Synergetic lubricating effect of MoS2 and Ti3SiC2 on tribological properties of NiAl matrix self-lubricating composites over a wide temperature range

NiAl matrix self-lubricating composites with MoS₂ and Ti₃SiC₂ lubricants were prepared by spark plasma sintering. The tribological behaviors of the NiAl–Ti₃SiC₂–MoS₂ composites against Si₃N₄ were investigated from room temperature to 800 °C. The results showed that the composites exhibited excellent self-lubricating and anti-wear properties over a wide temperature range. At 400 °C, the composites containing 5Ti₃SiC₂–5MoS₂ (wt.%) had a very low friction coefficient of about 0.13 and a low wear rate of 4.5 × 10⁻⁵ mm³ N⁻¹ m⁻¹. MoS₂ played the main role of lubrication at low temperatures, while Ti₃SiC₂ was responsible for low friction at high temperatures. Ti₃SiC₂ and MoS₂ lubricants in the NiAl–Ti₃SiC₂–MoS₂ composites showed the excellent synergetic lubricating effect over a wide temperature range from room temperature to 800 °C.     

Friction and wear behavior of polytetrafluoroethene composites filled with Ti3SiC2

In this work, polytetrafluoroethylene (PTFE) composites filled with Ti₃SiC₂ or graphite were prepared through powder metallurgy. The effects of different filling components, loads and sliding velocities on the friction performance of Ti₃SiC₂/PTFE composites were studied. Ti₃SiC₂/PTFE composites exhibit better wear resistance than graphite/PTFE composites due to the better mechanical properties of Ti₃SiC₂. The wear resistance was found to improve around 100× over unfilled PTFE with the addition of 1 wt.% Ti₃SiC₂. In addition, the 10 wt.% sample had the lowest wear rate of K = 2.1 × 10⁻⁶ mm³/Nm and the lowest steady friction coefficient with μ = 0.155 at the condition of 90 N–0.4 m/s. Ti₃SiC₂ was proved to promote the formation of a thin and uniform transfer film on counterpart surface and a protection oxide film on worn surface, which are the key roles for improving wear resistance.     

Tribological behavior of Ti3SiC2/(WC–10Co) composites prepared by spark plasma sintering

The dry sliding friction and wear behavior of Ti₃SiC₂/(WC–10Co) composites (TWCs) against GCr15 steel pair at room temperature was investigated through the determination of friction coefficient and wear rate under different conditions and the analysis of the morphologies and compositions of wear debris, worn surfaces of TWC and GCr15 steel. The friction coefficients of TWC with 3 wt.% WC–10Co were in the range of 0.40–0.48, and the wear rate varied from 0.6 × 10⁻⁴ mm³ (N m)⁻¹ to 1 × 10⁻⁴ mm³ (N m)⁻¹. At the load of 10 N and sliding speed of 0.353 m/s, the glazes were formed on the worn surfaces of TWC. The wear mechanisms were complicated, including micro-cutting and abrasive wear of TWC, oxidation wear of GCr15 steel, as well as adhesive wear caused by the glaze flaking.     

Tribological performance of TiAl matrix self-lubricating composites containing Ag,Ti3SiC2 and BaF2/CaF2 tested from room temperature to 600 °C

Dry sliding tribological behaviors of TiAl matrix self-lubricating composites (TMSC) containing varying amounts of Ag, Ti₃SiC₂ and BaF₂/CaF₂ eutectic (BaF₂–38 wt.%CaF₂) (ATBC) with weight ratio of 1:1:1 against Si₃N₄ from room temperature (RT) to 600 °C at the condition of 10 N–0.234 m/s were experimentally studied. The results implied that the ATBC could improve friction-reducing and anti-wear ability of TMSC over an extreme range of operating temperatures, which was attributed to the synergetic effect of Ag, Ti₃SiC₂ and BaF₂/CaF₂ lubricants. In addition, TMSC containing 9 wt.% ATBC exhibited the best tribological properties over the wide temperature range from RT to 600 °C.     

