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To improve the ablation resistance of graphite, AlSi alloy was used as a dissipative agent to fill the pores of graphite matrix by pressure infiltration method to prepare AlSi/graphite composites. The microstructure evolution and ablation behavior of the obtained AlSi/graphite composites were investigated under oxy-acetylene flame after ablating for varying lengths of time. Subsequently, the effect of heat dissipation through the AlSi alloy was quantitatively analyzed by data processing technique. Experimental results showed that the AlSi alloy reduced the surface temperature by about 300 °C in the first 20 s, and the linear ablation rate of the AlSi/graphite composite is found to be 119.3% lower than that of the graphite itself ablated for 10 s. The strengthening of ablation resistance is mainly achieved by heat dissipation and oxygen dissipation. However, it gradually decreases with continuous consumption of the AlSi alloy during ablation. Among these, the contribution of heat dissipation to the ablation resistance gradually increased from 10.1% at 10 s to 62.1% at 60 s.

In the present study, the effects of SiC nanowires (SiCnws) with diameters of 100 nm, 250 nm and 450 nm on the microstructure and mechanical behavior of 20 vol.% SiCnws/6061Al composites prepared by pressure infiltration were studied. It was found that the interface between SiCnws and Al matrix was well bonded, and no interface product was found. The thicker SiCnws are beneficial to improve the density. In addition, the bamboo-like and bone-like morphologies of SiCnws produce a strong interlocking effect between SiCnws and Al, which helps to improve the strength and plasticity of the material. The tensile strength of the composite prepared by SiCnws with a diameter of 450 nm reached 544 MPa. With a decrease in the diameter of SiCnws, the strengthening effect of SiCnws increases. The yield strength of SiCnws/6061Al composites prepared by 100 nm is 13.4% and 28.5% higher than that of 250 nm and 450 nm, respectively. This shows that, in nano-reinforced composites, the small-size reinforcement has an excellent improvement effect on the properties of the composites. This result has a guiding effect on the subsequent composite structure design.

Based on orthogonal experimental design (OED), the effects of the sintering pressure, sintering temperature and holding time on the mechanical properties of 50 vol% silicon carbide particle (SiCp)/2024Al composites prepared by spark plasma sintering (SPS) were investigated. The sintering pressure had the greatest effect on the density and bending strength of the material among these three factors, followed by sintering temperature and holding time. The optimised process conditions for producing the 50 vol% SiCp/2024Al were sintering at 550 °C for 5 min under 40 MPa, which resulted in a composite material with a density of 99.7% and good interface bonding with a comparatively high bending strength of 766.65 MPa. This work provides a promising method to produce high volume fraction composites that can meet high strength requirements.

Small solid rocket motors (SRM) require low density, low ablation nozzle-throat materials. In the present study, Al20Si alloy was infiltrated into the porous graphite matrix to develop Al20Si/graphite composites by pressure infiltration method. The ablation behavior of the as-prepared composite was investigated in a small SRM testing system with an average pressure of 13.3 MPa and 5 wt% Al for 1.4 s. The results show that the linear ablation rate of the Al20Si/graphite throat decreased by 92% compared to that of the C/C composite throat. The increased anti-ablative properties are provided by Al20Si alloy fillers, which reduce the degree of thermochemical ablation of the graphite matrix through heat dissipation, oxygen dissipation, and thermal blockage. Furthermore, the Al4SiC4 generated from Al20Si alloy and graphite fills graphite pores, which contributes to the oxidation resistance of the composite.

In this paper, to improve the hot deformability and corrosion resistance, a nanoamorphous B2O3 layer was designed and fabricated between B4C particles and an Al matrix successfully. The B4C@B2O3/Al composites were prepared by a hot-pressed sintering method. By contrast, the B4C/Al composites were synthesized using the same preparation method. The results show that the existence of an amorphous layer can effectively inhibit the formation of Al3BC, AlB12, and other reaction products at the interface, compared with B4C/Al composites. At the same time, the existence of an amorphous B2O3 layer can reduce the maximum deformation resistance of the composites under the compression conditions of 500 °C and 0.001 s–1, to about 76% lower than that of the B4C/Al composites, and improve the hot deformability significantly. Furthermore, the corrosion current density of B4C@B2O3/Al composites is 82.5% lower than that of the B4C/Al composites. The good corrosion resistance makes B4C@B2O3/Al composites a potential neutron shielding material.

