Wear Morphology Research Articles

Additive manufacturing SiC-reinforced maraging steel: Parameter optimisation, microstructure and properties

The unique deposition manner of additive manufacturing (AM) allows the near-net-shaping of components with multiple materials configurations and complex geometries, which sheds light on the process of high-performance metal matrix composites (MMCs). This work explores laser powder bed fusion (LPBF) AM of SiC-reinforced maraging steel MMCs to consolidate the merits of both ceramics and metal matrix for improving overall properties. The laser processing parameters were systematically optimised based on the density, roughness and hardness of the deposited samples. The effects of SiC content on the microstructures, mechanical properties, tribological performance, and wear resistance are elucidated. SiC particles are refined with uniform distribution in the metal matrix after laser processing. The highest tensile strength reaches 1611 ​MPa together with an elongation of about 10.1% with 3 ​vol% SiC addition. The tribological performance of MMCs is investigated by studying the coefficient of friction (COF), wear rate, and worn morphology. The COF has been slightly reduced with the SiC addition, and the wear rate of MS reduced from 3.25 ​× ​10 −5 to 1.72 ​× ​10 −5 mm 3 /Nm with the 12 ​vol% SiC addition. The underlying wear mechanisms are also investigated. Besides, the corrosion behaviour of MMCs is also investigated; the addition of SiC (≥6 ​vol%) has improved the corrosion properties of the matrix.

The effects of cryogenic cooling on tool wear and chip morphology in turning of tantalum-tungsten alloys Ta-2.5W

Tantalum‑tungsten alloy is particularly difficult to cut due to its high plasticity. Environmentally friendly liquid nitrogen cooling and hybrid minimum quantity of lubricant-low temperature CO2 (MQL + CO2) technology can improve the machinability of ductile materials. In this paper, the experimental and numerical turning of tantalum‑tungsten alloy Ta-2.5W were carried out under cryogenic cooling conditions. The effects of liquid nitrogen cooling and MQL + CO2 cooling on the wear mechanism of cutting tools and the formation mechanism of chips were studied. The Rehbinder effect induced by the surfactant in MQL + CO2 system was analyzed. The results show that the cutting tool life can be effectively improved by 50 % in turning of Ta-2.5W under both cryogenic cooling conditions. Different from the flank wear dominated by adhesive wear under water-based emulsified cutting fluid, the tool failure was mainly caused by the notch wear under cryogenic cooling conditions. The chips in turning of high plastic Ta-2.5W showed a “pomelo-meat shaped” morphology with non-uniformed and non-periodic folds. Rehbinder effect was induced by the surfactant in MQL + CO2 system, which transformed the “pomelo-meat shaped” chips into “layered-rock shaped” chips. Under this effect, the machinability of tantalum‑tungsten alloy was effectively improved with a reduction of chip thickness and increment of the tool life.

Influence of sliding orientation on tribological properties of hybrid PTFE/Kevlar fabric composites.

A fabric liner is an ideal self-lubricating material that has been widely used in self-lubricating spherical plain bearings. To investigate the influence of sliding orientation on the tribological properties of fabric liners, samples were prepared for different fiber orientations relative to the sliding direction and wear tests were conducted under normal loads of 25 N to 200 N. Composite-90° (sliding along Kevlar fibers) shows the best friction and wear properties under loads of 50 N and 100 N, while composite-0° (sliding along PTFE fibers) exhibits the best tribological properties when the load increases to 200 N. Due to the formation of a PTFE transfer film, the friction coefficient even decreases during the stable wear stage. Although the dry sliding condition is controlled by a transfer film formed on the friction interface, the contact geometry generated by the interlacing fibers as well as sliding direction continue to dominate the tribological properties under a light load. The combination of a suitable heavy load and sliding along the PTFE fiber is conducive to the formation of a stable and continuous transfer film of debris. Accordingly, the lowest friction coefficient of 0.105 and the lowest wear depth of 0.056 mm are achieved for composite-0° under 200 N.

