航空材料学报

Physical denotation of thermal expansion coefficient of low thermal expansion superalloys

LIN Zheng, ZHANG Shao-wei, WU Xue-ren, YAN Ming-gao

1999, 19(1): 1-5.

[Abstract](1512) [PDF 209KB](343)

Abstract:
The relationship between mean linear expansion coefficient and saturation magnetization of low thermal expansion superalloy with temperature was studied.Comparing the data gained in this experiment with those of conventional superalloy and low expansion alloy showed that in the proper scope of saturation magnetization the best result of the property of low expansion for the low expansion superalloy could be gained and such low expansion feature could be retained to the reasonable higher temperature;on the contrary,too high saturation magnetization was detrimental. We should pay much attention to raise Curie temperature and decrease the rate of lowering of the saturation magnetization.The results also showed that the one of the reasons of low expansion was that the change of the magnetic behavior overlapped on the normal expansion process;this behavior induced the negative expansion of superalloy.This investigation opened a new prospect and made a good foundation to the development of low expansion superalloy.

Microstructural stability of single crystal superalloy DD402 and its 1st stage turbine blades

YAN Ping, SHAN Xi, ZHAO Jing-chen, SHI Yan-yu, HUANG Qian-yao, SUN Jia-hua, HE Ji-sui

1999, 19(1): 6-12.

[Abstract](1579) [PDF 973KB](258)

Abstract:
The microstructure was inspected and compared for DD402 single crystal superalloy under different conditions:standard heat treatment,850℃/500h aging,850℃/1500h aging and 850℃/3000h aging.The high temperature stress-rupture properties for the specimens after long time aging and the microstructure of the ruptured specimens were examined.Also,the microstructure of DD402 single crystal turbine blade was analyzed after 800h engine test.The results showed that there was no TCP phase in the microstructure either in the long time aging specimens or in the tested blades and the shape of γ′ was stable.The γ′ rafts formed just under a certain time with combinative effect of high temperature and sufficient stress.

Effect of sulfur on creep behavior of IN718 alloy

SONG Hong-wei, GUO Shou-ren, HU Zhuang-qi

1999, 19(1): 13-16.

[Abstract](1409) [PDF 155KB](267)

Abstract:
The effect of sulfur on the creep behavior of IN718 alloy has been investigated.The results show that sulfur decreases the creep resistance of IN718 alloy.Increasing sulfur content to 0.02wt% causes a reduction of the aparent creep activation energy from 678.5kJ/mol to 634.8kJ/mol.The harmful effect mainly arises from the enhanced diffusion along grain boundary by sulfur.

Effect of Ru on microstructure of cast Ti-47Al alloy

ZHENG Yun-rong, YU Xi-hong, MA Shu-wei, WANG Xiao-ping

1999, 19(1): 17-21.

[Abstract](1363) [PDF 686KB](194)

Abstract:
Microstructure of cast Ti-47Al-XRu(at%) alloy with X=0.5,1 or 3 has been investigated.The results showed that elements Ru and Cr have similar behavior:they are strong β phase stabilizer and promote the formation of β2 phase.This phase is a Ru-riched phase and content of Ru in β2 phase is more than 10at%.In the alloy containing 1at% Ru the grained secondary β2 phase continuously precipitated during heat treatment of 1160～1200℃ temperature range,therefore the γ+α2 lamellar structure was interrupted and the new γ grains formed.The γ grains with average grain size less than 60μm obtained after treatment of 1200℃ for 48h.That means Ti-47Al-1Ru alloy is a finable grain cast alloy by heat treatment.As the content of Ru in alloys increases to 3at%,it is difficult to refine the grains of cast alloy by heat treatment,moreover alloy obviously becomes brittle.

A study of grain refinement with addition of refiner in superalloy K4169

ZHENG Jian-bang, PANG Shu-xian, LIU Lin

1999, 19(1): 22-28.

[Abstract](1488) [PDF 480KB](189)

Abstract:
Grain size and dendrite morphologies of Fe-Ni based superalloy K4169 are investigated with the melt addition of Ni-xAl-yTi-z refiner.It is found that the grain size of K4169 cast bar can be refined obviously to 0.1～0.2mm,close to the order of ASTM 1～3,due to adding refiner and lowering the melt homogeneous temperature during the melting and casting process.In addition,the microstructure and MC carbide morphology vary obviously.With refinement of grains,the additive NixAlyTiz has the advantage of little influence on the freezing characters,alloy composition as well as on phase constitutions because of its composition feature.It is considered therefore that the addition of Ni-xAl-yTi-z refiner is one of effective and practical method to obtain fine grained castings of K4169 superalloy.

