航空材料学报

The design, casting of an experimental Al-Zr-B alloy and its deformation characteristics

LI Yong-xia, ZHOU Tie-tao, ZHANG Yong-gang, CHEN Chang-qi

2001, 21(4): 1-4.

[Abstract](1485) [PDF 562KB](226)

Abstract:
To study the formation mechanism of ultra-fine grain microstructure in the process of equal channel angular pressing, we have designed and cast Al-0.27wt%Zr-0.064wt%B alloy specially. In this alloy, there is a large amount of fine B2Zr compound on its grain boundary, while there is little B2Zr can be seen in its grain. Annealing experiments after room-temperature-rolling and forging respectively show that B2Zr compound is highly stable, and doesn't move together with the re-crystallized grain boundary. Conclusions can be drawn that Al-0.27wt%Zr-0.064wt% B alloy can be used for researching the grain deforming process and fining mechanism in the intense plastic deformation processing.

Effects of pouring temperature and refiners on microstructures of superalloy K4169

XIONG Yu-hua, YANG Ai-min, LI Pei-jie, LIU Lin

2001, 21(4): 5-8.

[Abstract](1582) [PDF 568KB](225)

Abstract:
In the present study, the effects of pouring temperature and refiners on dendrite structures, interdendritic segregation, precipitates, inclusion and microporosity of cast superalloy K4169 were investigated. It is found that the higher the pouring temperature, the greater the length of the average primary dendrite axes (laxes) and the secondary dendrite arm spacing (SDAS). At the same pouring temperature, laxes was shortened with the addition of refiner. However, SDAS kept almost unchanged. Additionally, the morphology of grains was transformed from dendrite in conventionally cast castings to granulation in fine-grained castings and the segregation ratios of main elements were alleviated with the decrease of grain size, which are beneficial for the improvement in mechanical properties. The size, amount and morphologies of MC-type carbides and Laves phase had no remarkable change after grain refinement.Moreover, it is also found that trace addition of refiner to the melt did not bring in inclusion and change the phase constitution of the alloy. The amount of microporosity in samples with the addition of refiner can be greatly decreased.

Effect of heat treatment on microstructure and mechanical properties of high strength steel 25CrNiWVA

WANG Mao-qiu, DONG Han, HUI Wei-jun, ZHAO Su-wu

2001, 21(4): 9-14,17.

[Abstract](1461) [PDF 1563KB](404)

Abstract:
High strength steel 25CrNiWVA was thermally treated at different quenching and tempering temperatures. The results show that when 900～940℃quenched and 340℃ tempered, steel 25CrNiWVA was composed of fine martensitic microstructure and had superior mechanical properties as follows: σb≥1500MPa, σ0.2≥1300MPa, δ5≥12%, ψ≥60%, Aku≥50J. Steel 25-CrNi-WVA can meet with the requirement of high strength and high toughness of aerospace components due to its high resistance to tempering softening.

The magnetic properties mechanism study of Ho₂Co_17-xSi_x intermetallic compounds

LUO Guang-sheng, GUO Shun

2001, 21(4): 14-17.

[Abstract](1441) [PDF 177KB](211)

Abstract:
Effects of substituting small amounts of Si for Co on the structure and magnetic properties of Ho2Co17 compounds were studied by means of X-ray diffraction and magnetic measurements. All samples are of single phase with the Th2Ni17-type structure. The substitution of Si for Co leads to an approximately linear decreasing in the unit cell volume. The analysis indicates that the saturation magnetization and Curie temperature of Ho2Co17-xSix are-found to decrease as x increasing from 0 to 3. From theromagnetization curves measurement, it is assumed that a spin reorientation occurs from based plane to c-axis for 0.5x3.0 in the Ho2Co17-xSix compounds. Tsr, the temperature of spin reorientation, exists decreasing firstly, and then increasing with increasing of Si concentration, as there is a lowest point at x=2.5.

Study on the chemical compatibility of O-SiC_P/Fe

TANG Wen-ming, ZHENG Zhi-xiang, DING Hou-fu, JIN Zhi-hao

2001, 21(4): 18-22.

