Vacuum Hot Pressing Research Articles

Effect of multi‐angle lamination on mechanical properties and damages behavior of carbon fiber reinforced resin matrix composites

AbstractCarbon fiber reinforced resin matrix composites, when subjected to multi‐angle delamination during vacuum hot pressing, suffered from defects such as uneven fiber distribution, resin‐rich zones, and voids. These defects caused varied damage and failure behaviors in the composites, seriously affecting their mechanical properties. In this paper, the defect distribution, tensile and flexural properties, and damage behaviors of multi‐angle lay‐up specimens prepared in an autoclave were studied. The results indicated that irregularly shaped voids in laminates with a 0° angle difference primarily led to local stress concentration. Elliptical and elongated voids in laminates with a 90° angle difference were mainly susceptible to delamination. The [0/90]8 layer exhibited the best overall mechanical properties. The proportion of 0° laminates had a direct impact on the mechanical properties, with 0° contact laminates on the bending‐compression side capable of withstanding higher bending loads. The [+45/−45]8 plyer demonstrated pseudo‐delayed behavior, enabling the laminate to show better toughness under load. Variations in damage due to the proportions and positions of the laminates influenced the mechanical properties and damages behavior of multi‐angle laminates.Highlights Angular differences were observed to affect void and resin distribution. The best overall mechanical properties were attributed to [0/90]8 laminates. Pseudo‐delay behavior was exhibited by [+45/−45]8 laminates. Proportion of 0° layers impacted mechanical properties. Greater bending loads were withstood by the 0° contact layer.

Synchronous vacuum hot pressing ultra-high performance geopolymer: Ultrafast polymerization and early strength development

To overcome the application bottleneck of geopolymer in high-end industries, this study aims to develop ultra-high performance geopolymer products. By employing Synchronous Vacuum Hot Pressing, we have significantly enhanced the rate of polymerization and mechanical properties of Geopolymer based on Metakaolin-Fly Ash. The influence of Si/Al ratio, alkali equivalent, and molding time on the geopolymerization process, mechanical properties, and microstructure of geopolymers was investigated, while elucidating the underlying mechanisms. The compressive strength of SVHP-MFG reaches 90.92 MPa when the Si/Al ratio is 2, alkali equivalent is 8 %, and molding time is 30 min, owing to increased production of aluminosilicate gels and matrix structure densification. The ongoing reaction of unreacted particles and the subsequent transformation from "alumina-rich gel" to "silica-rich gel" in later stages further enhance the mechanical properties of the material. Additionally, the mean pore diameter of Synchronous vacuum hot pressing of metakaolin-fly ash geopolymer measures below 13.24 nm, thereby significantly enhancing the pore structure of the geopolymer. The synchronous vacuum hot pressing metakaolin fly ash-based geopolymers synthesized in this study represents a novel category of ultra-high performance ceramic-like geopolymers, exhibiting exceptional early strength and early stability. The research aims to promote the application of geopolymer in high-end industry and provide technical and theoretical support for the development of ultra-high performance geopolymer based products.

Mechanical properties of CoCrFeNi-X (X = Ti,Sn) high entropy alloy and tribological properties in simulated seawater environment

Five multimajor element CoCrFeNi-X(X = Ti,Sn) high entropy alloys (HEA) were prepared by vacuum hot press sintering. The phase composition, mechanical properties and tribological properties of CoCrFeNi-X(X = Ti,Sn) alloys in simulated seawater were investigated. The phase structure of CoCrFeNiTi high-entropy alloy is solid solution FCC phase, R phase, σ phase, and Laves phase. But after addition Sn elements, the phase structure become the FCC phase and Ni-Sn solid solution phase. CoCrFeNiTi alloy has lower density (7.17 g/cm3) and higher hardness (750 HV) than that of CoCrFeNiSn. The compressive yield strength of CoCrFeNiTi HEA is better than CoCrFeNiSn HEA. The CoCrFeNiSn high-entropy alloys showed lower wear rates. The main reason is that SnO2 is generated on the wear scar surface, which has good wetting and corrosion inhibition effects, so CoCrFeNiSn HEA shows better wear resistance in simulated seawater. The main wear mechanism of the CoCrFeNiSn HEA is abrasive wear, oxidative wear, exfoliation wear and corrosive wear.

