Microstructure Development and Tribological Behavior in AlCuFe Quasicrystalline Thin Films

A series of AlCuFe films were deposited by magnetron sputtering and subjected to X-ray diffraction and tribological testing to elucidate the correlation between quasicrystalline phase content and coefficient of friction. The sputter target was a pressed powder target comprised of a mixture of elemental powders combined in the ratio Al₆₅Cu₂₃Fe₁₂ and pressed at 400°C. This target was designed to produce film compositions within the single-phase icosohedral quasicrystalline regime. X-ray diffraction performed on the as-deposited coatings showed that they were comprised of a nanoscale/amorphous precursor phase with broad X-ray diffraction maxima. Anneals of the as-deposited films were performed at 450 or 500°C in argon for various times to cause partial or full development of the quasicrystalline microstructure, and films were tribo-tested in two separate systems. The first of these was an oscillating pin-on-flat system, in which a coated 2 mm diameter pin was used to test as-deposited films at temperatures of up to 220°C under vacuum and a 15 g load. The second system used a 0.25 diameter alumina ball and a load of 100 g to test films in air at temperatures of 25, 150, and 300°C. Various anneal conditions were also tested. For an as-deposited coating, a coating annealed for 2 h at 450°C, and a coating annealed for 1h at 500°C, the observed coefficients of friction were 0.45, 0.23, and 0.17, respectively. Correlation between quasicrystalline phase content, room temperature friction coefficient, and appearance of the wear track clearly showed that annealing to the fully developed quasicrystalline structure resulted in a harder film with a lower coefficient of friction.     

Nanowear of Hafnium Diboride Thin Films

Chemical Vapor Deposition-grown HfB₂ films were subjected to nanowear testing at normal loads of 50–500 μN. The material response was investigated by measuring residual wear depths and wear scar roughness and by calculating wear rates and specific energies. Films annealed for 1 h at 800°C showed significant reduction in wear rate and required a higher critical energy for wear, compared to as-deposited HfB₂ films. Analysis of roughness of the worn scars revealed that plowing effect dominates at higher loads (200–500 μN), whereas at lower loads, asperity flattening dominates. The excellent response of annealed HfB₂ films to nanotribological testing demonstrates the potential of these films for applications requiring high wear resistance at the nanoscale.     

Characterization and mechanical/tribological properties of nano Au-TiO2 composite thin films prepared by a sol-gel process

Nano Au-TiO₂ composite thin films on Si(1 0 0) and glass substrates were successfully prepared with a facile sol-gel process followed by sintering. The morphology and mircostructure of the films were investigated via X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The Au particles, of diameter 14-22 nm depending on the sintering temperatures used, were found to be well dispersed in the TiO₂ matrix, with a small amount of the particles escaped from the film. The surfaces of the films were uniform, compact and crack-free. Hardness and elastic modulus of the films were measured by using the nanoindentation technique. Friction and wear properties were investigated by using a one-way reciprocating tribometer. It was found that the highest hardness and elastic modulus values were obtained for the films prepared with 500 °C sintering temperature. The films displayed superior antiwear and friction reduction performances in sliding against an AISI 52100 steel ball. With 5.0 mol% Au, the friction coefficient was only 0.09-0.10 and the wear life was more than 2000 sliding cycles. The friction coefficient and wear life decreased with increasing sliding speed and load. The failure mechanism of the Au-TiO₂ films was identified to be light scuffing and abrasion. Those films can be potentially applied as ultra-thin lubricating coatings.     

Grain boundary enrichment in the FePt polymorphic A1 to L10 phase transformation

A series of Fe_54±1Pt_46±1 thin films have been sputter-deposited and annealed at various times and temperatures to facilitate the A1 to L1₀ polymorphic phase transformation. The annealing times span one minute to tens of minutes over temperatures of 300–800 °C. The films were characterized by X-ray and electron diffraction and atom probe tomography. This time–temperature regime provides ‘snap-shots’ into the compositional segregation evolution at the grain boundaries during the polymorphic phase transformation. The as-deposited A1 phase showed a preferential segregation of Pt to the grain boundaries. The reduction of Pt enrichment at the boundaries was observed for all L1₀ ordered films.     