[Abstract](1405) [PDF 804KB](218)

Abstract:
The dense oxide film of about 0.6μm is formed on the surface of the SiC particles by passive oxidation, when the SiC particles were treated at 1200℃ for 10h in a stationary air ambient. The film was determined to be βcristobalite using XRD. After treated at 1150℃ for 1h in a hydrogen ambient, the interfacial reaction of 3SiCP/Fe produces Fe3Si and graphite grains to form the reaction zone in situ, and Fe3C at the crystal boundary of the metal matrix to construct the flake pearlite. The interfacial reaction of 10SiCP/Fe is more severe due to increasing the reinforcement. It results in that the SiC particles are consumed completely, and the reaction zone of Fe3Si containing the random graphite precipitates forms in situ. The metal matrix of the composite is brittle due to its high Si content. The oxidation film on the oxidized SiC particles can inhibit the reaction between SiC and Fe in 3O-SiCP/Fe or 10O-SiCP/Fe in terms of isolating SiC and Fe and inhibiting the interdiffusion of the Si, C and Fe atoms, which improves the interface chemical compatibility of OSiCP/Fe.

Investigation on the microstructure of SiC_p/Al₂O₃-Al composites synthesized by oxidative infiltration of Al melt

CUI Yan, SONG Ying-gang, ZHANG Shao-qing

2001, 21(4): 23-27.

[Abstract](1439) [PDF 679KB](285)

Abstract:
SiCp/Al2O3-Al composites were synthesized by oxidative infiltration of Al melt at low cost. The microstructures of the synthesized composites were investigated using X-ray photoelectron spectrometer, optical microscopy, transmission electron microscopy, X-ray diffraction. The key controlling factor and controlling rule on microstructures of the composites were analyzed. The result indicates that the amount of co-continuous Al2O3 and Al (Si) phases in composites can be tailored by properly choosing SiC particle size. In the synthesized SiCp/Al2O3-Al composites, no reaction product or impurity phase is observed at the interface between various phases or grains. The second nucleation and direct growth of Al2O3 at the surface of SiC particle frequently occurs, which in turn form the integral Al2O3-SiC ceramic skeleton with excellent physical metallurgy bond.

Preparation of C fiber reinforced alumina-mullite composite assisted by silica sol infiltration

CHEN Zhao-feng, ZHANG Li-tong, CHENG Lai-fei, XU Yong-dong, XIAO Peng

2001, 21(4): 28-32,37.

[Abstract](1462) [PDF 281KB](368)

Abstract:
3D C fiber preform reinforced alumina-mullite composite was manufactured. The materials was produced by precursor infiltration and pyrolysis and subsequently strengthened by silica sol infiltration route after coating the fiber preform with a 0.2μm thick carbon layer by chemical vapor infiltration. The composite was manufactured by infiltrating the preform with aluminium nitrate saturation sol, drying in an autoclave and subsequently heat treating at 950℃ and pyrolysis of the aluminium nitrate. After ten cycles, the specimen was polished to remove the alumina matrix on the surface of the specimen, which generate "bottle effect" and prevent aluminium nitrate saturation sol from entering into the specimen. After another four cycles like above, the specimen was heated to 1150℃ and 1300℃ in Ar to transfer the amorphous alumina to γ-Al2O3 and α-Al2O3. The pore size and distribution in the specimens heat-treated in different temperature was determined. The specimen, which was heat-treated at 1150℃, was dipped in silica sol in vacuum condition, then drying in 100℃. Then the specimen containing silica was heated to 1400℃ for 2h in Ar to impel the reaction between γ-Al2O3 and silica to create mullite. The stick-like mullite was observed which make for the strength of the composite. At the same time, the micro-cracks were observed on the unpolished cross-section matrix of composite, which was defected around the C fiber and doesn't damage the C fiber. It indicated the C interface was a weak interphase between the C fiber and alumina matrix. The three-point flexural strength and the strain of the as-fabricated composite were 180MPa and 2.2%.

Fabrication of SiC matrix composites reinforced by carbon cloth using CSCVI method and microstructure

XIAO Peng, XU Yong-dong, HUANG Bai-yun

2001, 21(4): 33-37.

