航空材料学报

THE EFFECT OF TEMPERING ON STABILITY OF RETAINED AUSTENITE IN AUSTEMPERED 40CrMnSiMoV STEEL

Hu Guangli, Kang Mokuang, Hwa Wanjun, Hu Jianghai, Shang Zhenheng

1985, 5(1): 1-6.

[Abstract](1271) [PDF 4808KB](69)

Abstract:
The effect of tempering on stabili'y of retained austenite in 40CrMnSiMoV steel,subjected to austempering at 310℃ for holding 12 min,is investigated in this paper, The experiments carried out include determination of tempering transformation kinetics of retained austenite(AR),examination of micro-structures after temfering, and the study of stability of AR during tempering, the relationship between the mechanical stability of AR and tempering temperature under static and dynamic (repeated impact) stretch strain.The results indicate that, the TTT-Curve of AR consists of two strain.The results indicate that, the TTT-Curve of AR consists of two parts,i, e.upper part and lower part, between which there is a stable zone (375~475℃),the lower part with C-shape is similar in shape to TTT-Curve of overcooling austenite.The variation of thermal stability of AR with tempering temperature displays the curve like a saddle in shape, It means that,with increasing tempering temperature, the amount of AR decreases at first, and then increases, finally decreases again, As the tempering temperature increases,the mechanical stability of AR under static and dynamic stretch strain increases at first,and then decreases. The change of mechanical stability of A,depends mainly on its carbon content, The optimum combination of strength and toughness for this steel can be obtained by tempering at 260~280℃ as the mechanical stability of AR is the highest.

THE INFLUENCE OF ORIENTATIONS ON THE THERMAL-MECHANICAL FATIGUE BEHAVIOR IN SUPERALLOY STNGLE CRYSTALS

Liu, Changda, Wang Haiqing, Yan liIinggao

1985, 5(1): 7-12.

[Abstract](1245) [PDF 4716KB](58)

Abstract:
The effect of c.rystal orientations on the thermal-mechanical fatigue (TMF) behavior in single crystal of nickel base superalloy DD3 has been investigated. It was found that the TMF beha vior of DD3 specimens was noticely affected by the crystal orientations in a sequence of[111],[001] [137] and [011].The thermal-mechanical fatigue beha}aior of various crystal orientations h.;s been analyzed by using the damage mechanics method, It was recognized that the TMF performance depends primarily upon the critical damage value Dc,which is a function of the ductility and the primary cumulative strain rate of a specimen investigated, The rolationship of the ductility, the primary cumulative strain rate and the TMF life of a superalloy single crystal with the lattice rotation and Schmid factor of the operative slip systems during thermal-mechanical cyclic loading is discussed.

THE INFLUENCE OF DIRECT AGING TREATMENT ON THE STRUCTURES AND THE MECHANICAL PROPERTIES FOR GH169 ALLOY

Jin Zhe, Jiang Guizao, Zhou Ruifa

1985, 5(1): 13-19.

[Abstract](1177) [PDF 5419KB](67)

Abstract:
In this paper, the influence of direct aging (DA)treatment on the microstructures and mechanical properties for GH169 alloy was studied. The results indicate that the tensile strength, tensile plasticity and low-cycle fatigue properties are remarkably increased and stress-rupture properties are not changed basically by DA treatment,The strengthing of the alloy may be ascribed to the comprehensive effect of the higher density dislocation,sub-structure,fine grain and dispersed ',''and phase after DA treatment, In which the contribution of dislocation density() and subgrain size(L) on yield strength at room temperature can be expressed by the following equations. 0.2=672.8+5.910-41/2

A STUDY OF TENSILE DEFORMATION,FRACTURE CHARACTERISTICS AND日BRITTLENESS IN AN α+βTITANIUM ALLOY

Jiang Kaiyan, Cao Chunxiao, yan Minggao

1985, 5(1): 20-24.

