航空材料学报

Study on Heat Treatment of Second Generation DS Superalloy DZ6

HUANG Zhao-hui, JIA Xin-yun, TAN Yong-ning, ZHANG Hong-wei, ZHANG Qiang, ZHANG Jun, TANG Ding-zhong

2008, 28(6): 1-4.

[Abstract](1187) [PDF 835KB](195)

Abstract:
The heat treatment process of the 2nd DS superalloy DZ6(Re-bearing)includes pre-treatment,solution and three-stage aging.The experimental results show that the longitudinal and transverse stress rupture life are improved by adding the first stage aging at 1120℃.Meanwhile,the transverse rupture life at the condition of 870℃/448MPa and the elongation rate of the alloy are increased remarkably from 36 h to 244 h and from 0.6% to 4.5% respectively by aging treatment at 1120℃ followed by slow cooling.The 870℃/16 h aging makes longitudinal rupture life at the condition of 760℃/780 MPa to be twice as that for 900℃/4h aging.After the heat-treatment the γ' phase shows cubic shape and the grain boundary consists of γ'and blocky MC.The proposed heat treatment characterized by the combination of high-temperature aging with slow cooling,not only elevates the longitudinal rupture life of the alloy by one time but also contributes to its good transverse property.

Heat Treatment Processes and Microstructure and Properties Research on P/M Superalloy FGH97

ZHANG Ying, ZHANG Yi-wen, ZHANG Na, JIA Jian

2008, 28(6): 5-9.

[Abstract](1249) [PDF 994KB](385)

Abstract:
The microstructure and mechanical properties of superalloy P/M FGH97,taking two kinds of heat treatment processes,were compared The results show that the temperature of solution,quenching and aging,holding time and cooling-down method directly influence morphology,size,quantity and distribution of γ` phase and carbides in this kind of alloy.The well comprehensive mechanical properties are determined by different matching degree betweenγ` phase and carbides in samples of two kinds of heat treatment processes.The ductility of tensile and rupture-rupture as well as stress rupture property at 750℃ of the samples took heat treatment Ⅰare better than one took heat treatmentⅡ.At the same time,the tensile strength,rupture strength at 650℃,properties of creep resistance and LCF of the samples by heat treatmentⅡare superior to that by heat treatmentⅠ.

Phase Composition of Micro-Arc Oxidation Coating on Magnesium Alloys

LI Song, LIU Yao-hui, ZHANG Ji-cheng, SONG Li-min

2008, 28(6): 10-15.

[Abstract](1269) [PDF 1137KB](271)

Abstract:
Micro arc oxidation(MAO) processing is an emerging,environmentally friendly and simple magnesium alloys surface technique,which has a bright future in aviation,aerospace,walking machine and 3C etc.In this paper,the quantitative estimations for the mass percent of MgAl2O4 and MgO and the crystal size of MgAl2O4 are achieved by the XRD results,consequently,the corresponding response of phase composition to the corrosion resistance is proposed.The results show that the corrosion resistance of the MAO coating improves significantly when the mass percent ratio of MgAl2O4 to MgO is in the range of 0.6~1.0.The crystal size of MgAl2O4 in the coatings obtained with different oxidation time is in the range of 40~50nm.In addition,the crystal size is decreasing and then increasing with increasing the process time.

Friction Changing to Control Thickness Distribution of TC4 Deep Cylinder by Direct-Reverse Superplastic Forming

JIANG Shao-song, ZHANG Kai-feng, WU Hai-feng, XU Yi, LEI Kun, WANG Bin

2008, 28(6): 16-22.

[Abstract](1183) [PDF 1142KB](249)

Abstract:
Based on the direct-reverse superplastic forming TC4 deep cylinder,the influence to final thickness distribution of surface friction of preforming die and forming die was analysed with MSC.MARC.The results show that higher friction coefficient of preforming die can efficiently reduce the thickness of the regions which need to be thinned,resulting in a more uniform final thickness distribution along the component.Lower friction coefficient of forming die can make the sheet tend to integral formation,also resulting in uniform thickness distribution.According to the results of the simulation,the friction of preforming die was increased by machining and the friction of forming die was decreased by spraying lubricant.The aerospace TC4 deep cylinder with uniform thickness(1.50~1.78mm) was fabricated by direct-reverse superplastic forming experiment,compared to the thickness distribution(1.18~2.24mm) of common direct-reverse superplastic forming,the friction modifying direct-reverse superplastic forming was more efficient to form the uniform thickness components.

