MICROSTRUCTURE EVOLUTION AND GROWTH BE-HAVIORS OF FACETED PHASE IN DIRECTIONALLY SOLIDIFIED Al-Y ALLOYS I. Microstructure Evolution of Directionally Solidified Al-15%Y Hypereutectic Alloy
1 National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, China 2 Shenyang Liming Aero-Engine Group Corporation LTD, Shenyang 110043, China
Cite this article:
Liangshun LUO,Tong LIU,Yanning ZHANG,Yanqing SU,Jingjie GUO,Hengzhi FU. MICROSTRUCTURE EVOLUTION AND GROWTH BE-HAVIORS OF FACETED PHASE IN DIRECTIONALLY SOLIDIFIED Al-Y ALLOYS I. Microstructure Evolution of Directionally Solidified Al-15%Y Hypereutectic Alloy. Acta Metall Sin, 2016, 52(7): 859-865.
The intermetallic compound has been widely introduced in alloys as a reinforced phase due to its high strength, high hardness and enhanced heat stability. The size, morphology, distribution and volume fraction of these intermetallic compounds affect the mechanical properties of materials significantly. In this work, the microstructures evolution and growth behoviors of primary intermetallic Al3Y phase have been investigated in directionally solidified Al-15%Y (mass fraction) hypereutectic alloy at a wide range of pulling rates (1~100 μm/s). The as-cast Al-15%Y alloy is composed of primary intermetallic Al3Y phase and Al3Y/Al eutectic structure. At relatively low pulling rates (1~5 μm/s), primary Al3Y phase exhibits irregular and having a branching structure on the top of the specimens. Primary Al3Y phase also precipitates in a faceted growth with sharp edges and corners. As the pulling rate increases, the morphologies of Al3Y phase transit to elongated prism. Al3Y phase distributes dispersively in the eutectic structure at a higher pulling rate, presenting a crossing shape with two prisms crossed vertically. Further increasing the growth rate to 100 μm/s, the cross morphology such as two six prismatic vertical cross structure of primary Al3Y appear, similar to the growth in the form of dendrites. During the increase of pulling rates, the leading-phase at solid-liquid interface appear gradually, and the growth distance of primary phase increases with the pulling rates increase.
Fig.1 Schematic of the Bridgman solidification furnace used in the present work
Fig.2 Low (a) and locally high (b) magnified SEM-BSE images of as-cast Al-15%Y hypereutectic alloy
Fig.3 Low (a~c) and locally high (a1~a3, b1~b3, c1~c3) magnified OM images show the microstructure evolutions of directionally solidified Al-15%Y hypereutectic alloy at pulling rates V=1 μm/s (a, a1~a3), V=3 μm/s (b, b1~b3), V=5 μm/s (c, c1~c3) under temperature gradient G=20 K/mm (Dash lines in Figs.3a1, b1, c1 indicate solid/liquid interfaces)
Fig.4 Low (a~c) and locally high (a1~a3, b1~b3, c1~c3) magnified OM images show the microstructure evolutions of directionally solidified Al-15%Y hypereutectic alloy at V=10 μm/s (a, a1~a3), V=20 μm/s (b, b1~b3), V=100 μm/s (c, c1~c3) under G= 20 K/mm (Dash lines in Figs.4a1, b1, c1 indicate solid/liquid interfaces)
Fig.5 Low (a) and locally high (b) magnified OM images of transverse sections of Al-15%Y hypereutectic alloy at V=20 μm/s and G=20 K/mm
Fig.6 OM images of the solid/liquid interfaces in directionally solidified Al-15%Y hypereutectic alloy at V=1 μm/s (a), V=3 μm/s (b), V=5 μm/s (c), V=10 μm/s (d), V=20 μm/s (e) and V=100 μm/s (f) under G=20 K/mm (Dash lines indicate solid/liquid interfaces)
Fig.7 Longitudinal (a~c) and transverse (d~f) SEM images of Al3Y in directionally solidified Al-15%Y hypereutectic alloy at V=1 μm/s (a, d), V=20 μm/s (b, e) and 100 μm/s (c, f) under G=20 K/mm
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