航空材料学报

Features and effect factors of directional coarsening for γ′-phase during creep of single crystal nickel-base superalloys

TIAN Sugui, ZHANG Jinghua, YANG Hongcai, XU Yongbo, HU Zhuangqi

2000, 20(2): 1-7.

[Abstract](1348) [PDF 1136KB](246)

Abstract:
The microstructures of [001] single crystal nickel-base superalloys under the constant loading tensile creep were observed by means of SEM, and the chemical composition of γ and γ′phases were analyzed by EDAX in order to investigate the features and effect factors of the directional coarsening of γ′phase. Results showed that the various features display at different locations of the sample. Due to the difference of the stress and temperature fields, the γ′rafts near the fracture surface possessed a twisted feature and coarsened remarkably, which became less pronounced with the increase of the distance far from the fracture. The element W of the higher concentration in alloy 2, having the smaller diffusivity and partitioning ratio between the γ′/γ phases, may obstruct the diffusion of the other elements in the diffusion field of γ′phase directional coarsening, which reduced the γ′rafting rate in alloy 2.

Origin of transformation hysteresis expansion by deformation of shape memory alloys

ZHAO Xinqing, WANG Ermin, ZHAO Weibiao, ZHAO Zhenye, Han Yafang

2000, 20(2): 8-14,20.

[Abstract](1502) [PDF 300KB](255)

Abstract:
Recent experimental investigations have demonstrated that the pre deformation of shape memory alloys results in martensite stabilization opposing reverse transformation, hence leading to the expansion of transformation hysteresis. Here a kinetic study has been made in order to determine the relationship between the relaxation of elastic energy and the hysteresis expansion by pre-deformation of shape memory alloys. It is indicated that the relaxation of elastic energy stored during the forward martensitic transformation is responsible for the expansion of transformation hysteresis, which is in good agreement with experimental results associated with the hysteresis enlargement by deformation of NiTi, NiTi-based and CuAlNi shape memory alloys.

A simulation of rapid crack propagation using a modified B-E model

GE Dongyun, LIU Yuanyong

2000, 20(2): 15-20.

[Abstract](1342) [PDF 254KB](177)

Abstract:
The double parameter model simulating the rapid crack propagation is proved on the basis of the damage mechanics and the sudden damage model. In this model, the damage ratio is considered when the rapid crack propagation was simulated by finite element method. Using this model and the damage when the material is destroyed, the crack propagation rate can be obtained by FEM without the crack rate. And the result, gotten by the FEM is very close to the result gotten by the experiment. It is showed that this method can be used to simulate the crack propagation.

Study of effect of boron content on solidification process of IC6 alloys

WANG Xiaoping, ZHENG Yunrong, XIAO Chengbo, WANG Beilei, HAN Yafang

2000, 20(2): 21-27.

[Abstract](1326) [PDF 328KB](223)

Abstract:
Solidification behaviors of four IC6 alloys of different boron content (0B,0.02B,0.04B,0.07B,wt%) were studied using isothermal solidification method, the volume percent of solid and liquid of four alloys at different temperatures in the range between solidus and liquidus was measured and the effects of boron content on the solidification processes and castability of IC6 alloys were determined.The results show that there is no obviously effect of boron content on the liquidus and the precipitation of secondary γ′phase of IC6 alloys, but the addition of boron will lower the solidus significantly (thus widen the range between solidus and liquidus) and will promote the formation of low melting point phase M3B2. Moreover, B addition would make liquidus of interdendrite zones inter linked each other in a very wide range of temperature. The best castability is achieved in alloy 4#(0.07wt%B) by theoretical prediction.

Structures and properties of electrodeposited tin nickel alloy after heat treatment

ZHANG Guozhu

2000, 20(2): 28-34.

[Abstract](1383) [PDF 432KB](440)

Abstract:
The structures of tin nickel alloy and transformation upon heating were investigated. The wearability and corrodibility of them were comparably tested.The results showed plated structures were mainly made up of metastable phases of αNi(M) and NiSn(M),with high tin content forming equilibrium phases of Ni3Sn4 and βSn;metastable phases were transformed to equilibrium phases with heating temperature.Because of homogenous equilibrium phases precipitation, electrodeposited alloy hardness increased; Single phase of NiSn(M) had a bit lower corrodibility than stainless steel in strong oxide medium and its wearability at 400℃ was better than quenching medium carbon steel.

