航空材料学报

2014, 34(3): .

[Abstract](890) [PDF 261KB](91)

Abstract:

Phase Transformation and Microstructure Formation of K424 Superalloy with Different Cooling Rate

YU Huan, LI Lian, ZHOU Zhen-zhen, XIA Wei, YANG Wei, HU Xiao

2014, 34(3): 1-7.

[Abstract](1380) [PDF 3737KB](185)

Abstract:
Phase transformation processes of K424 superalloy with different cooling rates were investigated by differential scanning calorimetry. The variations of secondary dendrite spacing and concentration segregation as the function of cooling rate were analyzed by using OM, SEM and EDS. The results indicate that both the length of secondary dendrite spacing and the size of carbides reduce with the increasing of cooling rate. The refinement of dendrite structure and the acceleration of phase transformation rate result in the dispersive distribution of residual liquid phase and insufficient growth of primary phase, which weakens the richness of solute Ti and Nb elements in inter-dendrite region. Consequently, both the temperature and the transformation of carbides are suppressed, even with the absence of second formation.

Flow Stress Behavior of Spray-Formed Ultra-high Strength Aluminum Alloy during Compression at Elevated Temperature

SUN Peng, LI Zhi-hui, Xiong Bai-qing, ZHANG Yong-an, LI Xi-wu, LIU Hong-wei, WANG Feng

2014, 34(3): 8-14.

[Abstract](1235) [PDF 5112KB](135)

Abstract:
The Al-10.8Zn-2.8Mg-1.9Cu-0.12Zr aluminum alloy preforms were prepared by spray forming technology and subsequently processed by hot isostatic pressing (HIP). The flow stress behavior of the alloy during hot deformation was investigated by isothermal compression tests using Gleeble-3500 system in the temperature range from 340℃ to 430℃ and at strain rate range from 0.01s-1 to 10s-1. The constitutive equation and the processing maps were evaluated by linear regression analysis. The electron back scattered diffraction technique(EBSD) was employed to analyze the microstructure of the alloy pressed under various deformation conditions. The results show that the deformation activation energy Q of spray-formed Al-Zn-Mg-Cu alloy is higher than that of other Al-Zn-Mg-Cu alloyprepared by ingot metallurgy, processability is relatively poor, the suitable deformation temperature ranges from 380℃ to 405℃ and the strain rate should be below 0.5s-1. The flow stress of the alloy is significantly influenced by the strain rate and deformation temperature,the peak of flow stress decreases with increasing temperature and increases with a rise in strain rate, a higher strain rate and lower temperature are benefit to the formation of sub-grains microstructure.

Superplastic Deformation Based on Strain-induced and maximal m Value in TC4-DT Titanium Alloy

YU Miao-zhen, WANG Gao-chao, ZHENG Man-qing, XU Xue-feng

2014, 34(3): 15-20.

[Abstract](1305) [PDF 1652KB](119)

Abstract:
The superplastic deformation characteristics of TC4-DT titanium alloy were investigated at 850-900℃ and Pre-stain of 1.0-2.0 by the method of strain-induced superplastic deformation based on the maximal m value method. Then the optimum process parameters were determined. The results show that the elongations of the alloy increase and then decrease with the increasing of the deformation temperature under the same pre-stain. The elongations of the alloy increase and then decreased with the increasing of the pre-stain at the same temperature. Dynamic recrystallization obviously occurred in the alloys superplastic deformation.The main deformation mechanism of strain-induced superplasticity deformation based on maximal m value is grain boundary sliding and the anxiliary mechanism of deformation is dynamic recovery and recrystallization. The best process parameters of the strain-induced superplastic deformation were the deformation temperature of 870℃ and pre-strain of 1.5.and the elongation ratio could reach 1033%

Critical Strain of Dynamic Recrystallization in SAE9310 Steel

HUANG Shun-zhe, LI Yong, WANG Chun-xu, HAN Shun, LIU Xian-min, TIAN Zhi-ling

2014, 34(3): 21-27.

