航空材料学报

Effects of Antimony on Microstructure and Properties of AE41 Magnesium Alloy

LIU Zi-li, PAN Qing-lin, CHEN Zhao-feng, TAO Jie

2005, 25(6): 1-4,10.

[Abstract](1659) [PDF 947KB](331)

Abstract:
Effects of antimony on microstructure and properties of AE41(Mg-4Al-1RE)magnesium alloy were investigated.Results indicate that antimony additions cause formation of dispersed particles in the alloy matrix,which is mainly RE2Sb,and a complex of RE2Sb and RESb when Sb content is high.When the Sb content increases,the size and amount of the branched intergranular Al11RE3 reduce, while the size and amount of dispersed RE-Sb particles increase,and the amount of discontinuous β phase on grain boundaries increases.Sb additions improves fluidity of the alloys.The tensile strength,elongation,hardness and impact toughness increase firstly with increasing Sb content,however,the mechanical properties reduce at the excessive Sb content.

Effects of Surface Defects on the Rolling Contact Fatigue Behaviors of Cr4Mo4V Steel

LI Jin-feng, ZHAO Hong-ping, SHI Hui-ji, FENG Xi-qiao

2005, 25(6): 5-10.

[Abstract](1816) [PDF 1401KB](237)

Abstract:
The effects of surface defects on the rolling contact fatigue behaviors of Cr4Mo4V steel were studied experimentally.Different sizes of dents were artificially introduced on the rolling trajectories of the specimens by the Rockwell and Vickers Hardness Testers.The failure process from the initiation and propagation of the defect-induced cracks and spalling near the dents was observed by SEM.It was found that surface dents might influence greatly the rolling contact fatigue behaviors of Cr4Mo4V steel,and that the fatigue damage induced by Rockwell dents was more serious than that by Vickers dents.An obvious size effect of defect evolution was also observed:a bigger dent was much easier to crack than a smaller one.

An Investigation of Small-crack and Long-crack Propagation Behavior in Titanium Alloy TC4 and Aluminum Alloy 7475-T7351

DING Chuan-fu, LIU Jian-zhong, WU Xue-ren

2005, 25(6): 11-17.

[Abstract](1780) [PDF 1289KB](276)

Abstract:
Small-crack and long-crack growth behavior was investigated in titanium alloy TC4 and aluminum alloy 7475-T7351 under three-stress ratio loading(R=0.5,0 and -1).Single edge notch tension(SENT) specimens were used in small-crack tests.Small cracks were initiated naturally at root surface of the semicircular edge notch and were monitored by the plastic replication technique.Experimental results showed that significant small-crack effect were not found in the TC4 alloy for all constant-amplitude loadings.This was correlated with a pronounced deflected crack path and branched crack at early stage of small-crack growth. Classical small-crack effect was observed in the 7475-T7351 alloy at the low stress ratio(R≤0) and lower ΔK(≤4~6MPa√m).For the aluminum alloy,surface cracks initiated at inclusion-particle clusters and voids at notch surface.SEM observation found that influence of inclusion-particle clusters on crack initiation was more obvious than a single in inclusion-particle.

Experimental Study and Numerical Simulation of Creep Damage of Small Punch Creep Test Specimen of SS304 Stainless Steel

LING Xiang, ZHENG Yang-yan, YOU Ying-jun, CHEN Yu-xin

2005, 25(6): 18-23.

[Abstract](1804) [PDF 1024KB](439)

Abstract:
The finite element model was established based on the small punch creep test of SS304 steel specimen in the condition of constant temperature and different loads.The variation of central deflection and creep strain with time and the evolution of creep damage subjected to constant forces were analyzed using FEM incorprated with modified K-R creep damage constitutive equations.The test results were in agreement with those of numerical simulation and three different stages appeared in the curve of central creep,which was quite similar with conventional creep tests.The results also showed that the creep damage at the central part was high,and localization of damage was obvious.Initial failure occurred at the bottom surface,0.8mm away from the center which agreed well with the observation from the test.

Microstructures of SiC/Ti Alloy Joints Brazed with (Ag-Cu-Ti)-SiC_p Interlayer

LIN Guo-biao, HUANG Ji-hua, MAO Jian-ying, LI Hai-gang

2005, 25(6): 24-28.

[Abstract](1969) [PDF 834KB](372)

Abstract:
By using the mixed powder of alloying Ag-Cu-Ti and 15vol%～30vol% SiC powders as vacuum non-pressure brazing material,the joints of SiC ceramics/Ti-alloy with SiC reinforced Ag-Cu-Ti interlayer were acquired.Experimental results demonstrate that the SiC particles evidently reduce the thermal stress of the joints;the Ti in the interlayer react with SiC particles and SiC ceramics body,forming Ti3SiC2 reactive layers and Ti-Si compound distributing in Ag-Cu-Ti alloy.With the increase of the amount of SiC particles,the reactive layers become thin.The inter-diffusion between the Cu element in the interlayer and the Ti element in Ti-alloy results into the formation of interfacial Cu-Ti phase diffusion layers.

Superplastic Forming and Diffusion Bonding for Multilayer Structure of Ti-6Al-4V Alloy

HAN Wen-bo, ZHANG Kai-feng, WANG Guo-feng

2005, 25(6): 29-32,51.

