Microstructures and compressive properties of NiAl-Cr(Mo) and NiAl-Cr eutectic alloys with different Fe contents

Microstructures and compressive properties of NiAl-Cr(Mo) and NiAl-Cr eutectic alloys with different Fe contents were investigated. The result indicates that a fully eutectic structure is obtained in NiAl-Cr(Mo)-xFe (x = 5, 10 at %) alloys. When the Fe content increases to 15, 20 and 25 at%, the primary dendrite Cr(Mo) including (Ni, Al)-rich precipitate emerges, and the volume fraction of primary dendrite Cr(Mo) gradually increases. Moreover, the needle-like precipitate occurs in NiAl phase of NiAl-Cr(Mo)-25Fe alloy. The deep etching reveals that the precipitate in NiAl phase is not needle-like but plate-like, and it is identified as the abundant Fe-contained Cr(Mo) phase. In NiAl-Cr-xFe alloys, only NiAl-34Cr-2Fe alloy shows the similar fully eutectic structure to NiAl-34Cr eutectic alloy. When the Fe content increases to 4, 6, 8 and 10 at%, the primary dendrite NiAl including Cr-rich precipitate emerges, and the volume fraction of primary dendrite NiAl gradually increases. Moreover, the halo of alpha-Cr phase around the primary dendrite NiAl occurs. Moreover, the addition of 5 at%Fe significantly improves the compressive property of NiAl-Cr(Mo) eutectic alloy. When the Fe content increase further, the compressive strength decreases. However, the addition of Fe does not improve the compressive property of NiAl-Cr eutectic alloy but deteriorate it. The relevant discussion is done.