[Abstract](1389) [PDF 821KB](232)

Abstract:
In order to increase the densification rate of C/SiC composites fabricated by CVI process, a continuous synchronous chemical vapor infiltration (CSCVI) technologic route for fabrication of C/SiC composites reinforced by carbon cloth was brought forward. C/SiC composites were fabricated, and their microstructure were observed and analyzed. The results indicate that, in CSCVI process, deposition rate of SiC matrix is faster, therefore the densification degree is greater and SiC solid is more uniform. At the same time, that deposition rate of SiC is controlled only by the deposition temperature and the MTS (CH3SiCl3) flux enhances the maneuverability of CSCVI process, and enlarges the variety range of processing parameters.

Effect of cold plasma treatment on the interfacial properties of carbon fiber braid/epoxy composites

QIN Wei, ZHANG Zhi-qian, HUANG Yu-dong, YE Yang, LIU Ai-xue, LI Hai-chen, Wang Biao

2001, 21(4): 38-41.

[Abstract](1500) [PDF 196KB](346)

Abstract:
The cold plasma technology is used to treat the surface of carbon fiber braid/epoxy. Based on the analysis of the surface composition of carbon fiber by XRD, the effects of cold plasma treatment on the properties of carbon fiber braid/epoxy composite are examined in terms of interlaminar shear strength and impregnation. Results show that cold plasma treatment improves the surface polarity and impregnation of carbon fiber, which increases the bonding property of carbon fiber braid/epoxy composites, and therefore improves interfacial properties of composites.

Study on speciality of anti-circular cone impact for Kevlar composites

WEI Bo-rong, JIANG Hai-bin, JIN Bing, LI Ming-qi

2001, 21(4): 42-45.

[Abstract](1330) [PDF 550KB](195)

Abstract:
In order to study the factors which affect anti-penetrate capability of thin Kevlar composites, the composites have been impacted by circular cone (cone angle: 60°) in definite impact speed. The results show that the mostly factors which affect anti-penetrate capability of the composites are characteristic of fiber fabric,the areal densities, thickness and interface intensity of the composites.

Computational design for multi-layer absorber

ZHANG Tie-fu, CAO Mao-sheng, YUAN Jie, PENG Zhi-hui, XIAO Gang, NING Dan, WANG Biao, ZHU Jing

2001, 21(4): 46-49,62.

[Abstract](1465) [PDF 224KB](439)

Abstract:
The calculation and design theory for multi-layer absorber is present. Specially, the results of calculation and design for single, double and multiple layers absorber are given. The energy attenuation and frequency bands of absorber toward the incident wave are predicted. In order to prove the design result mentioned above, a serial of experiments were operated by means of surface-coating techniques. Technique index, such as frequency bands, absorption peak location and energy attenuation, were also measured. The results of calculation are consistent with experiments on the whole.

Recent progress in PM γ-TiAl base alloy

LIU Yong, HUANG Bai-yun, ZHOU Ke-chao, HE Yue-hui, TANG Zhi-hong

2001, 21(4): 50-55.

[Abstract](1636) [PDF 1210KB](440)

Abstract:
TiAl base alloys have been considered as new high temperature structural materials for promising application in aerospace and high-performance engines. The properties, applications of γ-TiAl base alloys have been reviewed, and the progress in fundamental aspects of these materials has been outlined. Subsequently, the process and mechanical properties of PM γ-TiAl base alloys have been introduced. Finally, the advantages and development of PM process in preparing and near net shaping of γ-TiAl base alloys have been described by citing the fabrication of γ-TiAl base alloy valves and plates.

The experimental principle of Nano Indenter II and its applications

LIN Zhi, WANG Yan-li, LIN Jun-pin, CHEN Guo-liang

2001, 21(4): 56-62.

[Abstract](1486) [PDF 299KB](402)

Abstract:
As a new system for determining the mechanical properties of materials, Nano Indenter II mechanical properties microprobe (MPM) is introduced.The MPM is an indentation system controlled by computer. Its displacement accuracy of indenter can reach +/-0.04nm. Therefore, it can be used to study mechanical properties of materials in micro-scale. Because of its high accuracy of indenter displacement, it has the advantage of studying thin foil materials, ion implanted materials and surface modified materials. The major difference between the MPM and the conventional hardness tester is that the MPM can record continually the load-displacement data and then figure out the hardness and elastic modulus from the data. In this way the measurement of indent area is not needed. Therefore, the error of the measurement is avoided. The experimental principle of the MPM and the calculations for hardness and elastic modulus are stated.Its applications in materials science are demonstrated.

2001 Vol. 21, No. 4