Effects of cryogenic gas jet cooling on milling surface roughness and tool life for GH4169 alloy additive manufacturing parts

Hybrid additive and subtractive manufacturing is development in metal additive manufacturing techniques, wherein the dry cutting cooling method for subtractive cutting is one of the key technologies. To improve the milling performance of GH4169 alloy (namely Inconel 718 nickel-based superalloy) additive manufacturing parts, a dry cutting cooling method with a cryogenic gas jet and its effects on the cutting performance were investigated in this study. The theoretical model of the cryogenic gas jet flow was established, and the geometric characteristics, motion characteristics, and temperature distribution of the jet flow were analyzed. Meanwhile, considering the design of the nozzle outlet, the jet flow core length with a single nozzle and jet flow field envelope effect on the cooling heat transfer process with multiple nozzles were analyzed using a finite element simulation. Then, milling experiments on GH4169 alloy additive manufacturing parts with different cryogenic gas jet flow parameters were carried out. To reduce tool wear and the machined surface roughness of various parts, the jet flow parameters were optimized using the response surface analysis method. The effects of the milling feed direction on the tool wear and machined surface roughness were investigated. Furthermore, the tool wear morphologies were observed under different continuous milling times. The chemical compositions of the worn zone and tool wear mechanism were analyzed. The results show that cryogenic gas jet cooling can significantly improve the tool life and machined surface roughness of parts for GH4169 alloy additive-manufacturing-part milling, and the continuous cutting time within the tool wear allowance can reach approximately 50 min.

Comparative study on the impact-sliding wear behaviour of CAD/CAM resin-ceramic materials and tooth enamel.

To compare the impact-sliding wear of different CAD/CAM resin-ceramic materials and tooth enamel, and explore the corresponding wear damage mechanism. Human tooth enamel (EN), Vita ENAMIC (Vita, VE), Lava Ultimate (3M, LU), and GC CERASMART (GC, CS) were used in this study. The hardness, elastic modulus, and roughness values of the samples were measured. Further, impact-sliding wear tests were performed in a ball-on-flat configuration with spherical zirconia antagonists and the coefficients of friction (CoF) were recorded simultaneously. Additionally, a white light interferometer was used to determine the volume losses and scanning electron microscopy was used to observe the wear morphology of the wear scars and the damage feature in the vertical sections to clarify the damage mechanism during the impact-sliding wear test. EN exhibited the highest elastic modulus and CoF, followed by VE, LU, and CS. The hardness and roughness of EN and VE were similar and were higher than those of LU and CS. Throughout the wear tests, VE exhibited the highest volume loss, whereas CS exhibited the lowest. The wear damage characteristics of VE were similar to those of EN, displaying brittle fractures of inorganic substances and plastic deformation of organic substances in the impact part, exhibiting plough marks in the sliding parts. In the case of LU and CS, the entire wear areas displayed plastic deformation of the resin matrix, exfoliation of the filler particles, and plough marks. Enamel and polymer-infiltrated ceramic network materials exhibit similar wear damage modes. Additionally, the high-density nanocomposite resin material is the most resistant to impact-sliding wear from a tribological perspective.

Fretting Wear Characteristics of SLM-Formed 316L Stainless Steel in Seawater

The fretting wear characteristics of two different energy density 316L stainless steels formed by selective laser melting (SLM) under different friction conditions are studied. The image method was used to study the porosity of two samples with different energy densities (46.88 J/mm3, 98.96 J/mm3) formed by SLM. The dynamic wear test, respectively, evaluates its wear morphology and wear depth under three conditions: dry friction, distilled water, and an 3.5% NaCl solution. The porosity of the samples with SLM forming an energy density of 46.88 J/mm3 and 98.96 J/mm3 are 7.66% and 1.00%, respectively. Under the three conditions, the friction coefficient and wear depth of the samples with high energy density are smaller than those of the samples with low energy density; the friction of the samples with two energy densities in aqueous solution is faster than dry friction in air and tends to be stable. The friction coefficient in 3.5% NaCl solution is the smallest; when the energy density is constant, the wear depth of the fretting wear is the largest under dry friction and the smallest in distilled water. Under dry-friction conditions, the wear mechanisms of fretting wear are mainly oxidative wear and adhesive wear. In the fretting wear in the distilled water and the 3.5% NaCl solution, both wear mechanisms are abrasive wear and fatigue wear.