Role of interface in burn of titanium alloys

ZHAO Yong-qing, ZHOU Lian, DENG Ju

1999, 19(1): 29-33.

[Abstract](1369) [PDF 428KB](305)

Abstract:
Titanium fire found in advanced aircraft engines has attracted interesting attentions.Influences of interface on the burning behavior are important.The results reveal that the interface between burning products and air is cracks and porous,which can not retard oxygen diffusion into the matrix and the burn.The interface between burning products and matrix for C.P.Ti and Ti-6-4 is also cracks and porous,however the interface of Ti40 alloy is tenacious,which is in the form of Cr2O3,and this product can retard oxygen diffusion into the matrix and reduces the buning velocity.Thereby burn resistant mechanism of suspending oxygen diffusion is put forward.

Study on thermal explosion delay time of NiAl(Fe) system

XU Xing-li, HUANG Yong, MA Li-guo, XIE Zhi-peng

1999, 19(1): 34-38.

[Abstract](1333) [PDF 273KB](255)

Abstract:
The ignition criterion of thermal explosion is presented in this paper.NiAl(Fe) system is studied experimentally.The effects of the relative density of mixture,the content of Al particle,the size of Al particle,the heating rate,the content of dilution Fe on the thermal explosion point temperature and the thermal explosion delay time are analyzed.The results show that:to reactant ratio and relative density of mixture,there exists a optimum value,which the thermal explosion reaction rate is maximum and the delay time is minimum.

Research on fatigue crack growth behavior of DZ17G at room temperature

LIAO E bin, GUO Jian-ting, WANG Shu-he

1999, 19(1): 39-44.

[Abstract](1371) [PDF 312KB](180)

Abstract:
Fatigue crack growth behavior of DZ17G at room temperature is studied at different testing conditions of loading direction and loading frequency.The results indicate that the fatigue crack growth rate(FCGR) is the largest on the specimen with loading angle 90°,smaller on that with loading angle 0°,and the smallest on that with loading angle 45° due to crack deflection effect.The influence of loading frequency upon FCGR is related to the range of stress intensity factor ΔK.The dimension of precipitate γ′ has influence upon the dislocation arrangement.Microcracks propagate along the γ channel.

An analysis on effective factors to fatigue lives of pull rod linking lugs of tube-shaped cases

XIE Ming-li, XI Nian-sheng, ZHAO Ai-guo

1999, 19(1): 45-50.

[Abstract](1407) [PDF 573KB](244)

Abstract:
The cause of the diversity of fatigue lives of linking lugs of five tube-shaped cases was investigated by microfractography and metallography techniques. The recrystallization degrees of microstructure of lugs are much different. It is the diversity of recrystallization degrees that results in that of fatigue lives of lugs. The diversity of the recrystallization degrees may be resulted from the difference in deformation magnitude and original grain size of materials in die forging. In addition, another important factor of decreasing lives of lugs is machining defects in hole wall surfaces of lugs.

The effect of codeposition of SiCr and heat-treatment after codeposition on mechanical properties of stainless steel

WEI Ping, WAN Xiao-ru

1999, 19(1): 51-57.

[Abstract](1287) [PDF 422KB](435)

Abstract:
In-situ codeposition of Cr and Si into steel Cr17Ni2 has been achieved using pack cementation. Through optimizing the processing parameters,a coating containing about 27wt% Cr and 2wt% Si has been obtained, and the layer thickness is about 120μm. Heat-treatment process after codeposition has great effect on mechanical properties.

Effects of SiC particle on physical properties for SiC_p/Cu composites

ZENG Qiang, ZHONG Tao-xing, WANG Rong-ming

1999, 19(1): 58-62.

[Abstract](1375) [PDF 226KB](260)

Abstract:
Multiple regression analyses were formulated to explore the influence mechanism on the coefficient of thermal expansion and thermal conductivity of the SiCp/Cu composites by three deterministic factors, which were content, granularity and purity of the SiC particles. The results revealed that the key factor to affect coefficient of thermal expansion of the composites was the content of the reinforcements. The coefficient of thermal expansion and thermal conductivity of the composites decreased with the increase of SiC particles. However, small reinforcements lead to decreased thermal expansion coefficient and increased thermal conductivity . Higher thermal conductivity can also be obtained by proper impurity in the composites.

1999 Vol. 19, No. 1