. The maximum static frictional force, which works on the driven upper solid, is always finite and obeys a certain scaling relation. The lubricant layer, however, shows a kind of phase transition from a pinned state to free sliding state when the strength of the interaction potential with the substrates decreases. We discuss the peculiar pinning mechanism of the upper substrate in the presence of a lubricant monolayer.

The purpose of this study was to determine the friction coefficients and wear rates of six commercially available dental ceramics including IPS Empress 2 (E2), Cergo Pressable Ceramic (CPC), Cercon Ceram (CCS) and Super porcelain EX-3 (SPE). Bovine enamel (BE) was also tested as a reference material for comparison purposes. Samples of the dental ceramics were prepared according to the instructions described by the manufacturers in disk-shape with nominal dimensions of 12 mm × 2 mm. The wear tests were performed by means of a pin-on-disk type tribometer. The friction coefficients and specific wear rates of the materials were determined at a load of 10 N and rotating speed of 0.25 cm/s without lubrication. Surface morphology of the wear tracks was examined using a scanning electron microscope. Statistical analyses were made using one-way ANOVA and Turkey's HSD (P < 0.05).

Nitriding is usually used to improve the surface properties of steel materials. In this way, the wear resistance of steels is improved. We conducted a series of studies in order to investigate the microstructural, mechanical and tribological properties of salt bath nitrided AISI 4140 steel. The present study has two parts. For the first phase, the tribological behavior of the AISI 4140 steel which was nitrided in sulfinuz salt bath (SBN) was compared to the behavior of the same steel which was untreated. After surface characterization using metallography, microhardness and sliding wear tests were performed on a block-on-cylinder machine in which carbonized AISI 52100 steel discs were used as the counter face. For the examined AISI 4140 steel samples with and without surface treatment, the evolution of both the friction coefficient and of the wear behavior were determined under various loads, at different sliding velocities and a total sliding distance of 1000 m. The test results showed that wear resistance increased with the nitriding process, friction coefficient decreased due to the sulfur in salt bath and friction coefficient depended systematically on surface hardness. For the second part of this study, four artificial neural network (ANN) models were designed to predict the weight loss and friction coefficient of the nitrided and unnitrided AISI 4140 steel. Load, velocity and sliding distance were used as input. Back-propagation algorithm was chosen for training the ANN. Statistical measurements of R², MAE and RMSE were employed to evaluate the success of the systems. The results showed that all the systems produced successful results.

In order to improve the tribological performance of AISI 316 stainless steel (316 SS) under grease lubrication, electrochemical processing was conducted on it to obtain a rough (surface texturing-like) surface by making use of the high sensitivity of austenitic stainless steel to pitting corrosion in Cl^--rich environment. Numerous corrosion pits or micro-ditches acted as micro-reservoirs on the obtained surface. While the grease could offer consistent lubrication, and then improve the tribological performance of 316 SS. Tribological behaviors of raw 316 SS and the treated sample were measured using a reciprocating type tribometer sliding against GCr15 steel counterpart under dry and grease lubrication conditions. The results showed that the mass losses of the two samples were in the same order of magnitude, and the raw sample exhibited lower friction coefficient in dry sliding. When the tests were conducted under grease lubrication condition, the friction coefficients and mass losses of the treated sample were far lower than those of the raw 316 SS. The tribological performance of 316 SS under grease lubrication was drastically improved after electrochemical processing.

