航空材料学报

Hot Deformation Behavior and Microstructure Evolution of TC11 Alloy

CHEN Hui-qin, LIN Hao-zhuan, GUO Ling, CAO Chun-xiao

2007, 27(3): 1-5.

[Abstract](1406) [PDF 1674KB](321)

Abstract:
The hot deformation behavior and microstructure evolution of TC11 alloy with β-transformed structure were studied in the temperature range 1030~1090℃ and strain rate range 0.001~10s-1 by hot compression tests.Characteristics of stress strain curves of the alloy deformed with the test parameters were analyzed.Kinetics analyses indicate that the stress exponent and deforming activation energy in β region are 3.32 and 135.5kJ×mol-1 respectively,which indicate that deformation would be occurred by diffusion mainly.Microstructure observation indicates that there are two different grain refining manner.One is characteristic of new fine grains along elongated prior β grain boundaries.The other is that of new fine grains located at the interior of elongated prior β grains,which have serrate grain boundaries.Softening behavior during holding processes at high temperature after deformation indicates that the grain refining manner is dependent on competing of dislocation storage and annihilation during deformation processes.

Microstructure Evolution of Ni-NbC Alloy Under High-Temperature Gradient Directional Solidification

SONG Yan-ping, LI Shuang-ming, FU Heng-zhi

2007, 27(3): 6-10.

[Abstract](1433) [PDF 981KB](168)

Abstract:
Directionally solidified microstructures of Ni-10.6wt%NbC alloy were investigated at various withdrawing velocities.The results show that at the given temperature gradient of 300K/cm and the withdrawing velocity in a range of 5μm/s to 20μm/s,the solidified interface morphology of Ni-10.6%NbC alloy is planar.As the withdrawing velocity increases to 50μm/s,the cellular eutectic microstructure forms.NbC phase with the tilobar and rod morphologies gradually transfer to the plate morphology with the increase of the withdrawing velocity.When the withdrawing velocity changes abruptly from 2μm/s to 10μm/s,the regular eutectic of Ni-10.6%NbC could keep;While from 2μm/s to 50μm/s and 100μm/s respectively,the cellular eutectic and primary dendrites of Ni are obtained in directional solidification microstructure.In addition,the solidified microstructure is refined by increasing the withdrawing velocity abruptly compared to the constant withdrawing velocity due to the nucleation of NbC phase ahead of the interface,which decreases the fiber spacing of NbC.

Analysis of Strengthening Mechanism in Two-Phase TiAl-Based Composites

WANG Fen, AI Tao-tao, LUO Hong-jie, ZHU Jian-feng

2007, 27(3): 11-16.

[Abstract](1472) [PDF 615KB](409)

Abstract:
The in situ exothermic reaction of Al-Ti-TiO2-Nb2O5 system was adopted to fabricate Al2O3 particles reinforcing TiAl-based composites.The phase composition,microstructure and mechanical properties of the composites were analyzed.Strengthening mechanism of the composites was investigated too.The results show that with Nb2O5 added in,a submicron α2/γ dual phase structure and Al2O3 second phase can be obtained.The fine second particles disperse around the grains.With increasing Nb2O5 content,there present a homogeneous structure and refinement grains.The Vickers hardness exhibits a linear increase and the relative density increases too.The composite with 6wt% content of Nb2O5 exhibits a good bending strength of 642MPa.The strengthening mechanism in two-phase TiAl-based composites is discussed with valence electron structures of biphase interface.And intra-granular particle residual stress strengthening is to explain the variation of strength with the content of Nb2O5.

Effect of Primary α Phase Volume Fraction on Tensile Property and Thermal Stability of Near-Alpha TG6 Titanium Alloy

DUAN Rui, CAI Jian-ming, LI Zhen-xi

2007, 27(3): 17-22.

[Abstract](1539) [PDF 1937KB](665)

Abstract:
The effect of primary α phase volume fraction on the tensile property and thermal stability of the near-α TG6 Ti-alloy is investigated using mechanical properties testing and fracture analysis.The tensile strength and ductility have no obvious difference when the primary α fraction varies from 20% to 50%.While the specimens are subjected to 600℃/100h exposition in the high temperature air environment,the tensile strength increases slightly and the specimens decrease seriously.The degree of ductility degradation is strongly depended on the equiaxed primary α fraction.Decreasing the primary α fraction may accelerate the ductility loss after thermal exposition.There are several structural and environmental factors enhance the ductility degradation for TG6 alloy,such as coherent α2 precipitation,silicide and surface oxidation,contrastively,coherent α2 precipitation during the thermal exposition plays the most important role.

Processing Study on Properties of Rare-Earth TbDyFe Magnetostrictive Alloy

LUO Guang-sheng, ZHOU Zheng-you, XIN Yong, LEI Yu

2007, 27(3): 23-27.

