- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
Single crystal superalloy turbine rotor blade is one of the core hot-end components of the aero-engine， which has a decisive role in the thrust and performance of the aero-engine. Additive manufacturing for repair technology is one of the most challenging tasks in the special machining of aviation equipment. In this paper， the repair processes and their application for single crystal superalloy turbine rotor blades were systematically reviewed. Aiming at the problems of hot cracking defect， the cracking formation mechanism， key influencing factors， and control methods were summarized. In addition， the research progress in microstructure and mechanical properties of single crystal superalloys repaired by additive manufacturing technology are summed up. Furthermore， the prospective developing direction of single crystal superalloy turbine rotor blade repair is indicated. Specific filler material composition design， new process development， and multi-objective collaborative optimization based on deep learning are considered to be important future research directions.
Laser powder bed fusion （LPBF） technology offers significant advantages， including high flexibility， no mold requirements， and rapid manufacturing capabilities， so it is well-suited for repairing complex and precision components such as aero-engine blades. It is difficult to efficiently and accurately reveal the evolution rules of defects and microstructures in the multi-scale and multi-physical field coupling LPBF process through experimental methods only. The finite volume method and a cellular automaton model were used to simulate the morphological evolution of the powder bed melt pool and the corresponding microstructure formation process. Combined with experimental observations， the evolution rules of metallurgical defects in the alloy and grain growth under different printing parameters are revealed. The results indicate that during the LPBF repair process， energy density significantly affects the morphology of the melt pool. When the energy density is less than 87.9 J/mm³， the powder particles are not completely melted， accompanied by the formation of defects such as pores and unmelted areas. When the energy density is greater than 137.4 J/mm³， the surface smoothness of the solidified melt pool is significantly reduced. The increase in energy density enhances the horizontal thermal flow disturbance in the melt pool， and the crystals are affected by shear forces， leading to a greater orientation difference with the substrate. Additionally， the laser power significantly affects the microstructure of the alloy. As the laser power increases， the temperature gradient gradually decreases. The low temperature gradient promotes the formation of the supercooled liquid region， which in turn facilitates the formation of new crystal nuclei. When the laser power increases from 150 W to 250 W， the epitaxial growth grains change from columnar crystals to a large number of polycrystalline grains. Based on the numerical simulation methods， the optimal process parameters for repairing DZ125 alloy by LPBF are determined as follows：P=200 W， V=1000 mm/s， and H=65 μm. This method helps to reduce experimental costs and accelerate the acquisition of reasonable process parameters for LPBF repair of alloys.
Laser melting deposition is more suitable for repairing thin-walled substrates of single crystal alloys compared to argon arc welding and micro plasma arc welding. This article used laser melting deposition technology for additive repair of DD6 single crystal superalloy. The microstructure characteristics of the repaired zone and heat affected zone of the additive repaired joint were analysed by optical microscopy， scanning electron microscopy， and EBSD. And the microhardness distribution and high-temperature tensile properties of the repaired joint were tested. The results indicate that in the heat affected zone adjacent to the repair interface， γ' phase is partially coarsened and dissolved， and the hardness decreases significantly. The microstructure of repaired zone is an oriented columnar crystal structure grown epitaxially， and composed of γ+γ' phase and a small amount of dispersed carbides between dendrites. Many elongated columnar stray grains remain in the repaired zone， mostly distribute near the fusion line. As the height of the repaired zone increases， the dendrite spacing and hardness of the epitaxial growth tissue increases gradually， and the proportion of fine grid γ' phase in the dendrites increases continuously. The tensile strength of the repaired joint at 980 ℃ reaches 102% of the base material， and the yield strength reaches 92% of the base material， but the elongation is relatively poor.
