航空材料学报

2013, 33(6): .

[Abstract](980) [PDF 1120KB](94)

Abstract:

Thermodynamic Calculation of Al-9.5Zn-2.0Mg-1.7Cu Alloy

LIU Jun-tao, ZHANG Yong-an, LI Xi-wu, LI Zhi-hui, XIONG Bai-qing, ZHANG Ji-shan

2013, 33(6): 1-7.

[Abstract](1306) [PDF 27143KB](96)

Abstract:
Thermodynamic calculation simulation of solidification paths and phases fraction for Al-Zn-Mg-Cu aluminum alloy were studied by using CALPHAD method. Experimental verifications were carried out by DSC, XRD and SEM. The result show that Al-9.5Zn-2.0Mg-1.7Cu alloy is consist of (Al), (MgZn2) phase, Al7Cu2Fe and a few (Al2Cu). Non-equilibrium solidification calculation is consistent with experimental observation. (MgZn2) fraction arrives at 11.1% when the Zn, Mg and Cu content are 9.5%, 2.0% and 1.7%, respectively. Cu/Mg=1 value is proposed as a criterion to judge the forming of (Al2Cu).

Dynamic Mechanical Behavior of α+β Titanium Alloys at High Strain Rate

CHEN Yang, PEI Chuan-hu, LI Zhen-xi, GAO Fan, LI Si-qing

2013, 33(6): 8-12.

[Abstract](1259) [PDF 12959KB](140)

Abstract:
The dynamic mechanical property, adiabatic shear susceptibility, adiabatic shear band and absorbed energy of 4 kinds of + titanium alloys, i.e., TC4, TC6, TC11 and TC17, at 3000s-1 strain rate, were investigated. The results show that the adiabatic shear susceptibility of TC17 and TC6 titanium alloys is lower than that of TC4 and TC11 titanium alloys, although the local area deformation occurs for all 4 kinds of alloys. The harmonious deformation ability of TC17 is the best of all due to its fine and uniform primary phase. Therefore, the adiabatic shear band is not observed in TC17. The flow stress, dynamic plastic strain and absorbed energy of TC17 are also higher than those of other 3 titanium alloys apparently. The adiabatic shear band of TC6 is created but not extended yet. However, the adiabatic shear band of TC4 and TC11 is extended to obvious cracks and these 2 kinds of alloys suffer adiabatic shear fracture. Therefore, the resisting impact ability of TC6 is much better than that of TC4 and TC11.

Characteristics of Cross Section Deformation of Double-Ridge Rectangular Tube of H96 Brass in Rotary Draw Bending Process

LIU Chun-mei, LIU Yu-li, SHEN Hua-wen, YANG He

2013, 33(6): 13-19.

[Abstract](1255) [PDF 3098KB](123)

Abstract:
Based on the platform of ABAQUS/Explicit, a three-dimensional finite element model of rotary draw bending process for double-ridge rectangular tube was established to study the cross section deformation characteristics of the forming process. The results show that the maximum deformation values of the height, width and spacing between two ridge grooves of the tube cross section is present in the vicinity of the bending angle 60 along the bending direction, and occurs at the webs near the top edges of the ridge grooves, the outer edge of the tube and the bottom edge of the ridge groove of the characteristic cross section respectively. The maximum deformation value of the width of the double-ridge appears in the vicinity of 20 along the bending direction, and occur at the top edge of the outer ridge groove of the characteristic cross section. The obvious asymmetry of the double-ridge appears after the deformation.

Microstructure and Tensile Property of Ru-Containing Ni Base Single Crystal Superalloy

GU Huai-peng, LIU Li-jun, CAO La-mei, XUE Ming, TANG Xin, CAO Xue

2013, 33(6): 20-26.

