Low-cost solid FeS lubricant as a possible alternative to MoS2 for producing Fe-based friction materials

Three reaction systems of MoS2–Fe, FeS–Fe, and FeS–Fe–Mo were designed to investigate the use of FeS as an alternative to MoS2 for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, micro-structures, mechanical properties, and friction performance were characterized. The results showed that MoS2 reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050°C. Iron-sulfides produced in the MoS2–Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The FeS–Fe–Mo system showed a phase composition, porosity, and density similar to those of the MoS2–Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the FeS–Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of fric-tion (COF) in all of the samples.     

Solid FeS lubricant:a possible alternative to MoS2 for Cu-Fe-based friction materials

Molybdenum disulfide (MoS₂) is one of the most commonly used solid lubricants for Cu-Fe-based friction materials. Nevertheless, MoS₂ reacts with metal matrices to produce metal sulfides (e.g., FeS) and Mo during sintering, and the lubricity of the composite may be related to the generation of FeS. Herein, the use of FeS as an alternative to MoS₂ for producing Cu-Fe-based friction materials was investigated. According to the reaction principle of thermodynamics, two composites-one with MoS₂ (Fe-Cu-MoS₂ sample) and the other with FeS (FeS-Cu₂S-Cu-Fe-Mo sample), were prepared and their friction behaviors and mechanical properties were compared. The results showed that MoS₂ reacted with the Cu-Fe matrix to produce FeS, metallic ternary sulfides, and Mo when sintered at 1050℃. The MoS₂-Cu-Fe and FeS-Cu₂S-Cu-Fe-Mo samples thereby exhibited similar characteristics with respect to phase composition, density, hardness, and tribological behaviors. Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers.     

Mechanical properties and friction behaviors of CNT/AlSi<Subscript>10</Subscript>Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi₁₀Mg composites produced by spark plasma sintering (SPS) were investigated. The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450℃. CNTs dispersed uniformly in the AlSi₁₀Mg matrix when the addition of CNTs was less than 1.5wt%. However, when the addition of CNTs exceeded 1.5wt%, the aggregation of CNTs was clearly observed. Moreover, the mechanical properties (including the densities, compressive strength, and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt%. Meanwhile, the minimum average friction coefficient and wear rate of the CNT/AlSi₁₀Mg composites were obtained with 1.0wt% CNTs.     

Solid FeS lubricant: a possible alternative to MoS2 for Cu-Fe-based friction materials

Molybdenum disulfide (MoS2) is one of the most commonly used solid lubricants for Cu-Fe-based friction materials.Nevertheless,MoS2 reacts with metal matrices to produce metal sulfides (e.g.,FeS) and Mo during sintering,and the lubricity of the composite may be related to the generation of FeS.Herein,the use of FeS as an alternative to MoS2 for producing Cu-Fe-based friction materials was investigated.According to the reaction principle of thermodynamics,two composites—one with MoS2 (Fe-Cu-MoS2 sample) and the other with FeS (FeS-Cu2S-Cu-Fe-Mo sample),were prepared and their friction behaviors and mechanical properties were compared.The results showed that MoS2 reacted with the Cu-Fe matrix to produce FeS,metallic ternary sulfides,and Mo when sintered at 1050℃.The MoS2-Cu-Fe and FeS-Cu2S-Cu-Fe-Mo samples thereby exhibited similar characteristics with respect to phase composition,density,hardness,and tribological behaviors.Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers.     

Electromagnetic modification of faceted-faceted Ni<Subscript>31</Subscript>Si<Subscript>12</Subscript>-Ni<Subscript>2</Subscript>Si eutectic alloy

In an electromagnetic field, the morphology of a binary faceted-faceted (FF) Ni31Si12-Ni2Si eutectic microstructure and the alloy’s mechanical properties were investigated. Hardness experiments demonstrated that the solidified ingots were significantly strengthened, and the hardness was improved to 63.1 and 786.6 on the Rockwell hardness C and Vickers hardness scales, respectively. Tests of friction and wear in stirred FF eutectic alloys showed excellent anti-fatigue and anti-adhesion wear performance. Alloy changed from an anomalous microstructure to a refined quasi-regular structure, and there was an increase in the lamellar microstructure fraction. The formation process of the refined quasi-regular microstructure and the resulting mechanical properties were investigated.     

