Tribological Behavior of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-20 wt.%TiO<Subscript>2</Subscript> Coating

Al₂O₃-20 wt.% TiO₂ ceramic coatings were deposited on the surface of Grade D steel by plasma spraying of commercially available powders. The phases and the microstructures of the coatings were investigated by x-ray diffraction and scanning electron microscopy, respectively. The Al₂O₃-20 wt.% TiO₂ composite coating exhibited a typical inter-lamellar structure consisting of the γ-Al₂O₃ and the Al₂TiO₅ phases. The dry sliding wear behavior of the coating was examined at 20 °C using a ball-on-disk wear tester. The plasma-sprayed coating showed a low wear rate (~4.5 × 10^?6 mm³ N^?1 m^?1), which was <2% of that of the matrix (~283.3 × 10^?6 mm³ N^?1 m^?1), under a load of 15 N. In addition, the tribological behavior of the plasma-sprayed coating was analyzed by examining the microstructure after the wear tests. It was found that delamination of the Al₂TiO₅ phase was the main cause of the wear during the sliding wear tests. A suitable model was used to simulate the wear mechanism of the coating.     

Tribocorrosion Behavior of Fe-Based Amorphous Composite Coating Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in 3.5% NaCl Solution

Although corrosion and friction/wear behavior of Fe-based amorphous coatings and their composites has been extensively studied during the past decade, there is very limited work related to tribocorrosion behavior. In this paper, the tribocorrosion behavior of a Fe-based amorphous composite coating reinforced with 20 wt.% Al₂O₃ particles was investigated in a 3.5% NaCl solution on a ball-on-disk tester and was compared to the monolithic amorphous coating and 316L stainless steel (SS). The results showed that the amorphous composite coating exhibited the highest tribocorrosion resistance among the three materials tested, as evidenced by the lowest coefficient of friction (~0.3) and tribocorrosion wear rate (~1.2 × 10^?5 mm³/N·m). In addition, potentiodynamic polarization measurements before and during tribocorrosion testing demonstrated that corrosion resistance of the amorphous composite coating was not influenced so much by mechanical loading compared to the amorphous coating and the 316L SS. Observations on the worn surface revealed a corrosion-wear- and oxidational-wear-dominated tribocorrosion mechanism for the composite coatings. The excellent tribocorrosion resistance of the composite coating results from the effect of chemically stable Al₂O₃ phase which resists oxidation and delamination during sliding, along with poor wettability with corrosive NaCl droplets.     

Surface Modification of C17200 Copper-Beryllium Alloy by Plasma Nitriding of Cu-Ti Gradient Film

In the present work, a copper-titanium film of gradient composition was firstly fabricated by the dual magnetron sputtering through power control and plasma nitriding of the film was then conducted to modify C17200 Cu alloy. The results showed that the prepared gradient Cu-Ti film by magnetron sputtering was amorphous. After plasma nitriding at 650 °C, crystalline Cu-Ti intermetallics appeared in the multi-phase coating, including CuTi₂, Cu₃Ti, Cu₃Ti₂ and CuTi. Moreover, even though the plasma nitriding duration of the gradient Cu-Ti film was only 0.5 h, the mechanical properties of the modified Cu surface were obviously improved, with the surface hardness enhanced to be 417 HV_0.01, the wear rate to be 0.32 × 10^?14 m³/Nm and the friction coefficient to be 0.075 at the load of 10 N, which are all more excellent than the C17200 Cu alloy. In addition, the wear mechanism also changed from adhesion wear for C17200 Cu substrate to abrasive wear for the modified surface.     

The Sliding Wear and Friction Behavior of M50-Graphene Self-Lubricating Composites Prepared by Laser Additive Manufacturing at Elevated Temperature

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si₃N₄ ball from 25 to 550 °C at 18 N–0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10^?7 mm³ N^?1 m^?1. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10^?7mm³ N^?1 m^?1). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer.     

Ti-Cr-B-N coatings prepared by pulsed cathodic-arc evaporation of ceramic TiCrB target produced by SHS

The method of pulsed cathodic-arc evaporation of composite targets based on self-propagating high-temperature synthesis has been applied for the first time to prepare nanocomposite coatings in the Ti-Cr-B-N system. The influence of the deposition-process parameters on the coating structure and properties has been studied. Structural investigations have been carried out using X-ray diffraction analysis, transmission and scanning electron microscopy, glow-discharge optical-emission spectroscopy, and optical profilometry. The coating properties have been determined by nanoindentation and tribological tests. The results of the study show that the coatings mainly consist of highly dispersed fcc phase based on Ti(Cr)N in the form of crystallites 1–2 nm in size; in addition, amorphous BNx phase has been found to exist in the coatings. The coatings obtained under optimal conditions have the following parameters: hardness 20–24 GPa, friction coefficient ～0.6, and reduced wear about 2 × 10^?6 mm³ N^?1 m^?1.     