For Ni3Al-based superalloy IC10 turbine blades， some defects， such as cracks and ablations， would appear after long-term service. To shorten the overhaul period， the turbine blades can be repaired using the brazing technology. In this study， an independently designed Co-based filler alloy （CoCrNi（W，Al，Ti，Mo，Ta）-B） was used to join the IC10 superalloy. The effects of the brazing gap and the brazing time on the joint microstructure and mechanical properties were investigated. The results show that the designed filler alloy has good brazeability at 1220 ℃ for IC10 superalloy. Because of the interreaction and mutual diffusion， the brazing seam is wider than the preset gap. Meanwhile， the matrix of brazing seam is γ＋γ′ dual phase which was similar to the IC10 base material. Because of the boron in the filler alloy， a large number of white borides are formed. The brazing holding time has little influence on the microstructure and strength of the joint， but the brazing seam has significant effect.With the brazing seam wider， the joint strength tested at 1000 ℃ increases gradually. When the brazing seam is set at 0.15 mm， the joint strength is 454 MPa， which is close to that of the IC10 base material. According to the joint fracture morphology， the increase in joint strength is mainly due to the small and diffuse white boride phase in the joint， inducing the tortuous crack propagation path.
The electron beam-physical vapor deposition （EB-PVD） technology was employed to fabricate yttria-stabilized zirconia （YSZ） thermal barrier coatings at different electron beam currents （1.2，1.8，2.4 A）. The phase structure and microstructural morphology of YSZ coatings at different electron beam currents were analyzed and characterized. The thermal barrier coatings were also subjected to a 1150 ℃ thermal cycling life test. The failure behaviors of coatings were analyzed by the evolution of the microstructure. The results show that YSZ coatings at different electron beam currents all possess a non-equilibrium tetragonal phase structure. As the electron beam current increases， the columnar grain tip structure of the coating evolves from a triangular shape to a pyramidal shape and then to a ridge-like shape， with the column structure changing from a slender structure to a coarse structure， the dendrites decreasing， and the arrangement becoming more orderly. The thermal conductivity is lower slightly due to the appearance of ordered nanopores in the column of YSZ coatings. The YSZ coating prepared at 1.8 A demonstrates the most excellent thermal shock life of 895 cycles， approximately twice that of the YSZ coating prepared at 1.2 A and 1.3 times that of the YSZ coating prepared at 2.4 A. The slender columnar grain structure prepared at a low electron beam current is prone to sintering failure， while the coarse columnar grain structure prepared at a high electron beam current is prone to thermally grown oxide （TGO） layer stress accumulation failure. The columnar grain structure prepared at 1.8 A could balance the two types of failure behaviors， effectively extending the thermal cycling life of the YSZ thermal barrier coating.
Thermal barrier coatings， consisting of a metal bonding layer， ceramic surface layer， and thermal growth oxide， are widely utilized in turbine blades for aero engines as protective coatings. The LaZrCeO/YSZ double ceramic thermal barrier coating was prepared on a Ni-based superalloy matrix using EB-PVD technology. The composition， phase structure， and thermal cycle life of the thermal barrier coating were investigated by adjusting the deposition energy of the ingot. Furthermore， the failure mechanism of the thermal barrier coating under 1100 ℃ thermal cycle was analyzed. The results indicate that the Zr content in the LaZrCeO coating increases proportionally with the rise in ingot deposition energy， while maintaining a consistent La/Ce ratio. Additionally， the increase in evaporation electron beam leads to changes in coating phase structure from single fluorite phase to compound pyrochlore and fluorite phase structure， and finally to single pyrochlore structure. Thermal cycling tests at 1100 ℃ demonstrate that the average thermal cycle life of LaZrCeO/YSZ ceramic thermal barrier coating with composite pyrochlore and fluorite phase structure reaches 1518 cycles， indicating excellent thermal physical properties. As the thermal cycle progresses， the Al element in the bond coat diffuses outward to form a thermally grown oxide （TGO） layer， while the Cr element reacts with LaZrCeO and oxygen to generate LaCrO3 and ZrO2. At elevated temperatures， Ni and Co elements diffuse and react with oxygen to produce （Ni，Co）（Cl，Al）2）O4 compounds. The chemical reactions induce cracks in either the TGO layer or the interface layer， reducing the toughness between the metal bond layer and ceramic layer， and leading to thermal barrier coating failure.