Tribological properties of self-lubricating NiAl/Mo-based composites containing AgVO3 nanowires

Silver vanadate (AgVO₃) nanowires were synthesized by hydrothermal method and self-lubricating NiAl/Mo-AgVO₃ composites were fabricated by powder metallurgy technique. The composition and microstructure of NiAl/Mo-based composites were characterized and the tribological properties were investigated from room temperature to 900 °C. The results showed that NiAl/Mo-based composites were consisted of nanocrystalline B2 ordered NiAl matrix, Al₂O₃, Mo₂C, metallic Ag and vanadium oxide phase. The appearance of metallic Ag and vanadium oxide phase can be attributed to the decomposition of AgVO₃ during sintering. Wear testing results confirmed that NiAl/Mo-based composites have excellent tribological properties over a wide temperature range. For example, the friction coefficient and wear rate of NiAl/Mo-based composites containing AgVO₃ were significantly lower than the composites containing only metallic Mo or AgVO₃ lubricant when the temperature is above 300 °C, which can be attributed to the synergistic lubricating action of metallic Mo and AgVO₃ lubricants. Furthermore, Raman results indicated that the composition on the worn surface of NiAl-based composites was self-adjusted after wear testing at different temperatures. For example, Ag₃VO₄ and Fe₃O₄ lubricants were responsible for the improvement of tribological properties at 500 °C, AgVO₃, Ag₃VO₄ and molybdate for 700 °C, and AgVO₃ and molybdate for 900 °C of NiAl-based composites with the addition of metallic Mo and AgVO₃.     

Synthesis and phases evolution of Si–C–Ti from polycarbosilane (PCS) and metal Ti

Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti₃SiC₂ phase was obtained firstly from reaction of PCS and Ti. Ti₃SiC₂ formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF₂ can promote the formation of Ti₃SiC₂ phase.     

Tribological behavior of Ni3Al matrix self-lubricating composites containing WS2, Ag and hBN tested from room temperature to 800 °C

Ni₃Al matrix self-lubricating composites (NMSC) containing varied amounts of WS₂, Ag and hBN (WAh) with weight ratio of 1:1:1 were fabricated by in situ technique using spark plasma sintering. The friction and wear properties of NMSC against the commercial Si₃N₄ ceramic ball at the load of 10 N and sliding speed of 0.234 m/s for 80 min from room temperature to 800 °C were investigated. The results showed that the tribological properties of NMSC strongly depended on the addition content of WAh. Moreover, NMSC with 15 wt.% WAh and 5 wt.% TiC exhibited the relatively lower friction coefficients and the less wear rates from RT to 800 °C. The excellent tribological behavior of NMSC with 15 wt.% WAh and 5 wt.% TiC was attributed to the synergetic action of composite lubricants of WAh and reinforced phase of TiC.     

Low energy implantation to inhibit wear in N+ ions implanted WC–Co composite

This work discusses the influence of nitrogen ion (N⁺) implantation on wear resistance of WC–Co composite. The WC–Co samples were bombarded at low N⁺ ions energies of 20 and 30 keV and doses of 10¹⁷ and 2 × 10¹⁷ ions cm⁻². Tribological tests were conducted against cylindrical 100Cr6 pin at 200 N load and 180 mm s⁻¹ speed. The tests use water lubrication and four sample types with Co binder content ranging in 6.5–25%. The X-ray spectra reveal that implantation is able to transform the original [CFC] Co structure of virgin surface to harder amorphous phase. However, it was found that excessive low binder content alters the wear behavior on non-implanted samples since it causes wear rate transition from 0.59 × 10⁻⁷ to 2.1 × 10⁻⁷ mm³/(mm² s) imposing hence instable wear regime. The SEM micrographs confirm the formation of transferred film within the implanted worn surface owing to (i) an enhancement in Co flow and (ii) a generation of oxides (Fe₂O₃, Fe₃O₄, Co₂O₃, WO₂). While the formed film acts to inhibit severe abrasion, the material removal process combining cobalt flow and carbide grains pull-out seems to be associated with oxidation mechanisms to be accentuated with energy increase. The most improvements in wear resistance were observed on samples with the highest Co content and the results were found more sensitive to N⁺ ions implantation energy than dose.     

Microstructures and wear properties of YPSZ/CeO2 reinforced composites deposited by laser cladding

In this study, the influence of YPSZ/CeO₂ on the surface performance of the laser-cladded composites was firstly researched. Laser cladding of the Fe₃Al/Co42B + YPSZ/CeO₂ pre-placed powders on Ti–6Al–4V alloy can form the composite coating, which increased the wear resistance of the substrate. With addition of 20 wt.%TiC, the longevity of the molten pool decreased, leading to the decreasing of the growth time of the precipitates and the content of CoTi, TiNi, AlNi, Ti₃Al and TiB phases. The addition of 20 wt.%TiC did not improve the tribological properties of the Fe₃Al/Co42B + YPSZ/CeO₂ laser-cladded composite coating.     

