航空材料学报

High-temperature Oxidation Behavior of Low Cr and High W Content Cast Ni-base Superalloys and Effect of Ta Alloying

ZHENG Liang, GU Chen-qing, YU Bao-zheng, SHE Li, TANG Ding-zhong

2005, 25(5): 1-7.

[Abstract](1467) [PDF 1341KB](210)

Abstract:
The static oxidation tests of three heats of Ta-free(6wt%Al,0wt%Ta) and Ta-containing(5wt%Al,4wt%Ta and 6wt%Al,4wt%Ta) low Cr and high W content cast Ni-base superalloys were carried out in air at 1100℃ for 2min100h.The oxides in the surface of the samples and the spalled oxide scales were analyzed by X-ray diffraction(XRD).The surface and the cross section of the oxidized samples were investigated by optical metallography,quantitive metallography,scanning-electron microscopy(SEM) and energy-dispersive spectrometry(EDS).The results show that the early stage oxidation for low Cr and high W content superalloys is mainly the preferential oxidation of refractory elements rich phases such as MC carbides,M6C carbides and α(W,Mo) phase.The ultimate oxides of both Tafree and Ta-containing alloys after 1100℃/100h isothermal oxidation are NiO,NiAl2O4 and NiWO4.In addition,small amount of NiNb2O6 and Ni(Ta,Nb)2O6 exist in Ta-free or Ta-bearing superalloys respectively.The oxidation kinetic curves of alloys follow a parabolic rate law in different oxidation stage.The Ta addition at the const content of Al can promote the formation of eutectic γ′ and decrease the harmful effects of element sulfur,then improve the oxidation resistance by decreasing the weight gain and retarding the spallation of the oxide scales.6wt%Al,0wt%Ta alloy possesses a similar oxidation resistance to that of the 5wt%Al,4wt%Ta alloy.Therefore,it is feasible to replace Ta by Al in case of only considering the high temperature oxidation resistance.

Effect of High-intensity Ultrasonic on the Microstructure and Grain Refinement of Al-5Ti-1B Master Alloy

HAN Yan-feng, LI Ke, WANG Jun, SUN Bao-de

2005, 25(5): 8-14.

[Abstract](1564) [PDF 1403KB](203)

Abstract:
The influence of high-intensity ultrasonic,which is applied in fabrication and remelting of Al-5Ti-1B master alloy,on microstructure and grain refinement of the master alloy is investigated.When the commercial Al-5Ti-1B master alloy is treated with high-intensity ultrasonic in the remelting process,its microstructure and grain refinement property are improved.The ultrasonic vibration in fabrication can accelerate the reaction of halide salts and aluminium melt,uniform the microstructure and increase the grain refining performance.The united ultrasonic treatments in fabrication and subsequent solidification of the master alloy can change not only the morphology of TiAl3 phase,but also the morphology of TiB2 particles agglomeration.As a result,the particles in the agglomeration do not conglutinate and are spawn-like form instead,and the performance of the master alloy is further improved.

First-principles Study on Electronic Structure of L1₀-TiAl Intermetallic Compound Alloyed by Mn or Nb

CHEN Lü, PENG Ping, LI Gui-fa, HU Yan-jun, ZHOU Dian-Wu, ZHANG Wei-min

2005, 25(5): 15-19.

[Abstract](1469) [PDF 395KB](304)

Abstract:
Using first-principles pseudopotential plane-wave method,the electronic structures and bonding characteristics of L10-TiAl intermetallic compound alloyed by Mn or Nb is calculated.By analyzing the forming enthalpy,it is found that Mn prefer to occupy the Al sites,while Nb is favored to occupy Ti sites.Mulliken population analysis showed that the bonding strength of(001) and(002) intra-layers in L10-TiAl supercell decrease when TiAl is alloyed by Mn or Nb.And Nb addition makes the bonding strength of the interlayer decrease,while Mn addition increase.After compared the ratio of intra-layer bonding strength and interlayer bonding strength,it is found Mn addition is favorable to improve the room temperature brittleness of L10TiAl intermetallic compound,while Nb addition is not helpful.

Study on Microstructures of Pulsed Electron Beam Remelted Carbon Steel 45

LIU Zhi-jian, HAN Li-jun, JIANG Xing-liu, LE Xiao-yun

2005, 25(5): 20-24.