NiCoCrAlYHf coating （HY5 coating） was prepared on DD6 alloy by vacuum arc ion plating method. After different diffusion temperature treatments， the ceramic coating was deposited by electron beam-physical vapor deposition（EB-PVD） method. The cyclic oxidation properties of thermal barrier coatings at different diffusion temperatures were investigated by analysing the phase composition and microscopic morphology of bond coating（BC） at different diffusion temperatures. The results show that the bond coating samples after diffusion treatment in a vacuum change from the single-phase structure of the deposited to the double-phase structure of the diffusively treated. The content of β-NiAl phase in the bond coating increases with the increase of diffusion temperature. After diffusion treatment， the coating surface is uniform and dense， gray-white and black phases are observed in the coating， the black phase is β-NiAl， and the gray-white phase is γ-Ni and γ'-Ni3Al phases， which demonstrates that diffusion treatment can change the phase structure of the bond coating. The coating with 900 ℃ diffusion treated has the longest cyclic oxidation life， exceeding 400 h； the cyclic oxidation life of 1100 ℃ diffusion treated coating is less than 300 h. When the diffusion temperature is 900 ℃， the oxidation rate of the bond coating and the thermally grown oxide thickening rate are the lowest. It is not that the more β-NiAl phase content the better， but there is a threshold in the phase composition， increasing the β-NiAl phase content within the threshold can obtain better service performance.
As an important component of aeroengines， the lightweight manufacturing of swirlers is of great significance for improving the service performance of engines. Lightweight， high-strength， and heat-resistant TiAl alloy is a high-temperature structural material with great application potential， but its inherent brittleness and difficulty in preparation and processing seriously limit its application in the fabrication of high-performance swirlers. Therefore， the powder injection molding （PIM） technology was used to prepare the complex thin-walled TiAl alloy swirlers in near-net shape without any machining process by combining the mold design method of water-soluble core and high conformal polyformaldehyde（POM）-based binders. The preparation processes mainly include catalytic debinding， thermal debinding， and two-step sintering. The results show that the binder with a composition of 82%（mass fraction， the same below）POM-5%high density polyethylene（HDPE）-5%ethylene-vinyl acetate copolymer（EVA）-8% stearic acid（SA） has a higher powder loading and better molding filling performance. The powder loading， the flow behavior index n， the viscous flow activation energy E， and the general rheological index α STV of the feedstock are 62%（volume fraction）， 0.56， 22.95 kJ/mol， and 9.59， respectively. The two-step sintering method under pressureless can achieve synergistic control of high relative density and fine grain. When the sintering process is set to 1430 ℃/1 h+1250 ℃/5 h， the relative density of PIM TiAl alloy reaches 96.3% with a lamellar colony size of about 100 μm. After hot isostatic pressing（HIP） treatment， nearly complete densification of the TiAl alloy is achieved， and the dimensional deviation and surface roughness R a of the prepared swirlers are ±0.1 mm and 1.046 μm， respectively. The room-temperature tensile strength， yield strength， and elongation of the HIP TiAl alloy are 577， 466 MPa， and 0.96%， respectively.