[Abstract](1299) [PDF 3724KB](145)

Abstract:
The microstructure and tensile property of a Ru-containing Ni base single crystal superalloy were investigated by using scanning electron microscope (SEM), electrical probe metal analysis (EPMA) and mechanical test. The results reveal that Re and W segregate strongly in the dendrite core, while Ta and Al in the interdendritic region. After heat treatment, the segregation of Re and W decrease. The volume fraction and size of cuboidal ' in the dendrite core and interdendritic region phase is 63%, 76% and 0.40m, 0.54m respectively. The results of tensile property under various temperatures (25℃, 760℃, 980℃) show that tensile and yield strength increase first and then decrease with the test temperature increasing. The tensile and yield strength at 760℃ are the best. Unfortunately, the elongation is only 8.8%. Furthermore, the deformation mechanism at 25℃, 760℃ and 980℃ are quasi-cleavage mode, slip split mode and the mixture of quasi-cleavage and dimple mode respectively.

Regulation Effect of External Electric Field Inducing Oxygen Flow on Molten Slag Oxidation in Submerged Arc Welding

LI Xiao-quan, YANG Zong-hui, CHU Ya-jie

2013, 33(6): 27-32.

[Abstract](1302) [PDF 1748KB](145)

Abstract:
During submerged arc welding, the direct current external electric field between molten slag and liquid metal was applied behind the arc to induce directional migration for free oxygen ion, so as to regulate electrochemical oxidation behavior with no change basicity index of molten slag. The variation of oxygen content in weld pool is caused by electrochemical reactions, which occurs at interface of slag-metal for external electric field was studied quantitatively based on Faraday law of electrolysis. Theoretical calculation and experimental test show that the oxygen content of weld metal can be regulated in certain degree with the change of current between slag and metal by external electric field change or regulating technological factors such as weld speed, fusion ration, and it may also influence the metallurgy behavior of active alloying elements in weld metal as well as the formation of inclusion.

Microstructure Evolution of Linear Friction Welded TC6 Joint

MA Tie-jun, ZHANG Xiao-qiang, ZHANG Xue-jun, ZHANG Yong, LI Wen-ya

2013, 33(6): 33-37.

[Abstract](1187) [PDF 3367KB](112)

Abstract:
Linear friction welding (LFW) was carried out on the TC6 titanium alloy using a LFW machine (type XMH-160). Microstructural features and forming process of the weld zone, thermo-mechanically affected zone (TMAZ) and flash were analyzed. The results show that the tensile strength of the LWFed TC6 joint is not lower than base metal, and microhardness corresponds to microstructure features of different zones. Recovery and recrystallization occurr in the weld zone, and the major microstructure are metastable ,martensite and secondary which forms during rapid thermal cycle and deeply deformation. Meanwhile, a small amount of deformed primary was reserved. Recrystallization only occurs in part of the metal in the TMAZ, where flow lines consist of deformed and existed.

Weld Defects and Fatigue Properties of Friction Stir Overlap Joints for 6061-T6 Aluminum Alloy

YANG Xin-qi, CUI Lei, XU Xiao-dong, ZHOU Guang

2013, 33(6): 38-44.

[Abstract](1441) [PDF 4104KB](152)

Abstract:
The fatigue performances of AA6061-T6 friction-stir-welded overlap joints and influences of welds defects were investigated and comparatively analyzed based on the fatigue experiments of single pass and double pass welded specimens. The results indicate that the hook defects always form at the bonded interface of friction stir overlap welded joints and have seriously influence on the fatigue properties of the specimen. The fatigue strength of overlap joints is less than 5.6% ultimate tensile strength of the base materials. The fatigue properties of single pass welded specimens are better than that of double pass welded specimens. The characteristic values of fatigue strength k(R=0.1) for single pass and double pass welded specimens are 17.45MPa and 13.91MPa, respectively. The double pass welding methods do not improve the distributive features of hook defects. The fatigue fracture surfaces of single pass lap-welded joints indicate the multiple crack initiations and the fatigue cracks always initiate from the bottom of the upper plate corresponding to the hooking places. The fatigue propagation zones show the transgranular fracture features are mainly characterized by the typical fatigue striations and some secondary cracks. The quantities of fatigue crack initiation positions and secondary cracks for the double pass welded specimens are greater than those of the single pass welded specimens which result in the lower fatigue properties.