Effect of Aging Condition on Fatigue Crack Growth in 7055 Aluminum Alloy

HUANG Min, CHEN Jun-zhou, DAI Sheng-long, ZHEN Liang, YANG Shou-jie

2008, 28(6): 23-26.

[Abstract](1353) [PDF 1154KB](427)

Abstract:
The fatigue crack propagation behaviors of 7055 aluminum alloy in under-aged and peak-aged states at room temperature in air were investigated.The microstructures and fatigue fracture surfaces of the alloy were examined by transmission electron microscopy and scanning electron microscopy.The results show that the fatigue crack propagation rate of under-aged alloy is lower than that of peak-aged alloy.The effects of aging conditions on the rate of fatigue crack propagation were explained in terms of the slip planarity of dislocations and the cyclic slip,reversibility.The fatigue fractures of under-aged and peak-aged alloy are all transgranular.In under-aged alloy,fatigue striations were observed.In peak-aged alloy,secondly crackles occur and no striations were observed.

Effect of Shot Peening on Solid Particle Erosion Behavior of AISI420 Stainless Steel

XI Yun-tao, LIU Dao-xin, HAN Dong

2008, 28(6): 27-31.

[Abstract](1312) [PDF 1460KB](244)

Abstract:
The aim of this paper is to study the effect of shot peening(SP) on solid particle erosion(SPE) behavior of AISI 420 stainless steel.The mechanisms of three factors of SP,i.e.,compressive residual stress(CRS),surface roughness(SR) and work-hardening on SPE resistance were investigated.The results show that the SPE resistance of the shot peened specimen is decreased at 90° impingement angle,while it is hardly affected at 30° impingement angle.However,with polishing treatment to the shot peened specimen,the SPE resistance can be improved obviously at both impingement angles.These results can be explained by follow: The high SR increases the effective area under the bunch of solid particles,so it decreases the SPE resistance of the shot peened specimen.The CRS induced by SP can increase crack closure and retard crack propagation,so it improves effectively the SPE resistance,especially at 90° impingement angle.The work-hardening improves obviously the SPE resistance of the shot peened specimen at 30° impingement angle because the micro-cutting resistance of the surface is increased.However,the work-hardening decreases the resistance of SPE at 90° impingement angle due to the poor multi-impact fatigue property of the hardened surface.

Research on Properties of High Speed Steel Prepared by Spray Forming

ZHANG Yong, ZHANG Guo-qing, LI Zhou, YUAN Hua, XU Wen-yong, LIU Na

2008, 28(6): 32-35.

[Abstract](1247) [PDF 897KB](229)

Abstract:
The microstructure and some mechanical properties of high speed steel(HSS) T15 preform made by spray forming were researched.The result indicated that the high-quality perform of HSS T15 exhibited high-density,refined grains and segregation-free macrostructure.The average density of perform before heat treatment(HT) is 8.208g/cm3 and three-point bending strength reaches 1860 MPa.All of them show that spray forming is an appropriate technics to fabricate high-property HSS.But some local porosities were found in HSS perform through scanning electron micrograph(SEM).In order to improve the properties more,some hot-machining to HSS preform made by spray forming.

Microstructure and Properties of Welding Joints for Lase-MIG Welding of AZ3B Transformative Magnesium

TAN Bing, CHENG Dong-gao, GAO Ming, FENG Jie-cai, WANG You-qi

2008, 28(6): 36-40.

[Abstract](1176) [PDF 534KB](281)

Abstract:
The transformative magnesium of 10mm thick AZ3B was welded by the lase-MIG welding.The appearance,the macrophotograph,the microstructure,the Alloy elements profile and the patterns of welded joint was analyzed by means of OM,SEM,X-ray diffraction,etc.The hardness and the strength of welded joint was measured.The result showed that the appearance was perfection by the lase-MIG welding;the width of heat affected zone(HAZ) is less than 100μm,Within welding joint,there were columnar grains of 15-25μm;the proportion of Al and Mn element was increased,becase Mg element was lossed by high welding temperature in the welding zone.There were Mg,Al and a little MgO in the welding zone.Hardness of the welding joint is almost uniformity.The strenghth of welding joint was 222MPa,and the microstructure of fracture is the section of mix fracture.