Titanium and titanium alloys with surface-prepared coatings have excellent overall performance as bipolar plates for proton exchange membrane fuel cells， but the bare plates will form passivation films with poor electrical conductivity during service， reducing the efficiency of the whole machine. By studying the feasibility of α-corrosion resistant titanium alloy Ti35 （Ti5Ta） and its Al alloying， the electrical conductivity of bare plate was improved on the premise of ensuring corrosion resistance. Using the cluster-type composition design method developed by the group and combing with the highest solid solution degree on the phase diagram， three kinds of Ti-Ta alloys with compositions of Ti-7Ta， Ti-8.3Ta， and Ti-9.6Ta and three kinds of Ti-Al-Ta alloys with compositions of Ti-2.6Al-5.8Ta， Ti-3.8Al-8.6Ta， and Ti-5Al-11.3Ta were designed. The experimental results show that the cathodic current density of the developed alloy is lower than that of the reference alloy TC4 under the simulated cathodic service environment （0.5 mol/L H2SO4+2×10-6 HF） at a constant potential polarization voltage of 0.6 V （vs. SCE） for 4 h. The cathodic current density of the designed alloy is lower than that of the reference alloy TC4， among which the Ti-8.3Ta alloy has the smallest value of 0.72 μA·cm-2. Under 1.5 MPa loading pressure， with the increase of Ta content， the interfacial contact resistance （ICR） value gradually decreases and is better than that of the pure titanium and TC4. The ICR value of Ti-5Al-11.3Ta alloy is the smallest， which is 18.3 mΩ∙cm-2， and its cathodic polarization current density is 0.91 μA·cm-2. In summary， the appropriate addition of Ta and Al can effectively improve the service performance of titanium alloy bipolar plates， and it is expected to realize the preparation of titanium alloy bipolar plate materials without coating.
The effects of the solid solution on the microstructure and mechanical properties of 6451 Al alloy sheets were investigated by using conductivity and tensile tests， combined with OM and SEM observations. The results show that when the solid solution temperature is 560 ℃， recrystallization occurs in the sheet at 3 s of solution treatment. When the solution time is extended to 5 s， the Mg2Si particles are slowly dissolved. When the time is extended to 7 s， the equiaxial grains are formed after the complete recrystallization， a large amount of Mg2Si particles are dissolved， and the strength of the sheet is rapidly increased. With the further extension of the solution time， the growth rate of the strength of the T4P-stated sheet slows down obviously， and the increment of the yield strength after baking is basically unchanged. After the solution time of 30 s， there is no obvious change in the grain size. When the solution time is increased to 60 s， the Mg2Si particle is completely dissolved， and the yield and tensile strengths of the T4P-stated sheet are improved to 125 MPa and 247 MPa， respectively， with a better elongation of 30%. The functional relationship model between the yield strength and solid solution variation of the T4P-stated sheet based on classical diffusion theory is established according to the research results.
To improve the impact resistance of metal and composite material joint structures， a metal synapse structure was manufactured using metal laser selective melting technology. The structure was co-cured and molded with T300 twill woven carbon fiber-reinforced composite material （CFRP） to form a through-thickness reinforcement joint structure. The impact resistance of the synapse joint structure was verified through Charpy pendulum impact tests. Analysis and optimization of the synapse morphology were conducted based on CFRP damage patterns and impact absorption energy， as well as other influencing factors. Finite element simulations and comparative calculations were performed. The experimental results indicate that the penetration-enhanced joint method can prevent metal stress concentration and carbon fiber cutting caused by drilling holes. The impact absorption energy measures at 68.54 J， with a 216.1% improvement compared to the bolted connections. Increasing the height of the synapses effectively inhibits the composite material impact delamination. The synapse feature size and synapse array density affect internal defects in the composite material. With increasing synapse feature size and synapse array density，the impact absorption energy first increases to a point and then decreases. Finite element simulations based on synapse feature size variations showed that the simulation results deviated from the experimental results by less than 17%， and the damage form is highly consistent.
Flexible textile composite materials have received increasing attention in the application of variable configuration aircraft due to their flexibility， and foldable and unfoldable properties. However， there are still great uncertainties about their mechanical properties. Uniaxial tensile experiments with five off-axial angles were conducted to study the uniaxial tensile mechanical behaviors of a quartz fiber/silicone rubber flexible textile composite material. A hyperelastic constitutive model was established based on the characteristics of the brittleness of quartz fiber and the toughness of silicone rubber， and the strain energy density function was decoupled into the strain energy density functions from fiber elongations along the warp and weft yarns direction， and the strain energy density function coupling silicone rubber elongation and fiber shear. The model parameters were determined based on the uniaxial tensile test data. Comparison with the results of off-axis tensile test shows that the prediction error of the hyperelastic constitutive model for the in-plane tensile behavior is less than 3.88%. According to the flexible and deformable characteristics of the quartz fiber/silicone rubber flexible textile composite material， a circular membrane pneumatic loading test verification method is adopted， which can uniformly apply load to the membrane surface. The proposed hyperelastic constitutive model is realized by the user subroutine UANISOHYPER_INV of the finite element software Abaqus， and the error between simulation data and experimental data is less than 2.9%， indicating that the established hyperelastic constitutive model has good applicability for mechanical characterization of the quartz fiber/silicone rubber flexible textile composite material.