Wear properties of NiAl based materials

The NiAl based materials including NiAl-TiC-Al2O3 composite,NiAl-Cr(Mo)-Hf-Ho eutectic alloy and NiAl-Cr(Mo)-CrxSy in situ composite were fabricated and their wear properties were tested at different temperatures.The results revealed that the NiAl-TiC-Al2O3 composite,NiAl-Cr(Mo)-Hf-Ho eutectic alloy and NiAl-Cr(Mo)-CrxSy in situ composite exhibited the excellent wear properties between 700℃ and 900℃.The microstructure observations exhibited that the self-lubricant films formed on the worn surfaces during the dry sliding test at high temperature,which decreased the wear rate and friction coefficient significantly.TEM observation on the self-lubricant film revealed that it was mainly comprised by ceramic amorphous and nanocrystalline.Compared with the NiAl-TiC-Al2O3 composite,the NiAl-Cr(Mo)-CrxSy in situ composite has lower friction coefficient at low temperature.Such phenomena may be ascribed to the addition of sulfide which contributes much to the formation of self-lubricant,and moreover the TiC addition increase the strength of NiAl based material and its wear resistance.     

Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core-shell-structured Ti/Al3Ti

An Al-based composite reinforced with core-shell-structured Ti/Al₃Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620℃ for 5h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core-shell-structured reinforcement, which is mainly composed of Al₃Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al₃Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al-Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.     

The evolution of microstructure and mechanical properties during high-speed direct-chill casting in different Al-Mg2Si in situ composites

The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al-Mg₂Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al-Mg₂Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg₂Si particles (from 28 to 12 μm), the spacing of eutectic Mg₂Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg₂Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg₂Si phase and the grains in the Al-Mg₂Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al-Mg₂Si composites and AA6061 alloy billets.     

Microstructure and improved mechanical properties of ultrafine-grained Mo-12Si-8.5B (at.%) alloys with addition of ZrB2

Multi-hierarchical Mo-12Si-8.5B-x Zr B_2(x=0,0.5,1.0,1.5,2.5 wt%)alloys consisting of three ultrafine-grained(UFG,0.47–0.81μm)phases of Mo_5Si B_2(T2),Mo_3Si and Mo solid solution(α-Mo)were prepared by mechanical alloying following hot pressing.Microstructure observations showed that the intermetallic phases(Mo_3Si and T2)distributed dispersedly in the continuousα-Mo matrix associated with the homogeneously embedded nanoscaled particles(10–225 nm)in the grain interiors and at the grain boundaries.The Mo-12Si-8.5B-x Zr B_2alloys exhibited monotonically increasing compressive strength to 3.13 GPa with increasing content of Zr B_2,and the fracture toughness increased about 27%and reached at 11.5 MPa m~(1/2)at 1.0 wt%Zr B_2,rendering the Mo-12Si-8.5B-1.0 wt%Zr B_2alloy possessing the best combined mechanical properties of high strength and high toughness.The underlying reason for the superior mechanical properties of the Mo-12Si-8.5B-x Zr B_2alloys is that the dispersedly distributed nanosized particles in the UFG multi-phased-matrix can not only effectively block the dislocation motion to increase the strength but also store the dislocations to increase the strain hardening ability during mechanical deformation.     

Electrical conductivity optimization of the Na3AlF6-Al2O3-Sm2O3 molten salts system for Al-Sm intermediate binary alloy production

Metal Sm has been widely used in making Al-Sm magnet alloy materials. Conventional distillation technology to produce Sm has the disadvantages of low productivity, high costs, and pollution generation. The objective of this study was to develop a molten salt electrolyte system to produce Al-Sm alloy directly, with focus on the electrical conductivity and optimal operating conditions to minimize the energy consumption. The continuously varying cell constant (CVCC) technique was used to measure the conductivity for the Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Sm₂O₃ electrolysis medium in the temperature range from 905 to 1055℃. The temperature (t) and the addition of Al₂O₃ (W(Al₂O₃)), Sm₂O₃ (W(Sm₂O₃)), and a combination of Al₂O₃ and Sm₂O₃ into the basic fluoride system were examined with respect to their effects on the conductivity (κ) and activation energy. The experimental results showed that the molten electrolyte conductivity increases with increasing temperature (t) and decreases with the addition of Al₂O₃ or Sm₂O₃ or both. We concluded that the optimal operation conditions for Al-Sm intermediate alloy production in the Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Sm₂O₃ system are W(Al₂O₃) + W(Sm₂O₃)=3wt%, W(Al₂O₃):W(Sm₂O₃)=7:3, and a temperature of 965 to 995℃, which results in satisfactory conductivity, low fluoride evaporation losses, and low energy consumption.     