High Temperature Tensile Properties and Facture Character of Ti14 Alloy after Semi-Solid Deformation

CHEN Yong-nan, WEI Jian-feng, ZHAO Yong-qing, QU Ke-peng, WANG Hui

2008, 28(6): 41-45.

[Abstract](1158) [PDF 793KB](181)

Abstract:
The tensile properties of Ti14,a new typical α+Ti2Cu alloy,after solid and semi-solid forging(SSF) were researched at high temperature.The fractography of specimens were analyzed by SEM.The fracture mechanisms of Ti14 alloy were studied.One kind of the specimens were processed by SSF showed high strength and low ductility under 300℃,and the other kind of the specimens were processed by two methods performed same tensile properties at high temperatures.The fractography of Ti14 alloy after SSF showed a feature of ductile fracture,and much microcracks were detected in fracture surface.

Study on Particle-Reinforced Metal Matrix Nano-Composites Prepared by Pulse Electrodeposition

XU Rui-dong, WANG Jun-li, GUO Zhong-cheng, WANG Hua

2008, 28(6): 46-50.

[Abstract](1264) [PDF 1198KB](226)

Abstract:
Ni-W-P/CeO2-SiO2 particle-reinforced metal matrix nano-composites were prepared on the carbon steel surface by pulse elecgtrodeposition of Ni,W,P,nano-CeO2 and nano-SiO2 particles,the effects of pulse peak current density and pulse duty cycle on the elecgtrodeposition were researched,the characteristics were assessed by nano-particle mass fraction,deposition rare,microhardness and surface morphology.The results show that increasing pulse peak current density or pulse duty cycle led to the grain size decrease of Ni-W-P matrix metal and the increase of nano-CeO2 and nano-SiO2 particles mass fraction.When the pulse frequency,pulse peak current density and pulse duty cycle were controlled at 1000Hz,40A/dm2and 50%,respectively,the fastest deposition rate of 56.24 m/h and the highest microhardness of 712Hv were obtained,the nano-composites possessed clear outline of the matrix metal crystallite,fine crystal size and compact microstructure,uniform distribution of nano-CeO2 and nano-SiO2 particles within the matrix metal.

Microstructure of Laser Remelted Al₂O₃-13wt%TiO₂ Composite Ceramic Coatings on TiAl Alloy Surface

WANG Dong-sheng, TIAN Zong-jun, SHEN Li-da, LIU Zhi-dong, HUANG Yin-hui

2008, 28(6): 51-56.

[Abstract](1241) [PDF 789KB](293)

Abstract:
The Al2O3-13wt%TiO2 composite ceramic coatings prepared by plasma spraying on TiAl alloy surface were remelted by laser.To reduce the crack origination,a lower laser power and energy density was used during laser remelting.The morphology,microstructure and phase constitution of coating were investigated using X-ray diffractometry(XRD),scanning electron microscopy(SEM) and energy dispersive spectroscope(EDS),respectively.The results show that the ceramic coating has smaller grains and higher compactness after laser remelting,and the lamellar structure of as-sprayed coating is also eliminated.The remelted coaing is almost without cracks or other defets.The metastable γ-Al2O3 phase in the remelted area transfers into stable α-Al2O3 phase.The ceramic coating cannot be total remelted due to low thermal conductivity of ceramic material.According to the microstructural difference,the ceramic coating can be divided into the remelted zone(fine equiaxed grains),the sintered zone and remained plasma-sprayed zone(lamellar-like structure).

Originate Mechanism and Prevent Process of Substrate Cracks in Laser Cladding MCrAlY Coatings on Nickel-Based Superalloy

WANG Hong-yu, ZUO Dun-wen, LU Ying-yan, XU Hong-hao

2008, 28(6): 57-60.