Tribological Effects of Water-Based Graphene Lubricants on Graphene Coatings

In this study, the friction and wear characteristics of graphene coatings were evaluated using lubricants with various ratios of graphene ink to deionized (DI) water. When dry graphene ink and pure DI water were used as lubricants, the graphene coating initially peeled off, and the friction coefficient rapidly increased to a large value. However, when a lubricant with graphene ink added to DI water was used, a lubricating film was formed on the graphene coating and the friction coefficient was reduced significantly. Under dry and pure DI water conditions, severe wear morphologies were formed on the graphene coating surface, whereas in the case of the lubricant with graphene inks added to DI water, insignificant wear morphologies were formed. When the mixing ratio between DI water and graphene ink was 100:10 and 100:5, the friction coefficient and wear rate were the lowest, respectively. As a result of a long-term experiment in which the sliding cycle was performed for up to 100,000 cycles under the same experimental conditions, the lubricant with a 100:10 mixing ratio showed excellent lubrication properties, confirming that the friction coefficient and wear rate were significantly reduced compared to that of the dry or pure DI water lubrication conditions.

Investigation of Machining Nimonic 75 with Hexagonal Boron Nitride Nanofluids: Tool Wear, Cutting Forces, Roughness, Residual Stress, and Chip Morphology

<div class="section abstract"><div class="htmlview paragraph">The present paper examined the machining of Nimonic 75 experimentally with hexagonal boron nitride-based cutting fluid. Three different types of hexagonal boron nitride (hBN) nanofluids with various hBN concentrations and cutting variables (cutting speed and feed rate) are applied in turning experiments. Tool wear, cutting forces, roughness, residual stress, and chip morphology in machining Nimonic 75 alloy with the hBN nanofluids are analyzed. The effects caused by the variation of hBN concentration and cutting variables are discussed. The results show that cutting speed decrease the force, surface roughness, specific energy consumption, and chip reduction coefficient except for shear angle, friction coefficient, and residual stress. The increase in feed rate increases the machining characteristics and chip-tool interface indices parameters except for flank wear and specific energy consumption. Finally, the optimal weight concentration to minimize machining and chip-tool parameters is 0.50 wt.% of hBN in cutting fluid. The weighted desirability approach is applied to determine the optimal parameters for both characteristics.</div></div>

Machining characterization and optimization under different cooling/lubrication conditions of Al-4Gr hybrid composites fabricated by vacuum sintering

In this study, the effects of different cooling/lubrication strategies and cutting parameters during milling hybrid composites based on Al-4Gr, a new material, were investigated. The main matrix was formed by adding Gr at a constant rate (4%) to Al. Hybrid composites were fabricated by vacuum sintering by adding WC and Al2O3 in different ratios (2-4-8 wt.%). Environmentally friendly cryogenic liquid nitrogen (cryo-LN2) and minimum quantity lubrication (MQL) fluids were used as cooling and lubricating environment in the milling process. Three different cutting speeds (150, 225, 300 m/min), three different feed rates (0.150, 0.225, 0.300 mm/rev) and a single depth of cut (0.5 mm) were selected for milling. Surface roughness, flank wear, cutting temperature, and chip morphology were evaluated for different cooling/lubrication environments. As a result, the cryo-LN2 environment reduced the surface roughness, flank wear, and cutting temperature by 34.9%, 18.5%, and 69.5%, respectively, compared to the dry medium. Adhesion wear was reduced in MQL and cryo-LN2 environments. In addition, it was determined by the analysis of variance that the most effective factor among the response parameters was cooling/lubrication. The cooling/lubrication environment has an effect of 74%, 58%, and 94% on surface roughness, flank wear, and cutting temperature, respectively.

