J.X.Dong
,
M.C.Zhang
,
Y.P.Zeng
,
X.S.Xie
金属学报(英文版)
The freckle formation and their phase characterization in freckle areas were investigated by means of microstructure analysis approaches and a thermodynamic equilibrium phase calculation method in a Ni-Cr-Mo-Fe-W alloy. These results show that in freckle areas a large number of M6 C, u and P phases precipitate in grain boundaries even within grain due to the enrichment and segregation of Mo and C during solidification, which results in small grains in freckle areas. Equilibrium phase and liquid segregation calculation can give an reasonable interpretation of the freckle feature for this alloy.
关键词:
freckle
,
null
,
null
J.X.Dong
,
M.C.Zhang
,
Y.P.Zeng
,
X.S.Xie
金属学报(英文版)
The freckle formation and their phase characterizatics in freckle areas were investigated by means of microstructure analysis approaches and a thermodynamic equilibrium phase calculation method in an lnconel 625 alloy. These results show that in freckle areas a large number of M6C, MC, Laves and 8 phases precipitate in grain boundaries even within grain due to the enrichment and segregation of Mo and Nb during solidification, which results in almost of these freckle areas covered by these complex precipitated phases and induces small grains in freckle areas. Equilibrium phase and liquid segregation calculation can give a reasonable interpretation of the freckle feature for this alloy.
关键词:
freckle
,
null
,
null
J.X.Dong
,
M.C.Zhang
,
S.K.Mannan
金属学报(英文版)
INCONEL725 is a highly corrosion resistant nickel based alloy capable of being age-hardened to high strength levels.The microstructure observations and the phase iden-tification after a standard heat treatment were investiguted.The results show that the precipitation phases include the strengthening phases γ′，γ″and δ phase,pri-mary carbide phase TiC,as well as M6C corbide and a little extent MC(mainly TiC) precipitates which nucleate mainly at grain boundaries.An isothermal aging study was carried out on this alloy for up to 10000 hours at 599℃.This additional aging did not affect the tensile strength.However,microstructures show that the thermal exposure has a little additional effect.With increasing the exposure time,the size of γ″ phase slightly increases,almost no change for γ′ phase,while M6C carbides pre-cipitated at grain boundaries have an increased and complex tendency on a few grain boundaries.The experimental results illustuate the excellent structure stability of the age-hardenable IN725 at 599℃.
关键词:
superalloy
,
null
,
null
J.X.Dong
,
M.C.Zhang
,
Y.P.Zeng
,
X.S.Xie
金属学报(英文版)
Alloy 718 is a precipitation strengthened nickel-hased superalloy based on the precipitation of γ’’-Ni3Vb(DO22 structure) and γ'-Ni3(Al, Ti) (Ll2 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in Alloy 718. In addition to the coalescence of γ'/γ'' and the amount increasing of 6 phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore,despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.
关键词:
alloy 718
,
null
,
null
Materials Science and Technology
The relationship between degeneration of the primary M7C3 carbide and precipitation of the secondary M23C6 carbide has been investigated in a cobalt base superalloy after 100 h aging at 850 degrees C. The results indicated that the primary M7C3 carbide could not transform in situ into the secondary M23C6 carbide. The M23C6 formed by a direct reaction between chromium and carbon atoms. The dissolution of M7C3 provided the precipitation of M23C6 with essential carbon, which acted as a carbon reservoir. Near M7C3, the chromium content is a controlling factor of M23C6 precipitation while away from it, the carbon content dominated the reaction. The precipitate free zone around M7C3 is attributed to chromium depletion which is inherited from the as cast condition. MST/4174
关键词:
LI Yuqing WANG Cirong GU Zhaofeng Research Institute of Daye Steel Works
,
Huangshi
,
China Senior Engineer
,
Research Institute of Daye Steel Works
,
Huangshi 435001
,
China
金属学报(英文版)
Determination of(Fe,Cr)_7C_3 in Cr27 cast iron results about 30 v.-%.Minor Si and Mn are present.Sectional area of the M_7C_3 grains is 1—50μm~2.Combining matrix analysis of elec- tron diffraction pattern with calculated angle between plane traces,{011}twins and also {013}twins producing local environment for Ru_7B_3 are observed in the orthorhombic M_7C_3. A crystallographic model for M_7C_3 is proposed.
关键词:
cast iron
,
null
,
null
,
null
,
null
刘勤
,
夏锄
,
刘晓东
金属学报
在170,190,210,230,250℃的温度下,采用3.7×10~2,7.4×10~2和1.1×10~(-1)min(-1)的应变速率(平均)对Zn-5%Al共晶合金的m-C-δ(或m-k-δ)关系曲线(简称m-δ关系曲线)进行了测定.所有的曲线均随应变的δ增加而快速上升.俟达到某一定的应变量(极限应变量δ1)后。开始缓慢下降并保持平稳直至断裂.Zn-5%A1共晶合金的m-δ关系曲线不存在k_(?)=k_I(k_(I 1),k_(I 2),k_(I 3),……)=k_F(或C_0=C_I(C_(I 1),C_(I 2),C_(I 3),……)=C_F=1)的简单情况.可应用m-δ方程式[4,5]对曲线上各点C值(包括所有的C_I和C_F值)进行计算.C值随δ值的增加成近似的直线上升.直线的斜率在极限应变(δ1)处突然减小.
关键词:
沈海军
功能材料
采用基于Tersoff势的分子动力学方法,模拟了温度T=300、700和1100K下C60、M@C60(M=Si,Ge)富勒烯分子的对径压缩过程.根据模拟结果,讨论了温度T对3种富勒烯分子压缩力学特性的影响以及它们压缩力学特性的差异.研究表明,在300～1100K范围内,温度T对C60、M@C60(M=Si,Ge)分子压缩力学特性无显著影响;当压缩应变至8%～16%左右,各富勒烯分子在加载点处开始"塌陷",当压缩应变至28%～32%左右,各富勒烯达到承载极限;C60、Si@C60、Ge@C60分子依次具有由低到高的承载能力.
关键词:
富勒烯
,
分子动力学
,
力学特性
,
内嵌M@C60富勒烯
ZHU Na-qiong
,
LU Li
,
HE Yan-lin
,
LI Lin
,
LU Xiao-gang
钢铁研究学报(英文版)
Coarsening of M23C6 precipitates in an Fe-12.4Cr-0.13C ternary alloy has been investigated ageing at 780 ℃ up to 200 h. Evolution of M23C6 carbides at different ageing times was determined experimentally using transmission electron microscopy. Particle size distribution was obtained with different measuring methods. Simulations of coarsening of M23C6 precipitates were carried out using computational thermodynamics and kinetics. Results showed low coarsening rates for M23C6 precipitates in the Fe-Cr-C ternary alloy. Interfacial energy of M23C6/ferrite interface is between 0.1 and 0.3 J·m-2 for the coarsening of M23C6 ageing at 780 ℃.
关键词:
M23C6
,
coarsening
,
PSD
,
interfacial energy
Materials Letters
Secondary M,C precipitation was investigated in K40S cobalt-base alloy after 100 h aging at 950 degreesC. The results showed that it was closely related to the tungsten-rich zones inherited from the as-cast condition and the degeneration of the primary M7C3 carbide. A direct element reaction, 6M + C --> M6C, in which C comes from the decomposition of the M7C3 carbides, is suggested as the mechanism of secondary M6C precipitation in K40S alloy. (C) 2001 Elsevier Science B.V. All rights reserved.
关键词:
M6C precipitation;aging;M7C3 carbide;superalloy
