航空材料学报

2012, 32(4): .

[Abstract](1366) [PDF 288KB](240)

Abstract:

Microstructures in Solidification of Aluminum Twin-Roll Casting Based on CAFE

CHEN Shou-dong, CHEN Jing-chao, HUANG Pan, LV Lian-hao, WANG Peng, PENG Ping

2012, 32(4): 1-7.

[Abstract](1782) [PDF 1992KB](372)

Abstract:
Nucleation and growth model based on Cellular Automation (CA) incorporated with macro heat transfer calculation was presented to simulate the solidification microstructure of aluminum twin-roll continuous casting, and the nucleation model based on the normal distribution was used in the calculation and the dynamics model of dendrite tip (KGT model) was amended in view of characteristics of aluminum twin-roll continuous casting. Moreover, the effect of different casting process parameters and solidification parameters on the formation of the microstructures was simulated. The results are helpful to explain the dendrite segregation and size segregation, columnar grains mainly distribute near the casting roller while equiaxed grains distributed far away from the casting roller in front of nip point.

High Precision Superplastic Forming of Titanium Alloy Using ZrO₂-TiO₂ Ceramic Die with Controllable Linear Expansion Coefficient

JIANG Shao-song, HE Xiao-dong, ZHANG Kai-feng, GAO Peng, LI Bao-yong

2012, 32(4): 8-14.

[Abstract](1978) [PDF 1602KB](383)

Abstract:
The ZrO2-TiO2 ceramic die with controllable linear expansion coefficient (LEC) and the high precision superplastic forming were studied. The influence of TiO2 fraction and relative density on linear expansion coefficient of ZrO2-TiO2 ceramic was analyzed. The Turner model was modified and the relative density was introduced into the model. The forming accuracy of ceramic die with the similar LEC to TC4 titanium alloy was measured. The ZrO2-TiO2 deep cylinder ceramic die was fabricated and its performance was evaluated by the superplastic forming experiment at 925℃. The results show that the LEC decreases with the increment of volume fraction of TiO2 and increases with the rising of relative density. The modified Turner model more accurately predicted. Using the ZrO2-TiO2 ceramic die with optimal LEC, the forming accuracy deviation significantly reduced and not exceed of 0.1%. The ceramic die owns enough sufficient thermal mechanical properties and excellent performance.

Structure of TiAl Based Alloy by Suction Casting

YE Xi-cong, SU Yan-qing, GUO Jing-jie, ZHANG Li-hong

2012, 32(4): 15-19.

[Abstract](1752) [PDF 1891KB](433)

Abstract:
The TiAl based alloy sheets were achieved by the permanent mould suction casting. This as-cast structures and the effect of alloy elements on structures were studied. The results indicated that because of force cooling, the as-cast structures of TiAl based alloy sheet by permanent suction casting are fine, and the average grain size is 60 m. The B2 phase counteracts phase grow, and the adding of W element benefits to form B2 phase. Therefore, the addition of W element can refine the grain size of TiAl based alloy structure. The Ti5Si3 phase formed by adding of Si element is mainly situated at the grain boundary. The particle of the Ti5Si3 phase counteracts the structure grow on solidification process, so the adding of Si element can refine the grain size of TiAl based alloy structure.

Wettability and Microstructures of High Temperature Ni-based Mixed Filler Powders for Wide Gap Brazing

LIANG Hai, YE Lei, MAO Wei

2012, 32(4): 20-25.

[Abstract](1940) [PDF 2374KB](332)

Abstract:
High temperature Ni-based mixed filler powders for wide gap brazing were produced by mixing a type of Ni-based high temperature filler powder containing aluminum and titanium and the 'precipitation strengthened Ni-based superalloy FGH95 powder. The experiment results indicate that the mixed powder filler metals with proper mixing ratio possess good wetting and spreading performances on the stainless steel 1Cr18Ni9Ti . Alloying effects in the brazing metal are considerable, and the maximum total content of aluminum and titanium elements is surprisingly up to 5.49%. The mixed brazing filler metals after high temperature brazing exhibit no remarkable element segregation except niobium and tungsten. After 1180℃/4h diffusion heat treatment, the element segregation is eliminated. The microstructures of the brazing metal are uniform comparatively ,and characterized by equiaxed solid solution dendrites with interdendritic blocky and short-stripy compounds and a little +'eutectic , and especially a large amount of fine dispersed 'precipitation hardening phases distribute in the solid solution, as expected.

Defects and Properties of Friction Stir T-Welded Joints for 6061-T4 Aluminum Alloy

ZHOU Guang, YANG Xin-qi, XU Xiao-dong, ZHANG Zhao-hua

2012, 32(4): 26-31.

