Antiwear and lubrication properties of polyurethane/polytetrafluoroethylene‐bonded coating

Polytetrafluoroethylene (PTFE) particles were irradiated with ⁶⁰Co γ‐ray to improve their dispersing capacity in polyurethane (PU), which was used as a binder of a PTFE‐based bonded solid lubricating coating. The PU/PTFE‐bonded solid lubricating coating was prepared on a steel block by spraying and curing at room ambient, and the tribological properties of the PU/PTFE coatings were evaluated on a ring‐on‐block tester at a speed of 1.25–2.5 m/s and a load of 314–785 N. The wear life of bonded coatings on PTFE volume concentrations, curing humidities and times, coating thickness, and sliding conditions was also investigated. It was found that a 60‐μm thickness coating, which has a 40% PTFE volume concentration, cured at 75% relative humidity for 4 days, has a longer wear life of 844 m/μm at 314 N and 1.25 m/s. The PTFE/PU coating was wear‐resistant when the load × speed value was less than 687 Nm/s^?1; at same time, the wear life for a thinner coating is sensitive to sliding condition variations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3454–3459, 2002     

Friction and wear properties of Si3N4-hBN ceramic composites using different synthetic lubricants

This paper presents a tribological investigation of Si₃N₄-hBN composite ceramics using synthetic lubricants. The friction and wear properties of Si₃N₄-hBN ceramic composites sliding against TC4 titanium alloy (Ti6Al4V) were investigated via pin-on-disc tests. An axial compressive load of 10?N was applied with a sliding speed of 0.73?m/s. Three different lubrication conditions including simulated body fluid (SBF), physiological saline (PS) and bovine serum (BS) were used. For SBF lubrication, the friction coefficients and wear rates of Si₃N₄-hBN/Ti6Al4V pairs were varying with the increase of hBN contents. When using 20?vol% hBN, the average friction coefficient and wear rate of Si₃N₄ (0.28 and 3.5?× 10^?4 mm³ N^?1 m^?1) were as good as that of the pure Si₃N₄ (0.34 and 3.69?× 10^?4 mm³ N^?1 m^?1). Meanwhile, the processability of the Si₃N₄ material would be improved by adding hBN. It was worth to mention that when using 30?vol% hBN, the tribological performance of bearing combination deteriorated with extensive wear from the ceramic pin. This may due to the reduction of mechanical property caused by adding hBN and the occurring of tribochemical reaction. According to the worn surface examination and characterization, the main wear mechanism was abrasive and adhesion wear. Scratch grooves were observed on the metal disc, and metallic transform layers were seen on the ceramic pin. Moreover, surface lubrication film consisting of TiO₂, SiO₂·nH₂O, Mg(OH)₂, and H₃BO₃ were formed on the metal disc when using SBF lubrication and 20?vol% hBN content. Among the three lubrication conditions, SBF generally led to the best tribological performance. No surface lubrication film was found during BS and PS lubrications. This may be resulted from the absence of essential ions to promote the formation of surface lubrication film (PS lubrication) and the formation of a protein barrier on the surface of the metal disc (BS lubrication).     

Wear behavior of graded Cr-CrN-Cr(1−x)Al(x)N coatings synthesized by closed-field unbalanced magnetron sputtering for advanced machining operations

Graded Cr-CrN-Cr_(1?x)Al_(x)N coatings were synthesized onto M42 HSS substrates used in advanced machining operations by closed-field unbalanced magnetron sputtering (CFUBMS). The tribological behavior of these graded coatings was explored in detail by advanced electron microscopy, confocal laser scanning microscopy, nanoindentation and dry sliding wear tests. The presence and magnitude of residual stresses in these coatings were determined by the XRD – sin²ψ method, which revealed increasing compressive stresses with increasing Al content. The coating surface morphology, mechanical properties were determined prior to dry sliding wear by atomic force microscopy (AFM) and nanoindentation methods, which yielded decreasing surface roughness (R_a) as well as enhancement of hardness and modulus along with increase in H/E and H³/E² ratios with increasing Al content. Tribological investigation was performed with a pin-on-disc arrangement by keeping the sliding velocity (0.2?ms^?1) and normal axial load (10?N) constant and varying the sliding distance. Specific wear rates of the order ~ 10^–17 m³ N^?1 m^?1 were encountered for all coatings with the wear rates increasing as the Al content increased implying a decrease of wear resistance of the coatings. Abrasive wear has been found to be the dominant wear mechanism during dry sliding wear. Increasing modulus mismatch between coating and substrate can be mainly attributed to a decrease in wear resistance of the coatings.     