In this study, the effect of diamond interlayer on the tribological properties of titanium aluminum nitride (TiAlN) film sliding against medium carbon steel is investigated in dry rotary friction tests, by evaluating the coefficients of friction (COFs), wear rates, worn surfaces and element transitions of the contacted surfaces in the cemented carbide (WC-Co)-steel, TiAlN-steel, microcrystalline diamond (MCD)-steel, TiAlN/MCD-steel, micro- and nano-crystalline diamond (MNCD)-steel and TiAlN/MNCD-steel contacting pairs. It is found that compared with the TiAlN monolayer, the TiAlN/MCD bilayer film shows 57% higher COF, while the COF of TiAlN/MNCD multilayer inversely drops as much as 54%, due to the distinguished surface diamond grain morphologies of the MCD and MNCD interlayers as well as the copied effect of the TiAlN layer with relatively small thickness. Meanwhile, the diamond interlayer can provide robust load support for the top TiAlN layer, induce the wear mechanism transform from the abrasive wear to adhesive wear, and result in the mild wear of TiAlN/MCD and TiAlN/MNCD multilayers compared to the TiAlN monolayer. Moreover, the softer TiAlN top layer on MCD and MNCD interlayers can effectively improve the storage capacity of element oxygen and worn steel ball debris as well as accelerating the surface chemical reactions to form a smoother continuous ionic metal oxides tribofilm in the contacted zones due to its good self-lubricating property. Among all the hard coatings discussed when sliding against medium carbon steel, the TiAlN/MNCD coating shows the lowest COF and mild wear, due to the robust load support capacity of the beneath MNCD layer as well as the good self-lubricated and tribofilm formation capacity of the top TiAlN layer, which shows broad application potential in carbon steel machining.

This study presents the tribological behavior of austenitic 316L Stainless Steel (SS) coated with nano Tungsten Carbide (WC). The nano WC particles were prepared by mechano chemical method. The tungsten and toluene have been ball milled for 40h led to the synthesis of WC nano particles. An average particles size of 48nm was achieved. The prepared nano WC particles were deposited on 316L SS substrate as a thin film using DC magnetron sputtering process. The thickness of the nano WC coating was 5$\mu$m. The synthesized nano WC particles and the thin nano WC film are characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Energy Dispersive X-ray Analysis (EDAX) technique. Vickers microhardness test was conducted to evaluate the microhardness of the thin film. A high microhardness value of 2242 HV${}_{10}$ was observed. The coated specimens are subjected to wear test using pin on disc setup and the tribological parameters such as friction and wear are analyzed. The results were compared with uncoated 316L SS specimen and micro WC particles coated 316L SS. The nano WC coated 316L SS possess high hardness and better wear resistance when compared with 316L SS and micro WC coated 316L SS specimen.

Although electroplated hard chromium coatings were extensively studied and applied in industry, the properties of the coatings after annealing at different temperatures were investigated insufficiently. In this work, the influence of heat treatment on the mechanical, tribological, and structural properties of chromium coating, electrochemically deposited on 38HN3MFA steel were investigated. A specific bath composition and deposition parameters were selected, which has been compared to the literature data. Parameter selections were based on data from military research industry and contain noticeably lower amount of sulfuric acid (1.2g/L), CrO₃ (180g/L) and lower current density (25A/dm${}^2)$. Coefficient of friction and coatings wear rate were measured by means of ball-on-disc method at the temperature of 30${}^{\circ }$C, 200${}^{\circ }$C, 500${}^{\circ }$C, and 700${}^{\circ }$C. The coefficient of friction has decreased from 0.71 for the temperature of 30${}^{\circ }$C to the value of 0.5 for 700${}^{\circ }$C due to the change of wear mechanism. Hardness of the as-received coating reaches the value of 11.4GPa and 9.5, 8.3, 6.4GPa for the samples after annealing in the temperature of 200${}^{\circ }$C, 500${}^{\circ }$C and 700${}^{\circ }$C, respectively. The influence of heat treatment on structural properties of electroplated Cr coatings was studied by X-ray diffraction. Scratch test showed that layer is characterized by excellent adhesion with no adhesive rupture. Cr-coated 38HN3MFA steel exhibits reduced susceptibility to high-temperature degradation by 25%, basing on the mass lost measured at 900${}^{\circ }$C.