Fatigue Crack Growth Behavior of Inertia Friction Welded Joints of GH4169 Alloy

HUANG Jia, JI Ying-ping, QIN Li-ye, WU Su-jun

2013, 33(6): 45-50.

[Abstract](1294) [PDF 16125KB](127)

Abstract:
The fatigue crack growth tests on different zones of inertia friction welded (IFWed) joints of GH6149 alloy were carried out at 23℃ and 650℃ temperatures, respectively. The microstructure and fracture surfaces were observed by OM and SEM. The results show that the fatigue crack growth rate(FCGR) of IFWed weld metal(WM) is lower than that of base metal(BM), due to the interaction of fine-grain strengthening and brittle precipitations. FCGR of three different zones of IFWed joints all increase along with the rise of temperature, resulting from the weakening crystal and grain boundary, accelerate oxidization in front of crack tip and the decrease of yield strength and elastic modulus at high temperature.

Effect of Shot Peening on Microstructure and Fatigue Life of 7A12 Aluminum

RU Ji-gang, LI Chao, WANG Liang, LI Hui-qu, YI Lin-na, LIU Ming, WU Xiu-liang

2013, 33(6): 51-56.

[Abstract](1435) [PDF 8667KB](122)

Abstract:
The effect of shot peening as mechanical surface treatment on high cycle fatigue property of the high-strength aluminum alloy 7A12 was investigated. The microstructure and fracture of the alloy before and after shot peening were analyzed using SEM and TEM. The residual stress was investigated by XRD.The results show that shot peening increases the fatigue strength by 26%. Shot peening causes residual compressive stress layer in which grain is refined and dislocation is increment. The increase of fatigue strength after shot peening is attributed to the inhibition of fine crystalline zones and dislocations on fatigue crack initiation and the prevent propagation of residual compressive stress on early fatigue crack propagation. Analysis of the fracture surface reveals that residual compressive stress and microstructure are beneficial to the reduction of the fatigue crack growth rate.

Effect of Stretching on Properties of Polytetrafluoroethylene

ZHANG Dong-na, KOU Kai-chang, ZHANG Yu, GAO Pan, ZHENG Zhen-chao

2013, 33(6): 57-61.

[Abstract](1289) [PDF 955KB](160)

Abstract:
Based on the poor resiliency of polytetrafluoroethylene(PTFE), PTFE was stretched at room temperature uniaxially. Samples were stretched to different lengths at the same tensile speed, and the effect of stretching on properties was investigated. Microstructures show that lots of fibrils and cavities form in PTFE. Density decreases with the increase of tensile length due to the formation of cavities. Tensile strength of the non-drawn one is 27.34MPa, and when the tensile length is 59%, tension strength reaches 46.90MPa. Elongation at break increases from 310% to 410% during the same process. Hardness is reduced because of the formation of cavities. The results of the test of compressibility and recovery indicate that with the increasing of tensile ratios, compressibility enhances from 6.74% to 14.29%, while resiliency improves from 4.17% to 6.07%. The stretched PTFE is more suitable to be used as high performance sealing material.

Tensile Failure Behavior of Composites Step-Lap Repair Structure with Different Overlay Direction

LI Na, WANG Zhi-ping, JI Zhao-hui, LIU Kuo

2013, 33(6): 62-69.

[Abstract](1359) [PDF 15759KB](93)

Abstract:
The composite laminates with four different lay-up sequences were repaired by step-lap repair. tensile properties were tested. A 3D finite element model was developed for the progressive damage analysis on step-lap repair of composite laminates. The tensile strength was predicted and the results show that the numerical simulation results are in good agreement with the experimental data. The fracture morphology were observed using SEM. The types of the fracture are mainly debonding between fiber and matrix. The stress distribution on the laminate, patch and adhesive of the repaired composite laminates with four different lay-up sequences were analysed. The results show that the different lay-up sequence has a great influence on stress distribution in matrix, patch and adhesive. The stress is mainly concentrated in the layers of 0 plies and on corner of step jumps greatly.

