航空材料学报

Influences of Directionally Solidified Techniques and Hf Content on a Nickel Base Superalloy

Wang Luobao, Chen Rongzhang, Wang Yuping

1982, 2(2): 1-7.

[Abstract](1185) [PDF 4414KB](64)

Abstract:
In this paper, the Influences of various Hf contents upon the microstructures and the mechanical properties of a Nickel-base superalloy by two different directionally solidified techniques(i.e. P.D process and H.R.S process)have been studied. The results show that Hf is always segregated along the interden-dritic regions and concentrated primarily in /' eutectic phases during sali-dification. The addition of Hf resulted in marked alteration of the microstructure of the alloy, i.e. the amount of /' eutectic phase increases obviously, and its morphology changes concurrently, the conditions of grain boundaries and interdendritic regions of the alloy are improved considerably, some minor Hf-rich phases, such as carbide MC(2), sulfurcarbide (M,Hf)2SC and Ni5Hf, were also observed. The stress-rupturs, properties, particularly the trensverse ones at 760℃ are enhanced with the increase of Hf content, however the stress-rupture life at 1040℃ decreased gradually with the increase of Hf content. The mechanical properties of the alloy prepared by H.R.S process at high and inter mediate temperature are considerably higher than those of the alloy prepared by P.D process. The mechanisms on the changes of microstructures and mechanical properties of the Hf-contained alloy were also discussed. The suitable range of Hf content in this alloy lies over 1.0～2.0% (by weight) and H.R.S technique should be adopted predominatingly,

The Investigation of Tempering Transformation of Retained Austenite in Isothermal Quenching Microstructures

Wang Ping, Yang zheng, Kang Mokuang

1982, 2(2): 8-15.

[Abstract](1252) [PDF 4822KB](80)

Abstract:
This paper has determined TTT curve of retained austenite (Ar) and made dynamic, static observations of tempering microstructures in the steel 3oCrMnSiNi2A after iso thermal quenching and studied the stability of Ar and tempered embrittlement in this steel. The results show that： the upper branch of TTT curve of Ar corresponds the upper (or inverse) bainite reaction and the lower branch corresponds the transformation of lower bainite or isothermal martensite；the heat treating technique can control the stability of Ar; the tempering embrittlement is caused by upper (or inverse) bainite, cementite film of Ar dicomposition during tempersoaking and martensite of Ar transformation during temper一cooling and deformation (especially in microstructures containing larger volume fractions of Ar). Therefore the workbiece after isothermal quenching should be tempered in range 250～300℃.

The effect of Different Solution Treatment Temperatures and Cooling Rates 011 the Microstructures of BT3—1 Titanium Alloy

Zhang Shaoqing, Huang Heng

1982, 2(2): 16-22.

[Abstract](1199) [PDF 4380KB](65)

Abstract:
The effect of different cooling rates (WQ, AC and FC) from various heating temperatures on the microstructures of BT3-1 titanium allay has been studied by means of X-ray diffraction, optical metallography and transmisson electron microscopy, The martensite structure was obtained by water quenching from P field temperatures, and the and phases from upper temperatures of (+) field. By quenching from 900℃, the a, and phases were confirmed, and only and phases were formed after water quenching from 850℃. The changes of lattice parameters, Sub-structures and microhardness of phase obtained by quenching from different temperatures were also investigated. Air or furnace cooling from difterent solution treatment temperatures produced various morphologies of and phases.

Models of Fatigue Crack Growth under Spectrum. Loadings and Their Application to the Life Prediction in Flight Spectrum Loadings

Zhang Yongkui, Gu Mingda, Yan Minggao

1982, 2(2): 23-30.

[Abstract](1164) [PDF 4377KB](60)

Abstract:
In this paper, the life prediction of fatigue crack-growth under spectrum loadings is discussed.The modif isd generalized Willenborg model and the modified Maarse model,which are considered to be two effective crack-growth models in present applications, have been selected. The improvement of the above models on calculation of the size of plastic zone and retardation eftect zone were also noticed. Using the above modified models, the prediction of the fatigue crack-growth life in multimission fighter spectrum loadings were performed. The analytical results were found to be correlated well with the experimental data.A comparison of these results showed that the present models are rather simple and efficacious and can be used in prediction of tlie fatigue crack growth under complex spectrum loadings.

Influence of Temperature on the AK_th and da/dN of LY₁₂CS Alumium Alloy

Mu Zaiqin, Yin Huaz, Tian Tiezhong

1982, 2(2): 31-37.