[Abstract](1384) [PDF 1013KB](299)

Abstract:
or iented rods of a TbDyFe giant magnetostrictive alloy has been successfully prepared by zone melting directional so lidification method.The different technologies of heat treamtent have been resea rched in a TbDyFe alloy with[110]pre ferred orientation.The results show that the annealing can influence the microstructure and magne tostriction in the TbDyF ealloy.The sphericity of the rare-earth phase and the crystal growth,which can decrease the resistance of the domainrotation,is a basic reason fo r high-tem perature annealing to miprove the magne to striction in the alloy.The dependent curves of magnetostriction,added magnetic conductivity and other magnetic parameters on magnetic field were measured by using multiple parameter magnetic measurement system.

Effect of Heat Treatment on S-Segregation of Microstructure for As-Cast High Nb Containing TiAl Alloy

XU Zheng-fang, XU Xiang-jun, LIN Jun-pin, ZHANG Yong, WANG Yan-li, LIN Zhi, CHEN Guo-liang

2007, 27(3): 28-32.

[Abstract](1264) [PDF 1891KB](446)

Abstract:
The effect of heat treatment on the S-segregation of the microstructure for as-cast high containing TiAl alloy was studied.The results show that S-segregation can be eliminated by the heat treatment at the temperature above Tα(1350～1400℃).A large number of β phase appears after short time holding,but β phase will completely dissolve after long time holding and then transform to α phase that becomes lamellar microstructures after cooling to room temperature.The S-segregation can not be eliminated below the temperature of Tα(1250～1330℃)owing to the existence of γ phase.For alloy samples after the heat treatment of 1350℃/24h+900℃/30min/AC and 1400℃/12h+900℃/30min/AC,the S-segregation can be efficiently eliminated and gain lamellar microstructures.The average lamellar colony size is 210μm and 120μm respectively.

Evaluation on Corrosion Resistance of Ceramic Coated Magnesium Alloy

YANG Pei-xia, GUO Hong-fei, AN Mao-zhong, WU Li-jun

2007, 27(3): 33-37.

[Abstract](1571) [PDF 822KB](323)

Abstract:
Ceramic coating was fabricated on magnesium alloys by micro-arc oxidation in solution containing silicate,fluoride,hydroxide and glycerol at constant applied current density.Dynamic polarization curves,electrochemical impedance spectroscopy(EIS),cyclic voltammetry curves(CV) and weight loss measurements were employed to evaluate the corrosion resistance of alloy substrate and ceramic coated magnesium alloy,all the results showed that the corrosion resistance could be improved considerably once micro-arc oxidation was employed on magnesium alloys.

Effect of EB-PVD TBCs Coating on Stress Rupture Properties at High Temperature of IC10 Alloy

WU Xiao-mei, HE Li-min, LI Jian-ping, HE Shi-mei

2007, 27(3): 38-41.

[Abstract](1375) [PDF 1035KB](260)

Abstract:
In this study,NiCrAlYSi bond coating had been deposited on IC10 alloy substrates by arc ion plating as YSZ had been deposited on the bond coating by EB-PVD technology.The effects of TBCs coating on stress rupture at high temperature property of IC10 alloy have been investigated.It has been found that the 980℃/200MPa stress rupture life of IC10 with TBCs coating increases,while the ductility of IC10 superalloy with TBCs holds the line.Namely,TBCs coating has not blight to the stress rupture at high temperature property of IC10 superalloy substrate and satisfies requirement for alloy application.

Isothermal Deformation Simulation and Canned Forging of Ti-45Al-5Nb-0.3Y Alloy

LI Bao-hui, CHEN Yu-yong, KONG Fan-tao

2007, 27(3): 42-46.

[Abstract](1445) [PDF 1697KB](330)

Abstract:
The hot deformation behavior of Ti-45Al-5Nb-0.3Y(at%) was studied on Gleeble 1500 thermo-simulation machine at different temperatures and different strain rates in order to determine the appropriate processing parameters.The results show that the true stress-strain curves present the typical dynamic recrystallization character.The flow stresses increase with the increase of strain rates and decrease of deformation temperatures.The compressed sample at the 1200℃/0.01s-1 condition is crack-free.Depending on the zener-Hollomon parameter,the calculated activation energy of deformation Q is 399.5kJmol-1.Canned forging was conducted using the parameter of 1200℃/0.05s-1 with a reduction of 70% height of ingot.The crack-free pancake was obtained.As-forged alloy has inhomogeneous microstructure comprised of major bended/broken lamella,minor dynamic recrystallization grains and remnant lamella.Dynamic recrystallization primarily occurs along the original lamellar colonies After 1150℃/80min annealing,the extensive recrystallization takes place and fine equiaxed γ grains(d=10μm) are formed,extremely minor remnant lamellae are retained.Compression tests at room temperature show that both strength and plasticity increase after forging and heat treatment.This is the result of the grain refinement and microstructural uniformity due to large deformation and subsequent heat treatment.