[Abstract](1279) [PDF 3896KB](74)

Abstract:
The tensile deformation and fracture behaviour of a heat-treated - titanium alloy TC-11 using a micro-tensile device under a microscope were investigated.The tensile properties and fracture characteristics of heat-treated specimens in comparison with that of conventionally - heat-treated alloy is also described in this paper.Experiment results indicate that the interfacial slide of a plates in widmanstatten structure developed during p heat-treatment appears to be a predominate mode of deformation for a heat-treated specimen under a tensile loading, The interfacial, slide of a plates promotes the void nuclea-tioa at interfaces of plate-like a and grain boundary - consequently leads to the crack growth preferentially along these interfaces, Hence the brittleness of a heat-treated ,titanium alloy may be considered as the occurrence of interfacial slide accelerates the void nucleatio n, coalesce and crack propagation in the wid.manstatten structures, from which a higher crack initiation and propagation rate in a heat-treated alloy than that in equiaxed structures would be expected.

A STUDY OF MICROSTRUCTURE OF A HIGH STRENGTH AND STRESS CORROSION RESISTANT ALUMINUM ALLOY

Hua Mingjian, Li Cliunzli, Liu Cunyu

1985, 5(1): 25-29.

[Abstract](1201) [PDF 3930KB](79)

Abstract:
The microstructures of Al-Zn-Mg-Cu commercial alloy have been investigated using transmission electron microscopy. Complex diffraction ,pattern from the matrix and precipitates were recorded.by means of selecte8 are electron diffraction method and analyzed by computer technique.It was Found that when the alloy reaches its peak strength and excellent stress corrosion resistance,its microstructure was characterized predominantly by the presence of }} truasition phase,from 40 to 60in size.The plate shaped n,precipitate has a hexagonal crystal st:ucture with lattice parameters a=4.96,c=8.63,and its orientation relationship with the matrix is {110}At//{100}',111At//001'.The improvement of the strength and the resistance to SCC of the present alloy can be attributed to the fine dispersion and the semi-coherency of ' transition phase.

SURFACE TREATMENT FOR CARBON FIBRES BY ELECTROPOLYMERIZATION

Li Bing, Shen Siting, Zhang Fengfan

1985, 5(1): 30-35.

[Abstract](1308) [PDF 4433KB](89)

Abstract:
Surface treatment for carbon fibres by electropolymerization can enhance the bond between the carbon fibres and the resin.The short beam interlaminar shear strength of the composite can be increased to above 800kg/cm2.The impact strength and the shear strength in net and at the temperature of 125℃ can be improved, This method promises to obtain the comprehensive excellent properties of the composite by controlling the structure and the thickness of the polymer electropolymerized,SEM, the infrared spectrascopy and the voltammetry were used in the experiment.

NUMERICAL SIMULATION OF SOLIDIFICATION OF A COPPER-BASE ALLOY CASTING

Zeng Xiancheng, Robert D.Pehlke

1985, 5(1): 36-46.

[Abstract](1156) [PDF 7947KB](36)

Abstract:
The solidificatio n process of cylin drical castin gs of 5-5-5-5 leaded red brass was monitored by placing eight thermocouples in the castings and the molds and automatically recording the thermocouple signals through a scanning device ,a digital thermometer and a teletypewriter, The reproducibi-lity of these experiments was excellent. In the computer simulation of the casting solidification,a new tecnmque to determine initial temperature distribution throughout the casting and the mold has been developed, In order to further improve the accuracy of the simulation of solidification,a method of treating the metal-sand interface condition was incorporated which includes calculating extra-nodes at the interface,analyzing a physical model of gap formation, and employing: more reliable heat transfer coefficient.The numerical simulation of the solidification process with correcteted initial and boundary conditions was very efficient and accurate.Computed temperature-time profiles from the heat transfer simulation are in excellent agreement with the experimentally measured cooling curves.

INVESTIGATION ON THE STATIC RELAXATION OF THE RESIDUAL. STRESS AND THE OPTIMUM RESIDUAL STRESS FIELD INTRODUCED BY SHOT PEENING

Qiu Qiong, Wang Renzhi

1985, 5(1): 47-54.