Microstructure and Thermal Properties of Nanostructured 8 wt.% CeO2 Doped YSZ Coatings Prepared by Atmospheric Plasma Spraying

Nanostructured 8 wt.% CeO₂-5.4 wt.% Y₂O₃-ZrO₂ (CeYSZ) coatings were prepared by atmospheric plasma spraying technology. The microstructure, thermal diffusivity, and thermal cycle behavior of CeYSZ were investigated. The results show that the as-sprayed nano-CeYSZ coatings consist of tetragonal ZrO₂ and Ce element is in solid solution with ZrO₂. The CeYSZ coatings are characterized by nano-zones (unmelted nanoparticles), melted dense areas, splats, and pores. The thermal diffusivity of nano-CeYSZ coatings is 0.548 × 10^?6 m²/s at room temperature. The addition of CeO₂ decreases the thermal diffusivity of nano-YSZ coatings, which is mainly caused by the point defect scattering and grain-boundary scattering. The thermal cycle life of nano-CeYSZ coatings is about 860 cycles at 1050 °C. The spallation of the coatings occurs at the interface of CeYSZ/TGO.     

Influence of Al Contents on the Microstructure, Mechanical, and Wear properties of Magnetron Sputtered CrAlN Coatings

CrAlN (0 < x < 0.1) coatings were deposited on SA304 substrate by a reactive magnetron sputtering. The microstructure and composition of the as-deposited coatings were systematically characterized by field emission scanning electron microscopy/EDS and atomic force microscopy, and the phase formation by x-ray diffraction (XRD). The hardness of the coatings was investigated using nanoindentation, while wear properties were investigated using pin-on-disk tribometer. XRD study reveals that the deposited CrAlN coatings crystallized in the cubic B1 NaCl structure. The minimum and maximum hardness of the coatings are found to be 15.28 and 18.81 GPa, respectively. The COF and wear rate are found to be 0.48 and 2.25 × 10^?5 mm³/N · m, which is lower than the CrN coatings deposited and characterized under the same environment (0.63 and 2.25 × 10^?5 mm³/Nm).     

Microstructure and Corrosion Behavior of Electrodeposited Ni-Co-ZrC Coatings

In this present work, ZrC particles incorporated Ni-Co composite coatings were electrodeposited. The objective of this article is to study the influence of Co content on the microstructure and properties of Ni-Co-ZrC coatings. Pure Ni and Ni-ZrC coatings have also been electrodeposited for comparison. Surface morphology, chemical composition, microstructure, and microhardness of Ni-Co-ZrC coatings were characterized by scanning electron microscopy, energy dispersive spectrometer, x-ray diffractometer, and Vicker microhardness tester. The potentiodynamic polarization technique was applied to measure the corrosion behavior of the coatings. By increasing Co concentration in electrolyte, Co content of the coatings was modified from 0 to 80 wt.% and ZrC particles content of the coatings was reduced. As the Co content increased, the dominant phase structure was changed from face centered cubic to hexagonal close packed crystal structure. Surface morphology of the Ni-Co-ZrC coatings was changed from nodular to sharp corner structure, and finally branched morphology with increasing Co content of the coating. Among the electrodeposited coatings, Ni-Co-ZrC coating with 42 wt.% Co content exhibited the highest microhardness. The corrosion potential of the coating was shifted to more positive with increasing the Co content from 0 to 64 wt.%. The lowest corrosion rate of 4.507 × 10^?7 g·h^?1·cm^?2 was found for Ni-Co-ZrC coating at the Co content of 75 wt.%.     