Tribological properties of spark-plasma-sintered ZrO2(Y2O3)-CaF2-Ag composites at elevated temperatures

Spark-plasma sintering is employed to synthesize self-lubricating ZrO₂(Y₂O₃) matrix composites with different additives of CaF₂ and Ag as solid lubricants by tailoring the composition and by adjusting the sintering temperature. The friction and wear behavior of ZrO₂(Y₂O₃) matrix composites have been investigated in dry sliding against an alumina ball from room temperature to 800 °C. The effective self-lubrication at different temperatures depends mainly on the content of various solid lubricants in the composites. The addition of 35 wt.% Ag and 30 wt.% CaF₂ in the ZrO₂(Y₂O₃) matrix can promote the formation of a well-covered lubricating film, and effectively reduce the friction and wear over the entire temperature range studied. The friction coefficients at low temperatures were at a minimum value for the composite containing 35 wt.% of silver. At this silver concentration, low and intermediate temperature lubricating properties are greatly improved without affecting high-temperature lubrication by the calcium fluoride in ZrO₂(Y₂O₃) matrix composites. The worn surfaces and transfer films formed during wear process have been characterized to identify the synergistic lubrication behavior of CaF₂ and Ag lubricants at different temperatures.     

Characterization and tribological investigation of sol–gel ceramic films on Ti–6Al–4V

SiO₂, TiO₂, and hydroxyapatite (HA) thin films with good biocompatibility were grown on Ti–6Al–4V (coded as TC4) substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 500 °C The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM) are applied to characterize the original unworn films. The tribological properties of thin films sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As the result, the target films composed of nano-particles ranging from 30 nm to 100 nm around were obtained. All the sol–gel ceramic films are superior in resisting wear compared with the TC4 substrate. Among all, HA film shows the best resistance while SiO₂ film shows the worst wear resistance both under higher (3 N) and lower load (1 N). TiO₂ shows good wear resistance under lower load (1 N). SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characteristic of abrasive wear. Differently, abrasion, plastic deformation and micro-fracture dominate the wear of ceramic films. The superior friction reduction and wear resistance of HA film is greatly due to the slight plastic deformation of the film. It is supposed that the deformation of the HA film is closely related to the special arrangement of the nano-particles and microstructure. HA film is recommended for clinical application from the point of wear resistance view.     

Investigation of Annealing Temperature on Structural and Morphological Properties of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles for Humidity Sensor Application

Cr₂O₃ nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temperatures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr₂O₃ varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr₂O₃ nanoparticles at 400 nm. The humidity sensor of the Cr₂O₃ nanoparticles was studied by two temperature method. 1000 °C annealed Cr₂O₃ nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr₂O₃ nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased.     

Tribological behaviors and mechanisms of Ti<Subscript>3</Subscript>AlC<Subscript>2</Subscript>

Tribological behaviors and the relevant mechanism of a highly pure polycrystalline bulk Ti₃AlC₂ sliding dryly against a low carbon steel disk were investigated. The tribological tests were carried out using a block-on-disk type high-speed friction tester, at the sliding speeds of 20–60 m/s under a normal pressure of 0.8 MPa. The results showed that the friction coefficient is as low as 0.1∼0.14 and the wear rate of Ti₃AlC₂ is only (2.3–2.5) × 10⁻⁶ mm³/Nm in the sliding speed range of 20–60 m/s. Such unusual friction and wear properties were confirmed to be dependant dominantly upon the presence of a frictional oxide film consisting of amorphous Ti, Al, and Fe oxides on the friction surfaces. The oxide film is in a fused state during the sliding friction at a fused temperature of 238–324 °C, so it takes a significant self-lubricating effect.     

