航空材料学报

Study of grain growth and mechanical properties of ahigh strength cobalt-free maraging steel

HE Yi, YANG Ke, MAO Ping-li, KONG Fan-ya, SU Guo-yue

2002, 22(4): 1-5.

[Abstract](1561) [PDF 786KB](385)

Abstract:
Grain growth behavior and its effect on the mechanical properties for 00Ni18Mo4Ti alloy,a high strength cobalt-free maraging steel, have been studied with Leica Metal Work software on the Leica Microsysteme optical microscope. The experimental results showed a normal grain growth behavior at the solution temperature range of 1073～1473K for the experimental steel. The grain growth exponent increases with increasing solution temperature and the activation energy remains in a range of 170～210 kJmol-1.The relationship between yield strength and grain size well accords with the HallPetch relation, but the KICincreases as the grain grows. A good combination of strength and toughness can be reached for this steel, i.e., YS=2050MPa,KIC=70MPa·m1/2, δ9% and 50%.

Analysis and simulation on cyclic superelastical deformation behavior of TiNi shape memory alloy subjected to loading and unloading

GONG Jian-ming, TOBU SHI HISAAKI, TAKATA KAZUYUKI, OKUMURA KAYO

2002, 22(4): 6-12.

[Abstract](1733) [PDF 320KB](267)

Abstract:
Superelasticity is one of the important mechanical properties of shape memory alloy (SMA). In the present paper, the superelastic deformation behavior of TiNi SMA under various loading conditions with different experimental temperatures and strain rates was discussed based on the experimental studies. The change of transformation stress and the modulus of elasticity during cyclic deformation was analyzed from the continuum mechanical point of view. The cyclic superelastic deformation of TiNi SMA subjected to loading and unloading is characterized by introducing three internal variables, that is, the residual stress and strain which are accumulated during cycling and the residual martensite phase which is also accumulated. The method of simulating cyclic super-elastic behavior deformation was proposed. The modulus of elasticity during the internal loop is expressed by the mixed rule with the function of transformation strain. It is important to design perfect SMA working elements and to evaluate their reliability.

Study of fretting wear behavior of K417 nickel base superalloy

XU Xiang-yang, XU Bin-shi, LIU Wen-jin, LIU Shi-can, ZHOU Zhong-rong

2002, 22(4): 13-17.

[Abstract](1484) [PDF 270KB](261)

Abstract:
Fretting wear behavior of K417 nickel base superalloy was investigated. The results show that process of fretting wear of K417 nickel base superalloy could be divided into three stages that are initiation, transition and stabilization stage. Mechanism of fretting wear is mainly fatigue delamination at steady stage. At high temperature, dense glazing oxide film could be formed at the wear surface of the K417 nickel base superalloy. Because of excellent high temperature strength K417 nickel base superalloy could sufficiently support glazing oxide film and make it continuous and integrate. Glazing oxide film that could decrease shear stress and change its distribution could alleviate fretting wear of K417 nickel base superalloy.

The study on lowering rolling temperature for Fe₃Si based alloy

NIU Chang-sheng, WANG Yan-li, LIN Zhi, LIN Jun-pin, CHEN Guo

2002, 22(4): 18-20,25.

[Abstract](1385) [PDF 174KB](249)

Abstract:
The various rolling and heat treatment techniques were used to study their effects on the plastic properties of the Fe3Si based alloy. Through the tensile tests of both room temperature and high temperature, it was found that the plastic properties of the Fe3Si based alloy could be greatly improved and the rolling temperature could be reduced to 300℃by water cooling treatment.

Quantitative study on influence of chemical heat treatment on apparent fatigue limit of 40Cr steel

GAO Yu-kui, YAO Mei

2002, 22(4): 21-25.

[Abstract](1463) [PDF 796KB](314)

Abstract:
The influence of chemical heat treatment on apparent fatigue limit of structural steel was studied quantitatively.Smooth and notched specimens made of 40Cr steel were quenched and tempered at high temperature. Nitriding as surface hardening tech-nology was used.5×106 cycles fatigue limits with stress ratio R equal to -1 were determined on rotating bending and torsion fatigue test machines.The results show that for nitrided 40Cr steel notched specimens,the fatigue notch sensitive coefficient,q,is about zero and it was explained clearly by micro-meso-process theory for fatigue crack initiation. The fatigue limits of 40Cr steel smooth specimens after nitriding increase by about 36%, while those of notched specimens increase by about 96%, and their fatigue crack source is moved from the surface to the internal region beneath the nitrided layer. Based on experimental works and theoretical analysis, a judgement for the optimization condition of the surface hardening processes is proposed.The technology should be considered to be optimum, if the fatigue crack source of surface hardened specimen has been moved to the internal matrix metal region beneath the hardened layer; and their apparent fatigue limit has been improved and got to a value, near to that predicted according to the concept of surface/internal fatigue limit.

Sub-microstructure titanium aluminide obtained by crystallization of mechanically alloyed amorphous Ti-50at%Al

ZHANG Jun-hong, HUANG Bai-yun, HE Yue-hui, LIU Yong, ZHANG Yong-hong

2002, 22(4): 26-30,45.