Investigation of microstructure and mechanical properties of aluminum hybrid nano-composites with the additions of solid lubricant

In this experimental study, the tribological behavior of Al 2024–5 wt.% SiC–X wt.% graphite (X = 5 and 10) hybrid nano-composites was produced using powder metallurgy (P/M) technique. All specimens were prepared by mechanical milling of Al 2024 and SiC–Gr nano-composite powders, followed by a blend–press–sinter methodology. Pin on disc type apparatus has been used for determining the wear loss. The sintered samples have been characterized by XRD. Wear mechanisms are discussed based on scanning electron microscopy observations of worn surface and wear debris morphology. The hardness and wear resistance of the hybrid nano-composites were increased considerably by increasing the reinforcement content. The nano-composite with 5 wt.% SiC and 10 wt.% Gr showed the greatest improvement in tribological performance. Primary wear mechanisms for hybrid nano-composites were determined to be formation of lubricating layer on the surface of samples. The overall results revealed that hybrid aluminium nano-composites can be considered as an outstanding material where high strength and wear-resistant components are of major importance, particularly structural applications in the aerospace, automotive and military industries.     

Tribological properties of MgO–CaO–SiO2–P2O5–F-based glass-ceramic for dental applications

Microhardness and tribological behavior of a glass-ceramic produced from a glass in the MgO–CaO–SiO₂–P₂O₅–F system have been investigated with regard to the phases formed and microstructure developed during crystallization. The results of X-ray diffraction analysis indicated that apatite and wollastonite are the predominant crystalline phases. Scanning electron microscopy examination revealed that the wollastonite crystal content decreases and apatite crystal content increases as the depth distance from the surface increases. Structure oriented changes in properties were evidenced. The indentation microhardness at the free surface was 650 ± 12 H_V. However, it decreased gradually with increasing depth distance from the free surface and attained 520 ± 8 H_V at a distance of 0.5 mm below the free surface. The wear rate at the free surface was 0.7 ± 0.05 × 10^− 4 mm³/Nm, but increased gradually as the distance from the free surface increased. The wear rate reached 2.9 ± 0.15 × 10^− 4 mm³/Nm at a distance of 0.5 mm below the free surface.     

Tribological properties of silicon nitride ceramics coated with DLC and DLC-Si against 316L stainless steel

Diamond-like carbon (DLC) is an adequate coating on a large variety of materials for tribological purposes, namely against iron alloys in automotive parts, bearings and forming tools. Herein, the tribological properties of DLC-stainless steel couples were assessed by unlubricated pin-on-disc experiments. Plasma enhanced chemical vapour deposition (PECVD) of DLC-Si or pure DLC coatings were performed, respectively, by conventional rf glow discharge from gaseous mixtures of methane and silane or taking only pure methane, with self-bias voltages varying from −200 to −800 V. Silicon nitride (Si₃N₄) was used as DLC substrate aiming the minimisation of adhesion problems, usually found when some metallic substrates are employed. An improved tribological response was obtained with pure DLC coated Si₃N₄ discs sliding against the stainless steel pins. This system almost instantaneously attains a steady-state friction regime with friction coefficients in the range 0.20–0.30 and a wear coefficient value of about 10⁻⁶ mm³ N⁻¹ m⁻¹, one order of magnitude lower than that of the DLC-Si coated ones. The application of a distinct self-bias during the PECVD process only marginally affected the tribological properties of the pure DLC coatings.     

An investigation on the tribological behavior of AZ91 and AZ91 + 3 wt% RE magnesium alloys at elevated temperatures

The wear behavior of AZ91 and AZ91 + 3 wt% RE magnesium alloys was investigated under a normal load of 20 N at the wear testing temperatures of 25–250 °C and sliding speeds of 0.4 and 1 m s⁻¹. As the sliding speed increased from 0.4 to 1 m s⁻¹ at the wear temperature of 25 °C, the wear rates of AZ91 and AZ91 + 3 wt% RE alloys decreased by about 8% and 60%, respectively. With an increase in the wear temperature to 100 °C, the wear rate of AZ91 alloy was reduced by 58% at a sliding speed of 0.4 m s⁻¹, while the wear rate was sharply increased at a sliding speed of 1 m s⁻¹. At higher wear temperatures, the wear of the AZ91 alloy at both sliding speeds soared as a result of the softening of β-Mg₁₇Al₁₂ phase. However, the wear rate of AZ91 + 3 wt% RE alloy showed a minimum at the wear temperatures of 100 and 200 °C at sliding speeds of 1 and 0.4 m s⁻¹, respectively. Superior wear behavior of AZ91 + 3 wt% RE at the elevated temperatures could be attributed to its higher thermal stability and strength. Furthermore, a rise in sliding speed led to a 55% reduction in the wear rate of AZ91 + 3 wt% RE alloy at the wear temperature of 100 °C due to the formation of stable oxide layers on the wear surface.     