Impact Damage and Post-Impact Compressive Strength Experiment of Nomex Honeycomb Sandwich Panel

SHI Xiao-peng, LI Shu-lin, CHANG Fei, YANG Zhe

2013, 33(6): 70-75.

[Abstract](1282) [PDF 2147KB](172)

Abstract:
Focused on the impact damage problem of nomex honeycomb sandwich panel, the damaged behavior of the honeycomb sandwich panel was studied after impact. Impact damage was prefabricated on the specimen and the form of specimen after impact was analyzed. The residual compressive strength test was carried out and the change of strain values was observed. Consequently,the flexural load and the breaking load were obtained and compared to that of before impact damage. The results show that the rate of remained flexural load is about 80.0% and the rate of remained breaking load is about 67.7%. Furthermore the rate of the max break strain is 62.9% after impact damage.

Fatigue Crack Growth Life Prediction Method of Attachment Lug Based on R-Curve of Material

WU Li-ming, HE Yu-ting, ZHANG Hai-wei, ZHANG Teng

2013, 33(6): 76-80.

[Abstract](1254) [PDF 1336KB](124)

Abstract:
Based on the R-curve and crack propagation energy release rate theory, the effective energy release rate Geff was narrated as the energy that makes the opened crack grow and is equal to the dissipated energy represented by R-curve in the same load cycle. The fatigue life prediction model which can reflect the physical essence of crack propagation was proposed. The fatigue crack propagation life can be predicted by adding up the length of crack grows in each load cycle using the model. The R-curve of 7050-T7451 aluminum alloy plate was determined and the expression was obtained by using the least square method. The crack growth test of attachment lugs with the same material was carried out. The fatigue crack propagation life of the test pieces was predicted by using the present model and compared with the test data. The results show that the model based on material's R-curve can predict fatigue crack growth life more accurately than Paris Model.

Low Cycle Fatigue Life Prediction of Turbine Disks Based on Walker Equivalent Strain

ZHANG Guo-qian, ZHAO Ming, ZHANG Sheng, SHANG Ti-song

2013, 33(6): 81-85.

[Abstract](1437) [PDF 2774KB](191)

Abstract:
A simplified Walker strain-life prediction model was proposed based on the research of the change of the Walker strain-life prediction model in the 103 ~105. The low cycle fatigue life (LCF) of the disk was predicted by using the simplified model. The experimental data of GH4133 material were used to verify the simplified model,and the fatigue life of disk was predicted by using different methods. The prediction value was also compared with the experimental results.The results show that the simplified model has a higher prediction accuracy. The prediction lives of turbine disks are in good agreement with the experimental results,and the simplified model is simple and easier for engineering applications.

Progress in Research on Stress and Distortion of Thermally Grown Oxides in TBCs

CHEN Yong

2013, 33(6): 86-95.

[Abstract](1255) [PDF 2008KB](173)

Abstract:
Progress in research on the stress and distortion of thermally grown oxides(TGO) was reviewed. The factors affecting the stress and distortion of TGO such as thermal expansion mismatch, creep of bond coat and TGO, growth of TGO, phase transformations of bond coat, interfacial morphology were evaluated. The research method and calculation model including analytical models and finite element models were introduced. In traditional FEM model, the fracture criterion of the TGO is hard to measure, and can't deal with the problem of interaction and growth of multiple cracks. The extended finite element method (X-FEM) coupled with cohesive zone model (CZM) and the Voronoi element model overcomes these shortfalls and shows advantage in simulation of crack problems in TGO without needing of re-meshing and some critical crack parameters which remain experimentally elusive. It will be an effective method in TGO stress, distortion and crack problem.

2013 Vol. 33, No. 6