航空材料学报

Structure and properties of Nano PA6、PP particles/SBS composite

AO Ning-jian

2001, 21(3): 1-4.

[Abstract](1387) [PDF 191KB](271)

Abstract:
Nano polyamide6(PA6) and polypropylene(PP) particles were prepared by using the pan type milling equipment and were mixed with styrene-butadiene-styrene triblock copolymer(SBS) to produce PA6/PP/SBS composite. The interface structures of the composites were studied by TEM and the mechanical properties of the composites were determined. The nano PA6 and PP particles prepared by pan-milling show a good Compatibility and interphase with SBS When the composites contain 4%-10%(wt) PA6 and PP particles, the mechanical properties of the composites enhance greatly. With the change of processing temperature, the nano PA6 and PP particles melt to form chain structure and the phase structures change obviously. The performances of the composites were promoted further.

Study of microstructure, properties and texture of Al-Cu-Li alloys

YANG Shou-jie, LU Zheng, SU Bin, DAI Sheng-long, YAN Ming-gao

2001, 21(3): 5-8.

[Abstract](1391) [PDF 419KB](182)

Abstract:
The microstructure, mechanical properties and texture of Al Li-Cu-(Mn)-(Zr) alloys in T8 state were investigated. It was found that they are quite different from their compositions. The processing(T8) has different effects on the alloys, since the elements Mn and Zr playing an important role on recrystallization. It may be concluded that there is a correspondence relationship between the crystalline texture and the mechanical anisotropy. The experimental results also imply that the ductility anisotropy is more serious than that of the strength, and an important method for controlling crystalline texture and mechanical anisotropy is utilizing the element Mn.

Effect of heat-treatment on microstructures of the Nb-10Si alloy

QU Shi-yu, WANG Rong-ming, HAN Ya-fang

2001, 21(3): 9-12.

[Abstract](1481) [PDF 236KB](267)

Abstract:
The Nb-10Si (at.%) alloy has been fabricated using the vacuum arc-melting method and heat-treated at 1850℃ and 1550℃ temperature for 2~100 hours in Ar atmosphere. The effect of heat-treatment on microstructures of the alloy has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with X-ray energy dispersive spectrum (EDS) and transmission electron microscopy (TEM). The results show that 1550℃/100h is the optimum heat-treatment to acquire the equilibrium Nb+Nb5Si3 two-phase microstructure. The microstructure of Nb-10Si alloy in the as-cast condition consists of the continuous Nb3Si matrix and the dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state In the case of 1850℃/2h heat-treatment the Nb particles coarsen evidently, however, in the case of heat-treatment at 1550℃ for 25 to 100 hours the growth of Nb particles is unconspicuous. After heat-treatment at 1550℃, Nb3Si phase transforms into the equilibrium Nb5Si3 and Nb phase with increase of heat-treatment time gradually TEM observations reveal that there are certain orientation relationships between the niobium silicide and Nb phase.

New constitutuve relationship for Ti-6Al-4V alloy

NIE Lei, LI Fu-guo, FANG Yong

2001, 21(3): 13-18.

[Abstract](1412) [PDF 666KB](413)

Abstract:
Through hot compressive simulation experiments, the numerical relationships among forging parameters (deformation rate, deformation temperature, deformation degree), flow stress, recrystallized structure and property are studied systematically, meanwhile, the regularities of the influences that forging parameters and microstructure evolution imposing on material property are discussed qualitatively, and a new constitutive relationship, which can reflect these effects well, is proposed with mathematic statistics analysis, therefore, a scientific basis is provided for both numerical simulation of forging process of Ti-6Al-4V alloy and rational choice and control of forging parameters.

Application of a foam RAM in the radome

HE Shan, XIONG Ke-min

2001, 21(3): 19-23.

[Abstract](1520) [PDF 596KB](452)

Abstract:
Based on the theory of microwave transmission lines, a broadband foam radar absorbing material (RAM) with multilayer structure has been developed. The RAM has a lower reflectivity (below-15dB) in the frequency range from 8 to 18GHz The mechanical and environmental experiments were carried out The results of simulating and flying tests show that the RAM can reduce interference to the antenna, caused by the metallic parts.

Investigation on grain structure refinement of superalloy K4169

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

2001, 21(3): 24-28.

[Abstract](1424) [PDF 244KB](321)

Abstract:
Grain structures of cast superalloy K4169 were investigated at different pouring temperature and with the addition of mixed refiner. It is found that lowering pouring temperature can lead to grain refinement of matrix and improve the proportion of equiaxed grains at traverse cross-section. While adding mixed refiner and with the melt homogeneous treatment, at a conventional pouring temperature of 1400℃ and 1420℃, the average equiaxed grains could be refined to the order of ASTM 1.7 and ASTM M10.5, respectively In addition, the proportion of equiaxed grains at traverse cross-section could be increased to 96% and 90%, respectively Furthermore, the mechanisms of grain refinement were proposed and the phenomenon that P was improved after grain refinement was analyzed

Microstructure of TC4/72Ag-28Cu joint and production mechanism of Ti-Cu compound at the interface

WU Ming-fang, JIANG Cheng-Yu, YU Zhi-shui, LIANG Chao

2001, 21(3): 29-32.