Preparation of Nanocomposite GDC/LSCF Cathode Material for IT-SOFC by Induction Plasma Spraying

Homogeneous mixtures of Ce_0.8Gd_0.2O_1.9 (GDC) and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) nanopowders were successfully synthesized using induction plasma by axial injection of a solution. The resulting nanocomposite powders consisted of two kinds of nanopowders with different mass ratio of GDC/LSCF, such as 3/7 and 6/4. The morphological features, crystallinity, and the phases of the synthesized powders were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), local energy-dispersive x-ray spectroscopy (EDS) analysis, and x-ray diffraction (XRD). The nanopowders are almost globular in shape with a diameter smaller than 100 nm and their BET specific areas are around 20 m² g^?1. The GDC and LSCF phases are well distributed in the nanopowders. In addition, suspensions, made with the as-synthesized composite nanopowders and ethanol, were used to deposit cathode coatings using suspension plasma spray (SPS). Micro-nanostructures of the coatings are discussed. The coatings are homogeneous and porous (51% porosity) with cauliflower structures.     

Effect of Spray Distance on Microstructure and Tribological Performance of Suspension Plasma-Sprayed Hydroxyapatite–Titania Composite Coatings

Hydroxyapatite (HA)–titania (TiO₂) composite coatings prepared on Ti6Al4V alloy surface can combine the excellent mechanical property of the alloy substrate and the good biocompatibility of the coating material. In this paper, HA–TiO₂ composite coatings were deposited on Ti6Al4V substrates using suspension plasma spray (SPS). X-ray diffraction, scanning electron microscopy, Fourier infrared absorption spectrometry and friction tests were used to analyze the microstructure and tribological properties of the obtained coatings. The results showed that the spray distance had an important influence on coating microstructure and tribological performance. The amount of decomposition phases decreased as the spray distance increased. The increase in spray distance from 80 to 110 mm improved the crystalline HA content and decreased the wear performance of the SPS coatings. In addition, the spray distance had a big effect on the coating morphology due to different substrate temperature resulting from different spray distance. Furthermore, a significant presence of OH^? and CO₃ ^2? was observed, which was favorable for the biomedical applications.     

The Ablation and Oxidation Behaviors of SiC Coatings on Graphite Prepared by Slurry Sintering and Pack Cementation

SiC coatings were generated on graphite using slurry sintering (SS) and pack cementation (PC). The samples’ ablation features were assessed by an oxyacetylene torch. The rates of mass ablation of the PC–SiC and SS–SiC coatings were approximated 2.17?×?10^?3 and 9.52?×?10^?3 g s^?1, respectively, decreased by 84.1 and 29.6% compared to the uncoated samples. It was mainly attributed to the formation of a SiO₂ layer on the surface. The continuous SiO₂ molten film formed via the PC–SiC oxidation generates a sealing mechanism which can be an obstacle against the oxygen diffusion and hinder more ablation. This is while discontinuous SiO₂ film formed from the thin SS–SiC cannot protect the graphite effectively. The non-isothermal oxidation test shows that without the SiC coating, the sample weight is lost largely from 25 to 1500 °C, and its weight loss was 2.2% after the TGA. However, after coating, the samples possessed excellent oxidation protection and weight losses of SS–SiC and PC–SiC coatings are down to 1.3 and 0.6%, respectively. The more oxidation of the graphite substrate occurred due to the formation of macrocracks in the coating during the TGA and also the formation of holes on SiO₂ glass layer owing to release of CO or CO₂.     

Microstructure and mechanical properties of B4C-TiB2 composite ceramic fabricated by reactive spark plasma sintering

B₄C-TiB₂ composite ceramic was prepared by reactive spark plasma sintering, using amorphous B, Ti, and graphite as the raw materials. The reaction process and the phase composition in the process of sintering were studied. The effects of the ratio of raw materials and sintering process on the microstructure and mechanical properties of B₄C-TiB₂ composite ceramic were investigated. The composition of the sintered sample was B₄C, TiB₂, and bits of residual unreacted graphite. B and Ti preferentially reacted to form TiB₂ at 800 °C, and then B and graphite reacted to form B₄C at 1250 °C. The 75 vol% B₄C-25 vol% TiB₂ composite ceramic synthesized with 60.6 wt% B, 25.8 wt% Ti, and 13.6 wt% graphite and sintered at 1900 °C for 15 min resulted in nearly full densification and optimal mechanical properties. The relative density, Vickers hardness, fracture toughness, and flexural strength were 98.6 ± 0.01%, 26.6 ± 0.01 GPa, 5.9 ± 0.13 MPa·m^1/2, and 605 MPa, respectively.     