Microstructure and tribological characteristics of ZrO2–Y2O3 ceramic coatings deposited by laser-assisted plasma hybrid spraying

ZrO₂–Y₂O₃ ceramic coatings were deposited on AISI 304 stainless steel by both a low-pressure plasma spraying (LPPS) and a laser-assisted plasma hybrid spraying (LPHS). Microstructure and tribological characteristics of ZrO₂–Y₂O₃ coatings were studied using an optical microscope, a scanning electron microscope, and an SRV high-temperature friction and wear tester. The LPHS coatings exhibit distinctly reduced porosity, uniform microstructure, high hardness and highly adhesive bonding, although more microcracks and even vertical macrocracks seem to be caused in the LPHS coatings. The ZrO₂ lamellae in the LPHS coatings before and after 800°C wear test consist mainly of the metastable tetragonal (t′) phase of ZrO₂ together with small amount of c phase. The t′ phase is very stable when it is exposed to the wear test at elevated temperatures up to 800°C for 1 h. The friction and wear of the LPHS coatings shows a strong dependence on temperature, changing from a low to a high wear regime with the increase of temperature. At low temperatures, friction and wear of the LPHS coatings is improved by laser irradiation because of the reduced connected pores and high hardness in contrary to the LPPS coating. However, at elevated temperatures, the friction and wear of the LPHS coatings is not reduced by laser irradiation. At room temperature, mild scratching and plastic deformation of the LPHS coatings are the main failure mechanism. However, surface fatigue, microcrack propagation, and localized spallation featured by intersplat fracture, crumbling and pulling-out of ZrO₂ splats become more dominated at elevated temperatures.     

Tribological Properties of a Nano-Eutectic Fe<Subscript>1.87</Subscript>C<Subscript>0.13</Subscript> Alloy Under Water Environment

Tribological properties of a nano-eutectic Fe_1.87C_0.13 alloy were investigated under distilled-water lubrication against AISI52100 steel ball for various applied loads and sliding speeds. For comparison, the tribological behavior of annealed coarse-grained Fe_1.87C_0.13 alloy was also examined under the same testing conditions. Worn surfaces of both alloys were analyzed by using a scanning electron microscope (SEM). The wear rate of nano-eutectic Fe_1.87C_0.13 alloy was on the order of 10⁻⁵ mm³/m. The wear rate of nano-eutectic Fe_1.87C_0.13 alloy was higher than that of annealed Fe_1.87C_0.13 alloy at lower load, but lower under higher load. The friction coefficients of the two alloys were similar and exhibited a slight increase with increasing sliding speed, but a small decrease with increasing applied load. The wear mechanism of the nano-eutectic Fe_1.87C_0.13 alloy was transformed from plowing and corrosion wear to slight fatigue cracking with increasing applied load, whereas that of the annealed coarse-grained Fe_1.87C_0.13 alloy was transformed from plowing and corrosion wear to severe fatigue flaking.     

Effect of deposition pressure on microstructure and tribological behavior of MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Mo nanoscale multi-layer films

MoS _x /MoS _x -Mo multi-layer films consisted of several bilayers and a surface layer on steel substrate were deposited by d.c. magnetron sputtering at different deposition pressures. Each bilayer contained a MoS _x layer with 80 nm in thickness and a MoS _x -Mo composite layer with 20 nm in thickness. With the increase of deposition pressure, the perpendicular orientation of the basal plane prevailed while the parallel orientation decreased. The tribological properties of the multi-layer films were investigated by using a ball-on-disk tribometer both in vacuum and in humid air. The multi-layer film deposited at 0.24 Pa had a compact, consistent layered structure with high intensity of (002) plane and low S content compared to the others deposited at 0.32 and 0.40 Pa, and showed the lowest friction coefficient and wear rate in humid air.     

Processing of hollow micro- and nanostructures using the hydrophilic nature of MgO

We show that covering the water-saturated MgO surface with an Al₂O₃ film using atomic layer deposition and then annealing it at 400 °C leads to plastic deformation of alumina by trapped water vapor with consequent development of hollow structures. This phenomenon is applied to thin films, nanopatterned surfaces and isolated 3D nanostructures.     

