快速凝固制备Laves相增强NiAl基复合材料的微观组织及力学性能

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LAVES PHASE STRENGTHENING NiAl BASE COMPOSITE FABRICATED BY RAPID SOLIDIFICATION

利用水冷Cu模喷铸快速凝固技术制备Laves相(Cr_2Nb)增强NiAl基复合材料,并对比研究了普通铸造和快速凝固工艺制备的NiAl/Laves相材料的微观组织和力学性能.结果显示,普通铸造合金中的Laves相相对粗大,呈不连续状分布于NiAl相周围,NiAl相中析出了棒状的Laves相,由于Ni和Al元素在Laves相中的存在,合金中Laves相在室温下拥有C14的晶体结构.快速凝固工艺有效地细化了NiAl和Laves相,并使NiAl相界的Laves相形成NiAl/Laves共晶层片,呈胞状结构包覆NiAl相.但是,快速凝固工艺仍然无法完全抑制细长针状Laves相在NiAl中的析出,但抑制了α-Cr相的析出.压缩性能显示,相对普通铸造工艺,快速凝固工艺制备的胞状Laves相增强NiAl基复合材料具有更佳的室温和高温性能,其性能的改善应归因于胞状Laves的结构以及胞状Laves相在高温变形过程中的纳米化.

The Laves phase strengthening NiAl base composite was fabricated by conventionally casting and rapid solidification, and their microstructure and mechanical properties were investigated together. The results exhibit that the Laves phase in the conventional cast alloy is relative coarse and distributes along the NiAl phase boundary. Moreover, small stick-like Laves phase precipitates in the NiAl phase. Due to the segregation of Ni and Al in Laves phase, it still keeps the C14 crystal structure. The rapid solidification refines the NiAl and Laves phase greatly and promotes the formation of NiAl/Laves phase eutectic structure, which surrounds the NiAl phase and forms the cell-like structure. However, the rapid solidification can not handicap the precipitation of needle-like Laves phase in the NiAl phase. But, the rapid solidification restrains the formation ofα-Cr phase. The compression tests show that the cell-like Laves phase strengthening NiAl base composite has better mechanical properties at ambient and elevated temperature, compared with the conventional cast alloy. The improvement of mechanical properties should be attributed to the cell-like Laves phase and the nanocrystallization of the cell-like Laves phase during high-temperature deformation.