[Abstract](1257) [PDF 850KB](280)

Abstract:
Aiming at substrate cracks in the laser cladding MCrAlY coatings on nickel-based superalloy,technological measures for preventing cracks by slow cooling rate treatment were presented based on the originate mechanism of substrate cracks in the paper.Two slow cooling rate treatments were respectively furnace cooling after heat preservation for 30 min under 300℃ and cooling in insulated cabinet which was heated to 300℃,and their prevent behaviors to substrate cracks were discussed.The results show that the reason which originates substrate cracks of the laser cladding MCrAlY coatings on nickel-based superalloy is the rapid-cooling of substrate in the course of laser cladding,and two slow cooling rate treatments can both effectively prevent the originate of substrate cracks.Moreover,the furnace cooling treatment causes coarse microstructure and obvious dendrite characteristic,but the cooling in insulated cabinet doesn't produce any negative effect.

Study on Characters of Corrosion Advancing Edge of Typical High Strength Aluminum Alloys

ZHU Li-qun, GU An, LIU Hui-cong, LIU Jian-zhong, YE Xu-bin, HU Ben-run

2008, 28(6): 61-66.

[Abstract](1172) [PDF 1458KB](469)

Abstract:
The micro structure of the corrosion advancing edge of typical high strength aluminum alloys(2024 and 7B04) were investigated.The samples were exposed in 3.5% NaCl solution for several durations.It was found that the expansion speed of corrosion,the shape modes of the pits and the micro structure of the pits including the micro crack of these two aluminum alloys were different.The corrosion mechanism and the influence of the micro structure of pits to the fatigue endurance were discussed.The fractal theory was used to quantify the structure of the corrosion advancing edge by determining the fractal dimensions of the cross-section contour of the pits.

Study on Action Mechanism of Y₂O₃ on High Temperature Oxidation-Resistance of Cr-Nb Alloy

SU Qian, LU Shi-qiang, LIU Zhi-he, ZHENG Hai-zhong

2008, 28(6): 67-71.

[Abstract](1244) [PDF 483KB](229)

Abstract:
Cr-Nb alloys with 0.5wt.% Y2O3 were prepared by mechanical alloying(MA) and hot pressing.The action mechanism of Y2O3 on the high temperature oxidation properties of Cr-Nb alloy was investigated at 1100℃ and 1200℃ respectively.The results show that the addition of Y2O3 slows down the oxidation speed at 1100℃;Though the weight gain of the sample added Y2O3 is slightly higher than that of Cr-Nb alloy without Y2O3 exposured at 1200℃,Y2O3 can,based on the results of SEM,increase the adherence of oxide film/substrate and improve the oxide film anti-flaking,which improve high temperature oxidation-resistance properties of Nb-Cr alloy to a certain extent.

Research on RTMable Polyimide Composites Toughened by Ex-situ Methed

LIU Zhi-zhen, LI Hong-yun, XING jun, YI Xiao-su, YANG Hui-li, WANG Zhen

2008, 28(6): 72-77.

[Abstract](1247) [PDF 844KB](371)

Abstract:
The effect of Ex-situ method on the mechanical properties and toughness of the RTMable polyimide composites were studied.The results showed that the interlaminar shear strength of composites toughened by the Ex-situ technique was improved from 97.9 MPa to 110 MPa.when the thermoplastic PI content is 15wt %,However,the Tg and the interlaminar shear strength of composites at high temperature(288℃) decreased slightly.The Mode I fracture toughness(GIC)of composites toughened by the Ex-situ method was improved from 310J/m2 to 459J/m2.From SEM results,the main reason is that the PI-9731/G827 composite toughened by the Ex-situ method with the thermoplastic PI,the phase inversion structure can be obtained in the rich resin regions,the PI-9731 particles that were wrapped by thermoplastic PI will be orientated and deformed in the process of crack extension.

Effect of Content of SiC on Properties of Ti₃SiC₂/SiC Composites

YIN Hong-feng, FAN Qiang, REN Yun, ZHANG Jun-zhan

2008, 28(6): 78-81.

[Abstract](1117) [PDF 1183KB](274)

Abstract:
Ti3SiC2/SiC composites were fabricated by reactive hot pressing method.Effect of the content of SiC on the densification,mechanical properties and the behavior of stress-strain of the composites were investigated.The results showed that:(1) It became more difficult for the composites to densify when the content of SiC in composites was increased.It need be sintered at higher temperature to get denser composite;(2) The flexural strength and fracture toughness of composites increases when the content of SiC added in composites was increased.However,when the content of SiC reached 50% the flexural strength and fracture toughness of composites decreased due to high content of pore in composites;(3) Ti3SiC2/SiC composites were non-brittle at room temperature.