Graphene has extremely high theoretical strength and electrothermal properties, and its application to Cu-based composites is expected to achieve a breakthrough in the performance of existing composites. As a nano-reinforced body, graphene often needs a long time of ball milling to make it uniformly dispersed, but the ball milling process inevitably brings damage to the graphene, causing the performance of the composite to deviate from expectations. Therefore, this paper uses CH4 as a carbon source to repair graphene through a CVD process to prepare low-damage graphene/Cu composites. The process of graphene defect generation was studied through the ball milling process. The effects of defect content and temperature on the graphene repair process were studied separately. The study found that the graphene defect repair process, the decomposition process of oxygen-containing functional groups, and the deposition process of active C atoms existed simultaneously in the CVD process. When the repair temperature was low, the C atom deposition process and the oxygen-containing functional group decomposition process dominated. In addition, when the repair temperature is high, the graphene defect repair process dominated. 3 wt% graphene/Cu composites were prepared by pressure infiltration, and it was found that the bending strength was increased by 48%, the plasticity was also slightly increased, and the thermal conductivity was increased by 10–40%. This research will help reduce graphene defects, improve the intrinsic properties of graphene, and provide theoretical guidance for the regulation of C defects in composites.

The effect of Zr (up to 1 at.%) addition on the formation of Fe–Zr metastable alloys and their thermal stability were investigated for their possible nuclear applications. Fe–xZr (x = 0.25, 0.5, 1%) alloys were synthesised by mechanical alloying under a high-purity argon atmosphere using stainless steel grinding media in a SPEX 8000M high energy mill. The milling was conducted for 20 h with a ball-to-powder weight ratio of 10:1. The formation of metastable solid solutions after milling was confirmed from the change in the Gibbs free energy analysis as per Miedema’s model. The microstructural characterisation was carried out by analysis of X-ray diffraction, atomic force microscopy and transmission electron microscopy. The effect of Zr on the thermal stability of Fe–Zr alloys was investigated by extensive annealing experiments followed by microstructural analysis and microhardness measurements. The stabilisation was found to occur at 800 °C and thereafter, no significant change in the crystallite s...

Si-Mo alloy was infiltrated into porous graphite to develop a short-term low-ablative SiMo/graphite composite material. 19.4 vol.% residual Si was retained in the composites and significantly improved the short-term (less than 60 s) ablation resistance without sacrificing long-term (∼180 s) ablation resistance. The excellent short-term low-ablative performance is ascribed to the melt and evaporation of Si, which reduces the rate of temperature rise and supplies the consumption of SiO2 in the ablation surface. With the progress of ablation time, the ablation surface forms a SiO2-MoSi2 double layer, which acts as a barrier between the oxyacetylene flame and the ablation surface.

The micro-creep behavior of metal matrix composite for inertial instrumentation was studied in this work. The interface, defect state and precipitation behavior during micro-creep were focused. The strain-time and strain rate-time relationships for SiCp/2024Al were investigated in-depth. The stress exponent and activation energy were measured 3 and 34.0 kJ/mol, respectively. It was found that the dislocation viscous slip dominates micro-creep mechanism. Moreover, the influence of load on precipitation behavior and the evolution of micro-creep microstructure were also discussed.

(TiB2 + h-BN)/2024Al and TiB2/2024Al composites were fabricated by pressure infiltration technique. The dry sliding tribological behavior of the two composites was investigated using a pin-on-disk wear tester at the room temperature in atmospheric environment. With the addition of h-BN particles, the TiB2 particles were uniformly dispersed in the 2024Al matrix, however, TiB2 particles were observed to be partially agglomerated at some zones in TiB2/2024Al composites. The results of dry sliding tests showed that the addition of h-BN could improve tribological performance significantly especially at low sliding speed and low load, which was attributed to the role of h-BN on hindering the formation of compacted layer. Under different experimental conditions, three wear regimes could be distinguished considering the tribological properties and microstructural features. The wear mechanism map was established and the dominant wear mechanisms controlling these wear regimes were also discussed. Keywords: Metal matrix composites, Pressure infiltration, Tribological behavior, Wear mechanism, Self-lubrication