Wettability surface and friction characterisation of ZrO2 ceramics by femtosecond laser texturing

PurposeThe purpose of this study is to process the wettability surface of the ZrO2 ceramics to improve their surface friction performance.Design/methodology/approachMicrotexture was processed on the surface of ZrO2 ceramics using a femtosecond laser. The three-dimensional texture morphology, surface contact angle, friction curve and wear morphology were measured by the laser confocal microscope, the contact angle meter, the reciprocating friction and wear tester and the scanning electron microscope, respectively. Based on Wenzel and partial impalement models, a geometric model of micro pits is established to study the influence mechanism of micro pit depth, diameter and distribution density on wettability and to analyze the relationship between surface wettability and tribological properties.FindingsThe results show that changing the geometric characteristics of the texture will lead to a change in the solid-liquid contact mode, and then lead to a change of in the surface contact angle. Wettability is an essential factor that affects the reduction of surface friction. The construction of a reasonable texture can enhance the surface hydrophilicity, which is conducive to the formation of a lubricating film on the ceramic surface, thereby reducing abrasive and adhesive wear, and improving the wear resistance of the ZrO2 ceramic surface.Originality/valueThe results provide a theoretical reference for femtosecond laser surface texture wettability regulation and tribological performance improvement.

Comparative Analysis in Drilling Performance of AA7075 in Different Temper Conditions

The widespread use of heat treatable7075 aluminum alloy in the aerospace industry requires a high machinability performance. The main objective of this study is to examine the machinability and the surface quality conditions of the AA7075 material with different temper conditions. For this purpose, various temper treatments are implemented to evaluate the impact of microstructural properties on tool wear and the surface quality of the drilled holes. The drilling operations have been done on O, F, T4, T6, and T7 temper conditions. Process parameters were three different spindle speeds (715, 1520, and 3030 rev/min) and three feed rates (0.1, 0.2, and 0.3 mm/rev) with HSS-G high-performance ground standard twist drill bit. The present work deals with the effects of temper conditions on thrust force, drilling temperature, tool wear, surface integrity, and chip morphology. Response surface methodology was used in the evaluation of experiment results. The optimization results showed that while thrust force and torque are not significantly affected by a change in spindle speed, they are sensitive to an increase in feed rate. Heat-generation on the drill bit is the lowest at low levels of both the feed rate and spindle speed parameters. The AA7075-T6 condition specimen was machined with continuous chip formation, resulting in the best hole surface quality. 3D Finite element modeling of the drilling process was carried out. Numerical analysis revealed the drilling performance of AA7075-T6 in terms of thrust, heat generation and chip formation.

Effects of the T6 heat treatment on the tribological behaviors of SiCp/7055Al composites

This study investigates the effects of T6 heat treatment on the dry sliding tribological behaviors of SiCp/7055Al composies under different temperatures and loads. SiC particle reinforced aluminum matrix composites (AMCs) with a volume fraction of 17% were prepared by spray deposition (SD). For T6 heat treatment composites were heated at 475 ℃ for 2 h and artificially aged at 120 ℃ for 28 h. The wear morphology, wear debris and cross-sectional microstructure and element distribution of the worn surface were characterized by energy dispersive spectrometer (EDS) mapping attached to the scanning electron microscope (SEM). Results show that the T6 heat treatment was effectively refined the coarse precipitation. The hardness of T6 treated composites increased from 72.62 HRB to 93.43 HRB. The coefficient of friction of T6 treated composites was lower and more stable than those for SD composites. The delamination of the composites is alleviated effectively by T6 heat treatment during friction. With the increasing of the loads and temperatures, the wear rates of the T6 treated composites decreases significantly than those for SD composites. The wear mechanism of T6 treated and SD composites are abrasive wear, fatigue wear, adhesive wear and oxidation wear at 100 ℃.