[Abstract](1421) [PDF 2556KB](145)

Abstract:
Based on the theory of work hardening, the curve of work hardening rate under large strain and inflection point criterion of dynamic recrystallization in SAE9310 steel were researched at deformation temperature from 900℃ to 1200℃ and strain rate from 0.01s-1 to 10s-1. By means of inflection point criterion and metallographic observation, the critical condition of dynamic recrystallization in SAE9310 steel was demonstrated and the dynamic recrystallization state diagram was established. The results indicate that two types of stress-strain curve is observed under the present deformation conditions. During dynamic recrystallization the critical strain c and critical stress c increase with strain rate increasing and deformation temperature decreasing. A certain correlation between critical strain c and peak strain p is according with c/p=0.30~0.42. The critical deformation increases and the dynamic recrystallization for the material becomes more difficult with parameters Z increasing.

Influence of Equilibrium Phases on Property of Al-7.8Zn-1.6Mg-1.8Cu-0.12Zr Alloy：First-principle Calculations

HUANG Yuan-chun, XIAO Zheng-bing, ZHANG Huan-huan, LIU Yu

2014, 34(3): 28-34.

[Abstract](1562) [PDF 1118KB](234)

Abstract:
To determine the influence of equilibrium phases on the 7085 alloy, the software of Thermo-Calc and JMatPro based on thermodynamic calculation was used to calculate the phases may present in the typical 7085 alloy (Al-7.8Zn-1.6Mg-1.8Cu-0.12Zr, mass fraction/%). Combined with the plane wave pseudo-potential method(PWP) and generalized gradient approximation(GGA). The heat of formation, cohesive energy, fermi energy and elastic constant for the phases exist in the alloy were calculated by the first principle using density functional theory(DFT) as implemented in the cambridge sequential total energy package(CASTEP), the change of corrosion resistance, strength and toughness maybe caused by the phases were studied. Results shown that three equilibrium phases, MgZn2, Al2Cu and Al3Zr may present in the Al-7.8Zn-1.6Mg-1.8Cu-0.12Zr alloy. The formation of Al2Cu, MgZn2 and Al3Zr is found to an exothermic process. And among them, MgZn2 has the largest electrode potential difference with -Al, they are prone to form micro batterys, thus decrease the corrosion resistance of the alloy, while the electrode potential difference between Al2Cu and -Al is not much. Al3Zr has the biggest bulk moduli, shear moduli, elastic moduli, and young's moduli, it increases the alloy's strength and toughness mostly

Effect of Solution Treatment on Microstructures and Mechanical Properties of 7136 Aluminum Alloy

SUN Wen-hui, ZHANG Yong-an, LI Xi-wu, LI Zhi-hui, WANG Feng, LIU Hong-wei, XIONG Bai-qing

2014, 34(3): 35-41.

[Abstract](1486) [PDF 4035KB](120)

Abstract:
The effects of solution heat treatment on microstructures and properties of 7136 aluminum alloy extrusions was studied by OM, SEM, DSC and room temperature tensile test. The results show that the main residual constituents in extrusions are T(AlZnMgCu) and S(Al2CuMg) phase; The optimal single-step solution temperature is 470℃; The size and number of residual constituents reduced gradually when the temperature is from 450℃ to 480℃, and the re-crystallized fraction continue increasing accordingly. When solution temperature reaches 475℃ or higher, overburning occurred. With 450℃/4h+470℃/8h solution treatment, the dissolution of residual constituents is relatively sufficient while re-crystallized re-fraction maintains minor, the tensile strength, yield strength and elongation of T6 is 701MPa, 654MPa and 12.2%, respectively. The dissolution of residual constituents is more sufficiently by three-step solution treatment with higher temperature, nevertheless, overburning occurres easily.

Law of Uniaxial Tensile Tests of Ultra-high Strength 300M Steel Treated by Quenching-partitioning(Q-P) Process

MA Shao-hai, LI Yong, WANG Chun-xu, HUANG Shun-zhe, HAN Shun, LIU Xian-min

2014, 34(3): 42-47.