[Abstract](1452) [PDF 1422KB](343)

Abstract:
High power density electron beams generated by multiplate pseudospark discharge chamber have been used for bombardments of 45# steel.The transformations of microstructure both on metal surface irradiated by electron beams and along it’s lengthways depth have been studied in this paper by SEM and TEM.The results showed that metal surface of bombardment region had been melted quickly,cooled and resolidified abruptly,finally became microcrystalline structure or disordered structure.The section has been divided into melting zone,martensite zone,heat affected zone and base metal.Melting zone was self-quenched under high temperature gradient.Martensite zone and heat affected zone was experienced many times of annealing or tempering processes at the bombardment of multiple pulses so that make crystal grains refined distinctly.The results of microhardness and corrosive resistance showed that mechanical properties of surface layer have been improved due to the refined grain.It is concluded that pulsed electron beam is beneficial to metal surface modification.

Strength of Ceramic Joints Bonded with Reinforcements of Intermetallic Compounds

ZHANG De-ku, WU Ai-ping, ZOU Gui-sheng, LIU Gen-mao

2005, 25(5): 25-28.

[Abstract](1490) [PDF 465KB](171)

Abstract:
The microstructures and properties of Si3N4 joints bonded with Ag-Cu-Ti foils and Ti/Ni/Ti multi-interlayer were investigated.The results showed that intermetallic compounds formed as high melting point phase in Ag-Cu matrix.The observation of interfacial reaction layer showed that it is a two-layer structure.The microstructures and joint strengths can be affected by the parameters such as holding time,bonding temperature,thickness of Ti,Ni,and Ag-Cu-Ti.In these experiments,when other parameters were constant,the maximal joint strengths obtained at 30min.970℃,in 30μm of Ti,60μm of Ni and 150μm of Ag-Cu-Ti respectively.

Study on Double Partial Transient Liquid Phase Bonding with Si₃N₄ Ceramic Using Ti/Cu/Ni Interlayer

ZOU Jia-sheng, JIANG Zhi-guo, CHU Ya-jie, CHEN Zheng

2005, 25(5): 29-33.

[Abstract](1514) [PDF 665KB](297)

Abstract:
The influence of Ti foil and bonding technical parameters on bonding strength and interface structure was studied under double PTLP bonding with Si3N4 ceramic using Ti/Cu/Ni interlayer.The results showed that influence of Ti foil thickness on bonding strength was embodied by thickness of reaction layer.Under our experiments conditions,double PTLP bonding technical parameters have no influence on thickness of reaction layer in Si3N4/Ti/Cu/Ni interface,but influence on bonding strength by changing of residual stress in joint.Microstructure of double PTLP bonding Si3N4/Ti/Cu/Ni interface is Si3N4/ reaction layer/Cu-Ni solid solution(a small quantity of Cu-Ni-Ti)/Ni.

Mullitization Behavior of Al₂O₃-SiO₂ Coating Deposited by CVD

CHEN Zhao-feng, CHENG Lai-fei, ZHANG Li-tong, YAN Bo, LI Cong

2005, 25(5): 34-37.

[Abstract](1482) [PDF 903KB](297)

Abstract:
The aim of the paper is to study the phase composition and the mullitization behavior of the Al2O3-SiO2 coating deposited by CVD at 550℃ using AlCl3-SiCl4-H2-CO2 precursor gaseous.The DTA and XRD were used to examine the mullitization behavior of the coating.The as-deposited coating was composed of γ-Al2O3 and amorphous SiO2. The DTA curve has four peaks.The very weak exothermic peak appeared at about 793℃ represented the formation of mullite.The first sharp exothermic peak appeared at about 984℃ represented the formation of δ-Al2O3.The very weak endothermic peak appeared at about 1240℃ represented the formation of α-Al2O3.The second sharp exothermic peak appeared at about 1337℃ also represented the formation of mullite.The results indicate the CVD process was no-oxidation and the Al2O3-SiO2 coating can become into mullite-alumina coating by heat-treating it at 1350℃ for 2h.

Effect of Infiltration Processes on the Microstructure and Mechanical Properties of C_f/SiC Composites Fabricated by Precursor Porolysis

JIAN Ke, CHEN Zhao-hui, MA Qing-song, ZHENG Wen-wei

2005, 25(5): 38-41.

[Abstract](1521) [PDF 1014KB](382)

Abstract:
Three-dimensional carbon fibres reinforced SiC composites(3D-B Cf/SiC) were fabricated via infiltration and pyrolysis of polycarbosilane(PCS)/divinylbenzene(DVB).The effects of infiltration processes on the microstructure and mechanical properties of the Cf/SiC composites were investigated.The results showed that comparison with the vacuum infiltration,heating and pressure infiltration could improve the infiltration efficiency and density so that the Cf/SiC composites exhibited higher flexural strength,reached 662MPa at room temperature.Furthermore,when tested at 1650℃ and 1800℃ in vacuum,the flexural strengths of the samples were 647MPa and 609MPa respectively.

