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Liu T.,Beihang University | Liu T.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Zhu Y.-R.,Beihang University | Zhu Y.-R.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | And 4 more authors.
Cailiao Kexue yu Gongyi/Material Science and Technology | Year: 2011

To understand the crystallization behaviors of amorphous alloys and to control their microstructures and properties, Gd36La20Al24Co20 BMGs were prepared by copper-mold casting. The crystallization behavior and thermal stability of Gd36La20Al24Co20 were investigated by X-ray diffraction and differential scanning caloricity (DSC). The results show that the activation energy of crystallization of Gd36La20Al24Co20 BMGs is 282.5 kJ/mol, and it has a higher thermal stability compared with light rare earth based metallic glasses. The isothermal kinetics was modeled by the Johnson-Mehl-Avrami equation. The Avrami exponents were calculated to be in the range of 2.78 to 3.3. The average value of local Avrami exponents shows that at the initial stage the value of n is about 2, indicating that the crystallization process is controlled by one-dimensional diffusion process. In the main crystallization stage, the value of n changes from 2.5 to 3.5. In this stage, the crystallites grow up at increasing nucleation rate with 2.5


Ni L.Y.,Beihang University | Ni L.Y.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Liu C.,Beihang University | Liu C.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | And 4 more authors.
Journal of Thermal Spray Technology | Year: 2011

Thermal Barrier Coatings with HVOF NiCrAlY Bond Coat is prepared on nickel-based superalloy substrates. The lifetime of the coating is about 1630 h for 1-h cycle at 1050 °C. Growth of the TGO (thermally grown oxide) approximately follows a parabolic kinetics, and the TGO presents a bi-layered structure. Failure of the coating occurs near the interface between the mixed oxides layer of TGO and top coat. A finite element method is employed to analyze the stress distribution in the coating. The results show that maximum stresses occur at the top coat/TGO interface near the edge of the coating. The maximum radial stress for TGO consisting of spinel and Al 2O 3 is about five times larger than that of Al 2O 3, while the maximum axial stress is about ten times larger. The mixed oxide layer of TGO plays an important role in the premature failure of TBCs. © 2011 ASM International.


Jin L.,Beihang University | Jin L.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Yu Q.,Beihang University | Yu Q.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | And 4 more authors.
Journal of Thermal Spray Technology | Year: 2012

Nanostructured 8 wt.% CeO 2-5.4 wt.% Y 2O 3-ZrO 2 (CeYSZ) coatings were prepared by atmospheric plasma spraying technology. The microstructure, thermal diffusivity, and thermal cycle behavior of CeYSZ were investigated. The results show that the as-sprayed nano-CeYSZ coatings consist of tetragonal ZrO 2 and Ce element is in solid solution with ZrO 2. The CeYSZ coatings are characterized by nano-zones (unmelted nanoparticles), melted dense areas, splats, and pores. The thermal diffusivity of nano-CeYSZ coatings is 0.548 × 10 -6 m 2/s at room temperature. The addition of CeO 2 decreases the thermal diffusivity of nano-YSZ coatings, which is mainly caused by the point defect scattering and grain-boundary scattering. The thermal cycle life of nano-CeYSZ coatings is about 860 cycles at 1050 °C. The spallation of the coatings occurs at the interface of CeYSZ/TGO. © 2012 ASM International.


Luo H.,Beihang University | Luo H.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Han Z.,Beihang University | Han Z.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | And 2 more authors.
Materials Science Forum | Year: 2011

The performance and life of machined components in service are mainly effect by their surface integrity. Burnishing process is a kind of chipless processing which improve the surface integrity obviously. A subsurface "hardness film" is formed during the processing. Subsurface mechanical behavior is the main part of surface integrity. Since the very small scale of the subsurface in burnished surface nanoindentation is used to identify how the local changes of microstructure influence the hardness distributions of subsurface mechanical properties. This study focuses on the relationships between burnishing parameters (burnishing feed and burnishing depth) and nanohardness. A series of burnishing processing experiments and nanoindentation tests were conducted on the surface of the burnished samples. The microstructure and nanoindentation research results indicate that there is no visible phase transformed region in the subsurface of burnished specimens, the hardening film is larger than 4 micro meters, the nanohardness is about 2.2∼3.5Gpa which depends on the burnishing parameters and distribution and position of the second phase particles, while the nanohardness in turned material is about 1.8Gpa. © (2011) Trans Tech Publications, Switzerland.


