A study of the friction and wear performance of MoSx thin films produced by ion beam enhanced deposition and magnetron sputtering

MoS_x thin films were deposited by ion beam enhanced deposition (IBED) and magnetron sputtering (MS) onto the surface of IBEN Si₃N₄ and TiN thin films. The friction and wear performances of thin films and 52100 steel were compared using an SRV model reciprocating testing machine. The results showed that all MoS_x films exhibit good tribological behavior. The MS MoS_x thin film has better wear resistance and the IBED MoS_x film has a longer wear life. The wear resistance of IBED Si₃N₄ and TiN thin film plus MoS_x film is 3–4 times and 8–20 times that of single IBED Si₃N₄ and TiN thin films and 52100 steel respectively. The analyses indicate that the difference in friction and wear performance between the two kinds of MoS_x thin film is determined by the x value of MoS_x, its microstructure and the atom mixing effect at the interface.     

Mechanical and tribological properties of nanostructured TiN/TiBN multilayer films

Nanostructured multilayer films of TiN/TiBN with different bilayer thicknesses (Λ) were deposited onto Si(1 0 0) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) at room temperature by reactive unbalanced magnetron sputtering in an Ar–N₂ gas mixture. The effects of different Λ values on mechanical and tribological properties were studied by atomic force microscope (AFM), scanning electron microscope (SEM), microindentation measurements, Rockwell-C tester, nano- and micro-scratch tester, impact tester, pin-on-disc tribometer, and Fourier-transform infrared spectroscopy (FTIR). It was found that the mechanical and tribological properties of multilayer films (typically 1.4 ± 0.1 μm in thickness) were closely related to Λ (varied from 1.4 to 9.7 nm). For the best multilayer film with Λ = 1.8 nm, a maximum hardness of 29.5 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L_C1 (37 N), L_C2 (>80 N) and the highest adhesion strength (HF1). Moreover, by the dynamic impact testing this multilayer film could endure impact cycles up to 4 × 10⁵ without adhesive failure. It was also found that the nano-scratch test under single-pass and constant-load conditions showed that the frictional coefficients decreased with Λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small Λ values improved the wear resistance and lowered the frictional coefficients. The frictional coefficients obtained at 5 N were kept at 0.5 and increased from 0.52 to 0.65 when Λ increased from 1.8 to 9.7 nm at 2 N. By FTIR analyses, the multilayer films with Λ = 1.8 and 2.2 nm showed the presence of h-BN which provided a lubricating function resulted in lower frictional coefficients and wear rates. The tribological properties of the TiN/TiBN multilayer films with different Λ values are also explained in terms of mechanical properties and wear mechanisms.     

The wear behaviour of high-chromium white cast irons as a function of silicon and Mischmetal content

The sliding wear behaviour of high-chromium white cast iron (16.8% Cr) has been examined as a function of silicon and Mischmetal alloy additions (1, 2, 3 and 5% Si and 0.1 and 0.3% Mischmetal). Such additions are known to modify the structure, but there is considerable controversy as to the exact effect. Silicon was found to refine the dendritic structure and increased the eutectic carbide volume fraction. However, for contents above 3%, transformation of the austenitic matrix to pearlite occurred in preference to martensite. Mischmetal additions reduced the austenite dendrite arm spacing, but did not have a significant effect on the carbide structure. The wear behaviour was investigated for each alloy in the as-cast (austenitic matrix) and hardened (martensitic) conditions using a block on ring configuration in pure sliding in the load range 42–238 N for a distance of 70 km against a hardened M2 steel counterface. For low loads (42 and 91 N), all the alloys showed a similar wear rate (3×10⁻⁴ to 4×10⁻⁴ mm³/m), associated with the formation of a thin (3 μm) oxide film of Fe₂O₃, the formation of very fine debris and a small depth of deformation below the worn surface (7 μm). For higher loads, wear was a strong function of microstructure, and was associated with a thicker film of the oxides Fe₂O₃ and Fe₃O₄ and greater depths of deformation. The iron with 2% silicon exhibited the best performance with a wear rate of 7×10⁻⁴ mm³/m and this was attributed to its finer structure and the formation of a thicker oxide film. In contrast, the iron with 5% silicon exhibited the worst performance, with a wear rate of 14×10⁻⁴ mm³/m, attributed to the pearlitic matrix. A linear relationship was observed between the depth of carbide fracture and the wear rate. The relationship between microstructure and wear mechanism is discussed.     