Effect of Ultrasonic Treatment on the Dispersion of Carbon Nanopowder in Phenolic Resion

ZHANG Jie, HUANG Yu-dong, LIU Li, ZHANG Zhi-qian, YANG Xiao-bo

2005, 25(5): 42-45.

[Abstract](1488) [PDF 861KB](364)

Abstract:
The key problem of the preparation of polymer nanocomposite is the homogeneous dispersion of nanoparticles in polymer matrix.In this paper,an ultrasonic method has been performed to improve the dispersion of carbon nanopowders in phenolic resin has been studied.The effects of ultrasonic treatment on viscosity and electrical conductivity of the resin system were investigated.The mechanisms of ultrasound such as the cavitation and agitation streaming aroused by ultrasound in the liquid were analyzed.Moreover,the dispersion characteristics of the carbon nanopowders were evaluated by atomic force microscopy(AFM).The results indicated that the ultrasonic treatment is an available method to decrease the aggregation of the nanopowders.

Study on Properties of a High Temperature Curing Epoxy Resin System

Wuyunqiqige

2005, 25(5): 46-49.

[Abstract](1485) [PDF 694KB](154)

Abstract:
Curing procedure,reaction kinetic parameters,thermal resistance of composite and mechanical performance of BC2526 resin was stutied in this paper.The curing procedure was determined by thermal analysis.According to Kissinger and Ozawa methods,the average apparent activation energy of the resin was calculated which was 91.86kJ/mol.Kinetic order of curing reaction calculated according to Crane method was 0.940.Thermal resistance and mechanical performance of carbon fabric composite were discussed also.

Dynamic Crack Propagation Behavior of the Mg-Li Alloys Under High Loading Rate

SHA Gui-ying, XU Yong-bo, HAN En-hou, YU Tao, LIU Lu, GAO Guo-zhong

2005, 25(5): 50-53.

[Abstract](1487) [PDF 697KB](237)

Abstract:
The impact experiments for the Mg-Li alloys with single phase-structure were carried out using the Hopkinson pressure bar.The dynamic crack propagation behavior and fracture mechanism of the alloys were investigated.The results show that the dynamic crack propagation for the Mg-Li alloys under high loading rate is a deceleration process.As increase in Li,the crack propagation of the alloy slowed down.The fastest crack propagation velocity for Mg-3.3Li alloy is 1253.37m/s,and 935.36m/s for Mg-14Li alloy.And the dynamic fracture surface for the Mg-3.3Li alloy mainly appears to be brittle fracture along grain boundaries, whereas the Mg-14Li alloy shows a ductile fracture mode.The main reason for these is proposed to be the transformation of hcp→bcc structure and the precipitation of the MgLi2Al and AlLi due to the increase of Li content and addition of Al in Mg-Li alloy.

Analysis and Simulation of Machining Deformation Resulting from Residual Stress

DONG Hui-yue, KE Ying-lin

2005, 25(5): 54-58.

[Abstract](1456) [PDF 743KB](361)

Abstract:
With the cutting away of parts of a stressed component,the state of residual stress equilibrium is generally disturbed,and the body has to react by deformation.Assuming stresses induced by the machining process itself may be neglectable, analytical method and finite element model,to investigate the relations of redistributed residual stress and deformation during machining,were used to compute uniaxial stressed rectangular plate with a known distribution of residual stress.The redistributed stress and curvature were computed after removing each layer of material,and the changing trend of residual stress during the operation was analyzed.The analytical and finite element result showed in good agreement.In addition,biaxial stressed plate was simulated using finite element and the results were compared with uniaxial case.Finally the differences of displacement and residual stress in remain part were discussed.

Damage Process of Surface-treatent Coating under Fatigue Loading

WU Wei-qing, RUAN Yu-zhong

2005, 25(5): 59-62.

[Abstract](1385) [PDF 804KB](172)

Abstract:
The effects of phosphate coating、electoless Ni-P coating heat treated at 400℃ and electrodeposited Fe-Ni-P alloy coating on fatigue property have been examined by three-point cyclic bending test.The damage processs of the surfacetreating coatings has been investigated by system analysis method.The results reveal that the fatigue damage of the phosphate coating is a continual process and the fatigue damage of electoless Ni-P coating and electrodeposited Fe-Ni-P alloy coating are a short process.The results also show that the crack of coatings initiates when the slip bands occur on the surface of base steel,and the system analysis method is effective in the surface fatigue damage detecting.

2005 Vol. 25, No. 5