As the initiative thermal protection materials applied in the field of aerospace industry, the high temperature performance evolution of the dissipation thermal protection materials is essential for keeping the carrying capacity of structure and the integrity of aerodynamic configuration in the aerodynamic environment. In this paper, flexural properties and compression properties of Mg–Zn/Graphite dissipation thermal protection materials are studied by three point bending tests and compression tests from room temperature to 1000°C, and fracture morphologies are observed and analysed by scanning electron microscope. The results showed that the flexural strength and compressive strength of composites were higher than that of matrix by 115 and 84% at the room temperature. With the increasing temperature, the strength of composite showed a downward trend. The fracture scanning showed that the internal defects of composite increased owing to oxidation of metal during the heating process. However, the t...

The mechanical properties and microstructural characteristics of ultrafine grained low stacking faulty energy (SFE) brass processed by cryorolling were investigated in the present work. The commercial brass with 18 wt.% Zn was subjected to cryorolling to obtain specimens with different percentage of reduction in area (RA). Short time post-processing annealing was carried out for the specimens with maximum RA (90%) to enhance their ductility. The mechanical properties of all the specimens were assessed by tensile tests and hardness measurements. Microstructural analysis was carried out by optical microscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and electron microscopy (EM). The maximum yield strength (YS) of 600 MPa with 2.1% ductility was obtained for the cryorolled samples with 90% RA. The YS decreased to 452 MPa with a corresponding increase in the ductility (10%) after annealing at 225 °C. The YS of the cryorolled + annealed sample is found to be 465% higher compared to that of the as-received specimens (YS = 80 MPa). Fractography analysis of the 90% rolled specimens showed a brittle fracture; while, presence of dimples marks on the fractured surface of the annealed specimens indicated a ductile failure. The low SFE of the alloy plays a vital role on the deformation mechanisms during cryorolling and simultaneous improvement of the YS and ductility. Hence, improvement in the mechanical properties has been discussed in the light of refinement of microstructure, formation of sub-grains and nano-twins driven by the low SFE.

A dense SiC–Si coating with average thickness of 580 μm was prepared on graphite by pack cementation. The surface morphology evolution and ablation mechanism of the coating at about 1780 °C were investigated by oxy-acetylene flame. After applying SiC–Si coating, the ablation surface temperature dropped about 300 °C. The ablation products SiO2 presented high viscosity and provided good protection in the early-to-middle stage of the ablation. The mechanical denudation gradually became severe with the ablation time increasing. Finally, the convection between the gases formed in the subsurface and the ablative gases turned out to be the primary ablation barrier.

In the present investigation, we report a simple and new technique to synthesize silicon carbide nanowires by high energy ball milling of silicon and carbon powders followed by annealing at elevated temperatures. The detailed structural analysis was carried out by X-ray diffraction, scanning and transmission electron microscopy, and FT-IR analysis. Nanocrystalline silicon particles were detected to be covered by amorphous carbon after milling. This typical structure was transformed to β-SiC nanowires during annealing by new growth mechanism. The β-SiC nanoparticles were found to be self-assembled one by one and formed a curly chain, and then rotated gradually in accordance to the same crystal orientation along the β-SiC [1 1 1] direction.

B4Cp/2024Al composite with volume fraction of 45% was designed and fabricated by pressure infiltration technology. Microstructure and friction and wear properties of B4Cp/2024Al composites were studied. The results show that reinforcement particles are uniformly distributed and a qualified relative density of the composite has been achieved. A high density of dislocations was observed to be in the peripheral area of the reinforcement particles, and a large number of fine acicular precipitates were found. Coefficient of friction of B4Cp/2024Al composites decreased slightly with increasing load and sliding speed, meanwhile, the wear rate increased with increasing load and sliding speed. Main forms of wear in B4Cp/2024Al composites were abrasive wear, adhesive wear and oxidation wear.

