标题: 铁-9.5铝-30.0锰-5.0铬-1.5碳合金之相变化
Phase transformations in the Fe-9.5Al-30.0Mn-5.0Cr-1.5C alloy
作者: 蔡国栋
Max G.-D. Tsay
刘增丰
C.F. Liu
材料科学与工程学系
关键字: 史宾诺多节点分解反应;Spinodal Decomposition
公开日期: 1998
摘要: 我们利用光学显微镜(OM),穿透式电子显微镜(TEM)以及X-光能量散布分析仪(EDS),研究铁-9.5铝-30.0锰-5.0铬-1.5碳之相变化。
在浇铸状态下,此合金的显微结构为γ+κ'+κ+D03的混合相。在淬火状态下,其显微结构为沃斯田铁相与细微κ'相的混和。其中细微κ'是在淬火过程中以史宾诺多节点分解反应(Spinodal Decomposition)产生,具有L'12结构。
当此合金在550℃时效处理后,我们发现κ'相碳化物在沃斯田铁基地内沿<100>方向成长,在晶界上并未观察到有析出物存在;在650℃时效处理后,不但在沃斯田铁基地的κ'相碳化物成长,而且在晶界上有晶粒状的κ相碳化物和板状的β-锰析出;在750℃时效后,沃斯田铁基地为κ'相和D03的混合相,其中D03相是在淬火过程中经由α→B2→D03的序化反应产生的,晶界上则仍为κ相碳化物和β锰;在850℃时效后,在沃斯田铁基地可发现粗大的κ'相碳化物,晶界上则有α和κ相析出;在950℃以上时效,仅能在沃斯田铁基地中观察到细微的κ'相碳化物,晶界则无析出,这与淬火状态下的显微结构相似。所以,随着温度由550℃至850℃,晶界上的反应为γ→κ相+β-锰→α相+κ相→γ。
Phase transformations in the Fe-9.5Al-30.0Mn-5.0Cr-1.5C alloy has been examined by means of optical microscopy(OM), transmission electron microscopy(TEM) and energy-dispersive X-ray spectrometer(EDS).
In the as-cast condition, the microstructure in the present alloy is the mixture of theγ+κ'+κ+D03-phases. When the alloy was solution heat-treated and then quenched, the microstructure of the alloy was austenite phase containing extremely fine (Fe,Mn)3AlCx carbides (κ'-carbides). Theκ'-carbides having an L'12-type structure were formed within the austenite matrix during quenching by a spinodal decomposition.
When the alloy was aged at 550℃, theκ'-carbides existing in the as-quenched austenite matrix grew preferentially along <100> directions, but no grain boundary precipitates could be observed. When the alloy was aged at 650℃, not only theκ'-carbides grew within the austenite matrix but also some plate-likeβ-Mn and granular-shaped κ-carbides precipitated on the grain boundaries. When the alloy was aged at 750℃, the microstructure within the matrix was the mixture of κ'-carbide and D03 phase. The D03 phase was formed by a α→B2→D03 continuous ordering transition during quenching. Moreover, the β-Mn precipitates and κ-carbides were formed on the grain boundaries. When the alloy was aged at 850℃, the coarseκ'-carbides could be observed within the austenite matrix, in addition, the precipitation of (α+κ) phases also occurred on the grain boundaries. When the alloy was aged at 950℃, only extremely fineκ'-carbides could be detected within the austenite matrix and no grain boundary precipitates could be examined, which was similar to that found in the as-quenched alloy. Therefore, when the alloy aged at temperatures ranging from 550℃ to 850℃, the phase transition sequence as the temperature increase was found to beγ→κ-phase +β-Mn→α-phase +κ-phase →γ.
URI: http://140.113.39.130/cdrfb3/record/nctu/#NT870159027
http://hdl.handle.net/11536/63931
显示于类别:Thesis