[Abstract](1280) [PDF 3997KB](58)

Abstract:
The threshold AKth and the fatigue crack-growth rate da/dN were investigated with LY-12CS aluminum.The temperature range for the AKth testing was from room temperature to 250℃.The temperature for da/dN testing was 200℃. Three load ratios R =0,0.33,0.67 were selected. The results showed that (1) The threshold AKth increased with increasing temperature.(2) In the case of three load ratios,crackgrowth rate da/dN was observed to decrease with increasing temperature. The da/dN in room temperature air was found to be 1 to 3 times higher than that at 200℃ when the stress inteu-$ity range K increased from 7 to 12kg/mm3/2.

The Investigation of the Fatigue Crack Propagation Characteristic of 30CrMnSiA in Salt Spray Environment

Ma Yushan, Yu Xiulin, Gou Baocheng, You Dexuan

1982, 2(2): 38-44.

[Abstract](1236) [PDF 4189KB](75)

Abstract:
The method of fracture mechanics was used in this work to investigate the fatigue crack propagation characteristic of aircraft structural material, 30CrMnSiA, in laboratory air and 5% NaCl salt spray environment.Using compact tension specimens, the tests were limited to certain ranges of stress intensity range 70～200kg/mm3/2The results of the tests were：In the early stages of the tests the crack propagation rate in salt spray environment was higher than in lab. air and it was increasing sharply with decreasing the frequency of cyclic loading. Usually a hydrogen embrittlement mechanism is proposed to explain the increase in growth rate.After the tests had gone on for 20～40 hours in the salt spray environment, the crack propagation rate was slowing even below that one in air due to the accumulation of corrosion deposits on the fracture surface.With an increase of the stress intensity range,the crack propagation rates in above two environments were getting close to each other.

Study on the Fatigue Crack Propagation Characteristics of Acrylic Sheets

Chen Ruoxi, Shao Yujun, Fan Tang

1982, 2(2): 45-53.

[Abstract](1167) [PDF 5598KB](62)

Abstract:
The effects of the absorbed water, and the water environment, and the elevated temperature and humid air aging,and the stress ratio and the frequency of test on the fatigue crack propagation properties of two kinds of acrylic sheets (PMMA) were studied.It was found that water is beneficial to the fatigue crack resistance of PMMA.Two models of microscopic mechanism of subcritical fatigue crack propagation under the effects of constant amplitude cyclic loading were proposed based on fractographic observations, and were used to explain the facture processes of fatigue crack of glassy polymers. Program (ALGOL) usable for treating fatigue crack propagation test data and predicting the failure life of specimens was made, and the calculated results coincide well with the test results.

The Effect of the Inclusion in Steels on the Fatigue Properties

Zhang Detang, Li Shuyuan, Xia Huiqin

1982, 2(2): 54-59.

[Abstract](1229) [PDF 3906KB](65)

Abstract:
The present paper has investigated effect which the inclusion in 38CrMoA1A and 30CrMnSiA steels on the fatigue properties the present study has shown that the inclusion sizes、shapes and distributions in steels have a marked effect on the fatigue properties under same inclusion content.The fatigue crack nucleation and propagation are controlled directly by inclusion particle sizes.As the mean diameter of inclusion particles is larger than 40jim, the frequency of the fatigue failures caused by non-metallic inclusions will be above 95%.On the basis of controling inclusion cotent, the fatigue properties can be impoved by decreasing the inclusion particles size and changing the unfavorable geometry shapes and distribution in steels.

Studies of Characteristics of Fatigue Crack Propagation at Near-Threshold Range and Its Affection Factors

Yan Minggao

1982, 2(2): 60-74.

[Abstract](1278) [PDF 9672KB](36)

Abstract:
This paper presents a review of the characteristics and mechanisms of fatigue crack propagation at near-threshold range in various metals and alloys.Experimental results from a series of microfractographic analysis of speci-mens and structures indicated that a type of crystallographic fracture,facets or river patterns, occurs predominantly at near-threshold range. A correlation of the orientation of facets for different metals and alloys with lattice structures, SFS and modes of slip was described. A general trend of FCP behaviors under uniaxial loading was prooosed. In this paper, the relation between the fatigue limits of plain- and notched-specimens and fatigue thresholds together with the mechanism of FCP behaviors in short cracks was evaluated. The crack propagation behaviors in short cracks can be generally expressed as,Kth= f(a)th(a) where f(a) is a function of the crack length and specimen geometry. The influence of stress ratio, microstructure and environment on fatigue crack propagation behaviors at near-threshold range was also reviewed, It is suggested that the concept of oxide-induced and roughness-induced crack closure may be useful for explaining the effect of the above mentioned factors pn FCP behaviors at pear-threshold level in structural materials.

Influence of Alloying Elements on the Mechanical Proparty of Al-5.7 %Ni Alloys, Hardened by Severe Plastic Deformation

Wea Zhong-yuang, Nobuzo Terao, A. Berghezan

1982, 2(2): 75-76.

[Abstract](1150) [PDF 16045KB](35)

Abstract:

1982 Vol. 2, No. 2