Influence of wood flour loading on tribological behavior of epoxy composites

A series of wood flour (WF) filled epoxy composites consisting of five samples were prepared by varying the concentration of WF in step of 10 wt%. These samples were characterized for its wear behavior in abrasive and sliding wear modes to study the influence of WF. It was observed that specific wear rate (k₀) of all the composites decreased with increasing load in sliding wear mode. Specific wear rate was of the order of 10⁻¹⁰ m³/Nm in abrasive wear mode and ∼10⁻¹⁴ m³/Nm in sliding wear mode. Composite containing 40 wt% WF exhibited the lowest specific wear rate in abrasive wear mode. While composite containing 20 wt% WF exhibited lowest specific wear rate in sliding wear mode. This was attributed to the fact that in abrasive wear mode, the wear debris consisting of mainly WF particles was maximum for 10 wt% composite and minimum for 40 wt% composite. In sliding wear mode, the exposed WF particles caused maximum roughening of steel counterface in the case of composite containing higher concentration of WF particles. Hence, they exhibited a higher value of specific wear rate. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Microstructure and tribological properties of multilayered ZrCrW(C)N coatings fabricated by cathodic vacuum-arc deposition

In this study, a series of ZrCrW(C)N multilayer coatings with various transition layers were deposited on AISI304 stainless steel using cathodic vacuum-arc deposition in N₂–C₂H₂ gas mixture. The tribological behaviors of sliding against Al₂O₃ balls under dry friction and lubricant conditions were investigated using a reciprocating tribometer. The results demonstrated that the ZrCrW(C)N coatings comprised (Zr, Cr, W) (C, N) crystallites and an amorphous carbon phase. It possessed a nano-hardness of 35.4 GPa and an elastic modulus of 417.7 GPa. The friction coefficient of the coating was reduced by 14% compared to that of the 304 matrices, and the wear mechanism changed from adhesive wear to slight abrasive wear under the lubrication steady state. Under dry friction conditions, the ZrCrW(C)N coatings with the entire CrWN transition layer exhibited wear rates of 1.27 ± 0.04 × 10^?8 mm³ (N m)^?1, which were one order of magnitude lower than that of the 304 steel. Compared with the untreated AISI304 stainless steel, the ZrCrW(C)N coating exhibits excellent mechanical and tribological properties under lubricated and dry friction conditions, which are crucial for engineering applications.     

Tribological and corrosion behaviors of fluorocarbon coating reinforced with sodium iron titanate platelets and whiskers

A series of sodium iron titanate (NFTO)–fluorocarbon composite coatings have been prepared with the liquid-phase blending method. The effects of two types of NFTO, NFTO platelets, and NFTO whiskers, on the tribological and corrosion behaviors of the composite coatings, are systematically studied. The results show that the addition of NFTO can significantly enhance the friction-reducing and wear resistance performances of the fluorocarbon coating. Under dry sliding, the minimum specific wear rate is 1.67 × 10⁻⁴ mm³/Nm for the platelet-filled composite coatings and 1.15 × 10⁻⁴ mm³/Nm for the whisker-filled composite coatings, respectively, showing a decrease of 83.5 and 88.6% than that of pure coating. Under a simulated seawater environment, the minimum specific wear rate is 5.44 × 10⁻⁵ mm³/Nm for the platelet-filled composite coatings and 0.84 × 10⁻⁵ mm³/Nm for the whisker-filled composite coatings, respectively, showing a decrease of 90.5 and 98.5% than that of pure coating. The morphologies of worn surfaces, wear debris, and transfer films are analyzed, and the corresponding wear resistance mechanisms are discussed. The electrochemical impedance spectroscopy certifies a remarkably improved corrosion resistance of the composite coatings which have been immersed in 3.5 wt % NaCl solution for 30 days. The composite coating reinforced with 7.5 wt % platelets shows the highest resistance of 256.3 × 10⁶ Ω·cm², approximately two orders of magnitude higher than that of pure coating. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48936.     