Effects of metal binder on the microstructure and mechanical properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based micro-nanocomposite ceramic tool material

The Al₂O₃-(W,Ti)C composites with Ni and Mo additions varying from 0vol% to 12vol% were prepared via hot pressing sintering under 30 MPa. The microstructure was investigated via X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Mechanical properties such as flexural strength, fracture toughness, and Vickers hardness were also measured. Results show that the main phases Al₂O₃ and (W,Ti)C were detected by XRD. Compound MoNi also existed in sintered nanocomposites. The fracture modes of the nanocomposites were both intergranular and transgranular fractures. The plastic deformation of metal particles and crack bridging were the main toughening mechanisms. The maximum flexural strength and fracture toughness were obtained for 9vol% and 12vol% additions of Ni and Mo, respectively. The hardness of the composites reduced gradually with increasing content of metals Ni and Mo.     

Preparation and radar-absorbing properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> composite powder

Al₂O₃/TiO₂/Fe₂O₃/Yb₂O₃ composite powder was synthesized via the sol-gel method. The structure, morphology, and radar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes (100-200 nm) and the other is spherical Al₂O₃ particles (smaller than 80 nm). Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 (at 15.68 GHz) in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increasing matching thickness. The effective absorption band covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.     

Corrosion-wear behavior of nanocrystalline Fe88Si12 alloy in acid and alkaline solutions

The corrosion-wear behavior of a nanocrystalline Fe₈₈Si₁₂ alloy disc coupled with a Si₃N₄ ball was investigated in acid (pH 3) and alkaline (pH 9) aqueous solutions. The dry wear was also measured for reference. The average friction coefficient of Fe₈₈Si₁₂ alloy in the pH 9 solution was approximately 0.2, which was lower than those observed for Fe₈₈Si₁₂ alloy in the pH 3 solution and in the case of dry wear. The fluctuation of the friction coefficient of samples subjected to the pH 9 solution also showed similar characteristics. The wear rate in the pH 9 solution slightly increased with increasing applied load. The wear rate was approximately one order of magnitude less than that in the pH 3 solution and was far lower than that in the case of dry wear, especially at high applied load. The wear traces of Fe₈₈Si₁₂ alloy under different wear conditions were examined and analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results indicated that the tribo-chemical reactions that involve oxidation of the worn surface and hydrolysis of the Si₃N₄ ball in the acid solution were restricted in the pH 9 aqueous solution. Thus, water lubrication can effectively improve the wear resistance of nanocrystalline Fe₈₈Si₁₂ alloy in the pH 9 aqueous solution.     

Microstructure and mechanical properties of Nb–Mo–ZrB2 composites prepared by hot-pressing sintering

Nb–Mo–ZrB₂ composites (V(Nb)/V(Mo)=1) with 15vol% or 30vol% of ZrB₂ were fabricated by hot-pressing sintering at 2000℃. The phases, microstructure, and mechanical properties were then investigated. The composites contain Nb-Mo solid solution (denoted as (Nb, Mo)ss hereafter), ZrB, MoB, and NbB phases. Compressive strength test results suggest that the strength of Nb–Mo–ZrB₂ composites increases with increasing ZrB₂ content; Nb–Mo–30vol%ZrB₂ had the highest compressive strength (1905.1 MPa). The improvement in the compressive strength of the Nb–Mo–ZrB₂ composites is mainly attributed to the secondary phase strengthening of the stiffer ZrB phase, solid-solution strengthening of the (Nb, Mo)ss matrix as well as fine-grain strengthening. The fracture toughness decreases with increasing ZrB₂ content. Finally, the fracture modes of the Nb–Mo–ZrB₂ composites are also discussed in detail.     

Effect of aging temperature on the microstructures and mechanical properties of ZG12Cr9Mo1Co1NiVNbNB ferritic heat-resistant steel

The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9Mo1Co1NiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant. The results show that the main precipitates during aging are Fe(Cr, Mo)₂₃C₆, V(Nb)C, and (Fe₂Mo) Laves in the steel. The amounts of the precipitated phases increase during aging, and correspondingly, the morphologies of phases are similar to be round. Fe(Cr, Mo)₂₃C₆ appears along boundaries and grows with increasing temperature. In addition, it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization. The hardness and strength decrease gradually, whereas the plasticity of the steel increases. What’s more, the hardness of this steel after creep is similar to that of other 9%–12%Cr ferritic steels. Thus, ZG12Cr9Mo1Co1NiVNbNB can be used in the project.     

