航空材料学报

The Investigation of Isothermal Transformation of the Titanium AlloyTi-6.5 Al-3.5Mo-2Zr-0.25Si (BT9)

Yan Wen, He Ming, Wang Zhongzhen, Zhang Baochang

1982, 2(1): 7-12.

[Abstract](1239) [PDF 4052KB](69)

Abstract:
In this paper, the isothermal transformation process of titanium alloy Ti -6.5Al-3.5Mo-2Zr-0.25Si (BT9) was investigated by the means of metallurgical and electron microscopy (TEM), electron d if fraction, optical dilatometry and hardness test. Based on the results of investigation, we established the T.T.T diagram of BT9 alloy and the relationship between its morphology of structure and mechanical properties. Furthermore, the mechanism of isothermal transformation of BT9 alloy was studied sketchily. In our tests, we have still proved that the start temperature of martensite transformation (Ms) of titanium alloy varies with cooling rate of P-phase, the higher the cooling rate, the lower the Ms.

Zhang Shaoqing, Lu Liqi, Yu Yingmei

1982, 2(1): 13-18.

[Abstract](1263) [PDF 4443KB](77)

Abstract:
The microscopic structural characteristics of extruded shapes of MBl5 magnesium alloy have been studied by optical metallography, X-ray diffraction and electron microscopy, and the reason why the strength of once extruded shapes is higher than that of twice extruded ones is set forth. It is shown by the results of experiments that once extruded shapes are in the condition of hot work dynamic recovery and textured strengthening. Therefore, they have higher strength properties. Whereas in twice extruded shapes the recrystallization is so strongly produced that the alloy is softened and its strength is reduced.

Researches on Wave Grain Boundaries Heat Treatment Processes for GH220 Alloy

Tan Jufen, Jang Shurong, Tian Shifan

1982, 2(1): 19-24.

[Abstract](1182) [PDF 4542KB](67)

Abstract:
In this paper, the changes of grain boundaries and grain structures of GH220 alloy during cooling with various cooling rates after solution treatment and their effects on the mechanical properties of this alloy were investigated. It was shown that wave grain boundaries can be obtained by the^slow cooling, iso-themal-quenching*and*slow cooling plus re-solution heat treatments and that a suitable combination of wave grain boundaries and desirable matrix structures would be quite beneficial to improve both creep-rupture strength and ductility and thus to obtain good overall properties. It is recommended that there are two heat treatment processes which appear to be better than the standard procedure for GH220 alloy.

Effect of the Heat Treatment on the Fine Structure and Mechanical Properties in Ultrahigh Strength Steels

Zhong Bingwen, Chang Lianrong

1982, 2(1): 25-31.

[Abstract](1172) [PDF 5007KB](68)

Abstract:
The fine structure of martensite, the type, morphology, and distribution of carbide precipitate, and the distribution of retained austenite in matrix were investigated by transmission electron microscope. The relation between mechanical properties and martensite substructures was also studied. The results indicated that there are some microtwins in lath martensite. Preferen-tial precipitation of cementite was frequently observed at boundaries of these microtwins. The decomposition of retained austenite during tempering occured in company with a diffusion process of carbon. One of the decomposition products is stringer-like cementite. The crystallographic orientation between interlath cementite and tempered martensite does not comform to the well-established Bagaryatskii orientation relationship. The decomposition of retained austensite during tempering belongs to upper bainitic reaction. The starting temperature of the decreasing of impact toughness is coincident with that of the decomposition of interlath retained austenite into stringer of cementite at these boundaries. The retained austenite in net form retarded the crack propagation rate.

Effect of the Overload Ratio on Fatigue Crack Growth Behavior in Ti-6A1 -4V

Ouyang Jie, Song Deyu, Yan Minggao

1982, 2(1): 32-39.

[Abstract](1245) [PDF 5230KB](67)

Abstract:
The effect of tensile overload ratio,r=PoL/PcA, on fatigue crack growth behavior of sheet titanium alloy was investigated. The variation of retardation effect with overload ratio was evaluated. From a further study of the main factors that cause the retardation effect, a schematic diagram of ret.ar-ding process and its acting mechanism was proposed. Besides, empirical expressions used for calculating the maximum plastic strain, 3max,ahebd of the crack tip and the increased cycles, ND, due to retardation effect were Suggested.