Tribological properties of anatase TiO<Subscript>2</Subscript> sol–gel films controlled by mutually soluble dopants

Tribological properties of TiO2 sol–gel thin films with mutually soluble dopants were studied on a glass substrate. The results showed that the formation of mutually soluble solid solution played a very important role in the growth of titania grains. The fine-grained TiO₂ films controlled by SiO₂ dopant were superior to pure TiO₂ film in wear resistance and endurance life, although both films greatly improve the surface characteristics of glass substrate, enhancing its tribological characteristics. High resistance to microfracture because of the very small grain size as well as a good adhesion of the film to the substrate is believed to be the determining factors influencing the tribological properties of SiO₂ doped TiO₂ films. However, excessive SiO₂ seriously deteriorates wear resistance of film due to phase separation. The wear mechanisms were also discussed based on the observation of the surface morphologies by scanning electron microscope (SEM).     

Tribological properties of ZrO2 (Y2O3)-Mo-BaF2/CaF2 composites at high temperatures

ZrO₂ (Y₂O₃) with different contents of BaF₂/CaF₂ and Mo were fabricated by hot pressed sintering, and the tribological behavior of the composites against SiC ceramic was investigated from room temperature to 1000 °C. It was found that the ZrO₂ (Y₂O₃)-5BaF₂/CaF₂-10Mo composite possessed excellent self-lubricating and anti-wear properties. The low friction and wear were attributed to enhanced matrix and BaMoO₄ formed on the worn surfaces.     

Synergistic Effect of Nano-MoS<Subscript>2</Subscript> and Anatase Nano-TiO<Subscript>2</Subscript> on the Lubrication Properties of MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> Nano-Clusters

A MoS₃ precursor deposited on anatase nano-TiO₂ is heated at 450 °C in an H₂ atmosphere to synthesize MoS₂/TiO₂ nano-clusters. The nano-clusters are then characterized, and their tribological properties are evaluated. MoS₂ is found to be composed of layered structures with 1–10 nm thicknesses, 10–30 nm lengths, and 0.63–0.66 nm layer distances. The MoS₂ sizes in the MoS₂/TiO₂ nano-clusters are smaller and their layer distances are larger than those of pure nano-MoS₂. The MoS₂/TiO₂ nano-clusters also present a lower average friction coefficient than pure nano-MoS₂, but the anti-wear properties of both the nano-clusters and pure nano-MoS₂ are similar. X-ray photoelectron spectroscopy indicates that nano-TiO₂ and the element Mo are transferred to the friction surface from the MoS₂/TiO₂ nano-clusters through a tribochemical reaction. This produces a lubrication film containing TiO₂, MoO₃, and other chemicals. The nano-MoS₂ changes in size and layer distance when combined with nano-TiO₂, producing a synergistic effect. This may further be explained using a micro-cooperation model between MoS₂ nano-platelets and TiO₂ solid nanoparticles.     

Mechanical and tribological behavior of the metal matrix composite AA6061/ZrO<Subscript>2</Subscript>/C

This study investigates the influence of zirconium dioxide (ZrO₂) and graphite (C) on the mechanical and tribological behavior of aluminum-based metal matrix composite (AA6061) fabricated through the stir casting. Metal matrix composites (MMC) are prepared with the following weight percentages: 100 % AA; 96 % AA-2 % ZrO₂-2 % C; 88 % AA-6 % ZrO₂-6 % C; 92 % AA-6 % ZrO₂-2 % C; and 96 % AA-2 % ZrO₂-6 % C. The microstructure and the mechanical and tribological behavior are characterized, and their correlations are obtained. Microstructural studies of the MMC reveal a uniform distribution of ZrO₂ and C particles in the AA6061 matrix. The addition of ZrO₂ improves the hardness from 6 % to 12 % (30 HRC to 40.94 HRC) and the ultimate tensile strength from 8 % to 15 % (128 MPa to 166.3 MPa) of the base metal (AA6061). The tribological behavior of wear and the frictional properties of the MMC are also studied by performing dry sliding wear test using pin-on-disc method. Result shows that the minimum and maximum wear rates of MMC are 5 E-9 and 6.2 E-9 (g/mm), respectively, at speed of 850 rpm and constant sliding distance of 1000 m.     