Influence of Pulse Electrodeposition and Heat Treatment on Microstructure,Tribological, and Corrosion Behavior of Nano-Grain Size Co-W Coatings

In the present study, Co-W nano-structured alloy coatings are produced on low-carbon steel substrate by means of pulse electrodeposition from a citrate-based bath under different average current densities and duty cycles. The results indicate that the coating deposited under 60% of duty cycle and 1 A/dm² of average current density exhibit optimum pulse plating conditions with 44.38 wt.% W, 37 nm grain size, and 758 HV microhardness. The effect of heat treatment temperature on microstructure, composition, corrosion behavior, and morphology of amorphous deposited Co-W alloy with 44 wt.% W was investigated. The microhardness of the coating increased to 1052 HV after heat treatment at 600 °C, which is due to the formation of Co₃W and CoWO₄ phases in the deposit. Furthermore, the coatings heat-treated at 600 °C had lower friction coefficients and better wear resistance under various loads than before heating.     

Cold-Sprayed Cu-MoS<Subscript>2</Subscript> and Its Fretting Wear Behavior

Cu and Cu-MoS₂ coatings were fabricated by cold spray, and the fretting wear performance of the two coatings was compared. A mixture (95 wt.% Cu + 5 wt.% MoS₂) was used as feedstock for the composite coating. Coatings were sprayed with identical gas flow conditions on the substrates pre-heated to approximately 170 °C. The morphology of coating top surface and polished cross sections was analyzed by scanning electron microscopy (SEM) and light optical microscopy (LOM). The influence of MoS₂ on Cu deposition was examined. The local MoS₂ concentration within the coating was found to affect the hardness. Fretting tests were carried out at two different normal loads, and the influence of MoS₂ on friction and wear was studied. The morphology and elemental compositions of the wear scars and wear debris were observed by SEM and energy dispersive x-ray spectroscopy (EDS), respectively.     

Tribological and Thermal Properties of Mullite Coating Prepared by Atmospheric Plasma Spraying

The primary mullitized andalusite powders were spray-dried and heat-treated to improve sprayable capability. Then, mullite coating was deposited by atmospheric plasma spraying and heat treatment was contributed to recrystallization of the amorphous phase present in the as-sprayed mullite coating. Scanning electron microscopy and x-ray diffraction were used to characterize the microstructure and phase composition of mullite coating. Meanwhile, the phase transition temperature, enthalpy, and specific heat capacity of as-sprayed coatings as well as recrystallized mullite coatings were determined by means of differential scanning calorimetry (DSC). Moreover, tribological properties of as-sprayed coating were investigated by SRV-IV friction and wear tester from 200 to 800 °C. It has been found that the as-sprayed coating possesses good thermal stability. DSC analysis reveals that recrystallization of the glassy phase present in the mullite coating occurs at about 980 °C. The friction coefficient of mullite coating was gradually increased from 0.82 at 200 °C to the highest value of 1.12 at 800 °C, while wear rates of the coating were at the order of 10^?5 mm³/Nm. The as-sprayed coating suffered the most severe wear at 800 °C. The observed wear mechanisms were mainly abrasive wear, brittle fracture, and pulling-out of splats.     

Effects of La<Subscript>2</Subscript>O<Subscript>3</Subscript> on Mechanical Properties and Corrosion Resistance of H62 Brass

In this article, the effects of lanthanum oxide (La₂O₃) on the microstructure and mechanical properties of H62 brass were investigated by using the universal testing machine, Brinell hardness tester, optical microscope, and scanning electron microscope (SEM). Immersion corrosion and electrochemical measurements were carried out to identify the influence of La₂O₃ on the corrosion behavior of the H62 brass. The phase constitution, microstructure, and phase composition of the H62 brass were analyzed by x-ray diffraction, SEM, and energy-dispersive spectrometer, respectively. The results show that the microstructure of α phase changes from dendrite grains to equiaxed grains, and the content and distribution of β phase are improved significantly. When the La₂O₃ content reaches 0.8 wt.%, the H62 brass obtains favorable comprehensive mechanical properties and the strength and hardness decrease but elongation increases, which is conducive to plastic processing. In addition, under the optimum amount of 0.8 wt.% La₂O₃ content, the corrosion rate of immersion corrosion attains the minimum values: As 12.6 g m^?2 h^?1, it decreases by 24%; as the corrosion potential changes from ?1.1327 V to ?0.328 V, it increases by 70.9%; and as the corrosion current density decreases from ?2.833 mA mm^?2 to ?3.28 mA mm^?2 corrosion, it decreases by 15.78%, when compared with H62 brass.     