Influence of ZrB2 hard ceramic reinforcement on mechanical and wear properties of aluminum

In this work, the effect of ZrB₂ (0, 5, 10 and 20?vol%) ceramic reinforcement on densification, structure, and properties of mechanically alloyed Al was investigated. The milling of Al-ZrB₂ powder compositions resulted in formation of agglomerates with varied size. In particular, the size of agglomerates was reduced considerably with increased addition of ZrB₂ to Al. Interestingly, the densification of hot pressed Al increased from 96.06% to 99.22% with ZrB₂ addition. The reduction of agglomerates size was attributed to the enhanced densification of Al-ZrB₂ composites. Pure Al showed relatively low hardness (0.94?GPa) and it was improved to 1.78?GPa with the addition of 20?vol% ZrB₂. The mechanical properties have significantly been improved for Al-ZrB₂ composites. Especially Al - 20?vol% ZrB₂ possessed a very high yield strength (529?MPa), compressive strength (630?MPa) and compressive strain of 19.25%. Realization of such a good combination of mechanical properties is the highest ever reported for Al composites so far in the literature. The coefficient of friction (COF) of Al-ZrB₂ varied narrowly between 0.33 and 0.40 after dry sliding wear against steel disc. The wear rate of Al-ZrB₂ composites was within mild wear regime and varied between 98.88?×?10^?6 and 34.66?×?10^?6 mm³/Nm. Among all the compositions, Al - 20?vol% ZrB₂ composite exhibited the lowest wear rate and high wear rate was noted for pure Al. Mild abrasion, tribo-oxidation, third body wear (wear debris) and delamination were the major material removal mechanisms for Al-ZrB₂ composites. Overall the hardness, strength and wear resistance of Al - 20?vol% ZrB₂ composite was improved by 84.3%, 84.3% and 64.2%, respectively when compared to pure Al.     

Tribological behavior of carbon nanotube and polytetrafluoroethylene filled polyimide composites under different lubricated conditions

The friction and wear behavior of polyimide (PI) composites reinforced with carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) were comparatively evaluated under dry sliding, water‐, oil‐ or alkali‐lubricated condition. The wear mechanisms of the composites were also discussed. Results indicate that, when comparison with the dry friction situation, PI‐based composites results lower friction coefficients and wear rates under oil‐ or alkali‐lubricated condition. The lowest wear rate of the CNT/PTFE/PI composite is recorded as 1.2 × 10⁻⁶ mm³/Nm during the composite sliding in alkali, which is only about 40% of the value sliding under dry friction condition. The worn surface of neat PI under dry sliding is characterized by severe adhesive wear, whereas abrasive wear is the main character for CNT/PTFE/PI composites. The worn surfaces of CNT/PTFE/PI composites sliding in oil or alkali lubricated condition are smoother than those under dry or water condition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Wear resistance and hardness properties of TiB2– Fe coating developed on AISI 1020 steel by tungsten inert gas (TIG) cladding