The effects of aging treatment on microstructure and properties of Fe-30.0Mn-9.6Al-1.0C low- density steel were studied by OM， SEM， XRD， EBSD， and TEM. The strain hardening behavior and strengthening plasticizing mechanism were also analyzed. The results show that after aging at different temperatures， the microstructure of Fe-30.0Mn-9.6Al-1.0C low-density steel remains mostly full austenite with κ-carbide precipitates. As the aging temperature increases， the increase in κ-carbide precipitation has an enhancing effect on the strength of the low-density steel， but it will deteriorate its plasticity. After solid solution at 1050 ℃ and aging at 450 ℃， the tensile strength of the low-density steel is 811 MPa，the elongation is 106.9%，and the product of strength and plasticity is 86.7 GPa·%. When aging at 500 ℃， the tensile strength of the low-density steel is 861 MPa，the elongation is 33.2%，and the product of strength and plasticity is 28.6 GPa·%. After solid solution at 1050 ℃ and aging tensile deformation at different temperatures， the strain hardening index of the low-density steel exhibits a double n-value phenomenon， and the strain hardening behavior shows a multi-stage variation pattern. After tensile deformation of the low-density steel， a large number of dislocation walls， Taylor lattice and microband structures， and fine κ-carbides together enhance the strength and plasticity of the low-density steel.
Combined with digital image correlation （DIC）， infrared thermal imaging （IRT）， electron backscatter diffraction （EBSD）， and microhardness distribution， the plastic instability behavior of medium-Mn steel processed by inter-critical quenching during uniaxial tension was analyzed. The results show that the strain-induced martensite transformation of experimental steel mainly occurs in the early stage of uniaxial tension. The Portevin-Le Chatelier（PLC）bands are obviously formed and propagated during this process， accompanied by thermal fluctuations. Moreover， the type of the PLC bands has transitioned from type A to type B and then to type A. The PLC bands are formed by the interaction between dislocation multiplication and interstitial solute atoms， i.e.， dynamic strain aging （DSA）. In the early stage of deformation， the dislocation will preferentially move to the low-density dislocation area， i.e.， propagate unidirectionally along the axis （the type A band）. Then， in the middle stage， the dislocation multiplication and initial interaction leads to the jumping （type B） PLC band formation. Finally， dislocation density and interactions increase in the later stage of deformation， leading to the formation of the type A PLC band again.
The novel Ti69NbCrZrX （X=Sn，W，Al，Mo，1%-2%， mass fraction） was used as an interlayer to join TiAl alloy with Ti2AlNb alloy by pulsed current diffusion welding at 900 ℃/30 min/8 MPa. The post-weld joint microstructure and properties were analyzed by SEM， EDS， EBSD， and room temperature tensile test. The results show that defect-free TiAl/Ti2AlNb joints can be obtained using Ti69NbCrZrX as the connecting interlayer. The joint interface microstructure is mainly composed of TiAl diffusion affected zone， interlayer diffusion zone， and Ti2AlNb diffusion affected zone. The TiAl diffusion affected zone structure is composed of white β phase and gray block α2 phase，the interlayer diffusion zone structure is mainly composed of gray block α2+ α phase， and white β/B2 phase composition， Ti2AlNb diffusion affected zone is composed of β/B2 matrix phase with lath and acicular O phase. The average value of room temperature tensile strength of the joint is 642.5 MPa， which reaches 91.57% of the strength of the base material. The fracture mode of the joints is dominated by brittle intergranular fracture， supplemented by brittle transgranular fracture.