[Abstract](1387) [PDF 1796KB](147)

Abstract:
The uniaxial tensile curves of 300M steel treated by Q-P process were measured. And the energy of the various tensile stages of 300M steel were analyzed. Influence of Q-P process on the properties and structures of 300M steel was studied by TEM,SEM and XRD. The results show that the strength of 300M steel treated by Q-P process decreases significantly apparently, and the elastic deformation energy Ee decreases, but the uniform plastic deformation energy Ep and the crack initiation energy Ee+Ep increase. The content of residual austenite can be raised to 15.62%, which exists between martensite lathes in film status and between prior austenite grain boundaries、lath packet boundaries in massive form. The phases of 300M steel treated by Q-P process consist of pre-formed lath martensite, fresh martensite, residual austenite and -carbide.Q-P process significantly improve crack initiation and propagation resistance of 300M steel, and extend the uniform plastic deformation stage of the material,and finally put off the necking creation.

Effect of Triethyl Phosphate on Performance of Anodized Aluminum Alloy with Sol-Gel Sealing

WANG Qiang, SUN Zhi-hua, ZHAN Zhong-wei, WANG Zhi-shen

2014, 34(3): 48-56.

[Abstract](1324) [PDF 3115KB](148)

Abstract:
Sol-gel sealing fluids for sealing anodized films of aluminum alloy were fabricated. The effects of triethyl phosphate on performance of anodized films with sol-gel sealing on aluminum alloy were studied. The morphology of the films was obtained by scanning electron microscopy (SEM). The effects of triethyl phosphate concentration on corrosion resistance of anodized films was investigated by electrochemical impedance spectroscopy (EIS) and salt spray test. The adhesive force between the coating and the anodized films was estimated by scribe test, and the mechanism of corrosion inhibition and sealing evaluated. The results demonstrate that the optimal concentration of triethyl phosphate is 2% (mass fraction), which makes the films uniform and dense; and demonstrate excellent corrosion resistance.

Research of Processing Characteristics and Mechanical Properties of Semi-prepreg RTM Composites

LI Wei-dong, LIU Gang, BAO Jian-wen, HU Xiao-lan, YI Xiao-su

2014, 34(3): 57-62.

[Abstract](1341) [PDF 2786KB](135)

Abstract:
A novel semi-prepreg resin transfer molding (RTM) process was developed to address difficulties associated with RTM process and to improve the mechanical properties of the resulting composites. Unidirectional semi-prepregs exhibiting relatively good overlay characteristics were prepared via prepolymerization of bismaleimide resin followed by wet winding. The processing characteristics and mechanical properties of composites fabricated via semi-prepreg RTM technology were compared with those of composites produced using a normal-prepreg compression molding process. The results show that the laminates fabricated by the semi-prepreg RTM process are of better internal quality and have superior mechanical properties as compared with laminates fabricated by the normal-prepreg compression molding process.

Effect of Monomer Feeding Modes on Particle Size Distribution of PS Microspheres

LI Zi-fan, QI Hong-fei, LIU Da-bo

2014, 34(3): 63-68.

[Abstract](1233) [PDF 2590KB](130)

Abstract:
Highly monodisperse polystyrene (PS) microspheres in the size range of 3.8~7.1m were synthesized by dispersion polymerization with dropwise monomer feeding procedure. The morphology, size, and particle size distribution (PSD) of the PS microspheres obtained by different monomer feeding modes were investigated. The PS microspheres with low coefficient of variation (CV) values all less than 4.8% obtained by the optimum feeding rates revealed better uniformity than those by batch polymerization. According to polymerization kinetics, the effects of monomer feeding modes on the polymerization reaction of the large-sized PS microspheres were clarified. It is found that the dropwise monomer feeding procedure is promising for the synthesis of large-sized monodisperse PS particles in 3.8~7.1m.

Preparation and Performance of ZrC/SiC Multi-components Modified C/C Composites

LI Xiu-qian, JIAO Jian, QIU Hai-peng, WANG Yu, CHEN Ming-wei, XIE Wei-jie

2014, 34(3): 69-73.