[Abstract](1228) [PDF 6477KB](71)

Abstract:
The phenomenon and mechanism of the relaxation of compressive residual stress introduced by shot peening under the static loading action at the ini-tial statge of fatigue and the optimum residual stress field have been inves-tigated, It is shown that the static relaxation of residual stress during the fatigue process is the result of the serious plastic deformation of the materials on the surface layer of the specimen.A amount of crystalline cracks would occured at grain boundaries, phase boundaries and other obstacles on the surface layer of the specimen due to the static relaxa-tion of residual stress which cause such serious damage of the materials that decrease the initiation period of the fatigue cracks.In order to avoid the damage by the static relaxation of residual stress at the initial stage of fatigue, the temper at the lower temperature after shot peening is used, which reduce the level of the highest compressive residual stress in the residual stress field resulting the establishment of the optimum resi-dual stress field, The relaxation of residual stress by means of the heat activation is the relaxation without any damage to the microstructure of the materials.'Therefore, the fatigue life in the area of the higher alterna-ting stress in S-X curve can be increased effecti}}ely after obtaining the optimum residual stress field.

A STUDY Oh LOW-AND HIGH-CYCLE COMBINED FATIGUE CRACK PROPAGATION FOR A SUPERALLOY GH36

Niu Kangmin, Tu Bailin, Yan Minggao

1985, 5(1): 55-60.

[Abstract](1191) [PDF 4620KB](79)

Abstract:
In this paper,the combined fatigue crack propagation behavior at 600℃ for a superalloy GH36 is presented.It was found that the effect of vibration loading on FCP in the combined fatisue testing may be divided into two Stages: 1)the deceleration stage,while the crack propagation is dependent primarily on the low-cycle loading; 2)the acceleration stage,in which the vibration loading becomes a dominant factor.n transition point between two stages was found to be at about △Kmin=3.5~5 MPam1/2.The vibration loading appeared to restrain the creep damage at elevated temperature and an interaction among LCF, HCF and creep in the course of the combined fatigue testing was noted.

PLANE STRAIN JR CURVES OF DIFFERENTLY HEAT-TREATED LY12 ALUMINIUM ALLOY

Qian Zongqi, Chen Changqi, Tian Shixing, An Dashun

1985, 5(1): 61-66.

[Abstract](1188) [PDF 4022KB](61)

Abstract:
Plane strain JR curves of the natural aged, underaged, peak-aged, overaged and hot-rolled LY12 aluminium alloy, in both L-T and T-L directions,were determined experimantly by a partially unloading compliance method.The curves-were fitted by least-squ area parabolas,their errors and correlation coefficients were computed, Following Hutchinson and Paris,the restricted conditions for the validity of the JR eurves were checked.

THE APPLICATION OF STATISICAL DISTRIBUTION THEORY TO TIME-DEPENDENT FATIGUE LIFE PREDICTION

Dong Zhaoqin, He Jinrui, Duan Zuoxiang

1985, 5(1): 67-72.

[Abstract](1184) [PDF 4100KB](50)

Abstract:
In this paper, the applications of normal distribution,lognorrnal distribution and Weibull(2 parameter)distribution to time一dependent fatigue life predic-tion are discussed. The focus is on the Frequency Separation model(FS) and the Strain Energy-Frequency Separation model (SEFS).The method discussed has evaluated by twelve kinds of materials and processes used both at home and abroad, The results show that for high strength nickel-base alloys and copper-base alloy, from the point of view of statistics, the predictability of SEFS appears to be much better than that of FS, and that the lognormal distribution is generally the best fit model for the results predicted by FS and is the best fit model for the results predicted by SEFS.

INFLUENCE OF ALUMINIDE COATING ON FATIGUE BEHAVIOR OF A NICKEL SUPERALLOY

Xu Jianping, Yiong Jiyuan

1985, 5(1): 73-79.

[Abstract](1174) [PDF 15335KB](38)

Abstract:
The influence of the technology and the thickness of an aluminidc coating onmechanical fatigue of a nickel-alloy at 700℃ has been studied, It was shown thatthe brittleness and the surface roughness of coating were the basic causes to theearlier rupture of a system.The thicker coating, the more harmful to fatieue per-formance.The mechanism of influnece of coating on metal fatigue and the possib-ility to estimate fatigue life of coating/alloy system were also discussed.It is beliaved that the stress concentration caused by coating crack; accelerated substrate-alloy to rupture.

1985 Vol. 5, No. 1