The present work is attempted to improve the microhardness and wear properties of AISI 1020 steel by depositing TiB₂–Fe composite coating using tungsten inert gas (TIG) cladding. In this study, different compositions of TiB₂–Fe paste form were preplaced on the substrate plates and then TIG heat input was applied to deposit hard composite coating layer. The main objective of the present work was to explore the influence of TIG input current as well as iron content on the microstructure and surface properties of deposited coatings. Microhardness, microstructural and phase characterization of the coating have been done by the Vickers microhardness tester, scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS) and X-ray diffractrometer (XRD). The results showed that the microhardness of the TiB₂–Fe coating was strongly influenced by the composition of the coating materials as well as the TIG processing current. The microhardness increases with decreasing Fe contents in the coating materials with constant processing current (90 A) as well as it also increases with decreasing processing current with the fixed composition of coating materials (80TiB₂–20Fe). The maximum average microhardness found was 3082 HV_0.1 for the coating of 100TiB₂–0Fe composition ratio and 90 A processing current which was about 18 times higher than that of the substrate average microhardness value (163 HV_0.1). Average wear rate evaluated by considering weight loss of the TIG cladded samples using pin on disc tribometer by the sliding distance of 864 m and 20 N normal loads. The wear results also showed that the coating contains 100 wt% of TiB₂ (0 wt% of Fe) exhibited lower rate of wear 6.74 × 10^?8 g/Nm which is about 24 times lower as compared to AISI 1020 mild steel wear rate (166.31 × 10^?8 g/Nm).     

Sliding Wear Behavior of TaC‐Containing Ti(CN)‐WC‐Ni/Co Cermets

Four compositions of TiCN‐WC‐Ni/Co cermets with or without TaC were prepared by pressureless sintering of respective powders, and unlubricated sliding wear behavior against bearing grade steel ball was studied at 5, 10, or 20 N load. Maximum hardness and fracture toughness were obtained for Ti(CN)‐5WC‐10Ni‐10Co‐5TaC (in wt%) cermet. With change in the cermet composition and sliding load, coefficient of friction varied from 0.3 to 1.0 and wear rate varied from 3 × 10^?7 to 7 × 10^?7 mm³/Nm. The increased material transfer and formation of iron oxide‐rich tribochemical layer were responsible for the reduction in friction and wear for Ti(CN)‐5WC‐10Ni‐10Co‐5TaC cermet.     

Surface Characterization and Biocompatibility of Selenium‐Doped Hydroxyapatite Coating on Titanium Alloy

Selenium‐doped hydroxyapatite (HA) was biomimetically coated on Ti6Al4V plates with the aim of combining the anticancer and antibacterial properties of selenium with the biocompatibility and bioactivity of HA. For the coating process, the composition of 1.5 × SBF (solution with ion concentrations at 1.5 times that of simulated body fluid, SBF) was modified to include 0.15 mM selenate (SeO₄^2?) ion. The selenium‐doped HA coating was characterized by several methods, such as scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. The cytotoxicity of selenium on osteoblast and osteosarcoma cells was determined. The coating was shown to inhibit the growth of Staphylococcus epidermidis.     

A comparative investigation on microstructure evolution and wear resistance of in situ synthesized NbC,WC, TaC reinforced Mo2FeB2 coatings by laser cladding

To improve the microhardness and wear resistance of Mo₂FeB₂ coatings, composite coatings were prepared by laser cladding using in situ synthesized NbC, WC, and TaC. The influence of different carbides on the morphology, microstructure, microhardness, residual stress, and tribological properties of the composite coatings was investigated. The results showed various microstructural morphologies in different composite coatings. Apparent herringbone structures were observed in most coatings except for the Mo₂FeB₂/TaC composite coating and a eutectic structure was formed in the Mo₂FeB₂/WC composite coating. In addition, the heat-affected zone was typically composed of acicular martensite and lath martensite. The microhardness of the Mo₂FeB₂/WC composite coating increased to 1543.6 HV_0.5 compared with 985.7 HV_0.5 observed for the Mo₂FeB₂ coating. Tensile stress existed in the coating, bonding zone, and heat-affected zone, whereas the substrate exhibited compressive stress. The Mo₂FeB₂/WC composite coating exhibited the lowest tensile stress (298 MPa). The Mo₂FeB₂/WC composite coating containing WC and the W₂C phase had the lowest coefficient of friction (0.38) and wear rate (3.90 × 10^?5 mm³/Nm), indicating its excellent tribological properties. Moreover, the wear mechanism of the Mo₂FeB₂ coating is severe adhesive and abrasive wear. The adhesive wear mechanism was mitigated by the formation of in situ synthesized NbC, WC, and TaC. The wear mechanism of the Mo₂FeB₂/WC composite coating was only a slight abrasive wear.     