Effects of Cr and Mo elements on the microstructures and compressive properties of the in situ (TiC_xN_y–TiB_2)/Ni cermets

In-situ(TiC_xN_y–TiB_2)/Ni cermets with 70 wt%TiC_xN_y–TiB_2 were successfully fabricated by combustion synthesis and hot pressing sintering in Ni-Ti-B_4C-BN powder systems.The microstructures,density,compressive properties,and hardness of the TiC_xN_y–TiB_2/Ni cermets with the addition of 0–8 wt%Cr/Mo to the Ni-Ti-B_4C-BN powder systems were compared and analysed.The results showed that the ceramic particles distributed uniformly in the cermets,and the size of the ceramic particles reduced with the Cr/Mo addition.Both Cr and Mo addition can improve the hardness,compressive properties,and fracture strains of the cermets.The hardness,compressive strength,and fracture strain of the(TiC_xN_y–TiB_2)/(Ni+Cr)cermets increased from 1561 HV,2.94 GPa,and 2.9%to 1864 HV,3.65 GPa,and 3.4%,respectively when the Cr content increased to 5 wt%.The hardness and compressive strength of the(TiC_xN_y–TiB_2)/(Ni+Mo)cermets increased from 1561 HV and 2.94 GPa to 1902 HV and 3.43 GPa,respectively when the Mo content increased to 8 wt%.The cermets with Cr had better compressive properties than the cermets with Mo.     

Hydrogen storage properties of MgH<Subscript>2</Subscript> co-catalyzed by LaH<Subscript>3</Subscript> and NbH

To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH₂ + 10wt%LaH₃ + 10wt%NbH was prepared by a mechanical milling method. The composite exhibited favorable hydrogen desorption properties, releasing 0.67wt% H₂ within 20 min at 548 K, which was ascribed to the co-catalytic effect of LaH₃ and NbH upon dehydriding of MgH₂. By contrast, pure MgH₂, an MgH₂ + 20wt%LaH₃ composite, and an MgH₂ + 20wt%NbH composite only released 0.1wt%, 0.28wt%, and 0.57wt% H₂, respectively, under the same conditions. Analyses by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping demonstrated that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH₂ + 10wt%LaH₃ + 10wt%NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH₂. The introduction of LaH₃ and NbH was beneficial to the hydrogen storage performance of MgH₂.     

Electronic structures and nonlinear optical properties of XAuPH<Subscript>3</Subscript>

The studies on model systems XAuPH3(X-H,F,Cl,Br,I,CN,CH3)have been carried out by using ab intiol HF and DFT B3LYP methods at pseudopotential and double-zeta LANL2DZ level.The results are compared with those of MP2,The properties of the models.i.e.the atomic net charge populations.the frontier molecular orbitals and nonlinear optical(NLO)properties have been investigated under an applied electric field on the basis of optimized structures.The computational results show that for these models characterized as electron acceptor-metal-electron donor(A-M-D)system,the NLO properties are due to intramolecular charge-transfer interaction between the acceptor and the donor.The more charges transfer gives,the better NLO properties.In the selected model systems,IAuPH3 has the biggest βvec and γof 1184.1942 a.u.and 17341.9214 a.u.,whereas IC6H4PH3^ ,A TYPICAL a-π-D organic conjugated system,has βvec and γof 710.7697 and 11664.1405 a.u.respectively.In comparison.IAuPH3 has significant NLO properties.     

Cu-Zn-Al2O3 nanocomposites:study of microstructure,corrosion,and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural, tribological, and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechanically alloyed powder was compacted followed by sintering of the obtained green compacts at 750℃ for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests, which revealed that, upon the addition of alumina nanoparticles, the coefficient of friction and the wear rate were reduced to 20% and 40%, respectively. The corrosion properties of the samples exposed to a 3.5wt% NaCl solution were studied using the immersion and potentiodynamic polarization methods, which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.     

Fabrication and properties of aluminum silicate fibrous materials with <Emphasis Type="Italic">in situ</Emphasis> synthesized K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> whiskers

To improve their mechanical and thermal insulation properties, aluminum silicate fibrous materials with in situ synthesized K₂Ti₆O₁₃ whiskers were prepared by firing a mixture of short aluminum silicate fibers and gel powders obtained from a sol-gel process. During the preparation process, the fiber surface was coated with K₂Ti₆O₁₃ whiskers after the fibers were subjected to a heat treatment carried out at various temperatures. The effects of process parameters on the microstructure, compressive strength, and thermal conductivity were analyzed systematically. The results show that higher treatment temperatures and longer treatment durations promoted the development of K₂Ti₆O₁₃ whiskers on the surface of aluminum silicate fibers; in addition, the intersection structure between whiskers modulated the morphology and volume of the multi-aperture structure among fibers, substantially increasing the fibers' compressive strength and reducing their heat conduction and convective heat transfer at high temperatures.