[Abstract](1465) [PDF 272KB](272)

Abstract:
A sub-microstructure titanium aluminide was obtained by crystallization of the amorphous Ti-50at%Al powders, which were prepared by high-energy milling in a planetary ball milling system for up to 100h. The X-ray diffraction, differential thermal analysis techniques and scanning electron microscope were used to characterize the structure evolution during the milling and the process of crystallization. Results show that, after 60h milling, aluminum completely dissolved into titanium to form an Ti(Al) hcp supersaturated solid solution, and at the same time a small amount of amorphous phase was produced. When the milling time was increased to 100h, the Ti(Al) hcp supersaturated solid solution disappeared, and only amorphous phase was left.The milling process can be describe by: Ti+Al→Ti(Al) hcp→Amorphous. Crystallization occurs at the process of decency during hot pressing, and the crystallization process can be describe by: Amorphous→disorderedα(hcp)→ordered -γTiAl phase(+ordered α2-Ti3Al phase). The disordered α phase is a metastable phase during this process, and with increased temperature and longer annealed time, the transformation of α→ γ(α2) occurs. From the micrograph of the hot-pressed γ-TiAl phase, it is supposed that the transformation may be a massive transformation.

Numerical computation of SIF_s for bimaterial-interfacial crack by meshless method

LOU Lu-liang, ZENG Pan

2002, 22(4): 31-35.

[Abstract](1467) [PDF 1255KB](337)

Abstract:
A modified meshless method was presented for numerical investigation of stress intensity factors (SIFs) for bimaterial interfacial cracks. The domain was diecretized into integral subdomains based on the nodal Voronoi diagram, which assured this method was a true meshless method. By adopting nodal refinement at the vicinity of the crack tip, the computational accuracy of displacement field was improved. Displacement extrapolation method was used to determine the SIFs, this could bypass the singularity of the stresses. Bimaterial structures, bonded by Araldite and Al-filled Araldite, were analyzed at the end of this paper. Three computational models: coarse model, uniform refinement model, and local refinement model were used and compared. The numerical results calculated with local refinement model agree well with the results from photoelastic experiment, which validates the efficiency of this method.

Influence of cross-linking reagent on the pyrolysate of polysiloxane as precursor to Si-O-C ceramics

MA Qing-song, CHEN Zhao-hui, ZHENG Wen-wei, HU Hai-feng

2002, 22(4): 36-39.

[Abstract](1451) [PDF 185KB](348)

Abstract:
Hydrogen-containing Polysiloxane (HPSO) was cured with vinyl-containing Polysiloxane (VPSO) and divinylbenzene (DVB) as cross-linking reagent, respectively. The pyrolysates of DVB/HPSO and VPSO/HPSO were characterized by XRD, FTIR, and element analysis (EA). The results showed that the structure and component of pyrolysate of DVB/HPSO were different from those of pyrolysate of VPSO/HPSO. The difference resulted from the different structures of cured DVB/HPSO and VPSO/HPSO.

Study on properties of SY-H1 paste adhesive

QIAO Hai-tao, ZOU Xian-wu

2002, 22(4): 40-45.

[Abstract](1587) [PDF 1236KB](265)

Abstract:
SY-H1 is amedium temperature curing one-component paste epoxy adhesive.Properties of SY-H1 adhesive such as curing process conditions,water resistance,thermal aging,temperature alternate cycles,room temperature storage,hotwet aging and fatigue are introduced in detail.SY-H1 adhesive has the characteristics of lower curing temperature,higher temperature resistance and also longer room temperature storage life.It can be used in bonding of steel,aluminum and composite.

Studing status on the secondary hardening phenomenon in ultra-high strength steels

ZHAO Zhen-ye

2002, 22(4): 46-55.

[Abstract](1718) [PDF 1945KB](495)

Abstract:
Studying development on the thermaldynamics,crystallology,kinetic stability and strengthening mechanism for precipitation of M2C carbide in ultrahigh strength steels has been evaluated. Investigation results show that M2C, nucleating on dislocation and coherent precipitating, can be used for strengthening phase although not in the equilibrium state. The driving force to nucleate and coarsening resistance for M2C is greater than any other carbides. Furthermore Co causes the markedly increase in the driving force to nucleate and nucleating coefficient for M2C. Mocauses the largest lattice parameter and enhances coarsening resistence for M2C.

Application of element Zr in aluminum alloys

XIE You-hua, YANG Shou-jie, DAI Sheng-long, LU Zheng

2002, 22(4): 56-61.

[Abstract](1686) [PDF 1016KB](866)

Abstract:
The appearance of element Zr in aluminum alloys was summarized in the paper. Effects of the element on aluminium alloys such as recrystallization behaviour, quench sensitivity, aging behaviour and comprehensive properties (tensile strength, fracture toughness and stress-corrosion resistance etc.) were emphasized on. Applications of element Zr in aluminum alloys, especially in high-strength aluminum alloys were briefly introduced. Based on the new tendency of current research and development, it was pointed out that the understanding and investigation of element Zr should be made much further.

2002 Vol. 22, No. 4