This study is focused on the tribological properties of micro- and nano-crystalline diamond (MCD and NCD), non-hydrogenated and hydrogenated diamond-like carbon (DLC and DLC-H) and nitrogen-based (CrN, TiN and TiAlN) coatings sliding against the super alloy Inconel 718, in terms of the maximal and average coefficients of frictions (COFs), the worn morphologies and the specific wear rates, by the rotating ball-on-plate configuration under dry condition. The results show that the nitrogen-based films show comparable COFs and wear rates with the WC–Co substrates. The DLC and DLC-H show lower COFs compared with the nitrogen-based films. Furthermore, their wear resistance is limited due to their low thickness compared with MCD and NCD, which have the same elemental composition. The DLC-H coating exhibits much lower wear rate compared with the DLC coating, which may be derived from the passivation of dangling bonds by the linking of H to C atoms. The MCD and NCD films show the lowest average COFs and mild wear after tribotests, due to their high hardness and low adhesive strength between pure diamond and the super alloy.

Among all the tested films, the NCD film-based tribopair presents the lowest maximal and average COFs, tiny wear debris particles, mild wear of ball and plate without scratching grooves, indicating that the NCD film may be suitable to be deposited on cutting tools for super alloy machining.

In this paper, retrogression and re-aging (RRA) heat treatment was applied to 7075 aluminum alloy in T6 condition at different times (30 and 90min) and temperatures (180^∘C and 240^∘C). While RRA heat treatments increase the corrosion resistance of the material, it does not harm its mechanical properties. On the other hand, the surface resistance of aluminum is low. Surface modifications are applied to overcome this deficiency. Among these, the micro-arc oxidation (MAO) method increases the corrosion resistance and attains excellent values in surface hardness. To better understand the RRA/MAO relationship, heat-treated (RRA) samples with four different parameters were coated with the MAO method. In this way, a ceramic oxide coating layer was created on the material surfaces. In order to determine the RRA parameter effect, the MAO process parameters are kept constant (anode voltage ($V_a$): 500V, cathode voltage ($V_k$): 300V, anode voltage open time ($t_a)$: 300$\mu$s, cathode voltage open time ($t_k$): 200$\mu$s, frequency: 160 coating with Hz, and process time: 20min). Surface properties (coating thickness, surface roughness, surface arc duct’s structure, etc.), phase analysis (X-ray diffraction (XRD)) and microstructures (coating cross-section studies: distance-dependent hardness, coating/backing material interface character, coating porosity ratio) were examined. XRD analysis showed that the main phase of the coatings is $\gamma$-Al₂O₃. A coating layer of around 125$\mu$m was achieved with the growth rate of 6$\mu$m/min. Surface roughness was between 5.5$\mu$m and 8$\mu$m for different RRA parameters. RRA/MAO relation with the characterization made was detailed, and predictions were made for the surface properties of the material (hardness, corrosion resistance, wear, etc.).

Bio-degradable lubricants are the need for industries to promote eco-friendly manufacturing process and protect the workers from health hazards. In this paper, the use of oil–water emulsions from the bio-substitute oils have been formulated and its process parameter on a machining process are optimized using response surface methodology. The emulsions are prepared from the vegetable oils such as castor, mahua, palm and neem oil with polysorbate as emulsifying agent. The friction and wear characteristics are studied with a standard pin on disc tribometer for all the emulsions prepared with the base oils namely castor, mahua and palm oil. From the tribological characterization tests, the castor oil emulsions have shown better performance and stability in comparison to other oils. Hence, castor oil emulsions have been tested for its machining performance studies against a conventional mineral oil emulsion in a turning process. Further, an emulsion based on castor oil and neem oil have been tested for tool wear to utilize the antimicrobial properties of neem oil for reducing the bio fouling effects. The machining performance is indicated based on the surface finish and tool wear. Response surface methodology have been used for optimization of the machining parameters, such as cutting velocity, feed rate and depth of cut to achieve an optimal surface finish for a maximum material removal rate. The results show that the castor oil based emulsion can be used as an excellent alternative for mineral oil emulsions.

