航空材料学报

Observation of the Microstructure in an Ultra-high Strength and High Toughness Stainless Steel

ZHAO Zhenye, LI Chunzhi, LI Zhi, LIU Tianqi, MA Xinwen, SUN Jiguang

2005, 25(2): 1-5.

[Abstract](1388) [PDF 1070KB](247)

Abstract:
The ultrafine microstructure in an ultra-high strength and high toughness stainless steel was observed by TEM. The results showed that martensitic laths (M) were broken to pieces by the small martensitic lath cluster (Mn) which was formed during quenching. Martensitic laths and martensitic packets were broken also to pieces by the reversed austenite. The orientation between matrix and revered austenie met the K-S relationship[011]A//[111]M,(111)A//(110)M. Both the ultrafine martensitic lath resulted from breaking and transformation plasticity induced by reverse austenite were the important mechanisms of strength-toughen in the experimental steel.

The Microstructure and Oxidation Behavior for NiAl-30.9Cr-3Mo-0.1Dy Alloy at High Temperature

ZHANG Guangye, GUO Jianting, YE Hengqiang

2005, 25(2): 6-11.

[Abstract](1496) [PDF 552KB](241)

Abstract:
The microstructure and isothermal oxidation behavior of NiAl-30.9Cr-3Mo-0.1Dy alloy at temperature range of 1300~1500K in air atmosphere was investigated.The results revealed that the microstructure of tested alloy was fined by doping Dy, which caused the more quantity of grain cells and the finer spacing between Cr(Mo) fibers as well as smaller Cr(Mo) rods. The strengthening phase Cr(Mo) and matrix NiAl phase reciprocally precipitated in each other, which was beneficial to form the duplex-layered oxidation scale and improve the anti-oxidation properties at high temperature. The Kinetics of isothermal oxidation of NiAl-30.9Cr-3Mo-0.1Dy alloy at 1500K obeyed parabolic rule, and followed quintic equation at 1300K, and the others obeyed the cubic relation. The oxidation rate constants decreased with the decreasing temperature and elongation of exposure time. The activation energy of isothermal oxidation was calculated about 205kJ/mol.

Study on the Flow Stress of 7A60 Ultra High Strength Aluminum Alloy

YANG Hongtao, LU Zheng, GU Jialin

2005, 25(2): 12-15.

[Abstract](1381) [PDF 567KB](310)

Abstract:
The flow stress of 7A60 ultra high strength aluminum alloy was studied by isothermal compress test at constant strain rate. The results showed that the flow stress of this alloy reduced with increasing deform temperature and increased with increasing strain rate. Based on experimental data analysis, it was concluded that the dominant factors affecting flowing stress were the strain rate and deforming temperature, and the two parameters were also important for deforming process control.

Research on Low Cycle Fatigue Properties of TA15 Titanium Alloy

JIN Lei, SU Bin

2005, 25(2): 16-19.

[Abstract](1267) [PDF 1086KB](232)

Abstract:
Low cycle fatigue properties of alloy TA15 was studied. After testing and analyzing the data of the LCF of the alloy TA15, parameters of median and probability (confidence γ=95%,probability of survival P=99.9%) were given. Strain-life and cyclic stress-strain curves were plotted. The results can be applied to design and life prediction of alloy TA15.

Study on Tearing Toughness of Laser-welded Joint for a 1420 Aluminum-lithium Alloy Sheet

ZHONG Fei, SHI Yaowu, LI Xiaoyan, GONG Shuili, CHEN Li

2005, 25(2): 20-25.

[Abstract](1334) [PDF 1453KB](269)

Abstract:
Tear test on Al-Li alloy 1420 and laser-welded joints was carried out. The test was based on the ASTM B 871-01, standard test method for tear testing of aluminum alloy products. Meanwhile, hardness distribution and microstructure of the alloy and welded joints were investigated. It was indicated from the tear test that energy at crack initiation was higher than that at crack propagation. Moreover, the energy at both crack initiation and propagation of base metal was higher than that of weld metal and heat affected zone. The energy at both crack initiation and propagation of base metal with L-T direction was higher than that with T-L direction. Fractography showed that there was long and deep tearing grooves on the fractography of the base metal, especially with the T-L direction. However, there was inter-granular or inter-subgranular brittle feature mainly on weld metal and heat affected zone. Transition from the higher toughness of the base metal to the lower toughness of the weld metal and heat affected zone was ascribed to the change of fracture model. The fracture model was changed from ductile void coalescence fracture to brittle inter-granular fracture.