In order to obtain high quality aluminium oxide tritium barrier coatings， micro-arc oxidation （MAO）technology was used to prepare micro-arc oxidation coatings on the surface of 1060 pure aluminium by doping Cr2O3 and graphene as additives in the electrolyte， using phosphate as the main electrolyte component. The surface morphology， elemental distribution， physical phase composition， thickness，hardness， abrasion and corrosion resistance of the micro-arc oxidation coatings were characterized by scanning electron microscope，X-ray diffractometer，eddy current thickness gauge，Vickers hardness tester， friction and wear tester， and electrochemical workstation. The results show that the surface morphology of the micro-arc oxidation coatings prepared by adding 3 g/L Cr2O3 and 1 g/L graphene into the electrolyte is more dense， and the proportion of α-Al2O3 and γ-Al2O3 in the coatings increases， with the thickness reaching 25.3 μm，the hardness reaching 763.01HV， and the average friction coefficient of 0.4781.At the same time，the self-corrosion potential is -0.185 V， and the self-corrosion current density is 1.095×10-9 A·cm-2.
The two-dimensional carbon material graphene oxide （GO） was modified by using quaternary ammonium cationic surfactant dodecyl dimethyl benzyl ammonium chloride （BKC） through π-π interaction to improve its dispersion and stability in aqueous solution. To further enhance the crosslinking effect， the modified GO composites （GB） was coated with polydopamine （PDA） in an alkaline solution. The gelatine/modified graphene oxide/polydopamine composite aerogel （GGB） using biomass material gelatin （Gel） as the skeleton material was prepared by sol-gel method and freeze-drying technique. The micro-morphology and structure of GGB composite aerogel were characterized by SEM， FTIR and XPS， etc. The GGB was used for the adsorption of levofloxacin hydrochloride （LEV） and the adsorption effects were investigated under different conditions such as pH values，contact time，reaction temperature，initial solution concentration，and dosage of adsorbent. Furthermore， the adsorption effects of GGB and composite unmodified graphene oxide aerogel （GGO） on LEV were compared. The results show that the GGB composite aerogel shows excellent adsorption capacity for the LEV， and the LEV adsorption capacity of GGB is increased more than 3 times than that of GGO. Moreover， the adsorption process is a spontaneous exothermic process and the experimental data of the adsorption process are more fitted to the Langmuir isotherm and the pseudo-second-order kinetic model， the theoretical maximum adsorption capacity of LEV on GGB is 476.42 mg/g. After 5 adsorption-desorption cycles， GGB maintained an equilibrium adsorption capacity for LEV exceeding 80 mg/g. It is indicated that the GGB exhibits significant promise as a highly efficient adsorbent for removing of LEV from wastewater.
Compared to traditional gas separation methods， membrane separation technology has advantages in low cost， easy operation， and high separation efficiency. In this study， the whisker mullite hollow fiber membrane （M0） with excellent high-temperature resistance， high strength， and large flux was used as the supporting layer. The PDMS with controllable viscosity was used as the intermediate transition layer. The PDMS coated on the surface of M0 and covered the defects on the substrate. Subsequently， the UiO-66-NH2 nanoparticles were modified with amino groups via the hydrothermal method. Trimesoyl chloride was used as the oil-phase monomer， and cysteamine was used as the water-phase monomer for interfacial polymerization. Through this interfacial polymerization process， UiO-66-NH2 was loaded on the top layer of the composite membrane to form the M0-PUi composite membrane. The properties of the membrane before and after modification were characterized by FT-IR， XRD， SEM， and water contact angle of the membrane surface. The CO2/N2 separation performance of the membrane was tested using a self-made gas separation device. The results show that the CO2 permeance of the composite membrane reaches 2765.3 GPU at room-temperature and under 0.2 MPa operating pressure， and its separation selectivity for CO2/N2 is 3.2. The stable separation selectivity of the composite membrane for CO2/N2 is 3.2-3.4 after continuous use at 80 ℃ or 120 ℃ for 6 h.