Modern technology demands have raised the popularity of aluminum metal matrix composites (AMMCs) as it best suits diverse industrial applications. The need to develop an advanced functional material for specific applications attracts global researchers. Commercial needs for cost-effectiveness, quality improvement, superior performance and high strength to low weight ratio are met by composites. Mass production of AMMCs for specific industrial applications prefer stir casting as a simple and cost-effective manufacturing method. In addition, the production of composites turn more economic by reducing the weight percentage of ceramics and adding natural fibers either in the form of fibers, milled powder or ash to achieve the targeted properties. Process parameters being a dominating factor for minimal defect composites, their effect on final cast products are discussed along with strengthening mechanisms. This paper also discusses the applications, challenges and future scope of natural fiber reinforced AMMCs.

Friction and wear phenomena are common problems in sliding equipment, so materials with excellent antifriction and wear resistance properties are getting increasingly more attention. Two-dimensional (2D) materials, such as graphene and molybdenum disulfide, have always been the research hotspots on account of their special structures and excellent tribological properties. In 2011, MXene, an important member of the 2D material family, was launched. With excellent properties such as ultra-high strength, rich surface end groups, and relatively low cost, MXenes have great potential as lubricant additives. Although these properties have proved to be the reason why MXenes are impressive, the preparation of MXenes composites and the understanding of their mechanical and tribological mechanisms remain to be further investigated. In addition, the abundant surface end groups of MXenes nanosheets make them relatively easy to be functionalized, which has attracted widespread attention. This review aims to comprehensively understand the tribological properties of MXenes nanolayers and to summarize and sort out recent research progress. First, the preparation of MXenes is reviewed, and then the latest research progress of MXenes in liquid lubrication, solid lubrication, and solid–liquid hybrid systems since the advent of MXenes is summarized. Finally, some current problems are presented and an outlook on the development of MXenes is given.

As an excellent solid lubrication material, the poor high-temperature tribological properties of diamond-like carbon (DLC) films severely limit their applications. In this study, tungsten (W) was incorporated into Si-doped DLC films fabricated via reactive magnetron sputtering. The effect of the W content ranging from 0 to 13.12 at.% on the film structure, bonding states, mechanical and high-temperature tribological properties of Si and W co-doped DLC (Si–W-DLC) films has been investigated. The results show that a small amount of tungsten incorporation (4.45 at.%, Si–${\text{W}}_{\text{L}}$-DLC) increases the mechanical properties of the Si–${\text{W}}_{\text{L}}$-DLC film without a significant decrease in the fraction of sp³ content. The incorporation of 4.45 at.% W improves the wear resistance and stabilizes the friction coefficient curves at temperatures up to $400^{\circ }$C. The high residual stress caused by the highly distorted C–W bond and the low friction coefficient attributed to the formation of WO₃ on the sliding surface should be responsible for the excellent tribological performance of the Si–${\text{W}}_{\text{L}}$-DLC film. It is believed that the Si and W co-doped DLC film can provide another strategy for expanding the high-temperature application of DLC films.

This paper aims to provide a method for improving the tribological properties of 316L stainless steels in seawater. During the experimental process, laser texturing technology was used to create biomimetic micro-textures inspired by turtle shell patterns on the 316L stainless steel surfaces. Then, CrAlSiN coating was deposited on the textured surface using the physical vapor deposition (PVD) technique, allowing us to study the frictional properties of the samples in both atmospheric and seawater environments. The results showed that, compared to polished 316L stainless steel, the specimens treated with micro-texture and CrAlSiN coating exhibited a reduction in wear rate by 52.1% and 71.8% under atmospheric and seawater friction conditions, respectively. Under atmospheric friction conditions, the micro-textures had a limited effect on reducing the friction of the 316L stainless steel substrate. However, the CrAlSiN coating, due to its excellent mechanical properties, significantly improved the wear resistance of the 316L stainless steel. Under seawater friction conditions, the continuous CrAlSiN coating played a role in reducing 316L stainless steel wear and seawater corrosion. At the same time, the micro-textures acted as reservoirs for wear debris and seawater, forming a more stable seawater lubricating film and reducing the friction coefficient. Therefore, the synergistic effect of the CrAlSiN coating and biomimetic micro-textures demonstrated remarkable improvement in the tribological performance of 316L stainless steel in seawater environments.