Cracking Sensitivity on Laser Cladding Inconel 738 on Directionally Solidified Ni-base Superalloy

SUN Hongqing, ZHONG Minlin, LIU Wenjin, HE Jinjiang, LI Xiaoli, ZHU Xiaofeng

2005, 25(2): 26-31.

[Abstract](1526) [PDF 2419KB](442)

Abstract:
The cracking sensitivity of laser cladding Inconel 738 alloys on directionally solidified Ni-base superalloy substrate for the purpose of strengthening and repairing the directionally solidified gas turbine blades was studied. The results indicated that laser cladding of Inconel 738 on directionally solidified Ni-base superalloy substrate was very sensitive to crack. The cracks were mostly the thermal cracks which originated in the grain boundary in the heat affected substrate. The cracks went through the interface between the directionally solidified substrate and the cladding layers, and then developed into multi-deposited cladding layers. Cracks also appeared inside the multi-deposited cladding layers, developing along the grain boundaries directly. The low melting point eutectics between the grain boundaries of directionally solidified Ni-base superalloy substrate were the main sources of the thermal cracks. Strict control of the heat input during laser cladding could dramatically decrease the cracking tendency. Directionally solidified layers were deposited by laser cladding on directionally solidified substrate with good shaping and free of cracks by optimizing the cladding technique and laser parameters.

Surface Modification of 2Cr13 Steel by Plasma Immersion Ion Implantation Combined with Ion Beam Enhanced Deposition

LIU Hongxi, TANG Baoyin, WANG Langping, WANG Xiaofeng, WANG Yuhang, YU Yonghao

2005, 25(2): 32-37.

[Abstract](1337) [PDF 333KB](322)

Abstract:
Surface modification of 2Cr13 stainless steel was carried out using plasma immersion ion implantation (PIII) combined with ion beam enhanced deposition (IBED) technique. The chemical composition, concentration-depth profile of various elements were characterized by Auger Electron Spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The microhardness, corrosion resistance, friction and wear behavior of the samples were evaluated. The results show that, titanium nitrogen (TiN) and chromium nitrogen (CrN) phase are existed in the surface layer. Compared with the substrate, the microhardness of the treated samples are enhanced significantly, the maximum is increased by 80.4%; friction coefficient is reduced to 0.2~0.3; wear track width and corrosion current density are decreased by 4 times and 26 times, respectively. Corrosion potential is increased by 5 times. The wear and corrosion properties are improved significantly by PIII-IBED techniques.

Nanoindentation Mechanical Properties of Al₂O₃/3wt% TiO₂ Detonation Sprayed Coatings

ZHAI Changsheng, YANG Li, WANG Jun, ZHAO Wenming, SUN Baode

2005, 25(2): 38-43.

[Abstract](1413) [PDF 1137KB](268)

Abstract:
Both the microstructures of the detonation sprayed Al2O3/3wt%TiO2 coating and the indentation load-displacement behavior of the coating tested with a Berkovich indenter were investigated. The coatings exihibited apparently anisotropic nanoindentation mechanical behaviors and dispersibility. Compared to the cross-section, the surface of the coatings had better ability to resist applied load and better elastic recovery after unloading. The mean hardness of the surface and cross-section of the coating were 10.3GPa and 2.9GPa, respectively. While mean Young's modulus of the surface and cross-section of the coating were 170.7GPa and 234.5GPa, respectively. The anisotropic nanoindentation mechanical properties were mainly due to anisotropic microstructures of the detonation sprayed coating. Other than the surface, the cross-section structure corresponded to splat interface and many cracks parallel to the substrate. The cross-section had more pores; bigger pore size and a more unhomogeneneous distribution than the surface.

Preparation of Epoxy/Nano-SiO₂ Hybrid Sizing and Effects on the Properties of Carbon Fiber Composites

ZHANG Zhiqian, ZHANG Chunhong, CAO Hailin, BAI Yongping

2005, 25(2): 44-48.