Dry sliding wear of fly ash particle reinforced A356 Al composites

In the present study aluminium alloy (A356) composites containing 6 and 12 vol. % of fly ash particles have been fabricated. The dry sliding wear behaviour of unreinforced alloy and composites are studied using Pin-On-Disc machine at a load of 10, 20, 50, 65 and 80 N at a constant sliding velocity of 1 m/s. Results show that the dry sliding wear resistance of Al-fly ash composite is almost similar to that of Al₂O₃ and SiC reinforced Al-alloy. Composites exhibit better wear resistance compared to unreinforced alloy up to a load of 80 N. Fly ash particle size and its volume fraction significantly affect the wear and friction properties of composites. Microscopic examination of the worn surfaces, subsurfaces and debris has been done. At high loads (>50 N), where fly ash particles act as load bearing constituents, the wear resistance of A356 Al alloy reinforced with narrow size range (53–106 μm) fly ash particles were superior to that of the composite having the same volume fraction of particles in the wide size range (0.5–400 μm).     

Wear properties of silicon nitride in rolling contact

The wear properties of silicon nitride were examined in dry rolling contact.

The wear coefficient of silicon nitride in pure rolling was of the order of 10⁻⁶ at the initial stage of wear and of the order of 10⁻⁸ at the steady stage of wear under hertzian pressures of 1.06, 1.30, 1.50 and 1.83 GPa.

The wear coefficient of silicon nitride in rolling-sliding was of the order of 10⁻³ under hertzian pressures of 1.06, 1.50 and 1.83 GPa.

The original grinding marks were decreased by the initial wear. Then a very smooth surface appeared in the steady state and its centre-line average roughness R_a was 0.02 μm.

In contrast, pitting and the adhesive accumulation of thin film debris on the surface started to occur in the steady stage of wear.

Three typical types of wear debris were distinguished. One of these, which was a glassy film, was confirmed to have an SiO₂ structure.     

Characteristics of Sputter-deposited Gadolinia-doped Ceria Thin Films on Al2O3/SiO2/Si Systems

Metal oxide films prepared by thin film technology have been reported for the potential applications on thin solid electrolyte layers for solid oxide fuel cells(SOFCs). Gadolinia-doped ceria(GDC) thin films and Al2O3 layers on SiO2/Si substrates are successively deposited by RF reactive magnetron sputtering from a cerium-gadolinium (90:10 at.%) alloy target and Al target in O2/Ar gas mixture and then perform post-thermal treatments at 300-700 ℃ and 900 ℃ for 2 h, respectively. Materials characteristics and chemical compositions of GDC films and Al2O3 layers are investigated by X-ray photoelectron spectroscopy(XPS), cross-sectional scanning electron microscopy(SEM), X-ray diffraction(XRD), and atomic force microscopy(AFM). Stoichiometric Al2O3 layers with polycrystalline structures are firstly prepared onto SiO2/Si substrates. A cubic fluorite structure with columnar crystallites of GDC films is successfully deposited on Al2O3/SiO2/Si systems. The chemical composition of 700 ℃-annealed GDC films is (Ce0.91Gd0.09)O1.94 and possesses a higher film density of 7.257 g/cm3. As a result, GDC thin films prepared by RF reactive magnetron sputtering and post-thermal treatments can be used as thin solid electrolyte layers for intermediate temperature SOFCs system as compared to the well-known yttria-stabilized zirconia(YSZ).     

Identification of intergranular phases in ceramic nanocomposites

Analytical FEG-TEM was used for nanostructural and nanochemical characterization of Al₂O₃–TiN (composite I) and Si₃N₄–TiN (composite II) ceramic composite systems. The presence of vitreous intergranular phases in pockets at multiple grain junctions and in thin films (≈ 0.8 nm thick) at grain boundaries was revealed by high resolution and Fresnel fringe imaging techniques. The existence of a Ti-rich thin intergranular film at alumina grain boundaries was revealed by EDS line-scanning across internal interfaces at the 1.5 nm lateral resolution level. Extracting interface specific information at subnanometre levels by means of quantitative spatial difference EELS allowed an identification of intergranular phases. Ti sub-oxide existed in thin films at Al₂O₃ and TiN grain boundaries, whereas a mixed Al–Ti–O–N glassy phase was observed in pockets at triple grain junctions in composite I. In composite II, residual siliceous oxide and oxynitride glass phases were identified in thin films at Si₃N₄ grain boundaries and multiple grain junctions, respectively. These observations indicated that the chemistry of the intergranular phase in thin grain boundary films is notably different from that in larger pockets at multiple grain junctions.     

