Influence of Ti3SiC2 content on tribological properties of NiAl matrix self-lubricating composites

NiAl matrix self-lubricating composites (NMCs) with various contents of Ti₃SiC₂ were fabricated by in situ technique using spark plasma sintering. The effects of Ti₃SiC₂ content on tribological properties of NMC were investigated. The results showed that NMC were composed of the matrix phase of NiAl alloy, enhanced phase of TiC and lubricating phases of Ti₃SiC₂ and C. NMC with 10 wt.% Ti₃SiC₂ exhibited low friction coefficient of 0.60 and wear rate of 5.45 × 10⁻⁵ mm³ (N m)⁻¹ at the condition of 10 N–0.234 m/s at room temperature. The optimum content of Ti₃SiC₂ was 10 wt.%. The excellent tribological performance of NMC could be attributed to the balance between strength and lubricity, as well as synergetic effect of enhanced phase and lubricating phases. The wear mechanisms changed with the increasing of the doped content of Ti₃SiC₂.     

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.     

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 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.     

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.     

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 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.     

Processing,microstructural characterization and mechanical properties of a Ti2AlC/nanocrystalline Mg-matrix composite

Herein we report on the processing and microstructural characterization of 50 vol.% Ti₂AlC/nanocrystalline (nc) Mg-matrix composites fabricated by pressureless melt infiltration at 750 °C for 1 h. X-ray diffraction and transmission electron microscopy both confirmed that the Mg grain size was ～35 ± 15 nm. The microstructure was also exceptionally stable; annealing for 6 h at 550 °C did not alter the size of the Mg-grains. Some Mg was dissolved in the Ti₂AlC confirming the existence of a (Ti_1-xMg_x)₂AlC solid solution, with x as high as 0.2. A small amount of Ti (3 ± 1 at.%) was also found in the Mg matrix. At 350 ± 40 the ultimate tensile strength is significantly greater than other pure Mg composites reported in the literature. At 700 ± 10 MPa, the ultimate compressive stresses of these composites were ≈ 40% higher than those of a 50 vol.% Ti₃SiC₂–Mg or a 50 vol.% SiC–Mg, in which the Mg-matrix grains were not at the nanoscale. The Ti₂AlC/nc-Mg composites are readily machinable, stiff (≈70 GPa), strong, light (2.9 g/cm³) and exhibited exceptional damping capabilities, that increased as the square of the applied stress to stress levels of the order of ≈ 500 MPa. The energy dissipated per cycle per unit volume at such stress levels is believed to be the highest ever reported for a crystalline solid and to be due to the formation and annihilation of incipient kink bands. The technological implications of having such solids are briefly discussed.     

The effect of fabrication processes on the mechanical and interfacial properties of SiCf/Cu–matrix composites

Three groups of SiC_f/Ti/Cu composites were prepared under conditions of 650 °C + 105 min (sample 1#), 750 °C + 85 min (sample 2#) and 840 °C + 50 min (sample 3#), respectively, by foil-fiber-foil method (FFF), and their room temperature tensile strengths were established. The aim is to model the reactive bonding states between Ti and SiC fiber and between Ti and Cu when Ti is used as interfacial adhesion promoters in SiC_f/Cu–matrix composites. The fracture surfaces, SiC_f/Ti interfaces and Ti/Cu interfaces were investigated by scanning electron microscopy (SEM), optical microscopy and energy dispersive spectroscopy (EDS). The tensile tests show that the tensile strengths of samples 1# and 2# are not obviously enhanced due to the weak bonding strength between SiC fiber and Ti, while those of sample 3# are achieved above 90% of ROM (the rule of mixtures) strength because of excellent bonding between SiC fiber and Ti. However, there are distinct Ti/Cu interfacial reaction zones after the three processes, which are approximately 5.4, 9.0 and 13.3 μm thick, respectively. The Ti/Cu interfacial reaction products are mainly distributed in four layers. In samples 1# and 2#, the products are predicted to be Cu₄Ti, Cu₃Ti₂, CuTi and CuTi₂ according to their chemical compositions determined by EDS, while in sample 3#, the products are Cu₄Ti, Cu₄Ti₃, CuTi and CuTi₂. Additionally, the relationships between the thickness of Ti interlayer and its reaction with C and Cu are also discussed, and an optimal thickness of Ti is introduced.     