A comparative study of microstructure and mechanical properties for carbon fibers and carbon nanotubes reinforced copper composites doped by Zr70Cu30 particles

Carbon fibers (CFs) and carbon nanotubes (CNTs) reinforced Cu composites doped by Zr70Cu30 alloy particles were fabricated by a conventional vacuum hot-press technique and their microstructures, mechanical properties and electrical conductivities were compared. The results revealed that the CNTs/Cu composite exhibited a superior combination between mechanical properties and electrical conductivity, having the highest relative density of 94.8 %, the maximum microhardness of 85.7 HV and the maximum electrical conductivity of 84.2 % IACS among various composites. The incorporation of Zr70Cu30 alloy particles led to limited contacts with CFs (or CNTs) reinforcements but caused the decrease of relative density and consequently the deleterious mechanical and electrical properties. The dominant strengthening mechanism for the fabricated Cu matrix composites was load transfer mechanism. The CNTs reinforcements demonstrated the highest reinforcement efficiency in the Cu matrix composites, which can provide some new insights for designing novel high-strength and high-connectivity Cu matrix composites.

First fluoride ceramics lasing at 605 nm at ambient temperature fabricated from chemically synthesized powders

Laser ceramics have emerged as promising candidates of solid-state laser gain media. However, most laser ceramics are currently focused on lasing in the infrared wavelength range. The very limited options of host materials and the increased optical scattering losses at shorter wavelengths within ceramics have greatly limited the development of visible laser ceramics. Here we report visible laser ceramics with a composition of 0.5%Pr3+,5%Y3+:SrF2, in which a visible (orange) laser oscillation at 605 nm has been successfully achieved at room temperature pumped by InGaN blue laser diodes with a maximum slope efficiency of 8.1%. The ceramics were fabricated by vacuum hot pressing (VHP) of wet-chemistry synthesized 0.5%Pr3+,5%Y3+:SrF2 powders, followed by hot isostatic pressing (HIP). It was found that the visible laser ceramics exhibited a lower optical scattering loss along the processing pressure direction of the VHP process, indicating a uniaxial anisotropy in optical transmission within the ceramics. To our best knowledge, the current work is the first report on visible laser ceramics lasing in the orange region at ambient temperature, fabricated from chemically synthesized powders, which could pave the way for future scientific research on and industrial applications of more sophisticated and cost-effective visible laser ceramics.

Microstructure evolution and mechanical properties of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite with a crossed-lamellar structure

TiAl alloys with low density, high creep resistance and high temperature performance are considered as candidate materials to replace nickel-based superalloys in the range of 700∼800 °C. However, the intrinsic brittleness of TiAl alloys has always been the biggest bottleneck restricting their development. In this paper, a bioinspired interpenetrating Ti2AlNb/TiAl composite with crossed-lamellar structure was prepared by combining selective laser melting (SLM) and vacuum hot press sintering (HPS) under the condition of 1150 °C/1 h/45 MPa, to improve the strength and toughness of the composite. Meanwhile, the metallurgical defects and microstructure of Ti2AlNb reinforcement skeleton printed under different volume energy densities (VEDs) were investigated, as well as the evolution of the microstructure at the interface region of the composite was systematically studied. What's more, we studied the mechanical properties of the composite including nanoindentation test, room temperature tensile and bending tests. The results show that the VED is 88.89 J/mm3, an almost completely dense reinforcement skeleton (∼99.8 %) is obtained. The interface region can be divided into four different reaction layers, namely LⅠ, LⅡ, LⅢ and LⅣ, due to the diffusion of elements. LⅠ is mainly composed of Othick/thin lath-like phase and O short rod-like phase. LⅡ is mainly composed of B2/β phase, acicular α2 phase and nanoscale ω-Ti3NbAl2 phase. The LⅢ mainly consists of B2/β phase. The LⅣ is composed of α2 phase. The deformability of each phase in the composite: B2/β phase > O phase >γ phase >α2 phase >ω phase. The tensile strength and fracture toughness of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite are increased by 24.0 % and 89.0 %, respectively, compared with TiAl alloy, which is mainly contributed to the strong interfacial bonding between matrix and reinforcement as well as the synergistic effect of Ti2AlNb reinforcement with high strength and toughness.