Nanotribological characterization of digital micromirror devices using an atomic force microscope

Texas Instruments’ digital micromirror device (DMD) comprises an array of fast digital micromirrors, monolithically integrated onto and controlled by an underlying silicon memory chip. The DMD is one of the few success stories in the emerging field of MEMS. In this study, an atomic force microscope (AFM) has been used to characterize the nanotribological properties of the elements of the DMD. An AFM methodology was developed to identify and remove micromirrors of interest. The surface roughness, adhesion, friction, and stiffness properties of the DMD elements were studied. The influence of relative humidity and temperature on the behavior of the DMD element surfaces was also investigated. Potential mechanisms for wear and stiction are discussed in light of the findings.     

Tribological behavior of select MAX phases against Al2O3 at elevated temperatures

The layered M_n+1AC_n ternary carbides – MAX phases – Ta₂AlC, Ti₂AlC, Cr₂AlC and Ti₃SiC₂ were tested under dry sliding conditions against alumina at 550 °C and 3 N load (for a stress of ≈0.08 MPa) using a pin-on-disk tribometer. Ta₂AlC and Ti₂AlC exhibited low specific wear rates, SWRs, (≤1 × 10⁻⁶ mm³/N m), while the coefficients of friction, μ, were 0.9 and 0.6, respectively. At 0.4, μ of Ti₃SiC₂ was the lowest measured, but the SWR, at ≈2 × 10⁻⁴ mm³/N m, was high. With a μ of 0.44 and a SWR of 6 × 10⁻⁵ mm³/N m the Cr₂AlC sample was in between. No visible wear of Al₂O₃ counterparts was observed in all the tribocouples. Tribofilms, which were mainly comprised of X-ray amorphous oxides of the M and A elements and, in some cases, unoxidized grains of the corresponding MAX phases, were formed on the contact surfaces. The correlations between observed tribological properties and tribofilm characteristics are discussed.     

空间光调制器DMD多级谱复频成像的研究

依据DMD空间光调制器的调制特性及复频成像特性,设计了一个紧凑的4f傅立叶变换系统,对DMD的多级衍射谱进行复频输出,极大改善了仅用DMD零级衍射谱作为图像读出的光亮度.利用DMD空间光调制器复频成像输出装置构建的一个合成全息图的拍摄系统,拍摄了具有高对比度、低噪音的合成全息图.     

Laser cladding of ti-6al-4v with bn for improved wear performance

Titanium and its alloys suffer from galling, seizing, ploughing and adhesion during sliding contacts. A laser-cladding method, to enhance the wear performance of titanium, was investigated. A 1.5 kW continuous-wave CO₂ gas laser was used to clad hexagonal BN powder with and without the addition of NiCrCoAlY on a Ti-6Al-4V alloy substrate. X-ray diffraction, scanning electron microscopy, optical metallography, and Vickers' micro-hardness tests were employed to characterize the clad layers. A pin-on-block reciprocating wear machine was used to evaluate the sliding wear characteristics of age-hardened, laser surface-melted and laser-clad Ti-6Al-4V alloys. Results indicated that the clad layers consisted of TiN, TiB₂, and various alloy phases. Claddings with excellent adhesion and thicknesses up to 600 μm, with a maximum hardness of 1600 HV, were obtained. Wear tests showed a substantial improvement (10–200 times) in wear resistance of claddings over age-hardened and surface-melted layers. The improved wear performance is attributed to the high hardness and low friction properties of clad layers.     