The molecular dynamics method was used to simulate the microstructure dynamic evolution， dislocation， and pore motion characteristics of AlCoCrFeNi high-entropy alloy at temperature 300 K and strain rate of 1×109 s-1， and the failure mechanism was revealed. The simulation results show that the maximum load-bearing， longitudinal modulus， and ductility of the nano-polycrystalline AlCoCrFeNi high-entropy alloy are lower than those of nano-monocrystalline. The strain reduction and peak stress reduction of nano-polycrystalline before yield are 25% and the peak stress reduction is 23.8%. The phase transition， dislocation， hole， and failure mechanism of the two nanocrystallines are different during the stretching process. During the stretching process of nano-monocrystals， the FCC structure is mainly transformed into a non-crystalline structure. The atomic position changes after the phase change， accompanied by a large number of Shorkly dislocations， and moves with the growth direction of the non-crystalline structure. The hole nucleation， growth， penetration， and failure fracture of non-crystalline structure area are mainly amorphous perforation fault. During the stretching process of nano-polycrystalline， the FCC structure mainly transforms to HCP structure and non-crystalline structure， and the atomic position changes after the phase change， accompanied by a large number of 1/6〈112〉 （Shortly） dislocations and a small number of 1/6〈110〉 （Stair-rod） dislocations， 1/3〈100〉 （Hirth） dislocations， and other dislocations continue to be generated and annihilated.The material undergoes certain plastic deformation， with nucleation of pores in the non-crystalline structure area of the grain boundary， growth and expansion along the grain boundary， and penetration through the grain boundary until failure fracture， showing mainly intergranular fracture.
Using fused corundum powder as raw material， silica sol as a binder， and aluminum fluoride trihydrate as mullite phase conversion promoter， the slurry composition of the ceramic shell for directional solidification molding of turbine blades was designed， and the ceramic shell was prepared. The microstructure and phase composition， high-temperature permeability， thermal expansion， high-temperature mechanics， and resistance to high-temperature deformation of the shell were studied. The results show that after sintering at 1200 ℃， with the help of the catalysis of aluminum fluoride trihydrate， the alumina in the shell reacts with silicon dioxide to produce a mullite whisker. Compared with the ceramic shell without aluminum fluoride trihydrate， the permeability of the shell is increased by about 1 time， the thermal diffusion coefficient is increased， and the thermal expansion coefficient is decreased. At the same time， the addition of aluminum fluoride trihydrate also reduces the high-temperature strength of the shell to a suitable range， improves the high-temperature yield of the shell， and makes the shell maintain a good high-temperature deformation resistance.
To solove the problem of the low surface energy of polyimide（PI） fiber and poor interfacial performance between PI fiber and epoxy， atmospheric air plasma was selected to modify the surface of PI fiber. The influence of treatment duration on the surface structure of PI fiber and the interfacial properties of PI/epoxy composites was investigated. Effects of atmospheric air plasma on the surface micromorphology of PI fiber and failure plane of PI/EP composites were observed by the SEM. Dynamic contact angle and lateral tow tensile strength tests were chosen to characterize the infiltration effect and interfacial performance between PI fiber and epoxy after plasma treatment. The flexural strength and interlaminar shear strength tests were selected as inspection items for composites performance. The results implicate that atmospheric air plasma treatment can increase the infiltration and interfacial connection between PI fiber and epoxy， the lateral tow tensile strength of PI fiber modified by plasma treatment for 6 min is 16.05 MPa， with increment of nearly 21%. The increases in flexural strength and interlaminar shear strength of PI/EP composites are 36.41% and 38.85% respectively. Atmospheric air plasma modification can remake the surface morphology of PI fiber， and improve the joining effect of PI fiber and epoxy. Furthermore， the failure model of PI/EP composites is transformed from interfacial failure to fiber surface failure.
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