Electrodeposition of hydroxyapatite coating on magnesium for biomedical applications

The effectiveness of hydroxyapatite (HA) coating prepared by electrodeposition technique in improving the corrosion resistance of commercially pure magnesium (CP-Mg) in simulated body fluid (SBF) is addressed. The coating formed in as-deposited condition is identified as dicalcium phosphate dehydrate (DCPD) (Brushite), which is converted to HA after immersion in 1?M NaOH at 80°C for 2?h. The XRD patterns and FTIR spectra confirm the formation of DCPD and HA. During electrodeposition, the H₂PO₄ ^? ion is reduced and the reaction between Ca²⁺ ions and the reduced phosphate ions leads to the formation of DCPD, which is converted to HA following treatment in NaOH. The deposition of HA coating enables a threefold increase in the corrosion resistance of CP-Mg. The ability to offer a significant improvement in corrosion resistance coupled with the bioactive characteristics of the HA coating establish that electrodeposition of HA is a viable approach to engineer the surface of CP-Mg in the development of Mg-based degradable implant materials.     

Microstructure and mechanical properties of TiB2-reinforced 7075 aluminum matrix composites fabricated by laser melting deposition

In this study, we adopt laser-melting deposition (LMD) technology to fabricate TiB₂/7075 aluminum matrix composites (AMCs), and we investigate in detail the effect of the TiB₂ content on the microstructure, nano-hardness, compressive properties, and wear performance. We prepare experimental samples by using a laser power of 800?W and a velocity of 0.01?m/s, and the results are evaluated. It was observed that the reinforcement particles dispersed irregularly throughout the Al matrix as the TiB₂ contents increased. The grain size of the fine-grain zone decreased appreciably by 31.9% from 8.41?µm (LMD sample without TiB₂ reinforcement) to 5.73?µm. Furthermore, the AMCs with 4?wt% reinforcement exhibited impressive mechanical properties, i.e., nanohardness of 1.939 Gpa, compressive strength of 734.8?MPa, and a wear rate of 1.889?×?10^?4 mm³/Nm. The wear resistance improved and the wear mechanism changed from adhesive wear to debris wear with the addition of TiB₂ reinforcement.     

Friction and wear property of a-CNx coatings sliding against ceramic and steel balls in water

The amorphous carbon nitride coatings (a-CN_x) were deposited on Si₃N₄ disks using ion beam assisted deposition (IBAD), and their composition and chemical bonding were determined by X-ray photoelectron spectroscopy (XPS). The a-CN_x coatings' hardness was measured by nano-indentation and the friction and wear property of the a-CN_x coatings sliding against Si₃N₄, SiC, Al₂O_3, SUS440C and SUJ2 balls in water were investigated by using ball-on-disk tribo-meter. The worn surfaces were observed using optical microscopy and analyzed by XPS. The results of XPS analysis showed that the a-CN_x coatings contained 12 at.% nitrogen and the major chemical bonding was sp² C = N and sp³C–N. The nano-hardness of the a-CN_x coatings was 29 GPa, higher than those of balls. Among five kinds of tribo-systems, the lowest friction coefficient was obtained in the range of 0.01 to 0.02 for the tribo-systems with SiC and Si₃N₄ balls, the largest wear rate of the a-CN_x coating of 1.77 × 10^− 7 mm³/Nm was obtained as sliding against Al₂O₃ ball, while the smallest wear rate of a-CN_x coating of 1.44 × 10^− 8 mm³/Nm was gotten as sliding against Si₃N₄ ball. However, SUJ2 ball showed the highest wear rate of 7.0 × 10^− 7 mm³/Nm, whereas Al₂O₃ ball exhibited the lowest wear rate of ball of 3.55 × 10^− 9 mm³/Nm. The XPS analysis on the worn surface for the a-CN_x coatings displayed that the nitrogen concentration decreased and the sp²-bonding-rich structure was formed after sliding tests in water.     