Graphite/SiC composites were prepared by reactive metal infiltration (RMI). The microstructure and the ablation mechanism under oxy-acetylene flame were investigated. The ablation surface was composed of a central zone, an intermediate zone and an outer zone. The surface of the intermediate zone was covered by a SiO2 layer due to the oxidation of Si and SiC. A particle layer, which consisted of SiC particles and graphite particles, was found beneath the SiO2 layer due to the large inner stress. In the central zone, an extra SiO layer was detected owing to the high temperature and the few oxygen in the particle layer. Due to the good wettability with graphite, the SiO2 layer exhibited excellent ablation resistance by inhibiting oxygen diffusion and lowering the mechanical erosion of the flame. Besides, the evolution of the gases formed inside the composite helped to improve the ablation resistance.

The blend compositions of Cu 99 Cr 1 (All the compositions are in atom% until otherwise mentioned.), Cu 94 Cr 6 , Cu 99 Cr 1 –4 wt.% SiC (average particle size ∼30 nm) and Cu 94 Cr 6 –4 wt.% SiC were ball-milled for 50 h in a stainless steel grinding media. The structural investigation and phase evolution during milling of the same compositions have already been reported in elsewhere ( [28] ). In the present study, we are reporting effect of microwave sintering on mechanical properties and electrical conductivity over vacuum and conventional sintering carried out at 900 °C. Relative densification and grain coarsening characteristics were investigated and compared. The microstructural features were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties, namely, Vickers hardness and wear resistance, and electrical conductivity were studied to investigate the suitability of the materials for electrical contact applications. The best combination of mechanical properties and electrical conductivity was obtained for microwave sintered specimens. This is possibly due to the enhanced densification and better grain size distribution achieved in microwave sintering technique. Difference in the properties is discussed in the light of electron scattering factor and densification in presence of ultra fine SiC particles in the nanocomposites.

In order to utilize the latent heat of metal fusion and evaporation, Al20Si/graphite was added into graphite by squeeze casting infiltration. Its ablation properties were tested by oxy-acetylene flame. Compared with graphite, linear ablation rates of Al20Si/graphite decrease nearly by one order of magnitude. However, linear ablation rate of Al20Si/graphite increases with ablation time, which is caused by the change of ablation mechanism. At the beginning of ablation process, thermal chemical erosion plays an important part and thermal protective effect comes from the melting of Al20Si, the alleviation of liquid Al 2 O 3 towards flame scouring and the decrease of porosities compared with graphite, while with ablation processing thermal mechanical erosion turns to dominate and thermal protective effect is mainly presented on the prevention of oxygen diffusion by the molten Al 4 SiC 4 covered on ablation surface and the oxygen diffusion barrier effect of Al 4 SiC 4 stuffed into graphite pores.

W f /Cu 82 Al 10 Fe 4 Ni 4 composite was fabricated by flow casting method. Dynamic compression tests with strain rate of 1600 s −1 at 20 °C, 200 °C, 400 °C and 600 °C were finished by means of Split Hopkinson Pressure Bar (SHPB). The results showed that the composites possessed obvious high temperature softening behaviors. The damages of W f /Cu 82 Al 10 Fe 4 Ni 4 composites all occurred within the tungsten fibers when compressed at 20 °C, 200 °C and 400 °C, indicating that the interface strength of the composites was high. While the damages of the composites occurred either in the tungsten fibers or in the matrix at 600 °C, in addition, the melt of matrix alloy also occurred. Microstructure of the composites after dynamic compressing at 600 °C was analyzed by transmission electron microscope (TEM), observation revealed that there were a lot of high-density dislocations, stacking faults and twins existing in the matrix. It was also found that the precipitated phase in the matrix played the role of the second phase strengthening.

SiO 2 covered β-SiC nanowires were directly synthesized with a novel method, annealing the milled Si,C nanopowders at 900–1100 °C on Si wafer or Al 2 O 3 substrate, and there is no any metal catalysts used. The diameters of the nanowires are range of 20 to 50 nm, and the lengths of the nanowires are up to several hundreds of microns. There is a uniform SiO 2 amorphous layer on the surface of SiC nanowires. The axial direction of SiC nanowires is , and there are stacking faults and twin lamellae in the SiC nanowires. The synthetic mechanism of SiC nanowires includes two solid–solid reactions and one gas–solid reaction between SiO, Si, C and CO.