Thermal properties of diamond/Al composites by pressure infiltration: comparison between methods of coating Ti onto diamond surfaces and adding Si into Al matrix

This study was pertained to the effects of Ti coating on diamond surfaces and Si addition into Al matrix on the thermal conductivity(TC) and the coefficient of thermal expansion(CTE) of diamond/Al composites by pressure infiltration.The fracture surfaces,interface microstructures by metal electro-etching and interfacial thermal conductance of the composites prepared by two methods were compared.The results reveal that Ti coating on diamond surfaces and only12.2 wt% Si addition into Al matrix could both improve the interfacial bonding and increase the TCs of the composites.But the Ti coating layer introduces more interfacial thermal barrier at the diamond/Al interface compared to adding 12.2 wt% Si into Al matrix.The diamond/Al composite with 12.2 wt% Si addition exhibits maximum TC of 534 W·m~(-1)·K~(-1)and a very low CTE of 8.9×10~(-6)K~(-1),while the coating Ti-diamond/Al composite has a TC of 514 W·m~(-1)·K~(-1)and a CTE of 11.0×10~(-6)K~(-1).     

Effect of Submicron and Nano SiC Particles on Erosion Wear and Scratch Behavior of Plasma-Sprayed Al2O3/8YSZ Coatings

This paper reports studies into the effect of submicron and nano SiC particles on microstructure, phase composition, hardness, erosion wear, and scratch behavior of Al₂O₃-20wt.%8YSZ (ZrO₂ + 8 wt.% Y₂O₃) coatings fabricated by atmospheric plasma spraying. The failure mode of erosion wear and scratch for coatings was established and analyzed. The hardness, density, erosion wear, and anti-scratch resistance of coatings fabricated from plasma treating feedstocks were higher than that of coatings made from sintering feedstocks. The erosion wear rate of coatings with SiC was evidently decreased, and there was some small debris on worn surface with characteristic of translamellar fracture. The spallation, fracture, plough, and cracking were main failure mechanism for coatings. In the scratch process, the critical load of coating with SiC was increased. The crack growth resistance of coatings was analyzed from crack length at end of scratch test.     

Microstructure and Properties of FeCrB Alloy Coatings Prepared by Wire-Arc Spraying

To improve the heat transfer ability and wear resistance of drying cylinders in paper production machines, a series of Fe_87?x Cr₁₃B _x (x = 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, and 4 wt.%) cored wires have been produced and used to prepare coatings by wire-arc spraying, in comparison with conventional X30Cr13 solid wire. All coatings presented dense layered structure with porosity of around 4%. The boron content in the cored wires significantly affected the thermal conductivity of the coating, which is attributed to the combined effects of the crystal structure, grain size, and oxide content of the coating. In the investigated range, the coating with 2 wt.% boron content exhibited the highest thermal conductivity, reaching 8.83 W/m-K, greater than that of X30Cr13 coating (5.45 W/m-K). Furthermore, the microhardness and relative wear resistance of the FeCrB coatings obtained from cored wires with boron addition were greatly increased compared with commercial X30Cr13 coating. Therefore, wire-arc-sprayed FeCrB coating has promise as an effective and economic approach to improve the heat transfer behavior and wear resistance of drying cylinders in the paper industry.     

Microstructure and Oxidation Behavior of Al and Al/NiCrAlY Coatings on Pure Titanium Alloy

To improve the oxidation resistance of Ti alloys, a NiCrAlY coating was deposited as diffusion barrier between aluminum overlay coating and pure Ti substrate by air plasma spraying method. The microstructure and oxidation behavior of Al coatings with and without NiCrAlY diffusion barrier were investigated in isothermal oxidation tests at 800 °C for 100 h. The results indicate that the weight gain of the Al/NiCrAlY coating was 4.16 × 10^?5 mg² cm^?4 s^?1, whereas that of the single Al coating was 9.52 × 10^?5 mg² cm^?4 s^?1 after 100 h oxidation. As compared with single Al coating, the Al/NiCrAlY coating revealed lower oxidation rate and excellent oxidation resistance by forming thin Al₂O₃ + NiO scales at overlaying coating/diffusion barrier and diffusion barrier/substrate interfaces. Meanwhile, the inward diffusion of Al and the outward diffusion of Ti were inhibited effectively by the NiCrAlY diffusion barrier.