Comparative wear in titanium diboride coatings on steel using high energy density processes

A comparison between the tribological properties of titanium diboride (TiB₂) deposited using high energy density processes such as Pulse Electrode Surfacing (PES) and Laser Surface Engineering (LSE) has been made. The wear resistance of TiB₂ coated surface is higher than AISI 1010 steel. The wear resistance of the LSE coated TiB₂ coating is even better than that of the PES deposited TiB₂ coating. Coefficient of friction values for LSE coated TiB₂ coating (μ=0.6) are lower than PES deposited TiB₂ coating (μ=0.7). Wear occurs in PES deposited TiB₂ coating by brittle fracture and attrition type mechanisms whereas mixed adhesive–abrasive wear in LSE deposited TiB₂ coating occurs by localized plastic deformation of the soft matrix phase Fe from a “composite” layer on the surface.     

Effect of working gap and circumferential speed on the performance of magnetic abrasive finishing process

Magnetic abrasive finishing (MAF) is one of the advanced finishing processes in which workpiece is kept between two magnets, and cutting force is controlled by working gap and magnetic field between the two magnets. MAF setup is designed for finishing cylindrical workpieces and it is mounted on lathe machine. The loosely bounded powder is prepared for experimentation by homogeneous mixing of magnetic powder (Fe powder of 300 mesh size (51.4 μm)), abrasive powder (Al₂O₃ of 600 mesh size (25.7 μm), and lubricant called servospin-12 oil. To investigate the effects of working gap and circumferential speed on material removal, change in surface finish and percent improvement in surface finish, a series of experiments have been conducted using in-house fabricated setup. Based upon the results, in general, material removal decreases by increasing working gap or decreasing circumferential speed of the workpiece. Change in surface finish increases by increasing circumferential speed of the workpiece.     

The structure of SiC-reinforced Mg casting alloys

The nature of the interface and interfacial reaction products formed between SiC particles and magnesium has been studied in two SiC_p-reinforced magnesium casting alloys, ZC63 and ZE63. In ZC63, a thin amorphous film was observed at the interface of the SiC particles. Energy-dispersive X-ray and electron energy-loss spectroscopy methods were used to characterize the films. They were found to contain Si, O and Mg, with the Si tetrahedrally coordinated to the O. The alloy ZE63 contains Zr and mischmetal (Ce, La, Nd, Pr), all of which are strong oxide formers. In the as-cast state, patches or continuous fine-grained oxide films were found at the interface of the SiC reinforcing phase in this alloy. Electron diffraction was used to identify these oxides as the tetragonal form of ZrO₂ and cubic CeO₂.     

Solidification and abrasion wear of white cast irons alloyed with 20% carbide forming elements

Three different white cast irons with compositions of Fe–3%C–10%Cr–5%Mo–5%W (alloy no. 1), Fe–3%C–10%V–5%Mo–5%W (alloy no. 2) and Fe–3.5%C–17%Cr–3%V (alloy no. 3) were prepared in order to study their solidification and abrasion wear behaviors. Melts were super-heated to 1873 K in a high frequency induction furnace, and poured at 1823 K into Y-block pepset molds. The solidification sequence of these alloys was investigated. The solidification structures of the specimens were found to consist of austenite dendrite (γ); (γ+M₇C₃) eutectic and (γ+M₆C) eutectic in the alloy no. 1; proeutectic MC; austenite dendrite (γ); (γ+MC) eutectic and (γ+M₂C) eutectic in the alloy no. 2, and proeutectic M₇C₃ and (γ+M₇C₃) eutectic in the alloy no. 3, respectively.

A scratching type abrasion test was carried out in the states of as-cast (AS), homogenized (AH), air-hardened (AHF) and tempered (AHFT) using the abrasive paper with 120 mesh SiC and 10 N application load. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the specimen no. 2 and highest in the specimen no. 1 except for the as-cast and homogenized states in which the specimen no. 3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the specimen no. 2 could be attributed to the fact that it contained proeutectic MC carbide, eutectic MC and M₂C carbides having extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed by heat-treatments to martensite, tempered martensite and austenite. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance of white cast iron.     

Direct observation of a Ti/Cu interface with atomic displacement under electron irradiation

A Ti film was deposited onto a Cu substrate by means of a radio frequency magnetron sputtering method. Cross-sectional thin foils for TEM observation were prepared using a focused ion beam. Electron irradiation was carried out using a high-resolution high-voltage electron microscope operated at 1.25 MV . The Cu/Ti interface of the foils was irradiated at 623 K. In-situ observation images during electron irradiation were recorded by a CCD camera with a digital video cassette. The (020)_Cu plane on the Cu/Ti interface preferentially moved towards the Ti film with irradiation. Composition analysis of the diffused region showed that its composition corresponded to Ti₃Cu₂.     