Residual Stresses,Warpage and Shrinkage Analysis of Injection Molded Transparent Panel Based on Optical Distortion

CHEN Yu-hong, YUAN Yuan, ZHANG Yi-sheng, LI Xi, ZHAN Mao-sheng

2008, 28(6): 82-87.

[Abstract](1260) [PDF 1691KB](338)

Abstract:
This paper investigates application of residual stresses and warpage simulation on the prediction of injection-molded transparency’s optical distortion.Numerical models of residual stresses and warpage were established,and HsCAE software modules were adopted to analyze residual stresses,warpage and shrinkage of injection molded transparent panel.The results show that residual stresses and thickness shrinkage in central zone of the transparent panel were much smaller and evener than in the panel edge,and warpage reached its maximum in pane centre and decreased uniformly from the centre to the surroundings.Panels were injection molded,and the test results verified the numerical simulations.Optical distortion tests indicate that the central zone where residual stresses and warpage were evenly distributed has a low optical distortion,but the panel edge where residual stresses and warpage were irregularly distributed shows a serious optical distortion.The results demonstrate the significance of numerical simulation on predication of injection-molded transparency’s optical distortion.

Preparation of Silicon Nitride Ceramics by Pyrolyzing Thiol-Vinyl Silizane Polymer Derived Precursor Cured by UV

SONG Jia-Le, CHEN Li-xin, WANG Ya-zhou, YU Cheng-yan, WANG Ru-min

2008, 28(6): 88-92.

[Abstract](1270) [PDF 534KB](282)

Abstract:
Silicon nitride ceramics were prepared by pyrolyzing the thiol-vinyl silizane polymer derived precurosors cured by UV.The pyrolysis behaviors of precurosors with different weight ratio of thiol to vinyl silizane were studied by TGA,and the ceramic phase compositions and the microscopic structures of samples were characterized by XRD and SEM,respectively.The results showed that there were two peaks of rate of mass loss at 325~350℃ and 475~505℃ in DTA pattern,and the value of the peaks enhanced with increasing the amount of thiol compound.Moreover,the crystallinity,the size of grain increased and the relative density,the yield rate of the ceramic decreased with incorporating more thiol compound.α-Si3N4 crystals were formed after pyrolysis under 1400℃ for 15h.α-Si3N4 could partially be converted into β-Si3N4 by prolonging pyrolysis time.The fiber-like and sheet crystals of nitrogen-rich SiNx were found in the holes of the microstructure.

Fabrication and Characterization of β-Si₃N₄ Seeds with Additive of MgO

TONG Jian-feng, ZHONG Ling-sheng

2008, 28(6): 93-95.

[Abstract](1195) [PDF 295KB](198)

Abstract:
In the sintering processing of the self-reinforced,the addition of β-Si3N4 as seeds material is effective for development and growth of long-pole crystal which can enhance the intensity and toughness of ceramics.In this paper,β-Si3N4 with completeness of phase transformation and pole-liked morphology have been developed by means of heating the initial Si3N4 powder with certain additive of MgO.The influence of MgO on phase transformation and seeds morphology was investigated.The result showed that taking MgO with 1.5wt% and 2wt% additive contents,under 1750℃ for two hours,the β-Si3N4 seeds with up to 95% β phase content could be gotten.

Effect of Z-pins on Connecting Performance of Single-Lap Composite Joints

TAO yong-qiang, JIAO gui-qiong, WANG bo, CHANG yan-jun

2008, 28(6): 96-101.

[Abstract](1137) [PDF 1256KB](199)

Abstract:
In this paper the single-lap joint reinforced by Z-pins is studied on its carrying capacity through experiments.The results indicate that Z-pins can restrain cracking and improve carrying capacity,because the varied load has a stabilization area.Area is shaped by the interaction between Z-pins and joint,during Z-pins draw from the joint.The paper stimulates the connecting performance of the single-lap joint reinforced by Z-pins,including no-pins,different diameters and spacing' Z-pins,modeling results are agreed with experimental results.The numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints.

2008 Vol. 28, No. 6