A homogeneous and continuous nanostructured SiC coating on the surfaces of T700 and M40 carbon fibres was synthesized by in situ reaction sintering at 1450 °C with the milled Si and C powders, and the coating was characterized. The results show that the slurry is easier to stick to the surface of M40 carbon fibres than that of T700 carbon fibres. A homogeneous, continuous and crack-free nanostructured SiC coating is formed on the surface of these two kinds of carbon fibres. The SiC coating is composed of huge amounts of nanometric SiC crystals. Coatings with thickness of about 30 nm and 150 nm were fabricated. Carbon fibres with SiC coating whose thickness is about 30 nm display good flexibility.

An Al–6Mg alloy matrix composite reinforced with Ti–6Al–4V meshes was fabricated by pressure infiltration method; its damage behaviors impacted by hypervelocity aluminum projectiles were investigated. Results showed that the thin Ti f /Al–6Mg composite target exhibits better protection efficiency and energy absorption ability than Al–6Mg alloy target. With projectile sizes increasing, bulge and spallation were observed on the back of the composite target. The Ti–6Al–4V meshes were tensed and deformed drastically in the spallation region, where micro-damages such as interfacial debonding and cracks were dominant. Shear localization was the primary failure characteristic for thin Al–6Mg alloy target. The adiabatic shear bands were observed near the crater of Al–6Mg alloy, not in Ti f /Al–6Mg composite target. It was ascribed to the Ti–Al interfacial bonding strength and the high temperature strength for Ti–6Al–4V alloy.

In this study, Ce conversion coatings are investigated as corrosion inhibitors of graphite fibers reinforcement aluminum matrix (Gr-f/Al) composites. The coatings are obtained by chemical immersion in solution containing Ce(NO3)3 onto composite surface, whereas the Ce conversion coating process produces a coating with highly heterogeneous nature of the surface, but micro-cracked layer with “dry-mud” morphology. The thickness of coating is about 3 μm. The coatings were composed of Ce-rich nano-particles (∼20 nm), which were piled up for this coating. TEM observation for Ce conversion coating of the corresponding ring-like SAED patterns could not be matched to any of the previously reported structures of cerium compounds. Results of high-resolution XPS spectra of Ce 3d obtained for Ce conversion coating results show that the Ce 3d spectra have several components with binding energies characteristic of Ce3+ and Ce4+. The Ce conversion coating process produces effective corrosion protecting of Gr-f/Al composites, which is verified by electrochemical measurement results. The Rt values of coating sample is higher than those of uncoating sample, this confirms the better corrosion resistance of coating obtained after immersion treatment for Gr-f/Al composites.

Molybdenum disilicide was synthesized by mechanical alloying (MA) technique through the elemental powder mixtures. Both α-MoSi 2 and β-MoSi 2 phases are created at the beginning stage; the final products of the mechanical alloying are β-MoSi 2 phase and amorphous state substance when milled for 96 h. The study also extended to determine the effect of the milling time on the kinetics of the phase transformation during annealing at low temperature. Mo 5 Si 3 is formed and the phase transformation of α-MoSi 2 to β-MoSi 2 occurred during the annealing at 800 °C, meanwhile, the crystallite size of α-MoSi 2 grows up obviously. MoSi 0.65 is formed during annealing for the powders milled for 48 and 96 h, which suggests that MoSi 0.65 phase is the predominant phase prior to the MoSi 2 during the crystallization of the amorphous substance. The main reaction of the powders milled for 48 and 96 h and annealed at 800 °C is the crystallization of the amorphous substance and a trace mounts of the phase transformation of β-MoSi 2 to α-MoSi 2 .

A multilayer interface was formed in the Al matrix composite which was reinforced by 30% volume fraction of TiNi fiber. The composite was fabricated by pressure infiltration process and the interface between the TiNi fiber and Al matrix was investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). When the TiNi fiber was pre-oxidized in the air at 773 K for 1 h, three layers have been found and characterized in the interface: TiNi–B2 layer near the TiNi fiber, Ti–Al compound layer with Ti and granular TiO2 near the Al matrix, and Ti–Ni compound layer between TiNi–B2 and Ti–Al compound layers. The effect of the multilayer interface on the mechanical properties of the composite was also discussed. The result showed that the uniaxial tensile strength of the composite at room temperature was 318 MPa, which was very close to the theoretical calculation value of 326 MPa. Moreover, the composite with good ductility exhibited a typical ductile-fracture pattern.