YSZ/MoS2 self-lubricating coating fabricated by thermal spraying and hydrothermal reaction

Thermal sprayed ceramic coatings have extensively been used in components to protect them against friction and wear. However, the poor lubricating ability severely limits their application. Herein, yttria-stabilized zirconia (YSZ)/MoS₂ composite coatings were successfully fabricated on steel substrate with the combination of thermal spraying technology and hydrothermal reaction. Results show that the synthetic MoS₂ powders are composed of numbers of ultra-thin sheets (about 7 ~ 8?nm), and the sheet has obvious lamellar structure. After vacuum impregnation and hydrothermal reaction, numbers of MoS₂ powders, look like flowers, generate inside the plasma sprayed YSZ coating. Moreover, the growing point of the MoS₂ flower is the intrinsic micro-pores of YSZ coating. The friction and wear tests under high vacuum environment indicate that the composite coating has an extremely long lifetime (>?100,000 cycles) and possesses a low friction coefficient less than 0.1, which is lower by about 0.15 times than that of YSZ coating. Meanwhile, the composite shows an extremely low wear rate (2.30?×?10^?7 mm³ N^?1 m^?1) and causes slight wear damage to the counterpart. The excellent lubricant and wear-resistant ability are attributed to the formation of MoS₂ transfer films and the ultra-smooth of the worn surfaces of hybrid coatings.     

Wear behavior of BCS glass ceramic coating on stainless still slab

The present study aims to assess the friction and wear characteristics of BSC glass-ceramic on 304L stainless steel, fabricated by air spray method.The dry sliding friction and wear behavior were investigated using a 4?mm diameter AISI52100 steel pin on disk geometry under 3–39?N loads, at different sliding speeds in dry conditions.Average friction coefficients (COF)and wear rates were varied in the range between 0.6–0.8 and 26?×?10^?2–0.001?mm³/N?m respectively. The results show that, the frictional behavior of glass-ceramic-metal couples depended on the metal transferred from the steel pin to the glass-ceramic's surface and the applied loads. It was found that the running–in period of G39 last shorter than the G3 one, also in the case of G39 the steady state friction coefficient was lower than G3.The wear tracks were examined using scanning electron microscope, it was revealed that, the intrinsic porosity of coat has affected on the amounts of debris as an important factor for the COF values.     

Effect of load on the friction and wear characteristics of Si3N4-hBN ceramic composites sliding against steels

The tribological behaviors of Si₃N₄-hBN ceramic composites sliding against steels (austenitic stainless steel (ASS) and 45 steel) under dry friction conditions at different loads were investigated by using an MMW-1 type vertical universal friction and wear tester. The experimental results showed that the friction coefficients and wear rates first showed a decrease and then an increase with an increase in the load under dry friction conditions. The better tribological performance was exhibited by the SN10/ASS sliding pair under a load of 20 N (the friction coefficient was as low as 0.27 and the wear rates of both pin and disc had a magnitude of 10⁻⁶ mm³ N⁻¹ m⁻¹). This may be attributed to the formation of a black surface film (consisting of B₂O₃, SiO₂, and Fe₂O₃). For the same sliding pair, when the load was 10 N, the dominating wear mechanism was abrasive wear. Hence, the friction coefficient was higher (0.7). When the load increased to 30 and 50 N, the wear mechanism of the SN10/ASS sliding pair was a combination of abrasive and adhesive wears, and higher friction coefficients (0.48 and 0.72 under loads of 30 and 50 N, respectively) were obtained. On the other hand, the contents of hBN also showed a significant impact on the tribological behaviors of the Si₃N₄-hBN/ASS sliding pairs. When the hBN content was less than 10%, the friction coefficients of the Si₃N₄-hBN/ASS sliding pairs decreased with an increase in the hBN content. On the other hand, at hBN contents of 10% or more, the friction coefficients of the sliding pairs increased with an increase in the hBN content. Under the same experimental conditions, the Si₃N₄-hBN/45 steel pairs showed poor tribological properties as compared with the Si₃N₄-hBN/ASS pairs.     