Microstructure and mechanical properties of in situ TiC and Nd2O3 particles reinforced Ti–4.5 wt.%Si alloy composites

(TiC + Nd₂O₃)/Ti–4.5 wt.%Si composites were in situ synthesized by a non-consumable arc-melting technology. The phases in the composites were identified by X-ray diffraction. Microstructures of the composites were observed by optical microscope and scanning electron microscope. The composite contains four phases: TiC, Nd₂O₃, Ti₅Si₃ and Ti. The TiC and Nd₂O₃ particles with dendritic and near-equiaxed shapes are well distributed in Ti–4.5 wt.%Si alloy matrix, and the fine Nd₂O₃ particles exist in the network Ti + Ti₅Si₃ eutectic cells and Ti matrix of the composites. The hardness and compressive strength of the composites are markedly higher than that of Ti–4.5 wt.%Si alloy. When the TiC content is fixed as 10 wt.% in the composites, the hardness is enhanced as the Nd₂O₃ content increases from 8 wt.% to 13 wt.%, but the compressive strength peaks at the Nd₂O₃ content of 8 wt.%.     

Influence of W5+ ions on the optical properties of doped Bi12TiO20

There have been studied single crystals of undoped and doped Bi₁₂TiO₂₀ with two concentrations of W⁵⁺ (2.62 × 10¹⁷ cm⁻³ and 2.62 × 10¹⁸ cm⁻³). There have been obtained absorption spectra in the energy range of 10,482–15,408 cm⁻¹ by classical measurements. There have been determined the cross-section (σ_a) of the impurity absorption and the oscillator strength of d–d transitions. There have been calculated the refractive index of doped crystals and the concentration of Ti³⁺ ions in an undoped sample through an experiment.     

High work-hardening effect of the pure NiAl intermetallic compound fabricated by the combustion synthesis and hot pressing technique

The pure NiAl intermetallic compound was fabricated by the combustion synthesis and hot pressing technique. Microstructure examination showed that the NiAl intermetallic compound contained fine grains. Analysis of the X-ray diffraction and the HRTEM studies showed that the phase in the intermetallics was the only NiAl phase. The NiAl showed prominent compression properties. The true ultimate compression strength and the fracture strain of the NiAl are 1002_? 94^+ 72 MPa and 21.6_? 1.8^+ 1.8%, respectively. The work-hardening capacity (H_c) is 1.40_? 0.07^+ 0.09 and the Vickers micro-hardness is 360_? 19^+ 15 HV. The finer grains, the high density dislocation and the seriously distorted lattices in the matrix, and the intense interactions between dislocations contribute to the prominent compression properties.     

Effects of TiO2 nanoparticles addition on microstructure,microhardness and tensile properties of Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The effects of TiO₂ nanoparticles addition on the microstructure, microhardness, and tensile properties of Sn–3.0 wt.%Ag–0.5 wt.%Cu–x wt.%TiO₂ (x = 0, 0.05, 0.1, and 0.6) composite solders were systematically investigated. Scanning electron microscope (SEM) was used to observe the microstructural evolution of the composite solders, measure the size of the Ag₃Sn grains, and estimate the spacing between the Ag₃Sn grains in the solder matrix. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to identify the phases of eutectic areas in the composite solder matrix. Results show that both the average size of Ag₃Sn grains and the spacing between the Ag₃Sn grains decrease significantly, which might owe to the strong adsorption effect and high surface free energy of the TiO₂ nanoparticles. The microhardness is improved by 37% compared with TiO₂-free noncomposite solder as the weight percentage of TiO₂ nanoparticles is 0.1 wt.%. The improvement is due to the microstructural change of the composite solders, which is in good agreement with the prediction of the classic theory of dispersion strengthening. Tensile tests reveal that the TiO₂-containg composite solder alloys have higher ultimate tensile strength (UTS) than TiO₂-free noncomposite solder alloy due to solid solution hardening. UTS of solder alloys have a logarithmic increase relation with strain rate ranging from 10⁻³ s⁻¹ to 10⁻¹ s⁻¹ and decreases with an increase of test temperatures ranging from 25 °C to 125 °C.     