Spatial distribution and polarization dependence of the optical near-field in a silicon microfabricated probe

This paper reports on the spatial distribution and polarization behaviour of the optical near-field at the aperture of a Si micromachined probe. A sub-100 nm aperture at the apex of a SiO₂ tip on a Si cantilever was successfully fabricated by selective etching of the SiO₂ tip in a buffered-HF solution using a thin Cr film as a mask. The aperture, 10–100 nm in size, can be reproducibly fabricated by optimizing the etching time. The optical throughput of several apertures was measured. For a 100 nm aperture, a throughput of 1% was approved. The probe shows a very high optical throughput owing to the geometrical structure of the tip. The spatial distribution of the near-field light is measured and simulated using a finite difference-time domain method. The polarization behaviour of apertures with different shapes was analysed using a photon counting camera system.     

Counterface effects on the wear of a composite dry-bearing liner

Plastics-based dry-bearing liners used for flight control bearings in aircraft are usually mated against counterfaces of 440C stainless steel hardened to about 700 HV and finished to R_a ≈ 0.05 μm. In this paper experiments to examine the possibility of reducing liner wear by modifications to the counterface are described. Accelerated (pin-on-disc) tests were made against 440C stainless steel of varying hardness and roughness, electroplated with copper and cadmium, ion implanted with nitrogen, copper and cadmium, vacuum deposited with TiN and TiC, diffusion treated with nitrogen, boron, sulphur, Sn-Cu and Sn-Sb and coated with ceramics-cermets (Al₂O₃, Cr₂O₃, (Cr₂C₃)-Ni-Cr and WC-Co). The most important counterface properties influencing liner wear are the hardness and surface roughness, and for ceramic and cermet coatings, the harder and smoother the surface, the lower is the liner wear. No evidence was found to indicate that the chemical nature of the counterface has a major affect on the liner wear.     

氩气与氮气流量比对磁控溅射法制备TiN薄膜的影响

用直流反应磁控溅射法在Si(100)基底上制备了TiN薄膜,采用X射线衍射仪和原子力显微镜对其结构和形貌进行了表征,利用四探针测试仪测量了TiN薄膜的方块电阻,使用紫外可见分光光度计测定了薄膜反射率;研究了溅射沉积过程中氩气与氮气流量比对TiN薄膜结构及性能的影响.结果表明:在不同氩气与氮气流量比下,所制备薄膜的主要组成相是(200)择优取向的立方相TiN;随着氩气与氮气流量比的增加,薄膜厚度逐渐增大,而表面粗糙度与电阻率先减小后增大;当氩气与氮气流量比为15:1时,薄膜表面粗糙度和电阻率均达到最小值;TiN薄膜的反射率与氩气与氮气流量比的关系不大.     

Quantitative electron spectroscopic imaging studies of microelectronic metallization layers

The combination of focused ion beam (FIB) sample preparation and quantitative electron spectroscopic imaging is an ideal tool for the investigation of layered structures used in microelectronic metallization schemes. In the present work, Si₃N₄/Cu/Si₃N₄/SiO₂/Si and Al/TiN/Ti/SiO₂/Si metallization layers produced by physical vapour deposition are investigated. We apply series of energy filtered images in the low loss region for a mapping of the sample thickness which makes it possible to refine the parameters of the FIB process. We also show how series of energy filtered images in the core loss region can be used to obtain elemental distribution images and chemical bonding information on these samples on a nanometre scale. For materials with a small grain size and/or a strong variation in Bragg orientation, the intensity distribution of the elemental map is strongly influenced by the superimposed Bragg contrast. This detrimental effect can be reduced greatly by using hollow cone illumination, as is demonstrated for polycrystalline Cu. One striking feature observed in Cu layers prepared with FIB is strong, regularly arranged contrast variations caused by subsurface defects in the Cu grains. We suppose that these defects are a consequence of a strong interaction of Ga atoms from the FIB with Cu.