The rock salt oxide Li2MgTiO4: Type I dielectric and ionic conductor

The exploration of the Li–Ti–Mg–O system, using both sol–gel technique and solid state reaction method, allowed a new phase, Li₂MgTiO₄, with disordered rock salt structure (a = 4.159 Å) to be synthesized. The latter is shown to be a good type I dielectric material, with a relative constant of 15 at high frequency and low dielectric loss (tanδ < 10⁻³) over the temperature range −60 to 160 °C. It is also observed that the sintering temperature of this phase is strongly lowered by adopting the sol–gel technique compared to solid state reaction (1150 °C instead of 1300 °C). Finally we show that this phase exhibits cationic conductivity above 400 °C (σ_600 °C = 9 × 10⁻⁵ S cm⁻¹).     

Structural and chemical characterization of precipitates in Al-2024/TiC composites

Structural characterizations based on transmission electron microscopy observations were carried out on as-fabricated and heat-treated Al-2024/TiC composites. These composites types reinforced with TiC particles were produced with a pressureless melt infiltration route at 1200 °C for 2 h under argon atmosphere. The composites were heat-treated at 530 °C during 150 min, cold-water quenched and subsequently artificial and natural aged at 190 °C for 12 h in an argon environment and at room temperature for 96 h, respectively. Different precipitate types were obtained and they were identified as CuAl₂, Al₃Ti, Ti₃AlC and Ti₃Al. Most of the precipitates were found to be uniformly distributed in the matrix and some regions show precipitates which have a cubic morphology (Ti₃Cu). High-resolution electron microscopy images were partially used for the characterization of the precipitates in these composites.     

Stearic acid sol–gel synthesis of ultrafine-layered K2Nd2Ti3O10 at low temperature and its acid-exchanging property

A rapid and simple method was developed to prepare ultrafine K₂Nd₂Ti₃O₁₀ powders by combustion of stearic acid precursors. The acid-exchanging properties of obtained product were also studied. Results showed that by using stearic acid sol–gel method (SAM) the fabricating temperature was lowered (from 1100 to 800 °C) and the reacting time was shortened (from at least 11 to 2 h). Comparing with the product by traditional solid-state reaction (SSR), the particle size of the K₂Nd₂Ti₃O₁₀ synthesized by SAM is smaller, BET surface area is higher (more than 16.97 m²/g), and has different acid-exchanging properties. It can be easily exfoliated in 2 mol L^− 1 HNO₃ solution and the exfoliated monodisperse sheets scrolled to 20 × 100 nm nanotubes automatically.     

Brazing of SiO2f/SiO2 composite modified with few-layer graphene and Invar using AgCuTi alloy

Due to the poor wettability of the AgCuTi alloy on the SiO_2f/SiO₂ composite, direct brazing of the composite with an Invar alloy could hardly achieve a reliable joint. To overcome that, the SiO_2f/SiO₂ composite was decorated with few-layer graphene (FLG) by a plasma enhanced chemical vapor deposition (PECVD) method. Sessile drop experiments indicate that the contact angle dropped from 123.8° to 50.7° after FLG was grown on the surface of the SiO_2f/SiO₂ composite. Afterwards, the effects of brazing temperature and Ti contents on the microstructure evolution and mechanical properties of joints (Invar/SiO_2f–SiO₂ modified with FLG) were investigated. The typical interface structure of the joint is SiO_2f–SiO₂/Ti₅Si₃ + TiO₂ + Cu_xTi_6 − xO(x = 2,3)/Ag(s,s) + Cu(s,s) + Cu–Ti blocks/wave-like Fe₂Ti + Ni₃Ti/Ag(s,s) + Cu(s,s) + Fe₂Ti + Ni₃Ti blocks/Invar. As the brazing temperature and Ti contents increase, the reaction layer on the SiO_2f/SiO₂ side becomes thicker and cracks gradually propagate. Meanwhile, a few dispersive Fe₂Ti + Ni₃Ti phases change into large-area wave-like compounds and more Cu–Ti compounds form with the increase of the Ti content. The microstructure evolution significantly affects the shear strength of the brazed joints. The highest shear strength is 26 MPa brazed at 860 °C for 10 min with 4.5 wt.% Ti content.     

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.     