[Abstract](1964) [PDF 2220KB](352)

Abstract:
The processes of friction-stir-welded T-joints for 3mm thick AA 6061-T4 were investigated,and the influences of welding speeds and rotating speeds on welding defects and mechanical properties were discussed specifically. It was found that for given fixture and tool, when v was kept constant, tunnel defects were easily produced at the fillet corner of stringer nugget along advancing side which became smaller with the increasing /v. Clear Z line was tended to appear near the retreating side. Two soften zones that were enlarged with the increasing were found in the skin. The hardness in the center of weld was increased with the increased. The stringer thermo-mechanically affected zone was also softened and its hardness was reduced 17.0%. The decreased hardness was the main factor to reduce the tensile strength of all T-joints along skin direction. The best tensile strength was only up to 73.8% compared to base material. Tunnel defect was the main reason to reduce tensile strength in the stringer direction for =1008r/min. And the softer microstructure of thermal mechanical affected zone in T-joints was contributed to the decrease of tensile strength for =1541r/min and =2256r/min. The highest tensile strength reaches to 83.5% of the base material when /v=1541/218 r/mm.

Microstructure and Mechanical Properties of Submerged Friction Stir Processed AZ91 Magnesium Alloy

CHAI Fang, ZHANG Da-tong, ZHANG Wen, QIU Cheng

2012, 32(4): 32-37.

[Abstract](1833) [PDF 3347KB](540)

Abstract:
Normal and submerged friction stir processing (SFSP) were applied to prepare fine-grained AZ91 alloy, and microstructure and mechanical properties of the processed materials were investigated. The results show that owing to cooling water, the stir zone (SZ) area of SFSP is smaller than that of normal FSP, and microstructures are significantly refined, which the average grain sizes were 1.9m and 3.5m respectively. The fibrous structure in the thermal-mechanically affected zone (TMAZ), but the average grain size of SFSP was finer. Microstructure of the normal FSP coarsened in the heat affected zone (HAZ), while the grain size of the SFSP plate was almost equal to that of the base material (BM). The second phase -Mg17Al12 of both two processes were changed from network into particles in SZ. The hardness, tensile strength and elongation of SFSP material were higher than those of normal FSP.

Influence of Aging Heat Treatment to Mechanical Properties of Joints Welded by 0Cr15Ni5Cu4Nb Steel

LI Neng, GUO Shao-qing, ZHOU Biao, SUN Bing-bing, ZHANG Xue-jun, ZHANG Wen-yang, TANG Si-yi

2012, 32(4): 38-43.

[Abstract](1849) [PDF 2318KB](361)

Abstract:
Microstructures and properties of joints welded by 0Cr15Ni5Cu4Nb martensitic precipitation-hardened stainless steel were studied. The aging heat treatment at four different temperatures was carried out. The results show that, as the temperature or time of aging heat treatment increased , the impact toughness, 5 and increased, however, the tensile strength and yield strength reduced, the major fracture mode altered from quasi-cleavage to dimple. The joints after aging heat treatment of 550℃/4h show reasonable properties beyond 95% of parent metal: the tensile strength is 1071MPa, the impact toughness is 283 J/cm2.

TEM Technology to Fe₂Mo in M50NiL High Temperature Carburizing Bearing Steel

LOU Yan-zhi, LUO Qing-hong, LI Chun-zhi, ZHAO Zhen-ye

2012, 32(4): 44-48.

[Abstract](1842) [PDF 1619KB](366)

Abstract:
The morphology, structure of Fe2Mo and its orientation relationship with martensite in M50NiL high temperature bearing steel were observed by high resolution electron microscopy (HREM). The results show that there is plate martensite in cementite surface layer,and lath martensite in the center of bearing steel M50NiL. A little of twin martensite is observed in the cementite surface layer, and the twin plane is martensitic 112 crystal plane. Precipitates Fe2Mo with width of 2-3nm were observed in experimental steel, and grown along the twin plane between martensite bars, the width direction is perpendicular to the twin plane and the length direction parallel to the twin plane; the orientation relationship between the nano-precipitates Fe2Mo and twin martensite is {112}M//{001}Fe2Mo,[1 11]M//[100]Fe2Mo.

Effects of Hard Chromium Electroplating on Performance of TC6 Titanium Alloy

TANG Zhi-hui, WANG Chang-liang, GONG Xing-jia, YU Bo, LIU Jiang, XIE Dao-xiu, FENG Qi

2012, 32(4): 49-52.