Fabrication and Reaction Mechanism of High Purity of Ti₂SnC

BEI Guo-ping, LI Shi-bo, ZHAI Hong-xiang, ZHOU Yang

2007, 27(3): 47-50.

[Abstract](1408) [PDF 495KB](282)

Abstract:
Ti2SnC is a promising candidate material for diverse applications because it combines many good properties of metals and ceramics.However,it is difficult to make a high purity of Ti2SnC powder.Thus,synthesis of high purity of Ti2SnC powder becomes a worldwide task.The influences of starting composition,ratios and parameters on the high purity of titanium tin carbide(Ti2SnC) have been investigated systematically.Ti/Sn/C and Ti/Sn/TiC were sintered at 950~1250℃ for 15~360 min at vacuum atmosphere.The results demonstrated that high purity of Ti2SnC has been obtained by pressureless sintering the above mixture powders.XRD,EDS and SEM were used to characterize Ti2SnC powder.Ti2SnC grains with smooth surfaces are plate like,and less than 10 μm in size and 1~2 μm in thickness.The reaction mechanism was also analyzed on the basis of the XRD and EDS analyses as well as SEM observation.In the Ti-Sn-C reaction system,Ti-Sn compounds were first formed between Ti and Sn,then TiC began to form between Ti and C,at last Ti-Sn compounds reacted with TiC to form Ti2SnC.The above mechanism was further tested by the Ti-Sn-TiC reaction system.

Friction Stir Welding of Magnesium Alloy Processed by Equal Channel Angular Pressing

WANG Kuai-she, WANG Wen, XU Ke-wei

2007, 27(3): 51-54.

[Abstract](1486) [PDF 994KB](216)

Abstract:
An investigation was carried out on the FSW of AZ31 magnesium alloy processed by equal channel angular pressing with a thickness of 15mm.The basic characterization of the weld formation and the mechanical properties of the joints were discussed.The result shows that the effect of welding parameters on welding quality was evidence and welding quality is sensitive of traveling speed.Sound joint can be obtained when welding speed is 37.5mm/min and rotating rate of welding pin is 750r/min.

Microstructure and Crack Susceptibility of Aluminium-Lithium Alloy Weldment

LI Xiao-fei, LI Xiao-hong, XIONG Hua-ping, LI Yan, GUO Shao-qing, ZHANG Xue-jun

2007, 27(3): 55-59.

[Abstract](1431) [PDF 1116KB](301)

Abstract:
By using the transvarestraint test,the welding hot cracking susceptibility of aluminium-lithium(Al-Li) alloy and 2024 alloy has been estimated.The microstructure of the tested alloys were systemically investigated by means of optical microscope and JSM-5600 scanning electron microscope(SEM),and the relation between microstructure and the welding hot cracking susceptibility was discussed.The results have shown that the microstructure of A alloy in welding metal was columnar dendritic,and,due to heterogeneous nucleation mechanism,there was fine equiaxed grains region(EQZ) adjacent to the fusion boundary.By contrast,the microstructure of 2024 alloy was cellular dendritic due to epitaxial growth mechanism.The different microstructure caused higher welding hot cracking susceptibility of A alloy.

Synthesis and Characterization of Asymmetric Polyimides with High Transparency

LIU Jin-gang, YANG Hai-xia, WANG Kai, ZHAO Xiao-juan, FAN Lin, YANG Shi-yong

2007, 27(3): 60-65.

[Abstract](1554) [PDF 594KB](891)

Abstract:
A series of polyimides had been prepared via one-step high temperature polycondensation procedure from 1,4-bis(3'-amino-5'-trifluoromethylphenoxy) biphenyl(m-TFDAB) and 3,3',4,4,'-biphenyltetracarboxylic dianhydride(s-BPDA) or 2,3,3',4'-biphenyltetracarboxylic dianhydride(a-BPDA),respectively.Two polyimides,PI-1(s-BPDA/m-TFDAB) and PI-2(a-BPDA/m-TFDAB) have been successfully prepared by one-step procedure,whose properties were widely researched.The results showed that asymmetry wouldn't greatly affect the thermal and mechanical properties of the polyimides.On the contrary,asymmetry enhanced the solubility of the polyimides in organic solvents and increased the transparency of the PI film.PI-2 was soluble not only in polar aprotic solvents,but in many common solvents.PI-2 film showed good transparency in the visible light region with transmittance of 86% at 450nm wavelength.Furthermore,PI-2 exhibited good thermal stability with the initial thermal decomposition temperature of higher than 580℃ in nitrogen and 67% of residual weight ratio at 700℃.

