MICROSTRUCTURE AND PERFORMANCE OF Ni-Hf BRAZING FILLER ALLOY

In consideration of the envelopment of γ dendrites by the Hf-rich melts at the late period ofsolidification of the cast Ni-base superalloys containing Hf,a heat of brazing filler alloycomposed of Ni-18.6Co-4.5Cr-4.7 W-25.6Hf(wt-%)was prepared.This alloy ishypereutectic.γ phase is the leading phase in eutectic γ+Ni_5Hf and γ bars are surrounded byNi_5Hf phase.At the section perpendicular or parallel to the γ growing direction,the eutecticmorphology is cellular or laminar respectively.The content of Ni_5Hf in the alloy is 68.7v.-%.The compositions of primary and eutectic Ni_5Hf are very similar.Ni,Co and Hf are the mainelements and solubility of Cr and W in Ni_5Hf is very low.This alloy is an ideal brazing fillersuitable to the directional or single crystal superalloy,and the elements are beneficial tosuperalloys properties.This filler alloy is of low melting point and of good fluidity.After braz-ing at 1240℃,5 min+1190℃,I h in 10~(-3) Pa vacuum,the microstructure of bond is the sameas that of Hf-bearing superalloy.No Si and B contamination is involved.