Phase transformations in Ti-6.8Mo-4.5Fe-1.5Al
Phase transformations in Ti-6.8Mo-4.5Fe-1.5Al
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DOI：
10.1007/s11661-998-0217-8
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发表时间：
1998-10
期刊：
影响因子：
--
通讯作者：
S. Azimzadeh;H. Rack
中科院分区：
文献类型：
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作者：
S. Azimzadeh;H. Rack
采用硬度测量、X射线衍射、光学显微镜和电子显微镜研究了Ti-6.8Mo-4.5Fe-1.5Al合金在300 °C ~ 750 °C人工时效和等温时效过程中的相变。固溶处理和水淬后的人工时效最初涉及非热ω相的生长。随后形成α相，或者与ω相结合，通过基体内的均匀沉淀，或者通过异质晶界成核。同样，亚稳β相的等温分解导致ω相的析出，其呈现椭球形态。虽然ω在345 °C下立即沉淀，但在390 °C下老化后观察到潜伏期。高于该温度的等温时效涉及α相的直接沉淀，在β基体内均匀地沉淀或在β晶界处不均匀地沉淀。等温时效过程中非均相α形核的程度取决于时效温度，较低的时效温度促进均相形核，较高的时效温度促进α非均相形核。最后，继续时效导致α相的粗化和球化，而与时效路径无关。
Phase transformations during artificial and isothermal aging of Ti-6.8Mo-4.5Fe-1.5Al have been investigated over the temperature range from 300 °C to 750 °C utilizing hardness measurements, X-ray diffraction, optical microscopy, and electron microscopy. Artificial aging following solution treatment and water quenching initially involved growth of the athermalωphase. This was followed by formation of theαphase, either in association with theωphase, through homogeneous precipitation within the matrix, or through heterogeneous grain-boundary nucleation. Similarly, isothermal decomposition of the metastableβphase resulted in the precipitation ofωphase exhibiting an ellipsoidal morphology. While precipitation ofωwas immediate at 345 °C, an incubation period was observed upon aging at 390 °C. Isothermal aging above this temperature involved direct precipitation of theαphase, either homogeneously within theβmatrix or heterogeneously atβgrain boundaries. The extent of homogeneousvsheterogeneousαnucleation during isothermal aging depended upon aging temperature; low aging temperatures promote homogeneous nucleation and higher aging temperatures promoteαheterogeneous nucleation. Finally, continued aging resulted, independent of aging path, in coarsening and spheroidization of theαphase.