Measurement and analysis of tool wear and surface characteristics in micro turning of SLM Ti6Al4V and wrought Ti6Al4V

Parts produced using additive manufacturing (AM) have a significant transition in the features such as surface quality, residual stresses, microhardness, etc. To make the AM component suitable for an application, post-processing of the parts is required to remove the non-desirable features. In this regard, the micro turning of selective laser melted (SLM) Ti6Al4V are conducted to examine the surface characteristics, tool wear and chip morphology. The results obtained for SLM Ti6Al4V are compared with the results of wrought Ti6Al4V. Attributed to the higher strength and hardness, the SLM Ti6Al4V shows a higher tool wear and surface roughness than the wrought Ti6Al4V. The main tool wear mechanisms involved are built-up edge formation, adhesion, abrasion, and edge chipping for both the materials. The surface roughness is found increased with increasing cutting speed and feed. The wrought Ti6Al4V shows less feed marks and chip adhesion compared to SLM Ti6Al4V. Moreover, the materials side flow is observed in SLM Ti6Al4V only. The chips produced are long and continuous for wrought Ti6Al4V, whereas they are discontinuous for SLM Ti6Al4V. Morphology of the chips shows that they are of scaly structure for SLM Ti6Al4V for all the parameters, whereas they are of lamella structure for wrought Ti6Al4V, particularly at low feed and cutting speed.

Machinability characteristics analysis of hard turning operation on AISI 4340 steel using physical vapor deposition multilayer coated carbide cutting tool in the dry environment

AISI 4340 hardened steel is usually used in axle shafts, main shafts, gear, and couplings. Using multi-layer physical vapor deposition a coated tool, an attempt was made to optimize the input variables on precise turning on hardened AISI 4340 grade steel. The cutting speed, feed rate, and depth of the cut were the applied process factors in the dry-cutting environment. Furthermore, surface roughness (Ra), flank wear (VBc), cutting temperature ( T), and chip morphology were considered as technological responses. The Taguchi L27 standard orthogonal array with three levels and three factors was used in the experiment. Furthermore, scanning electron microscopy and energy dispersion spectroscopy were used to analyze tool wear and chip morphology characteristics. The relevance of the input process factors on the measured responses was determined using analysis of variance analysis. The feed rate was observed to have a dominant impact on the surface roughness in the trials. At an optimal parametric combination with 80 m/min cutting speed, 0.05 mm/rev feed rate, and 0.3 mm depth of cut obtained from the Taguchi-TOPSIS optimization method. The enhancement of the closeness coefficient was observed to be 0.2372. The generated second-order regression model was demonstrated to be of high significance. The strategy and outcomes of this research will help metal machining enterprises to augment manufacturing productivity when working with hardened steel.

Experimental investigation of ultrasonic vibration assisted turning of Inconel 825 using TiAlN/TiAlCrN coated WC cutting tool insert

Modern manufacturing processes require materials like Inconel 825 that have high strength, hardness, and corrosion resistance for applications in aerospace, biomedical, and marine industries. But their low thermal conductivity and higher affinity towards cutting tools limit their machining through conventional turning due to high cutting force and excessive tool wear. Here, the UVAT process is employed during the turning of Inconel 825, and its turning characteristics are analysed through grey relational analysis methodology to determine the optimum turning condition. TiAlN/TiAlCrN-coated WC insert has been adopted during UVAT to identify the effect of coating on turning performances. Also, an attempt has been made to develop a feed-forward artificial neural network model to simulate the turning process and predict the surface roughness, cutting force and temperature at work–tool interface. The proposed 4-16-3 model is reliable and accurate while estimating the turning characteristics for an actual machining condition because of the low error rate and nearer to one regression score. UVAT process substantially reduces the surface roughness, cutting force and interface temperature due to the intermittent cutting action. Whereas, multilayer TiAlN/TiAlCrN coating reduces the intensive friction at the work–tool interface by enhancing the lubricity action at the interface due to the formation of complex alumina and chromia-like tribo-film. It provides a highly finished surface with low cutting force and temperature while improving the cutting tool life. Tool wear and chip morphology is analysed through a scanning electron microscope. X-ray diffraction analysis is also performed on the workpiece and chip to identify the crystallographic phases, crystallite size, and lattice strain.

