航空材料学报

INVESTIGATION ON MICROSTRUCTURE OF A LOW EXPANSION SUPERALLOY

Wang Rongming, Li Chunzhi, Yu Jiantong, Yan Minggao

1995, 15(4): 1-7.

[Abstract](1441) [PDF 394KB](190)

Abstract:
The microstructure and Chemical composition of ε phase and different kinds of grain boundary phasesin low expansion Superalloy GH907 have been investigated using transmission electron microscopy(TEM)and Energy-dispersive X-ray analysis(EDX ).The orientation relationship between ε/γ phases has alsobeen studied.

EFFECT OF Al AND Ti CONTENTS ON MICROSTRUCTURE OF TiAl BASE ALLOY

Zheng Yunrong, Wang Xiaoping, Ruan Zhongci, Ma Shuwei

1995, 15(4): 8-14.

[Abstract](1441) [PDF 439KB](273)

Abstract:
In order to obtain the fine grain microstructure in as-cast TiAl base alloy, 3 at% Cr and 6 at% Cr wereadded into Ti-44Al (at%) and Ti-48Al (at%) alloys respectively. The results showed that Cr had little ef-fect on grain size in as-cast α2 +γ alloys,but it can obviously refine grains by heat treatment. Optimum effi-ciency of refining grains was achieved by heat treatment of 1150℃ /168h and 1200℃ /24h for Ti-44Al-3Crand Ti-48Al-3Cr alloys respectively. Moreover ,in Ti-48Al alloys the fine grain microstructure can be easilyobtained after heat treatment. Cr promotes the formation of the ordered Cr-rich β2 phase. This phase eithercoexists with α2 phase, or exists in the grain boundary of γ phas,hindering the growth of γ grains. The sol-ubility of Cr in β2 , α2 and γ hases reduces gradually ,it mainly substitutes for Ti in γ and α2 phases. As a re-sult,the ratio of Al/Ti for γ and α2 phases raises with the increase of Cr content in alloy. Besides ,the addi-tion of Cr can promote the formation of twins in the γ phase.

X-RAY DIFFRACTION ANALYSES OF PHASE RELATIONSHIPS IN A RAPIDLY SOLIDIFIED Ti₃Al-BASED ALLOY

Xu Rui, Cui Yuyou, Li Dong, Hu Zhuangqi, Xu Daming, Li Qingchun

1995, 15(4): 15-19.

[Abstract](1432) [PDF 327KB](171)

Abstract:
The phase transformation in aging of a rapidly solidified Ti-25Al-10Nb-3V-1Mo alloy was studiedwith X-ray diffraction in this paper. The results show that metastable β0 phase in rapidly solidified alloytransformed to different phases in the various temperatures. The isothermal β0→O transition took place inthe alloy aged in the temperature between 600～800℃ while O+α2+β0 phases was found in the alloy agedat 810℃ and α2+β0 phases aged at 950℃.

ON TEMPERED MICROSTRUCTURE AND PROPERTIES OF 11.73Ni-13.85Co-3.13Cr STEEL

Ling Bin, Zhong Ping, Zhong Bingwen, Zhao Zhengye, Zhang Shaoqing

1995, 15(4): 20-26.

[Abstract](1447) [PDF 507KB](131)

Abstract:
The effect of tempering on the microstructure and mechanical properties of ultrahigh strength11. 73Ni-13.85Co-3.13Cr steel was studied. Upon tempering at 430℃, the martensite decomposed to forma lot of cementite platelets concomitant with a significant drop in toughness. Tempering at 440～455℃ re-sulted in peak strength due to the precipitation of coherent zones of fine carbides. The attainment of peakin toughness is due to absence of cementite and formation of reverted austenite. Tempering at higher tem-peratures resulted in loss of both strength and tonghness. The drop of the strength is due to precipitationscoarsening and loss of the coherency with the matrix.

MICROSTRUCTURE, MECHANICAL AND PHYSICAL PROPERTIES OF A SiCW/Al-Li-Cu-Mg-Zr COMPOSITE

Dong Shangli, Mao Jianfu, Cui Yuexian, Yang Dezhaung

1995, 15(4): 27-33.