Effect of element N on microstructure and tribological properties of CoCrFeNiV alloy at severe temperature

In this study, CoCrFeNiV non-equiatomic high entropy alloys (HEAs) with varying N content were prepared using vacuum hot-press sintering. The effects of N content on the alloy's microstructure, mechanical properties, and tribological behavior at different temperatures were investigated. The results indicate that the N-added alloys primarily maintain an FCC phase. With increasing N content, the σ phase in the alloy gradually decreases, while the VN content increases, leading to grain refinement. This results in a 10.7 % increase in hardness, a 9 % increase in compression strength, and a 56 % increase in compression deformation. Below 400 °C, the primary wear mechanisms are adhesive wear, spalling wear, and slight oxidative wear, while above 600 °C, oxidative wear dominates. The addition of N reduced the wear rates of the alloy by 33.8 %, 8.1 %, and 31.3 % at RT, 200 °C, and 600 °C, respectively, and decreases the coefficient of friction at all temperatures. In summary, N addition improves the alloy's tribological performance at various temperatures.

Enhanced mechanical behavior and texture development of Al/Al2O3 composites produced by spark plasma sintering (SPS) and vacuum hot pressing (VHP) followed by simple shear extrusion (SSE)

Green compacts of Al-3vol% Al2O3 composites were produced by powder metallurgy (PM) and subsequently processed by spark plasma sintering (SPS) and vacuum hot pressing (VHP). The manufactured samples were then processed by the simple shear extrusion (SSE) process. Three SSE dies with the distortion angles (α) of 8°, 10° and 22.5° were used in this study. The SPS-ed/SSE-ed specimens for α = 10° were successfully deformed up to sixteen passes, while the VHP-ed/SSE-ed samples failed after six passes. In addition, the SPS-ed sample for α = 22.5° only underwent one pass of SSE. The SPS-ed/SSE-ed composites resulted in the highest shear punch test (SPT) load, modified porosity amount and the best reinforcement redistribution, as compared to the vacuum sintering and stir-casting manufacturing methods, which was confirmed by microstructure evaluation and porosity measurements. The crystallographic texture of the SPS-ed/SSE-ed composites for α = 10° was investigated in the sixteenth pass using the X-ray method. The results of texture development showed the very low intensity of shear and cube texture with {100} <011> and {001} <100> components, subsequently.

On the Mechanical Behavior of LP-DED C103 Thin-Wall Structures

Laser Powder Directed Energy Deposition (LP-DED) can produce thin-wall features on the order of 1 mm. These features are essential for large structures operating in extreme environments such as regeneratively cooled nozzles and heat exchangers, which often make use of refractory metals. In this work, the mechanical behavior of LP-DED C103 was investigated via quasi-static tensile testing and low cycle fatigue (LCF) testing. The effects of vacuum stress relief (SR) and hot isostatic pressing (HIP) heat treatments were investigated for specimens in the vertical and horizontal build orientations during tensile testing. The AB and SR properties were lower than literature values for wrought and laser powder bed fusion (L-PBF) bulk components but higher than electron beam powder bed fusion (EB-PBF). The application of a HIP cycle improved strength by 7% and ductility by 27% past the initial as-built condition. Fracture images reveal that interlayer stress concentration sites are responsible for fracture in specimens in the vertical orientation. Meanwhile, fracture in the horizontal specimens mainly propagates at a slanted angle typical of plane stress conditions. The LCF results show cycles to failure ranging from 100 cycles to 8000 cycles for max strain levels of 2% and 0.5%, respectively. Fractography on the fatigue specimens reveals an increasing propagation zone as max strain levels are increased. The impact of these findings and future work are discussed in detail.