Experimental study on effect of additional torsional load on bending fatigue behavior and failure mechanism of steel wire rope

Regularly replacing steel wire rope (SWR) is a mandatory measure to ensure the safe operation of the hoisting system. However, in the manual rope replacement process, the torsion accumulated in the used rope will be transmitted to the new one, thereby aggravating the damage of the new rope and shortening its fatigue life. For the sake of exploring the effect of additional torsional load on the fatigue characteristics and damage behavior of SWR, a custom fatigue test apparatus was utilized to perform relevant tests. First, the impact of torsional angle on the torque and elongation of SWR was explored; subsequently, the number and distribution of broken wires were counted, based on which the fatigue life of SWR was predicted; finally, the scanning electron microscope and confocal three-dimensional contour measuring instrument were employed to observe the wear and fracture surface morphology of the steel wire. It is found that both twisting and untwisting boost the elongation of SWR, reduce the endurance of SWR almost linearly. Of the two, twisting has a greater impact on the endurance of SWR. The surfaces of wear scars take on a regular elliptical shape in the case of twisting, and the deflection angle, together with the maximum wear depth grows with the increase of the torsional angle. In contrast, the wear scars are irregular in the case of untwisting, and the deflection angle and the maximum wear depth fall as the torsional angle increases.

Evaluation of Surface Roughness, Tool Wear and Chip Morphology during Machining of Nickel-Based Alloy under Sustainable Hybrid Nanofluid-MQL Strategy

Nickel-based super alloys exhibit high strength, oxidation and corrosion resistance; however, the machining of these alloys is a challenge that can be overcome with effective cooling/lubrication techniques. The use of a minimum quantity lubrication (MQL) technique is limited to lower cutting parameters due to the tremendous heat produced during the machining of Inconel 718. Sustainable and eco-friendly machining of Inconel 718 can be attained using MQL and lubricants based on nanofluids because of their improved heat transfer capabilities. For that purpose, the performance of hybrid nanofluid-MQL is examined. In this novel study, graphene and hexagonal boron nitride (hBN) nanoparticles are reinforced with palm oil and delivered to the machining interface using an MQL setup. The machining experiments are performed under the conditions of dry, wet, MQL and MQL with graphene/hBN deposited in palm oil. The machining performance under selected cutting conditions is assessed by analyzing the surface roughness, tool wear, chip morphology and surface quality of the machined workpiece. A comparison of results showcased the effectiveness of hybrid nanofluid-MQL with improvement in surface finish, reduction in tool wear and favorable chip forms concerning all other machining conditions.

Research on design and fabrication of micro ball end milling tool with flat edge and conical flank