[Abstract](1899) [PDF 1722KB](420)

Abstract:
The influences of chromium electroplating on hydrogen content, mechanical and fatigue properties of TC6 titanium alloy were studied by hydrogen testing equipment, tensile testing machine and fatigue testing machine. The results show that the hydrogen content of TC6 titanium alloy increased after chromium electroplating up to the top limit of the acceptance range. The hydrogen brittleness specimens made of TC6 were failure in the hydrogen embrittlement test. So these materials with chromium coating were not suggested to use for high stress concentration and load-carrying structure. The tensile strength of TC6 was kept constant. The elongation decreased by 17.3%, and section reduction decreased by 24.0%.The fatigue strength of TC6 after chromium electroplating decreased significantly from 626.0 MPa to 201.3 MPa by the tensile stress of chromium coatings.

Corrosion and High Temperature Oxidation Resistance of Ni₄₇Ti₄₄Nb₉ Shape Memory Alloy

WANG Er-min, NI Zhi-ming, HONG Qi-hu, YANG Gen-lin, HAN Jin

2012, 32(4): 53-56.

[Abstract](1896) [PDF 1826KB](357)

Abstract:
The oxidation resistance and corrosion resistance of the Ni44Ti47Nb9 shape memory alloy were studied. The result shows that Ni47Ti44Nb9 alloy exhibits good oxidation resistance at 450℃. Further more, the oxidation curve of Ni47Ti44Nb9 alloy follows the parabolic law in the temperature range of 600-800℃. Experimental results indicate that a multi-layer scale, which is composed of outer layer and transition layer, is formed on the surface of Ni47Ti44Nb9 alloy after high temperature oxidation. The results of electrochemical corrosion test show that the corrosion resistance of Ni47Ti44Nb9 alloy increases and the corrosion potential shifts positively as the temperature and the NaCl content of NaCl solutions decreases.

Preparation of Reaction-Formed Porous SiC Ceramics

ZHANG Zhi-jin, YU Xiao-dong, WANG Yang-wei, LI Kai, LUAN Zhi-qiang

2012, 32(4): 57-61.

[Abstract](1693) [PDF 2663KB](325)

Abstract:
The carbon foam template was produced from the mixture of mesophase pitch and 55% Si particles(mass fraction). The SiC porous ceramics were fabricated by infiltrating Si into the carbon foam template at 1500℃ for 1-6h in the vacuum furnace under argon atmosphere. The micrograph and identify phase of porous SiC ceramics were observed by means of SEM and XRD respectively. Moreover, the mechanism of reactive infiltration of molten Si into carbon foam was also discussed. The results show that the microstructure of porous SiC ceramics is identical with carbon foam template. The bending strength of porous ceramics is increasing first and then decreasing with holding time prolonged at 1500℃, however, the porosity is reverse. The porous SiC ceramics obtained at 1500℃ for 4h is composed of the major phase -SiC. The bending strength and porosity are 26.2MPa and 45% respectively. Both the outer molten Si and inner Si of carbon foam react with C simultaneously to form SiC, and then bonds together to form densest porous SiC ceramics.

Surface Morphology and Evolution Mechanism of Carbon Fiber/Phenolic Resin Composites on Atomic Oxygen Irradiation

ZHAN Mao-sheng, GUO Dan-dan, WANG Kai

2012, 32(4): 62-69.

[Abstract](1798) [PDF 2798KB](346)

Abstract:
The carbon fiber/phenolic resin composites were prepared and the atomic oxygen exposure test was conducted in a ground-based AO effects simulation facility. The effect of atomic oxygen on the composites was studied by scanning electron microscopy (SEM), attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR) and the X-ray photoelectron spectroscopy (XPS).The results show that the atomic oxygen environment, the mass loss are happened in the phenolic resin and carbon fiber and carbon/phenolic composite, and the mass loss of carbon/phenolic composite mass loss rate is greater than the total mass loss of phenolic resin and carbon fiber. Its mechanism shows the interaction of atomic oxygen with phenolic resin and carbon fiber agree with Undercutting Model. For phenolic resin, the methylene bridges and ether bond both can be oxidized after AO exposure, which result in void distributed on the surface of phenolic resin. For carbon fiber, the sizing agent is etched first and then the fiber is oxidized into OC=O and C=O after AO exposure with the result that the size of carbon fiber diminishes and the cylindrical carbon fiber is out of shape with shallow and broad groove distributed on the surface.

Reaction of Polytetrafluoroethylene Grafted GMA

ZHANG Dong-na, KOU Kai-chang, HOU Mei, GAO Pan, WU Guang-lei

2012, 32(4): 70-74.