[Abstract](1763) [PDF 804KB](321)

Abstract:
The superplastic forming and diffusion bonding(SPF/DB) with gas pressure control for multilayer sheets structure was investigated.The optimum parameters were: bonging temperature T=930℃,bonding time t=30min,bonding pressure P=10MPa.Microstructure study was carried out with the bonded samples.The microstructure showed an excellent bonding at the interfaces.The optimum parameters for the SPF process were: forming temperature Tf=930℃,forming pressure Pf=0.6MPa,forming time tf=55min.The distribution of thickness after SPF was investigated.

The Modeling of the Friction Stir Process Under Different Pressures on the Shoulder

ZHANG Zhao, CHEN Jin-tao, ZHANG Hong-wu

2005, 25(6): 33-37.

[Abstract](1675) [PDF 943KB](293)

Abstract:
The 3D flow in friction stir welding was simulated by using finite element method based on solid mechanics.A good correlation between the equivalent plastic strain and the microstructure zones was found.The load on the pin had an effect on the distributions of the equivalent plastic strain only in the nugget zone and the change of the load had a quasi-linear relation with the change of the equivalent plastic strain.The change of the load could only affect the flow near the welding line in the friction stir process.

Microstructure and Tribological Behavior of Nibased Spray-welding Coating on Titanium Alloys Substrate

WANG Hong-yu, XU Xiao-jing, CHEN Kang-min, LIU Gui-ling, XU Wen-wei

2005, 25(6): 38-42.

[Abstract](1710) [PDF 1621KB](468)

Abstract:
Improving wear resistance of titanium alloy by the flamed sprayed welding could resolve the problem of engineering adaptation in technical process better.However,the improvement of wear resistance is the ultimate aim to a surface technique using in wear resistance treatments.The microstructure and tribological behavior of three Ni-based sprayed welding coatings on titanium alloy substrate were investigated.The results show that three coatings all are characterized by a wear resistant microstructure composed by tough substrate and hard particles.Their substrates are Ni-based solid solution,but the buildup of hard particles is different obviously.The wear loss of the F102 coating,the RE compound coating including 4% La2O3 and the Ni-WC coating including 25%WC were apiece 1/6,1/8 and 1/10 of that titanium alloy.It is indicated that modifying wear resistance of titanium alloy by the flamed sprayed welding could improve effectively wear resistance of titanium alloy surface.

Effect of Crystallization on Oxide Formation of Ni-20Cr-0.6Al Alloy Deposited by EB-PVD

GUAN Chun-long, HE Xiao-dong, LI Yao, YI Jian

2005, 25(6): 43-45.

[Abstract](1703) [PDF 811KB](220)

Abstract:
Ni-20Cr-0.6Al(wt%) alloy thin sheet with 0.5mm thick was deposited by electron beam physical vapor deposition(EB-PVD).The grain size of the alloy was less than 100nm.Oxide formation of Ni-20Cr-0.6Al alloy after 100h oxidation at 1000℃ in air was studied.The results indicated that a continuous and dense -Al2O3 scale was formed after 100h oxidation.When the content of Cr was 20%,the minimal content of Al for the formation of a continuous Al2O3 scale significantly decreased by crystallization.

Effects of Surface Modification Pitch Carbon Fiber of on Mechanical Property of Carbon/carbon Composites

JIN Zheng, MENG ling-hui, ZHANG Zhi-qian, LIU Chong-de, LI Jie

2005, 25(6): 46-51.

[Abstract](1719) [PDF 604KB](201)

Abstract:
Ozone method was used to modify surface activity of pitch carbon fiber to improve the interfacial adhesion between fibers and matrix.The surface structure of untreated and treated pitch carbon fibers were investigated by AFM and XPS,and the measurement of contact angles were used to understand the change of surface energy of pitch carbon fibers.And the SEM was employed to characterize microstructure of the composites.The results show that oxidation of ozone method increases the carbonyl functional group and the surface roughness and improves the impregnation of pitch carbon fibers,which enhances the compressive strength and flexural strength of the carbon/carbon composites.

The Effect on Carbon Fiber Surface Structure and Tensile Strength Irradiated by γ-ray

LI Jun-qing, HUANG Yu-dong, WANG Zhuo, XU Zhi-wei

2005, 25(6): 52-56.

[Abstract](1782) [PDF 470KB](329)

Abstract:
It is a new technique that high-energy radiation modificate on the surface of carbon fiber(CF) which is high efficiency,save energy and environmental protection.Polyacrylonitrile(PAN) based CF was irradiated by 60Co γ-ray at different absorbed dose(0~1000kGy).Atomic force microscopy(AFM) was used for characterized the surface morphology of carbon fiber.At the nanometer scale,AFM images revealed a moderate increase about the amount of grooves at lower absorbed dose(30kGy) and decreased at higher absorbed dose.The grooves became deepen and widen as the dose increasing.The Raman curves were fitted by Gaussian-Lorentazian function.It was shown that the structure of the CF slightly alternated by irradiated and that the more dose treatments induced the higher surface crystallinity,as detected by Raman measurements.The CF strength that after irradiated was analyzed by different gauge length single filament strength,which was combined with two-parameters Weibull theory.

Effects of Pure Carbon Green Density on Reaction-bonded Silicon Carbide

ZHOU Hao, ZHANG Chang-rui, WEI Wei, WANG Yao

2005, 25(6): 57-60.

[Abstract](1726) [PDF 534KB](284)

Abstract:
A near-net-shape SiC was prepared by reaction-bonded from a pure carbon perform which was fabricated by mould from graphite power as raw and phenolic resin as binder.The effects of green density on the constitution,structure and properties of SiC composites were studied.

2005 Vol. 25, No. 6