[Abstract](1423) [PDF 426KB](167)

Abstract:
The microstructure characteristics of SiCW/Al-Li-Cu-Mg-Zr composite fabricated by a squeeze castingmethod were studied by means of SEM, TEM and HRTEM techniques. Tensile test was conducted at roomtemperature. The results show that the SiC whiskers distribute uniformly in the matrix of the as-castedcomposite. The major precipitates in the T6-treated composite are δ′(Al3Li), S′(Al2CuMg) and β′(Al3Zr) phases. There is no obvious chemical reaction between the whiksers and the aluminum-lithiummatrix. The prepared composite exhibits higher tensile strength and elastic modulus as well as lower coffi-cients of thermal expansion.

STUDY ON THE DISSOLUTION MODEL OF BASE METAL IN THE LIQUID NICKEL-BASED AMORPHOUS AND CRYSTALLINE BRAZING FILLER METALS DURING VACUUM BRAZING

Zhang Xinping, Shi Yaowu, Ren Yaowen

1995, 15(4): 34-40.

[Abstract](1476) [PDF 442KB](290)

Abstract:
In this paper,the dissolution of stainless steel base metal (1Cr18Ni9Ti) in the liquid Nickel-based (Ni82Cr7.5Si4.5B3Fe3) amorphous and crystalline brazing filler metals during the vacuum brazing has been investi-gated on a wedgeshape variable brazing clearance specimen, and a physical-mathematical model for quanti-tatively calculating the dissolution thickness of the base metal in liquid brazing filler metals has been putforward. The vacuum brazing experimental results obtained from the parallel and wedge-shape variableclearance specimens have verified that the brazing parameters such as the brazing temperature and holdingtirne as well as brazing clearance have an important influence on dissolution thickness of base metal duringvacuum high temperature brazing, and shown that the dissolution model of base metal has good accuracyand reliability, it can be used to investigate the dissolution characteristics of base metal and estimate thecorrosion of brazing filler metals

MECHANICAL PROPERTIES AND STRESS CORROSION CRACKING OF 16Co14Ni10Cr2Mo STEEL

Zhong Ping, Gu Baozhu, Jin Janjun, Wang Hongtao

1995, 15(4): 41-46.

[Abstract](1466) [PDF 414KB](198)

Abstract:
The strength, impact toughness, fracture toughness and stress corrosion cracking behavior (in 3.5 PctNaCl) of 16Co14Ni10Cr2Mo steel were studied after different temperature tempering 5h. At 510℃ tempering, the higher strength, the best fracture toughness and stress corrosion properties were obtained. Underthese conditions KISCC is as high as～75MPa √m with facture toughness of～175MPa √m and a yieldstrength of～1580MPa. The improved stress corrosion cracking resistance at higher tempering temperaturemay be related to the loss of stress resuIting from Mo2C/matrix coherency and the recovery of the dislocation substructure and coarsening of precipitaties. These would lead to a decreased concentration of hydrogen.

MECHANICAL BEHAVIOR OF THE STRANDS IN UPWARD CONTINUOUS CASTING

Zhu Yuefeng, Zeng Daben, Huang Huisong, Wu Dehai

1995, 15(4): 47-53.

[Abstract](1420) [PDF 411KB](167)

Abstract:
A force transducer was designed to measure the pulling force by which the strands were withdrawnduring upcasting. With the results of ternperature field in the strands, the friction between the strands andthe mold was analysed. The distribution of the friction was proposed and the maximum friction and its action position were determined according to experimental results. Based on the rheologic characteristics ofthe strand alloy at elevated temperature, effects of the friction on the surface quality of the strands werestudied. A formula used to calculate the sizes of ring marks in the strand surface was deduced. According tothe Griffith's energy criterion, mechanical and geornetric conditions under which the surface ring markswould develop to cracks and effects of the casting technological parameters on the conditions were discussed.

EFFECT OF HOLD TIME ONLOW CYCLE FATIGUE CRACK GROWTH BEHAVIOR AT HIGH TEMPERATURE IN TWO TURBINE DISK ALLOYS

Shen Zhumin, Xie Jizhou

1995, 15(4): 54-61.

[Abstract](1403) [PDF 482KB](117)

Abstract:
The low cycle fatigue crack growth behaviors with and without hold time on upon peak load and itspropagation life prediction model were investigated for two turbine disk superalloys used extensively.

1995 Vol. 15, No. 4