[Abstract](1428) [PDF 718KB](344)

Abstract:
Epoxy/nano-SiO2 hybrid sizing for carbon fiber surface was prepared through sol-gel reaction, the structure and properties of the sizing films were analyzed, and the effects of the sizing on the properties of composites were also investigated. First, epoxy resin was grafted by γ-isocyanatopropyltriethoxysilane to modify in situ nano-SiO2 precursors, then epoxy/nano-SiO2 hybrid sizing was made by using the modified nano-SiO2 precursors. FT-IR, AFM and Thermoanalysis Instrument were employed to analyze the structure of modification in situ of nano-SiO2 precursors, the micro-morphology and thermal properties of the sizing films. The results indicated that epoxy/nano-SiO2 hybrid sizing was prepared successfully, SiO2 particles dispersed in the hybrid sizing film homogeneously with nanoscale, the thermal properties of the hybrid sizing film were improved because of the introduction of nano-SiO2. Carbon fibers were modified by the epoxy/nano-SiO2 hybrid sizing to confirm that the hybrid sizing increased both ILSS and impact properties of the composites through the investigation of mechanical properties.

The Analysis of Friction and Wear Performance of C/C-SiC Composites

ZHANG Yanni, XU Yongdong, LOU Jianjun, ZHANG Litong, CHENG Laifei, CHEN Zhiju

2005, 25(2): 49-54.

[Abstract](1413) [PDF 786KB](625)

Abstract:
The carbon/silicon carbide composites (C/C-SiC) were prepared by chemical vapor infiltration (CVI) method, and the braking disks with different density and component content were finally obtained. The friction and wear performance of the C/C-SiC composites were investigated. It was obtained that, the coefficient of friction was 0.23, the friction stability was 0.43, the liner wear rate was 9.3μmcycle-1, and the weight wear rate was 2.6mgcycle-1.The friction coefficient and stability were significantly improved by about 70% and the fluctuation range of friction coefficient decreased with increasing the material density from 1.6g/cm3 to (2.2 g/cm3) and increasing the carbon content from 35% to 55%, by contrast, the result was opposite with increasing SiC content. The C/C-SiC composites were not sensitive to the braking number, which demonstrated a good stability of friction. The continuous braking test of C/C-SiC disks suggested nearly constant curves of the coefficient of friction, which demonstrated the good stability of this friction material against fading. The wear quality of friction surfaces for C/C-SiC disks was analyzed finally, and the result indicated that the wear quality was in the range of the aviation standard.

Introduction Process of SiC Fillers into Carbon Fiber Preform by Vacuum Infiltration

ZHENG Wenwei, CHEN Zhaohui, YAO Juntao

2005, 25(2): 55-58.

[Abstract](1390) [PDF 414KB](288)

Abstract:
SiC fillers were introduced into carbon fiber preform by vacuum infiltration in order to shorten the fabrication cycles of three-dimensional braided carbon fiber preform (3D-B Cf) reinforced SiC ceramic matrix composites by precursor-infiltration-pyrolysis (PIP).Effects of diameter of SiC fillers and ratio of SiC/EtOH on volume fraction of introduced SiC fillers in carbon fiber preform were investigated. The results showed that the volume fraction (about 10%) of SiC fillers could be achieved by vacuum infiltration when the diameter of SiC fillers was 0.4μm and the ratio of SiC/EtOH was 1:1 and 1:2, which could shorten the fabrication cycles of Cf/SiC composites via PIP, and enhance the mechanical properties of the composites, within same times of infiltration and pyrolysis.

Surfacial Modification for Carbon Fiber and Its Effect on the Mechanical Property of CF/PAA

LIU li, FU Hongjun, HUANG Yudong, YANG Ming

2005, 25(2): 59-62.

[Abstract](1386) [PDF 692KB](383)

Abstract:
Polyarylacetylene (PAA) is a new kind of thermal protection material, however there are some disadvantages due to its non-polar characteristics when it is used as the matrix resin, such as inertia structure make it hard to impregnate carbon fiber. So the grafting method after anodic oxidation was used to treat carbon fiber so as to investigate the suitable interface for the non-polar matrix. Results show that the polar functional groups on the surface of carbon fiber increase after anodic oxidation treating so as to enhance the reaction of carbon fiber with the acrylic acid and import double-bond which is similar to the structure of PAA. The double-bond imported on the surface of CF will be benefit to improve the interface adhesion of CF/PAA composites and increase the mechanical properties of CF/PAA composites.

2005 Vol. 25, No. 2