Tribological Property of Ni<Subscript>3</Subscript>Al Matrix Composites with Addition of BaMoO<Subscript>4</Subscript>

The Ni₃Al matrix composites with addition of 10, 15, and 20 wt% BaMoO₄ were fabricated by powder metallurgy technique, and the tribological behaviors were studied from room temperature to 800 °C. It was found that BaAl₂O₄ formed during the fabrication process. The Ni₃Al composites showed poor tribological property below 400 °C, with high friction coefficients (above 0.6) and wear rates (above 10⁻⁴ mm³/Nm). However, the composites exhibited excellent self-lubricating and anti-wear properties at higher temperatures, and the composite with addition of 15 wt% BaMoO₄ had the lowest wear rate (1.10 × 10⁻⁵ mm³/Nm) and friction coefficient (0.26). In addition, the results also indicated that BaAl₂O₄ for the Ni₃Al composites did not exhibit lubricating property from room temperature to 800 °C.     

Fabrication and characterization of ZnO thin film for hydrogen gas sensing prepared by RF-magnetron sputtering

A ZnO thin film-based gas sensor was fabricated using a SiO₂/Si substrate with an integrated platinum comb-like electrode and heating element. The structural characteristics, morphology, and surface roughness of the as-grown ZnO nanostructure were investigated. The optical properties were examined by UV–vis spectrophotometry. The film revealed the presence of a c-axis oriented (0 0 2) phase of 20.8 nm grain size. The sensor response was tested for hydrogen concentrations of 50, 70, 100, 200, 400, and 500 ppm at operating temperatures ranging from 250 °C to 400 °C. The sensitivity toward 50 and 200 ppm of hydrogen at the optimum operating temperature of 350 °C were about 78% and 98%, respectively. The response was linear within the range of 50–200 ppm of hydrogen concentration. Our results demonstrated the potential application of ZnO nanostructure for fabricating cost-effective and high-performance gas sensors.     

厚度效应对Pb(Zr0.53Ti0.47)O3薄膜微结构、铁电、介电性能的影响

用改进的溶胶-凝胶法在Pt(111)/Ti/SiO₂/Si(100)衬底上制备了不同厚度的高度(111)取向的Pb(Zr_0.53Ti_0.47)O₃薄膜.运用X射线衍射(XRD)和原子力显微镜(AFM)分析了薄膜的微结构,原子力显微镜表明厚度为0.3μm和0.56μm的PZT薄膜的晶粒尺寸和表面粗糙度分别为0.2～0.3μm、2～3μm和0.92nm、34nm.0.3μm和0.56μm PZT薄膜的剩余极化(Pr)和矫顽场(Ec)分别为32.2μC/²、79.9kV/cm, 27.7μC/cm²、54.4kV/cm;在频率100KHz时,薄膜的介电常数和介电损耗分别为539、0.066,821、0.029.     

Growth and characterization of V2O5 thin film on conductive electrode

Vanadium pentoxide V₂O₅ thin films were grown at room temperature on ITO coated glass substrates by electrochemical deposition. The resulting films were annealed at 300, 400 and 500°C for 1 h in ambient environment. The effect of heat treatment on the films properties such as surface morphology, crystal structure, optical absorption and photoluminescence were investigated. The x‐ray diffraction study showed that the films are well crystallized with temperatures. Strong reflection from plane (400) indicated the film's preferred growth orientation. The V₂O₅ films are found to be highly transparent across the visible spectrum and the measured photoluminescence quenching suggested the film's potential application in OPV device fabrication.