Study on the microstructure, recrystallization, and mechanical properties of hot-press sintered (TiC + B4C)/6061Al composites during hot rolling

Hot rolling is a vital secondary processing technique for aluminum matrix composites. To explore the forming mechanism of (TiC+B4C)/6061Al composites during hot rolling, the 6061Al and (TiC+B4C)/6061Al composites were fabricated via vacuum hot-press sintering followed by hot rolling. The results show that reinforcing particles changed the distribution of Si and resulted in the in-situ generation of SiC in hot-rolled (TiC+B4C)/6061Al composites. During hot rolling, reinforcing particles inhibited the elongation and refined the size of Al grains, and contributed to further enhancing the hardness and strength of hot-rolled 6061Al. With the hot rolling reduction rate increasing, the hardness and strength of hot-rolled (TiC+B4C)/6061Al composites improved, and the refinement effect of reinforcing particles intensified. Both reinforcing particles and hot rolling exhibited effects on the recrystallization behavior of 6061Al during hot rolling, primarily through particle induced nucleation mechanism and strain induced grain boundary migration mechanism. Remarkably, the strength achieved by hot-rolled (TiC+B4C)/6061Al composites at a 20% hot rolling reduction rate rivals that of hot-rolled 6061Al at an 80% hot rolling reduction rate, while still preserving high plasticity. Hot-rolled (TiC+B4C)/6061Al composites predominantly exhibited the ductile fracture of aluminum matrix and cleavage fracture of particles, and the ductile fracture characteristics gradually weakened with the hot rolling reduction rate increasing. The dislocation increment strengthening mechanism contributed the most to the strength improvement of hot-rolled (TiC+B4C)/6061Al composites. This study can provide valuable insights into aluminum matrix composites.

Cr-Diamond/Cu Composites with High Thermal Conductivity Fabricated by Vacuum Hot Pressing.

Chromium-plated diamond/copper composite materials, with Cr layer thicknesses of 150 nm and 200 nm, were synthesized using a vacuum hot-press sintering process. Comparative analysis revealed that the thermal conductivity of the composite material with a Cr layer thickness of 150 nm increased by 266%, while that with a Cr layer thickness of 200 nm increased by 242%, relative to the diamond/copper composite materials without Cr plating. This indicates that the introduction of the Cr layer significantly enhanced the thermal conductivity of the composite material. The thermal properties of the composite material initially increased and subsequently decreased with rising sintering temperature. At a sintering temperature of 1050 °C and a diamond particle size of 210 μm, the thermal conductivity of the chromium-plated diamond/copper composite material reached a maximum value of 593.67 W∙m-1∙K-1. This high thermal conductivity is attributed to the formation of chromium carbide at the interface. Additionally, the surface of the diamond particles in contact with the carbide layer exhibited a continuous serrated morphology due to the interface reaction. This "pinning effect" at the interface strengthened the bonding between the diamond particles and the copper matrix, thereby enhancing the overall thermal conductivity of the composite material.