[Abstract](1918) [PDF 1024KB](333)

Abstract:
Polytetrafluoroethylene(PTFE) was activated with the mixture solution of tert-Butyllithium(t-BuLi) and ethylenediamine(EDA), and grafted GMA onto the PTFE. The chemical structure of activated and grafted PTFE was analyzed by using FTIR. It shows that GMA was successfully grafted onto the PTFE. SEM was used to observe the surface morphology of grafted PTFE. The grafting ratio of 5.83% was achieved, which was measured by TGA. The effect of reaction time and temperature for the grafting ratio was studied finally. The grafting ratio was increased with the elongation of reactive time, and basically constant after 8h. The grafting ratio reaches its maximum when the reaction temperature is 70℃.

Organic-Inorganic Hybrid Transparent Abrasion Coatings for Aeronautical Transparency

HA En-hua, JI Jian-chao, SUN Shi-bin, ZHONG Yan-li

2012, 32(4): 75-79.

[Abstract](1623) [PDF 1052KB](389)

Abstract:
UV-curable acylate-modified polyurethane/nanosilica hybrid coatings was prepared through the Sol-gel process of tetraethoxysilane in the presence of acylate-modified polyurethane. The sliane coupling agent methacryloxypropyltrimethoxysilne was used to stabilize the nanoparticle of silica formed via the Sol-gel precess.The hacryloxy group of the sliane coupling agent methacryloxypropyltrimethoxysilne would react with acylate-modified polyurethane during UV curing,and form a strong interfacial interaction between the organic and inorganic phases.The nanosilica can be dispersed in UV curable hybrid materials homogeneously,and the UV cured hybrid films exhibit high hardness and abrasion.

Tensile Properties and Failure Analysis of 2D-C/SiC Composite Laminates with Circular Holes

GUO Hong-bao, WANG Bo, JIAO Gui-qiong, YANG Cheng-peng, LIU Yong-sheng

2012, 32(4): 80-86.

[Abstract](1889) [PDF 2656KB](511)

Abstract:
Tensile properties and failure modes of the 4mm and 6mm open-hole specimens of a 2D-C/SiC composite under tensile loading were investigated. The influence of notch size on the open-hole specimen's tensile strength was analyzed by comparing with standard specimen's experimental results. Compared with the standard specimen, the tensile strength values of 4mm and 6mm open-hole specimens decrease by 1.0% and 6.6% separately. By sticking strain gauges at different locations of the open-hole specimen, the strain variation in the narrowest net section was obtained during the tensile test, and the strain concentration effect was also clearly expressed. Meanwhile, by finite element analysis (FEA), the strain distribution in the open-hole specimen was simulated. The FEA results have good consistence with experimental data. By Acoustic Emission (AE) measurement, the damage evolution of the notched specimen was derived. The AE parameters reflect the macroscopic damage process of the open-hole materials. Combined with fracture section observations, the failure behavior of the open-hole specimens was concisely discussed.

Fracture Toughness of ZTi6Al4V Casting Titanium Alloy under Different Annealed Conditions

DANG Ning, ZHAO Jia-qi, NAN Hai, WU Guo-qing

2012, 32(4): 87-91.

[Abstract](1837) [PDF 1067KB](346)

Abstract:
The theory of notch strength was used to judge the damage tolerance capability of ZTi6Al4V casting titanium alloy,for example,the effect of annealing temperature on three-point bending fracture toughness.The results show that fracture toughness KQ1, which was tested by notched specimens,is not equal to the KQ tested by the standard testing method. But it was used to compare qualitatively fracture toughness of casting titanium alloy with different annealing processes. The changing of annealing temperature can adjust strength and fracture toughness of ZTi6Al4V casting titanium alloy.Samples annealed at 700℃and 800℃ for 2h have better toughness, the KQ values are 78.11 MPam1/2 and 79.44MPam1/2.They also have a relatively better match of strength and plasticity, that is the yield strength is up to 782.74MPa and 771.49MPa, tensile strength reaches 860.18MPa and 853.0MPa, and the elongation reaches 8.10% and 7.46% respectively.

Effect of Shot Peening on Fatigue Life and Reliability Model of Prestretching Aluminum Alloy 2024

ZHANG Zhi-yuan, ZHI Xi-zhe, YAN Wu-zhu, LIU Jun, YANG Shi-chao

2012, 32(4): 92-96.

[Abstract](1898) [PDF 1859KB](411)

Abstract:
A series of fatigue tests were carried out on prestretching aluminum alloy 2024 plate aimed to explore the effect of shot peening on fatigue lives and reliability models. The experiment results show that fatigue lives of prestretching aluminum alloy 2024 plates are remarkably increased after shot peening. Experiment data were analyzed by goodness of fit test approach. The fitting results show that the fatigue lives of prestretching specimens obey Weibull distribution while the fatigue lives of shot peening specimens obey the lognormal distribution. Then, the statistical distribution and reliability model of fatigue lives before and after shot peening of prestretching aluminum alloy 2024 plates were established.

2012 Vol. 32, No. 4