Guo L.,Beihang University | Guo H.,Beihang University | Guo H.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Ma G.,Beihang University | And 3 more authors.
Ceramics International | Year: 2012

BaLa 2Ti 3O 10 (BLT) with Ruddlesden-Popper structure is investigated as a material for thermal barrier coatings (TBCs). BLT shows excellent sintering resistance and remains phase stability at 1500°C for 110 h. After annealing at 1500°C for 1 h, BLT bulk material exhibits c-axis textured structure with c-axis parallel to the hot pressing direction. Thermal expansion coefficients of BLT in a-b plane are in the range of 9.5 × 10 -6-11.3 × 10 -6 K -1, whereas those along c-axis range from 10.4 × 10 -6 to 12.1 × 10 -6 K -1, which are comparable to those of 8YSZ. The thermal conductivities of BLT in a-b plane and along c-axis are 1.41-1.71 and 1.31-1.60 W/mK, respectively, nearly 20% lower than those of 8YSZ. The anisotropy in thermo-physical properties is attributed to the insertion of weakly bonded BaO layer in the BLT crystal. © 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Yang Y.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Zhao Y.-F.,Aerospace Research Institute of Materials And Processing Technology | Wang J.-Y.,Aerospace Research Institute of Materials And Processing Technology | Zhao C.,Aerospace Research Institute of Materials And Processing Technology | And 3 more authors.
Journal of Applied Polymer Science | Year: 2016

Acrylate-based epoxy resin (AE)/low molecular weight polyamine (LPA) composites were developed. The chemical structure, curing behavior, fracture morphology, damping properties, and mechanical properties were evaluated by Fourier transform infrared (FTIR), 1H-nuclear magnetic resonance (1H-NMR), gel permeation chromatography (GPC), Differential scanning calorimeter (DSC), scanning electron microscope (SEM), Dynamic mechanical thermal analysis (DMTA), and electro mechanical machine. Transmission electron microscope (TEM) and SEM pictures exhibited nanoscale micro-phase separation between epoxy and acrylic segmers. DMTA results indicated that the loss factor of cured AE/LPA system could reach 1.84 and temperature range of tan δ>0.5 was about 84°C. Tensile strength and elongation at break of the cured AE samples can reach 6.5 MPa and 185%, respectively. © 2016 Wiley Periodicals, Inc.


Wu Q.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Li M.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Gu Y.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | Wang S.,Key Laboratory of Aerospace Materials and Performance Ministry of Education | And 2 more authors.
Polymer Composites | Year: 2014

The influence of sizing agent on interfacial shear strength (IFSS) of carbon fiber/epoxy (CF/EP) and carbon fiber/bismaleimide (CF/BMI) was investigated. Since sizing agent can alter physicochemical properties of CF surface, possible affecting factors, including sizing reactivity, chemical reactions between sizing and resin, wettability of fiber with resin, fiber surface roughness, and chemical composition of fiber surface, were discussed. It is found that contact angle of fiber with resin and sufficient chemical reactions between sizing and resin reveal strong correlation with the interfacial adhesion of CF/EP and CF/BMI, while the effect of surface roughness and the amount of oxygen on the fiber surface are relatively weak. Due to EP type of the composition, the sizing agent tends to improve the wettability of CF with EP, while goes against for the fiber with BMI. © 2014 Society of Plastics Engineers.

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