A new artificial aging technique exploration of 2024 aluminum alloy

TIAN Xiuyun, LIU Yanhong, GAO Lizhu

2000, 20(2): 35-39.

[Abstract](1506) [PDF 193KB](422)

Abstract:
In order to reduce the natural aging time of 2024 aluminum alloy, a new artificial aging technique of 2024 which aging time is shorter than that of the natural aging technique, based on the hardness and conductivity test and aging principle analysis, was proposed in this paper. The aging temperature of the new aging technique is 45±5.5℃, and the aging time is 12 hours. The aircraft staying time for structural repair will be greatly decreased by this new artificial aging technique.

Analysis on inner defects in TiAl based alloy exhaust valve during the centrifugal foundry process in permanent mold

SHENG Wenbin, GUO Jingjie, SU Yanqing, DING Hongsheng, JIA Jun

2000, 20(2): 40-45.

[Abstract](1481) [PDF 237KB](290)

Abstract:
The filling rules of TiAl based alloy melt in centrifugal field has been concluded basing on the mathematical model. Results show that centrifugal field has an important influence on the filling process and melt fills the mould with variational cross-section and inclined angle. Cross-section area decreases and inclined angle increases respectively when filling length increases, and the change becomes more obviously near the entrance. In addition, the forming reasons of entrapping poles and prejudicial shrinkage existing in the TiAl based alloy valves poured in permanent mould during the centrifugal casting process have been discussed.

A smoke generator for use in fluid flow visualization in CVI reactors

XIAO Peng, XU Yongdong, ZHANG Litong, CHENG Laifei

2000, 20(2): 46-48,54.

[Abstract](1397) [PDF 169KB](235)

Abstract:
The effect of fluid flow in the CVI reactors on the deposition velocity and quality is very important. The visualization of perplexing and invisual fluid flow phenomenon in simulation-CVI reactor can be realized using the smoke generator based on forming TiO2 by reaction between TiCl4 and H2O. The smoke generation system fulfills these requirements, adjustable rate and density, long-time visualization of highly turbulent flow and uniformity of smoke while preserving simplicity of construction and operation. The flow field photographs demonstrate the effectiveness of the smoke generator, and the color, density and quantity of the smoke are very good for application to flow visualization studies for CVI reactors.

Tension control system in equipment of preimpregnated material manufacture

GAO Dianbin, JIANG Xiuming, YANG Gongyuan

2000, 20(2): 49-54.

[Abstract](1397) [PDF 443KB](177)

Abstract:
This paper deals with the processing principle of the tension control system, the constructing of mathematical models, and the implementing of control measures,while fibre bobbins open rolling and close rolling in the process of preparation of preimpregnated materials. These are all practiced and verified in the equipment for preparing preimpregnated materials, and it shows good results.During the process of fibre pick up, the new product “ratio electromagnet-mechanically restraining device (REMRD)” adjusts and controls the reel tension, so plays a critical role in keeping the fibre roving tension constant. The basic theory of REMRD is described in the article. In the course of prepreg take-up, the tri-roller-swinging arm-compensator is used, companied by linear velocity follower control and rolling-up-transmission compensator control, to attain prepreg draw-off roller’s and take-up roller’s immediate following ability and tension stability.

Damage characterization and failure analysis in fiber reinforced composites

XI Niansheng, YU Zhicheng, TAO Chunhu

2000, 20(2): 55-63.

[Abstract](5124) [PDF 348KB](1501)

Abstract:
The basic failure modes in unidirectional composite laminates have been given and the damage characteristics in multi directional composite laminates have been summarized. In composite laminates there are four basic failure modes: matrix cracking, delamination, fiber breakage and debonding. Although numerous and complicated failure modes can be combined from the four basic failure modes mentioned above, all the failures in composite laminates can be divided into two kinds:"fiber dominated modes" and "matrix dominated modes". The failure analysis methods for composite laminates have been also discussed in this paper. At present, the knowledge of fractography of composite materials is growing and paid much attention.

2000 Vol. 20, No. 2