Development and characterization of laser clad high temperature self-lubricating wear resistant composite coatings on Ti–6Al–4V alloy

To enhance the wear resistance and friction-reducing capability of titanium alloy, a process of laser cladding γ-NiCrAlTi/TiC + TiWC₂/CrS + Ti₂CS coatings on Ti–6Al–4V alloy substrate with preplaced NiCr/Cr₃C₂–WS₂ mixed powders was studied. A novel coating without cracks and few pores was obtained in a proper laser processing. The composition and microstructure of the fabricated coating were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) techniques, and tribological properties were evaluated using a ball-on-disc tribometer under dry sliding wear test conditions at 20 °C (room-temperature), 300 °C, 600 °C, respectively. The results show that the coating has unique microstructure consisting of α-Ti, TiC, TiWC₂, γ-NiCrAlTi, Ti₂CS and CrS phases. Average microhardness of the composite coating is 1005 HV_0.2, which is about 3-factor higher than that of Ti–6Al–4V substrate (360 HV_0.2). The friction coefficient and wear rate of the coating are greatly decreased due to the combined effects of the dominating anti-wear capabilities of reinforced TiC and TiWC₂ carbides and the CrS and Ti₂CS sulfides which have excellent self-lubricating property.     

High-temperature dielectric and electromagnetic interference shielding properties of SiCf/SiC composites using Ti3SiC2 as inert filler

Ti₃SiC₂ filler has been introduced into SiC_f/SiC composites by precursor infiltration and pyrolysis (PIP) process to optimize the dielectric properties for electromagnetic interference (EMI) shielding applications in the temperatures of 25–600 °C at 8.2–12.4 GHz. Results indicate that the flexural strength of SiC_f/SiC composites is improved from 217 MPa to 295 MPa after incorporating the filler. Both the complex permittivity and tan δ of the composites show obvious temperature-dependent behavior and increase with the increasing temperatures. The absorption, reflection and total shielding effectiveness of the composites with Ti₃SiC₂ filler are enhanced from 13 dB, 7 dB and 20 dB to 24 dB, 21 dB and 45 dB respectively with the temperatures increase from 25 °C to 600 °C. The mechanisms for the corresponding enhancements are also proposed. The superior absorption shielding effectiveness is the dominant EMI shielding mechanism. The optimized EMI shielding properties suggest their potentials for the future shielding applications at temperatures from 25 °C to 600 °C.     

Investigation on the effects of PbO content and seeding layers of TiO2 and ZrO2 on the orientation and microstructure of Pb(Zr0.52Ti0.48)O3 ferroelectric films grown by reverse dip-coating method of sol–gel

Lead zirconate titanate Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on Si (100) and Pt(111)/Ti/SiO₂/Si(100) substrates by a new reverse dip-coating method of sol–gel process. The method was first proposed and applied to coat films. It has several advantages over the conventional sol–gel coating method, including: no consideration of the mechanical transmission that is difficult to manipulate with costly exact apparatus in classical dip-coating procession, convenient processing control, simplicity, low cost, less pollution, and easy fabrication films on large areas and irregular shaped devices etc. This paper studied the factors including PbO content of precursor, TiO₂ and ZrO₂ layers, which are related to raw materials of PZT precursor and influence greatly the crystal orientation of the final thin films. We find that the PZT films deposited by precursor with 20% mole excess Pb displayed strong (111) preferred orientation, with 5% mole excess Pb showed a little (100) orientation and pyrochlore phase. The precursor with 10% mole excess Pb was found prompting the PZT films phase transformation with (110) preferred orientation. In addition, the results show that the TiO₂ and ZrO₂ seeding layers had totally different effects on the preferred orientation of PZT films. The films with TiO₂ seeding layer were highly (111) oriented and exhibited better ferroelectric properties (remnant polarization Pr = 14.2 μC cm^− 2, coercive field Ec = 59.1 Kv cm^− 1) than those of the films with ZrO₂ seeding layer shown (100) orientation (Pr = 7.4 μC cm^− 2, Ec = 42.9 Kv cm^− 1).