Development of large-size dissimilar stainless steel/α-Ti alloy joints by diffusion bonding using vacuum hot press: Interface microstructure and tensile response in the temperature range of 77–773 K

In the present study, dissimilar metal joints of SS321 and Ti–5Al-2.5Sn (α-Ti alloy) are produced by diffusion bonding at temperatures of 850, 900, and 950 °C under 10 MPa pressure for 30 min duration using a vacuum hot press (VHP). The interface of the joints was characterized through scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscattered diffraction analysis for examining microstructure, morphology, and microchemistry across the interface. The effect of change in the heating process during diffusion bonding on the growth kinetics of interface layers was investigated. The interface of the joints comprised of intermetallic phases of σ phase, χ phase, (Fe,Cr)2Ti, FeTi and β-Ti. The joint produced at 900 °C has exhibited a maximum tensile strength of 315 MPa, 253 MPa, and 208 MPa at the test temperatures of −196 °C (77 K), room temperature (300 K), and 500 °C (773 K), respectively. Reduction in joint strength was noticed at test temperatures of RT and −196 °C for the samples bonded at a higher temperature of 950 °C due to the increased widths of the intermetallic phases at the interface. The effect of the bonding temperature on the tensile strength of the joints at an elevated test temperature of 500 °C was found to be negligible; however, the joints displayed good retention of strength along with substantial strain hardening followed by ductility at 500 °C. Fracture surfaces of RT and −196 °C tested samples showed the mixed mode of featureless smooth and cleavage fracture, whereas the 500 °C tested sample displayed planar interface failure. The zone of failure of the joints was noted to be around the interphase layer made of (Fe,Cr)2Ti + FeTi intermetallics.

Microstructure and performance of carbon fiber reinforced aluminum matrix composites with molybdenum carbide coating on carbon fibers

In this work, a molybdenum carbide coating on the surface of short carbon fibers prepared using molten salt method was proposed to ameliorate the interfacial bonding and improve the performance of carbon fiber/Al composites. The carbon fiber/Al composites were produced using vacuum hot pressing. The characteristics of molybdenum carbide coating were analyzed. Besides, the microstructures, bending strength and thermal properties of the carbon fiber/Al composites were explored. Furthermore, the interfacial thermal resistance of the composites was investigated in relation to theoretical evaluations derived from the combined Maxwell-Garnett effective medium approach and acoustic mismatch model schemes. The results indicated that a homogeneous Mo2C coating with a thickness of 0.5 μm was obtained by proper molar ratio of carbon fibers, MoO3 and chloride salts mixture and heated at 1000 °C for 60 min. The Mo2C coating greatly enhanced the bond between the aluminum matrix and carbon fiber, leading to improvements in the densification behavior and bending strength of the coated composites. The enhanced thermal properties including improved thermal conductivity and reduced coefficient of thermal expansion (CTE) were also achieved by the Mo2C coating. The in-plane thermal conductivity of 60 vol.% Mo2C-coated carbon fiber/Al composite was 221 W·m−1·K−1 enhanced by 92% compared to that of uncoated composite and the CTE was 6.0 × 10–6 K−1 which was suitable for electronic packaging materials.

Effect of the TiB2 content on the mechanical and tribological properties of TiB2/AZ91 composites fabricated by vacuum hot-press sintering process incorporating vacuum ball milling

Magnesium alloys have poor strength and wear resistance, restricting their application greatly, while Mg matrix composites can improve these deficiencies. TiB2/AZ91 composites with high TiB2 content were prepared by vacuum hot-press sintering process incorporating vacuum ball milling. The effects of TiB2 content on the microstructure, mechanical properties and tribological properties of the composites were investigated in detail. The results suggested that the TiB2 particle exhibited good bonding with the Mg matrix. With the increasing TiB2 content, the ultimate tensile strength, yield strength and elongation of TiB2/AZ91 composites firstly increased and then decreased, while the wear rate and wear surface roughness presented an opposite trend, and the hardness and coefficient of friction gradually increased. The composites with 5 wt% TiB2 obtained the maximum tensile properties (UTS: 234 MPa YS: 91 MPa EL: 7.3 %). This improvement in mechanical properties was attributed to the uniform distribution of TiB2 particles and the well bonding at the interface. The strengthening mechanisms were found to be the load transfer strengthening and the thermal mismatch strengthening. Furthermore, the composites with 15 wt% TiB2 demonstrated the lowest wear rate of 1.06×10−6 mm3/Nm and lowest wear surface roughness of 2.971 μm. This wear resistance was enhanced because of the significant increasing in hardness. The dominant wear mechanisms observed in TiB2/AZ91 composites were abrasive wear and oxidation wear.

