航空材料学报

Mathematical model of hydrogen diffusion in treble layer structure wall of hydrogenation reactors

YU Gang, ZHANG Xue-yuan, DU Yuan-long

1999, 19(2): 1-7.

[Abstract](1448) [PDF 485KB](258)

Abstract:
Based on the principle of the electrochemical hydrogen permeation presented by Devanathan-Stachurski, the mathematical model for calculating the hydrogen concentration distribution in the treble layer wall of hydrogen reactor at the condition of steady diffusion of hydrogen was suggested by using the electrochemical probe described in the Chinese Invention Patent: 95111971.0 for determining hydrogen permeation rate in metals. The process of hydrogen permeation was controlled by the hydrogen diffusion step under the operation condition of the reactor. As long as the steady hydrogen permeation current density i∞ was detected in the hydrogen probe at a given temperature, the interface hydrogen concentrations on the key interfaces and hydrogen distribution at any given radial section in the single, double or treble layer wall of hydrogenation reactor could be found by applying the presented equations through suitable parameters input of computer program. The theoretical bases were provided for detecting or monitoring the concentration of atomic hydrogen in the walls of hydrogenation reactors.

Optimization analysis of delamination growth in fiber reinforced metal laminates under cyclic loading

CUO Ya-jun, WU Xue-ren

1999, 19(2): 8-12.

[Abstract](1519) [PDF 298KB](176)

Abstract:
Based upon a theoretical model for predicting the fatigue crack growth and the delamination growth in fiber reinforced metal laminates, the effects of some factors on the delamination growth rates, including the ply thickness, the residual stresses, the modulus of the fibers, the bonding strength and the shear modulus of the adhesive were estimated. It has been shown from the analysis that the delamination growth can be significantly improved by decreasing the ply thickness and the residual stresses in the constituent metal layers. The effects of the bonding strength and the modulus of the fibers are relatively small, and the effect of the shear modulus of the adhesive can be neglected.

Fatigue behavior of molybdenum alloy under high-temperature thermomechanical stress cycles

SHI Hui-ji, KORN C, PLUVINAGE G

1999, 19(2): 13-19.

[Abstract](1526) [PDF 701KB](280)

Abstract:
High temperature isothermal mechanical fatigue and in-phase thermomechanical fatigue (TMF) tests in stress control were carried out on a molybdenum alloy. Two temperature levels of 350 and 500℃ were applied to isothermal fatigue tests and a temperature interval of 350-500℃ to TMF tests. The fatigue lives obtained in the in-phase TMF tests is lower than the ones obtained in the isothermal mechanical tests at the same stress amplitude. It appears that an additional damage produced by the reaction of mechanical stress cycles and temperature cycles in TMF situation. Ratching phenomenon occurred during the tests with an increasing creep rate and it was dependent on temperature and load amplitude. The observations of the microstructure of the damaged specimens demonstrated that the fracture was a brittle process under higher cyclic stress conditions. A simple model of lifetime prediction was developed and it is based on Woehler-Miner law. The lifetime prediction gives results corresponding to experimental data.

The spallation mechangsm of thermal barrier coating during statec oxidation

HUO Xiao, SHEN Wen-yan, CHEN Meng-cheng, LI Jian-ping

1999, 19(2): 20-26.

[Abstract](1497) [PDF 437KB](297)

Abstract:
The oxidation resistance of a thermal barrier coating, whose bonding layer NiCrAlY was prepared by cathode vacuum arc deposition and top layer Y-PSZ was coated by electron beam physical vapor deposition, was evaluated using a static oxidation test at 1100℃. The effect of the pre-treatments of the bonding layer on spallation modes of the top layer and the microstructure charcateristics of the failured interface were stressed. In addition, the phase transformation of the top layer and the oxidation dynamics of the thermal barrier coating during oxidation at 1100℃ were investigated and the failure mechanism of the top layer during the oxidation was discussed. The experimental results indicated that in present experimental conditions, the oxidation of the bonding layer was main cause resulted in the spelling of the top layer of the thermal barrier coating, which was related to the loss of oxidation resistance of the bonding layer caused by non preoperative pre-treatment processes.