Preparation,phase structure and microwave dielectric properties of CoLi2/3Ti4/3O4 ceramic

A new low loss microwave dielectric ceramic with composition of CoLi_2/3Ti_4/3O₄ was prepared by a conventional solid-state reaction method. The compound has a cubic spinel structure [Fd-3m (227)] similar to MgFe₂O₄ with lattice parameters of a = 8.3939 Å, V = 591.42 Å³, Z = 8 and ρ = 4.30 g/cm³. This ceramic has a low sintering temperature (～1050 °C) and good microwave dielectric properties with relative permittivity of 21.4, Q × f value of 35,000 GHz and τ_f value of ?22 ppm/°C. Furthermore, the addition of BaCu(B₂O₅) (BCB) can effectively lower the sintering temperature from 1050 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added CoLi_2/3Ti_4/3O₄ ceramics are good candidates for LTCC applications.     

Y2O3–Nd2O3 double stabilized ZrO2–TiCN nanocomposites

Yttria-neodymia double stabilized ZrO₂-based nanocomposites with 40 vol% electrical conductive TiCN were fully densified by means of pulsed electric current sintering (PECS) in the 1400–1500 °C range. The Y₂O₃ stabilizer content was fixed at 1 mol% whereas the Nd₂O₃ co-stabilizer content was varied between 0.75 and 2 mol% in order to optimise the mechanical properties. The mechanical (Vickers hardness, fracture toughness and bending strength), electrical (electrical resistivity) and microstructural properties were investigated and the hydrothermal stability in steam at 200 °C was assessed.The nanocomposites with 1–1.75 mol% Nd₂O₃, PECS at 1400 or 1450 °C, have an excellent fracture toughness of 8 MPa m^1/2, although the grain size of both ZrO₂ and TiCN phases after densification is in the 100 ± 30 nm range. Moreover, the composites combine a hardness of about 13 GPa, a bending strength of 1.1–1.3 GPa with a low electrical resistivity (1.6–2.2 × 10^?5 Ω m) allowing electrical discharge machining. The hydrothermal stability of the double stabilizer nanocomposites was higher than for yttria-stabilized ZrO₂-based composites with the same overall stabilizer content.     

Influence of CuO addition to BaSm2Ti4O12 microwave ceramics on sintering behavior and dielectric properties

Microwave dielectric ceramics of tungsten–bronze-type BaSm₂Ti₄O₁₂ were prepared by doping CuO (up to 2 wt.%) as the liquid-phase sintering aid. The effects of CuO additive on the densification, micro structure and dielectric properties were investigated. Due to the liquid-phase effect, the sintering temperature of BaSm₂Ti₄O₁₂ ceramics with 1 wt.% CuO addition can be effectively reduced to 1160 °C, about 200 °C lower than that of pure BaSm₂Ti₄O₁₂ ceramics, while good microwave dielectric properties of ɛ_r = 75.8, Q*f = 4914.6 GHz and τ_f = −7.65 ppm/°C were still achieved.     

Mechanical properties and damping capacity of SiCp/TiNif/Al composite with different volume fraction of SiC particle

SiC_p/TiNi_f/Al composite with 20 Vol.% TiNi fibers were fabricated by pressure infiltration method. The effect of volume fraction of SiC particle on the mechanical properties and damping capacity of the composite were studied. Four different volume fractions of SiC particle in the composite were 0%, 5%, 20% and 35% respectively. The microstructure and damping capacity of the composites was studied by SEM and DMA respectively. As the gliding of dislocation in the Al matrix was hindered by SiC particle, the yield strength and elastic modulus of the composites increased, while the elongation decreased with the increase in volume fraction of SiC particle. Furthermore, the damping capacity of the composites at room temperature was decreased when the mount of strain was more than 1 × 10⁻⁴. In the heating process, the damping peak at the temperature of 135 °C was attributed to the reverse martensitic transformation from B19′ to B2 in the TiNi fibers.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..     

Thermal history induced variable relaxor behavior in the high TC ternary ferroelectric 0.6Bi(Mg1/2Ti1/2)O3–0.05Bi(Zn1/2Ti1/2)O3–0.35PbTiO3

Studies carried out on a perovskite-structured rhombohedral 0.6Bi(Mg_1/2Ti_1/2)O₃–0.05Bi(Zn_1/2Ti_1/2)O₃–0.35PbTiO₃ (xBZT–yBMT–zPT) ceramic quenched from temperatures below 1000 °C show that the dielectric properties are dramatically altered by the thermal history. Samples quenched from temperatures 650 °C–900 °C show classical ferroelectric switching behavior that is not observed on either side of this temperature range. The quenched states lose their switchable ferroelectric properties when heated to temperatures as low as 400 °C. The results demonstrate for the first time that the dielectric and electromechanical response, as observed at room temperature, can be varied between normal to relaxor behavior by changing thermal quenching conditions.