Comparative study on microstructure evolution, mechanical properties, and wear behavior of TiC and B4C single-reinforced and hybrid-reinforced Al–Mg–Si alloys by vacuum hot-press sintering

To explore the variances between single-reinforced and hybrid-reinforced Al–Mg–Si alloys with TiC and B4C, 10 wt.%-(TiC + B4C)/6061Al, 10 wt.%-B4C/6061Al, 10 wt.%-TiC/6061Al and 6061Al were prepared via wet mixing for 8 h followed by vacuum hot-press sintering at 580 °C and 30 MPa for 2 h. Microstructure evolution, mechanical properties, and wear behavior were investigated in this study. The results show that unlike single reinforcement of TiC, single reinforcement of B4C and hybrid reinforcement of TiC and B4C altered the distribution of Si and facilitated the in-situ formation of SiC. Both single reinforcement and hybrid reinforcement resulted in mixed fracture characteristics of ductile fracture and cleavage fracture, while hybrid reinforcement of TiC and B4C demonstrated superior strength and plasticity matching. At equivalent particle mass fractions, single reinforcement of TiC was more conducive to inducing recrystallization during sintering, followed by single reinforcement of B4C, and hybrid reinforcement of TiC and B4C had the least effect. At equivalent particle mass fractions, single reinforcement of B4C had the most significant effect on improving the wear resistance, followed by hybrid reinforcement of TiC and B4C, and single reinforcement of TiC had the least effect. All particle addition methods demonstrated a mixed wear mechanism involving abrasive wear, adhesive wear, and spalling wear. This study provides valuable insights into the development of aluminum matrix composites.

Enhanced fracture toughness of Ti2AlNb/Ti6Al4V layered metal composite

Drawing inspiration from the intricacies of nacre structure, Ti2AlNb/Ti6Al4V layered metal composite was fabricated by vacuum hot pressing and achieved high fracture toughness. The fracture toughness of the composite registers at 48.5 MPa∙m1/2, surpassing the theoretical fracture toughness calculated based on the rule of mixture (ROM) and exhibiting 54 % improvement compared toTi2AlNb alloy. The introduction of a layered configuration imparts complex crack propagation pathways to the composite. The occurrences of crack deflection, crack bridging, crack passivation, and interface delamination serve to increase the resistance to crack propagation. Moreover, the plastic deformation of the ductile Ti6Al4V layer and the large plastic zone size of the crack tip can release the stress concentration and delay the fracture of the composite. This understanding not only advances our comprehension of the toughening mechanisms but also has practical implications for the application and development of layered Ti2AlNb alloys.

Tribological investigation of ceramic incorporated novel compositionally graded multilayer tungsten alloys

In this study, novel compositionally graded tungsten alloys incorporating ceramics were prepared using mechanical alloying and pressure-assisted vacuum hot press (VHP) sintering. Three distinct tungsten compositions (W1, W2, and W3) were developed with varying alloying elements and reinforcements, were stacked layer-wise, and then sintered using VHP. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were employed to analyze the morphology and microstructural features of synthesized alloys. The effect of alloying elements and reinforcements on mechanical properties and wear behavior was examined. The results showed improvement in mechanical characteristics and enhanced wear resistance of the compositionally graded tungsten alloys. The hardness was increased due to the formation of carbide phases during milling and sintering. The W1 side exhibited a hardness of 8.4 GPa, while the W3 side reached a hardness of 13.3 GPa. Additionally, the wear behavior of both sides (W1 and W3) was also investigated under different applied loads. At a load of 10 N, the W1 surface exhibited a minimum specific wear rate of 3 × 10−6 mm3/Nm, attributed to the presence of MWCNTs and WC phase. However, the W3 surface reinforced with TiC and cBN showed a minimum specific wear rate of 9 × 10−7 mm3/Nm at a higher load of 20 N. This indicates that the W3 side possessed superior hardness and wear resistance ability as compared to the W1 side of compositionally graded tungsten alloys. The novel compositionally graded approach is useful for developing tungsten alloys with tailored mechanical properties for wear resistance applications.