Investigation on the microstructure of NiCrAlY deposition with different conditions

RU Ji-lai, WANG Ren-zhi

1999, 19(2): 27-34.

[Abstract](1380) [PDF 285KB](159)

Abstract:
NiCrAlY deposition produced by Arc Plasma Deposition was used to protect DD2, a nickel based single crystal materials, from high temperature oxdidation. The surface and inner phase analysis of the deposition with different states including original, diffused, plastic deformation and aged after plastic deformation have been investigated. It has been showed that the main phases within NiCrAlY deposition with the depth of 130μm are Ni3Al matric (ordered or non ordered structure), NiAl and Cr, but the phase composition are different for different states. It has also been pointed out that the new phase NiAl precipitated during diffused treatment can be soluted by plastic deformation, while NiAl can be precipitated again from the plastic deformed deposition ageing at 1100℃.

Tensile properties of NiAl alloy matrix in situ composites fabricated by reactive hot pressing techniques

LU Yu-xiang, TAO Chun-hu, YANG De-zhuang, ZHANG Jun-shan

1999, 19(2): 35-42.

[Abstract](1438) [PDF 683KB](233)

Abstract:
The room tensile properties and microstructure are investigated in 20vol.%TiCp/Ni50Al20Fe30 in-situ composites fabricated by reactive hot pressing processes (including reactive hot axial direction pressing (RHP) and reactive hot isostatic pressing (RHIP) techniques). Results show that TiC in-situ particles are fine and even, however, it is difficult for the composites to be densely fabricated by reactive hot pressing processes, Existence of porosity seriously decreases the tensile properties of the composites. The evenness of microstructure and density of composites are improved by an additional hot rolling process, which obviously increases their room temperature mechanical properties.

Study on metal/shell interaction in ZrO₂ ceramic mould during titanium investment casting

LI Bang-sheng, JIANG Hai-yan, LI Zhi-qiang, FAN Hong-bo, AN Ge-ying

1999, 19(2): 43-47.

[Abstract](1457) [PDF 308KB](367)

Abstract:
The metal/shell interface has been prepared by means of investment casting and diffusion bonding, respectively. Then the obtained interfaces are thoroughly studied using SEM、EPMA and micro hardness analysis. Finally, an interaction mechanism on the basis of thermal diffusion of Zr、O into titanium matrix is founded.The experimental results show that other than advancing uniformly on the whole interface,the interface reactions preferably take place in the areas where there are undulations of concentricity,temperature,and energy,as well as appropriate surface orientation of ceramic particles.

Pressure ressure brazing of Si₃N₄ ceramics with Al-Li alloy and high temperature properties of the joints

ZOU Gui-sheng, WU Ai-ping, REN Jia-lie, PENG Zhen-shan

1999, 19(2): 48-53.

[Abstract](1429) [PDF 339KB](196)

Abstract:
Pressure brazing of Si3N4 ceramics in vacuum with Al-3wt%Ti alloy was performed, and effects of bonding pressure on the microstructures of braze metal and the joints’strength were investigated. For solid-liquid state brazing, bonding pressure will not only reduce the width of braze metal but also modify its microstructures, which results in that the joint’s strength is improved. Bonding pressure imposition can be used as one of the methods modifying braze metal. The high-temperature properties of joints brazed with Al-3wt%Ti alloy which braze metal contains a large amount of Al3Ti phase are improved significantly compared with that of the joints brazed with pure Al, and their shear strength at 600℃ is 29MPa and 4.5 MPa, respectively.

Review on sand erosion of composites

SHEN Zhen, YANG Sheng-chun, Margherita Clerico

1999, 19(2): 54-62.

[Abstract](1396) [PDF 361KB](137)

Abstract:
Some basic principles on erosion and erosion test devices are introduced. Survey on sand erosion and erosion mechanisms of composites is summarized. Factors influencing erosion rate and protective coating effects are discussed.

1999 Vol. 19, No. 2