[Abstract](1417) [PDF 274KB](241)

Abstract:
The effect of brazing time on microstructre and morphology of joint TC4/72Ag-Cu/TC4 at 1103 K was studied.based on the experimental results,it has been found that for short holding time,eutectoid transfomation took place between Ti and Cu concentrated at the interface and the compound Ti2Cu was produced in the followed cooling stage,which limited the increase of tghe tensile strength of joints. With the increase of holding time,the joint growth mechanism of compound Ti2Cu at the interface was studied from the point of thermodynamics.

Effect of equal channel angular pressing on microstructure and mechanical proper ties of high pure aluminum

LI Yong-xia, ZHANG Yong-gang, CHEN Chang-qi

2001, 21(3): 33-38.

[Abstract](1492) [PDF 281KB](398)

Abstract:
Severe plastic deformation was exerted on high pure aluminum at room temperature through equal channel angular pressing (ECAP) technique, the grain refinement of high pure aluminum was realized by the combination pressing is, the size of sub-grains is smaller than 0.4μm, the hardness and yield stress increased remarkably. The analysis results show that the combination pressing can cause the using diffenent angel dies, which results in ultra-fine grain structures at relatively low strain in high pure aluminum. It tells a fact that the shear plane has an important effect on the grain refinement and the formation of high angle grain boundary during ECAP.

Precursor synthesis and mechanical properties of silicon oxynitride

ZHANG Jun-bao, WEN Guang-wu, JIA De-chang, LEI Ting-quan, ZHOU Yu

2001, 21(3): 39-42.

[Abstract](1351) [PDF 190KB](268)

Abstract:
Silicon oxynitride precursors with different nitrogen content were synthesized from hydrolysis and ammonolysis of SiC4 Pyrolyses of the precursors were completed from in-situ polymerization and inorganic conversion via amino group releasing. Silicon oxynitride ceramics were successfully fabricated by hot-pressing of resulted powders Analysis results indicated that crystallization temperature of silica was increased 150℃ by introduction of nitrogen, mechanical properties of silicon oxynitride were significant increased by proper crystallization Flexural strength and fracture toughness reached 156MPa and 1.8MPa·m1/2 for the material with 24.3 mol% nitrogen sintered at 1400℃, being 4.58 and 2.25 times of that of SiO2 matrix material respectively.

Low cycle fatigue behavior of DD6 single crystal

LI Ying, SU Bin, WU Xue-ren

2001, 21(3): 43-45.

[Abstract](1485) [PDF 142KB](334)

Abstract:
The low cycle fatigue tests on nickel base single crystal superalloy DD6 were conducted at 980℃ under total axial strain control Specimens having crystallographic orientations near, and were tested under fully reversed strain. The experimental result shows that the fatigue behavior depends on the crystallographic orientation and total strain amplitude. A model with hysteretic energy was established to predict the low cycle fatigue life.

Effect of mechanical surface treatments on fatigue properties of commercial purity titanium

ZHANG Jian-bin, MA Qin, JI Gen-shun, ZHOU Qi, WANG Jing-yi

2001, 21(3): 46-50.

[Abstract](1466) [PDF 284KB](361)

Abstract:
The fatigue strength of commercial purity titanium was variously improved by shot-peened (SP) or cold-rolled (CR). In an effort to determine the mechanisms, microstructures, compressive residual stress and surface roughness have been characterized, and the following results were obtained:1) At the microscopic level of TEM, both dislocations and deformation twins are observed:Odd and dispersed twins are formed in the CR,but piles up twins and deformation bands are observed in the SP After 106 cyclic deformations, twin twin interactions in the SP and twin-grain boundary interactions in the CR play an important role, respectively. 2) Surface residual stress has higher relaxation in the SP than in the CR condition during fatigue deformation, but the surface compressive residual stress has the same values after fatigue deformation. 3) Roughness resulting from SP is ten times of CR.

Meshless method for numerical simulation of crack propagation

LOU Lu-liang, ZENG Pan, NIE Lei

2001, 21(3): 51-56.

[Abstract](1552) [PDF 680KB](348)

Abstract:
Crack propagation is an important failure mechanism in aeronautical materials that requires accurate numerical model to capture stress singularity at the crack tip As a promising numerical simulation method, meshless computation has some outstanding advantages over the traditional finite element method (FEM) in treatment of arbitrary evolving discontinuity. Because of the independence of elements, the adaptive refinement can be easily achieved, which makes the crack-propogation analysis dramatically simplified. By introducing enriched basis and nodal refinement, the computational accuracy was improved. The continuous crack propagation was modelled as a series of linear crack-growth increment. At each increment the crack growth direction was determined based on the stress intensity factors. The key technique and the flowchart of the method were presented. The paper concludes with a sample calculation of oblique center-crack plate of Ti-6Al-4V alloy under uniaxial tensile load The predicted crack trajectory by meshless method is in good agreement with the experimental data.

Long-term stress analysis of single-lap weldbonded joint

YIN Yong, TU Shan, Tung

2001, 21(3): 57-62.

[Abstract](1361) [PDF 442KB](298)

Abstract:
Weldbonding is a new joining technique that combines the spot-welding with the adhesive-bonding method. It was adopted more and more in recent years because of its many advantages However, the researches on this new technology are few especially on the long-term stress and strength of the weldbonded structures. A three-dimensional viscoplastic finite element model of single-lap weldbonded joint was developed in this paper to investigate its stress redistribution Some advice on joint design and material choice were discussed.

2001 Vol. 21, No. 3