Effect of oxide and carbide nanoparticles on tribological properties of phenolic-based nanocomposites

The phenolic-based composites and components are widely used because of their excellent thermal, tribological and mechanical behaviors. In the present study, phenolic resin composed of hexamine, novalac, furfural, and furfuryl alcohol has been used. The effects of two carbide nanoparticles (SiC and TiC) and two oxide nanoparticles (TiO₂ and ZrO₂) on the tribological properties of phenolic resin were experimentally investigated. This paper intends to identify the effects of different fillers, fraction of particles and normal load on wear rate and coefficient of friction in dry sliding wear of phenolic-based nanocomposites against hard metal. The proportions of fillers were 0.5, 1 and 2?vol% and experiments were carried out under 40, 50, 60 and 70?N loads and at 0.2?m/s speed. The fillers were mixed with phenolic resin and molded in the form of a cylinder (8.5?mm diameter?×?25?mm height). The samples were cured at 135?°C with a special heating cycle. The wear tests were performed on pin-on-disk testing apparatus at ambient temperature. The composite pins were tested in dry sliding against carbon steel disk. The worn surfaces of samples have been investigated by SEM and the effects of nanometer particles showed different wear mechanisms. Observations showed that carbide particles have better enhancing effect on tribological properties of phenolic resin as compared to the oxide particles. Nanocomposites with SiC particles showed the best tribological properties among the investigated samples. The optimal content of SiC nanoparticles were 1?vol%.     

Phase stability,thermo-physical properties and thermal cycling behavior of plasma-sprayed CTZ,CTZ/YSZ thermal barrier coatings

ZrO₂ co-stabilized by CeO₂ and TiO₂ with stable, nontransformable tetragonal phase has attracted much attention as a potential material for thermal barrier coatings (TBCs) applied at temperatures >?1200?°C. In this study, ZrO₂ co-stabilized by 15?mol% CeO₂ and 5?mol% TiO₂ (CTZ) and CTZ/YSZ (zirconia stabilized by 7.4?wt% Y₂O₃) double-ceramic-layer TBCs were respectively deposited by atmospheric plasma spraying. The microstructures, phase stability and thermo-physical properties of the CTZ coating were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimeter (TG-DSC), laser pulses and dilatometry. Results showed that the CTZ coating with single tetragonal phase was more stable than the YSZ coating during isothermal heat-treatment at 1300?°C. The CTZ coating had a lower thermal conductivity than that of YSZ coating, decreasing from 0.89?W?m^?1 K^?1 to 0.76?W?m^?1 K^?1 with increasing temperature from room temperature to 1000?°C. The thermal expansion coefficients were in the range of 8.98?×?10^?6 K^?1 – 9.88 ×10^?6 K^?1. Samples were also thermally cycled at 1000?°C and 1100?°C. Failure of the TBCs was mainly a result of the thermal expansion mismatch between CTZ coating and superallloy substrate, the severe coating sintering and the reduction-oxidation of cerium oxide. The thermal durability of the TBCs at 1000?°C can be effectively enhanced by using a YSZ buffer layer, while the thermal cycling life of CTZ/YSZ double-ceramic-layer TBCs at 1100?°C was still unsatisfying. The thermal shock resistance of the CTZ coating should be improved; otherwise the promising properties of CTZ could not be transferred to a well-functioning coating.