[Abstract](1370) [PDF 2178KB](131)

Abstract:
Carbon-carbon composites of low density were prepared by chemical vapor infiltration process (CVI) using carbon felt as fiber reinforcement. ZrC/ SiC modified C/C composites were fabricated through precursor infiltration and pyrolysis process (PIP) using a hybrid precursor including polycarbosilane and organic zirconium-contained polymeric precursor as impregnant on the basis of C/C of low density. Mechanical properties and microstructural analysis were performed by Z100 universal electron test equipment and scanning electron microscope respectively. The results show that the silicon carbide phase including zirconium carbide particle dispersed symmetrical in the matrix of C/C composites, meanwhile the mechanical properties ascend earlier and descend later as the content of organic zirconium-contained polymeric precursor increased. The flexual properties and modulus maximum are 241MPa and 17.25GPa separately when the ratio of organic zirconium polymeric precursor is 25%.

Effect of Load Ratio and Corrosion on Fatigue Behavior of AerMet100 Ultrahigh Strength Steel

LI Song-mei, WU Ling-fei, LIU Jian-hua, YU Mei, WEN Chen

2014, 34(3): 74-80.

[Abstract](1421) [PDF 2135KB](140)

Abstract:
The effecs of load ratio and environment on the fatigue crack growth (FCG) behaviors of AerMet 100 steel was studied. Different crack growth zones were focused. The fracture morphologies were observed by scanning electron microscope (SEM). The results show that raising the load ratio reduces the threshold stress intensity(Kth), below 10-5mm/cycle. Further more,Kthbecame a constant at R0.5. However, the effect of load ratio on FCG rate is slight above 10-5mm/cycle. It tended to be converge in the range. And the corrosion environments accelerate the FCG above 10-5mm/cycle.Whenthe rate below 10-5mm/cycle, the situation is changed. The aggressive environment reduces the FCG rate, and the threshold-value of FCG is larger due to the crack closure of corrosion.

Effects of Vibration on Creep Aging Forming of 7055 Aluminum Alloy

WANG Yu, DENG Yun-lai, KANG Jian-ke, ZHANG Jin

2014, 34(3): 81-85.

[Abstract](1345) [PDF 2171KB](126)

Abstract:
The Vibratory field was applied to the process of creep aging forming of water-quenched 7055 aluminum alloy sheets, which were operated on the self-made single curvature die and vibratory platform. The effects of temperature and vibration mode on the springback value、mechanical properties and microstructures were investigated. The results show that within a certain range of time, the springback value is reduced and the rate of stress relief is accelerated. Meanwhile, the precipitation is promoted and the distribution of precipitates is more dispersion, as a consequence, the strength of the alloy is improved on a considerable extent. On the experimental conditions of this paper, the strength of the VCAF specimens is increased with 7%, and the springback value is decreased with 12.3%

Comparative Research on Accumulative Damage Models under Multiaxial 2-stage Step Loading Spectra for LY12CZ Aluminium Alloy

XIA Tian-xiang, YAO Wei-xing, XU Li-pu

2014, 34(3): 86-92.

[Abstract](1294) [PDF 793KB](140)

Abstract:
Six accumulative damage models, which were common used or novel, were used to calculate the critical damages of the LY12CZ aluminum alloy under different kinds of 2-stage step loading spectra and the accuracy rate of each model was counted. According to the comparison result, for a certain kind of spectra, the prediction capabilities of the six models have disparity, and none of them is the best model for all kinds of spectra.

Creep Characteristics of 2024 Alloy at Cryogenic Temperatures

XIA Tian-xiang, YAO Wei-xing, XU Li-pu

2014, 34(3): 93-96.

[Abstract](1245) [PDF 1100KB](125)

Abstract:
The tensile creep tests in the range from 77K to 150 K were performed to investigate the creep behavior on 2024 alloy aging at 190℃ for 12h. It is found that there exists a creep and creep strain and logarithm time follows linear law during primary creep. The primary creep lasts over 500h at 100K and 150K and steady creep did not occur after 1000h at 77K. The dislocations configurations of 2024 alloy before and after cryogenic creep were observed by TEM. It is showed that under the constant load, the density and interaction of the dislocations after creep increase with rise of the temperature. Long distance slip of dislocations occurs when the temperature is 150K. The results indicate that the creep mechanism at cryogenic temperature is dislocation mechanism.

2014 Vol. 34, No. 3