Study on the Fracture Toughness of Aircraft Acrylic Sheets

Chen Ruoxi, Shao Yujun, Fan Tang

1982, 2(1): 40-46.

[Abstract](1246) [PDF 4795KB](77)

Abstract:
Considerable works on the fracture toughness of glassy polymers have been done, yet there were still controversies about the definition of Klc. In this paper,the author attempted to discuss the plane strain fracture toughness Kic of PMMA(polymethyl methacrylate) based on the theory of linear elastic fracture mechanics and the intrinsic characteristics of macromolecular motion in polymeric materials. The effects of the absorbed water in material，environmental humidity and humid air aging at elevated temperature on the fracture behaviours of two kinds of acrylic sheets, YB-3 and YB-4, were studied. It was found that the present of water or humidity is of benefit to the fracture resistance of PMMA materials.

The Study of the Uniaxial Compressive Stability of the Carbon Fiber Composite Stiffened Plates

Qin Renzhi, Shen Sitang, Wang Zhenming

1982, 2(1): 47-52.

[Abstract](1226) [PDF 3841KB](61)

Abstract:
By means of the finite element methods, the numerical solutions of the integral and the local critical buckling stresses of the stiffened plates of carbon fiber composite are found. Three test specimens of longitudinal stiffened plates made from carbon fiber composite are subjected to uniaxial compressive stability test under the condition of simple supported on the sides, the critical buckling stresses thus determined show in better agreement with the numerical results calculated from finite-element methods.

A Formula of High-Low Cycle Fatigue Crack Propagation Rate and Its Application

Liu Shaolun, Xie Jizhou

1982, 2(1): 53-64.

[Abstract](1289) [PDF 6826KB](76)

Abstract:
On the basis of the fatigue crack propagation rate expression for TBP specimen at room temperature, we deduced the formulas of high-low sycle fatigue crack propagation rate lor CT specimen where D, D〃， are material constants, n is hadening exponent. The high cycle formula of CT specimens is equivalent to Paris's formula,whereas its low cycle formula is conformable to Coffin-Manson's equation. Thus, for the cycle J integral of CT specimens is measured , hysteresis loop of load-displacement needn't be recorded, only crack length and corresponding load cy-clic numbers need be measured. Furthermore, the quantitative correlations between low cycle fatigue parameters and low cycle fatigue crack propagation rate parameters were proposed. Then low cycle fatigue crack propagtion rate parameters may be directly estimated from low cycle fatigue parameters.

A Fracture Mechanics Approach to High Cycle Fatigue

A.F.Blom

1982, 2(1): 65-76.

[Abstract](1195) [PDF 8408KB](54)

Abstract:
The concept of utilizing the fatigue threshold stress intensity factor Kth as a design criterion is discussed. This concept is of particular importance for structures sustaining very many load cycles. Determination of stress intensity factors K by means of the finite element method is treated. The experimental evaluation of Kth 1S discussed and the influence of various para meters on Kth is scrutinized.

Study of the Structure and the Mechanical Prope rties of Iron-Boron Alloys

Wen Zhongyuang, Nobuzo Terao

1982, 2(1): 77-78.

[Abstract](1225) [PDF 12608KB](34)

Abstract:

Stress Corrosion Cracking of the Metastable Austenitic Stainless Steel

Wang Renzhi, Li Xiangbin, Yin Yuanfa, Yan Minggao

1982, 2(1): 1-6.

[Abstract](1192) [PDF 4147KB](72)

Abstract:
The stress corrosion cracking of metastable austenitic stainless steel has been investigated. The following results are obtained, (1) The plastic induced phase transformation occurs in the plastic zone ahead of crack tip. Thus the shallow layer of fracture surface consists of phase. (2) SCC for such metastable austenitic stainless steel is,as metter of fact, a cleavage-like fracture. The crack propagation and the fracture process are as follows.

1982 Vol. 2, No. 1