Influences of the Process on Thickness Uniformity of Films Deposited by Magnetron Sputtering

WEN Pei-gang, YAN Yue, ZHANG Guan-li, WANG Yong-lin

2007, 27(3): 66-68.

[Abstract](1598) [PDF 300KB](713)

Abstract:
The film thickness uniformity is an important reflection of the film quality and the device performance.The influence of the target substrate distance,sputtering power and working pressure on the film thickness uniformity deposited by self-designed magnetron sputtering deposition equipment has been studied.The film thickness measured by SENTECH Instruments GmbH's Spectroscopic Ellipsometry SE800.The result indicates that,the film has a good uniformity at a long target substrate distance.The sputtering power and working pressure also have influence on the film thickness uniformity.

Accelerated Aging and Life-Span Forecast of Sulfured NBR in Glycol

ZHU Li-qun, HUANG Huijie, ZHAO Bo

2007, 27(3): 69-73.

[Abstract](1670) [PDF 1456KB](695)

Abstract:
High temperature accelerated aging was adopted to investigate property changes and life-span of sulfured nitrile-butadiene rubber(NBR) in glycol.Mass loss,mechanical property change,cross-section morphography of sulfured NBR aging in glycol at 70℃,90℃,110℃ were studied.According to Arrhenius equation,regard elongation as criterion,the relationship of velocity constant of aging and temperature was deduced.All results show that substance exchange exists between sulfured NBR and glycol,while sulfured NBR loses weight,sulfured NBR becomes brittle in glycol,holes and flaws also develop,life-span of sulfured NBR in glycol at a certain temperature could be deduced by high temperature accelerated aging.

Preparation of Nanometer Crystalloid Barium Titanate Powder by Improved Citrate Sol-Gel Method

HOU Tie-cui, LI Zhi-hui, LU Hong-xia, ZENG Zhao-huan

2007, 27(3): 74-76.

[Abstract](1482) [PDF 624KB](283)

Abstract:
The method of preparing barium titanate powder by citrate Sol-Gel is simple and the powder got by this way is finer and cheaper than the other ways,but the characteristic of sol-gel system is not steady,so the method can't be developed rapidly.We raised the technique by without introducing H+ and NO3--ions in the preparation process in this paper.The quality of the sol-gel system was enhanced,and the square crystalloid nanometer barium titanate powder was gained after being calcined at 700℃ by the improved citrate Sol-Gel method.The temperature is far lower than the routine method.The powder's average size is about 20nm.

Mechanical Parameter Measurement of Coating on Nickel-Based Directionally Solidified Superalloy

JIA Da-wei, SHI Hui-ji, ZHONG Bin, YU Hui-chen, NIU Li-sha

2007, 27(3): 77-81.

[Abstract](1401) [PDF 575KB](199)

Abstract:
A new method,on consideration of the thickness of coating on nickel based superalloy was presented.This method,which could conveniently measure the hardness and elastic modular of coating,can be employed to study the effect of coating surface and interface condition of the system.the results of conventional nano-indentation technique and that of the same coating on another.DS superalloy matrix, affirmed the validity of the present experimental results.

Multi-objective Optimization of Radar Absorbing Coating Using the Genetic Algorithm

LI Qing-yan, YANG Dong-fang

2007, 27(3): 82-86.

[Abstract](1384) [PDF 1057KB](284)

Abstract:
Multi-objective optimization of radar absorbing coating was designed using the genetic algorithm in this paper.Based on reasonable design for objective functions and the concept of Pareto optimality,multi-objective optimization was investigated.The optimization results show that the algorithm(NSGA) uses sharing and Niche technology and the results can dividedly converge at the Pareto front.Compared with conventional methods,this algorithm with clear physical meaning is more scientific and has extensive pertinence for the decision-makers.

Compressive Properties of Plain Woven Hgbrid Composite Laminate with a Hole

XU Yan-min, CHENG Xiao-quan, CHEN Hao, HU Ren-wei

2007, 27(3): 87-90.

[Abstract](1427) [PDF 1058KB](311)

Abstract:
Experimental study was carried on with the compressive properties of plain woven hybrid composite laminates with a hole.The influence of ply volume proportion and ply stacking sequence on the compressive properties was discussed.Meanwhile the point stress criterion and the average stress criterion were applied to predict the residual strength of the laminates.The results show that the compression strength is distinctly increased with the rising of the volume proportion of 0° ply;and the volume proportion of(±45) ply is good to be between 20~25 percent;meanwhile it is verified that both the point stress criterion and the average stress criterion are suitable for the compression strength prediction of the hybrid composite laminates.

2007 Vol. 27, No. 3