The microball end mills are widely used in the processing of micro parts in the fields of aerospace. These micro parts are often made of hard to machine materials with high hardness and strength, such as martensitic stainless steel. As the main processing tool of these parts, the micro cutting tools wear fast and have a short service life. At the same time, because of the small diameter and complex structure of the micro ball end milling tool, its preparation process is complex, and its quality is difficult to guarantee. In order to solve the above problems, a micro ball end milling tool with a flat edge and conical flank (FC-MBMT) made of cemented carbide is proposed, which reduces the difficulty of tool preparation through the design of the flat edge, and reduces the friction between the flank and the machined surface through the design of the conical flank. Firstly, based on the theory of the spherical helix, the mathematical model of FC-MBMT was established. Then, the motion expression of each axis of the machine tool in the grinding process of FC-MBMT is obtained by deriving the transformation matrix between the machine tool coordinate system and the tool coordinate system. The precision grinding of the FC-MBMT is realized, and its geometric parameter error is less than 8%. Finally, based on the above methods, two kinds of FC-MBMT with a flank width of 16 μm and a flank width of 24 μm were prepared, and their cutting performance was verified by micro groove milling experiments of martensitic steel. Ordinary equal guide cutting edge ball end milling tool participated in the machining as a comparison item. The milling experiment results show that the surface roughness of the FC-MBMT is less than 0.52 μm and the total cutting force is less than 7 N. The machining quality of the FC-MBMT with a conical flank width of 16 μm is better than the FC-MBMT with a flank width of 24 μm, and its cutting force is smaller than the FC-MBMT with a flank width of 24 μm, which indicates that it has better cutting performance with a conical flank width of 16 μm. The wear morphology shows that the wear forms of the FC-MBMT are chip adhesion on the conical flank and slight cutting edge wear. The anti-wear ability of the FC-MBMT with a conical flank width of 16 μm is obviously better than the FC-MBMT with a flank width of 24 μm. Compared with the ordinary micro ball end milling tool, the cutting performance and wear resistance of the FC-MBMT with a flank width of 16 μm are not significantly different. The experimental results verify the feasibility of the proposed tool structure.

Investigation of corrosion-time effects on fretting wear behaviours of copper-magnesium alloy

The premature failure of integral droppers was attributed to the environmental corrosion and fretting wear due to mechanical vibration. Due to its complex working environment, the research on the fretting wear of corroded copper-magnesium alloy is rarely reported in the literature. In this work, an experiment was designed to investigate the effect of corrosion time on the fretting wear behaviours of the copper–magnesium alloy (CuMg0.4) used in integral droppers. The running conditions fretting map of CuMg0.4 at dry conditions and room temperature were successfully constructed by fretting wear tests. Representative testing parameters from different fretting regions (i.e. partial slip, mixed slip and slip regimes) were selected to carry out fretting tests using the CuMg0.4 cylinder after salt spray corrosion for the first time. The running characteristics, wear morphologies and fretting damage mechanisms of tribo-pairs were analysed. Results indicated that the fretting wear mechanisms of CuMg0.4 included adhesion, oxidation, abrasive and fatigue wear mechanisms. After corrosion, the oxide layer on the matrix surface could avoid cracks in a short time, but with increased corrosion time, the overall wear degree of the specimen deepened, and the damage was aggravated. This work further provides theoretical basis for failure analysis and other aspects of integral droppers.

Effect of roughness and acidic medium on wear behavior of dental resin composite

BackgroundThe aim of the study was to investigate whether the citric acid and rough surface have a synergistic effect leading to severe wear behavior of resin composite.Materials and methodsDisk-shaped (Ø15 × 1.5 mm) specimens of resin composite (n = 12) with different initial roughness were prepared. Reciprocating ball-on-flat wear tests were performed under distilled water and citric acid (pH = 5.5) respectively. The coefficient of friction (COF), wear volume loss, and duration of the running-in period were quantified to assess the wear performance. And the values were analyzed with one-way ANOVA (α = 0.05). Regression analysis was applied to examine the influence of Ra values and mediums on the wear data. The wear morphology was analyzed by scanning electron microscopy and a 3D profilometer.ResultsThe average COF was higher in distilled water than in citric acid but was independent of the surface roughness. For the composite, the volume loss of worn area and running-in period increased with surface roughness when tested under distilled water. However, these increasing trends were not found in citric acid. All specimens exhibited mild wear behavior with low COF and less superficial abrasion in acidic medium.ConclusionsThe effect of initial roughness on wear behavior depends on the medium. In distilled water, resin composites with high initial roughness exhibit a longer running-in time, which eventually leads to a significant increase in material loss. The adverse effects of high roughness can be alleviated by the lubrication of citric acid, which can maintain a mild wear behavior regardless of initial surface roughness.