Effect of ball milling and solid solution treatment on microstructure and mechanical properties of ZrMgMo3O12p/2024Al composites

The 10 vol% ZrMgMo3O12/2024Al composites were fabricated using the powder metallurgy process and consolidation via vacuum hot pressing. The effects of the ball milling process and solution treatment time on the composites’ microstructure, Vickers hardness, and compressive properties were studied. Increasing the ball milling speed and extending the ball milling duration reduce the size of ZrMgMo3O12 particles, resulting in a more uniform dispersion within the aluminum matrix. Extending the solution treatment duration facilitates the dissolution of more primary Al2Cu phase into the aluminum matrix reducing the presence of coarse primary Al2Cu phase and increasing the number of fine Al2Cu precipitates formed during the aging process. The results indicated that an appropriate increase in ball milling speed, extension of ball milling duration, and solution treatment time can enhance the Vickers hardness and room temperature compressive strength of the composites. Specifically, the composites processed with a ball milling speed of 350 rpm for 6 h, a solid solution treatment at 495 °C for 24 h, and an aging treatment at 190 °C for 8 h exhibited a Vickers hardness of 277 HV and a compressive yield strength of 687 MPa, along with a compressive strain of 7.8 %.

Electrical sliding friction wear behaviors and mechanisms of Cu–Sn matrix composites containing MoS2/graphite

Cu–Sn matrix composites were prepared by vacuum hot press sintering technique with the addition of MoS2, graphite and a mixture of MoS2/graphite, respectively. The friction wear behaviors and contact resistance of the three composites under different currents were investigated and compared. The friction film formed on the friction surface was analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The wear mechanism and the evolution of friction film composition of the composites under different currents were revealed. The results showed that MoS2 and graphite had synergistic lubrication effects. The Cu–Sn-Graphite-MoS2 composite exhibited low wear rates and the lowest and most stable contact resistance. MoS2 could effectively promote the formation and integrity of the friction film and optimize the friction wear performance. With the increase of current, the graphite content in the friction film rose, which helped to reduce the oxidation and consumption of the friction film. The increase in current accelerated the shedding of lubricating particles and the softening of lubricating film, making the lubricating film denser and reducing the oxidation depth.

Microstructure Characterization and Mechanical Properties of the NiTif‐Reinforced Ti/Al‐Laminated Composites Using Vacuum Hot Pressing with Ultrasonic Consolidation Assisted

A novel method of preparing continuous NiTif‐reinforced Ti/Al‐laminated composites is proposed via ultrasonic consolidation (UC) and vacuum hot pressing. The microstructure of the composites is characterized by X‐ray diffraction, scanning electron microscopy, and electron backscattering diffraction. The tensile properties of the composites are measured by a universal testing machine. Results indicate that the composite exhibits multilayer structure consisting of residual NiTi fiber, intermetallic compounds (IMCs) layer, reaction layer, Ti layer, and Al layer. The intermetallic layer is composed of Al3Ti and Al3Ni, and some Ni‐rich precipitates are dispersed in the matrix. And with the introduction of UC assisted, grain refinement occurs at the IMC/Al interface, texture variation emerges at the NiTi fiber/IMCs interface, and a weakening of texture strength is observed at both interfaces. Compared to NiTif‐reinforced Ti/Al‐laminated composites without UC assisted, both the tensile strength (from 872.4 to 826.5 MPa) and failure strain (from 17.5% to 20.4%) of NiTif‐reinforced Ti/Al‐laminated composites with UC assisted increase due to the contribution of UC assisted. The reinforcing and fracture mechanisms of the UC assisted are also discussed.