Effect Of B And Ce On Microstructure And Properties Of Co-8.8Al-9.8W-2Ta Superalloy

Co-Al-W superalloy is a kind of new Co-base superalloys,which is strengthen by??-Co₃(Al,W)phase with L1₂ structure,and owns better high-temperature strength and oxidation resistance.Co-Al-W superalloys are strengthen by coherent strengthen,unlike Ni-based superalloys strengthen by anti-phase boundary,the mismatch between strengthening phase and matrix phase is about 1%,resulting in poor deformability,which is one of focuses for Co-Al-W superalloys.Boron Can effectively improve ductility of alloys,cerium is a good grain boundary strengthening element,both can effectively increase the grain boundary strength and restrain the brittle fracture of grain boundary.This paper was based on the group's previous research on Co-8.8Al-9.8W superalloys,in the microstructure of Co-8.8Al-9.8W and Co-8.8Al-9.8W-2Ta alloys,it was found that Ta element can availably enhance the volume fraction of strengthening phase,but it also can promote precipitation of detrimental secondary phases.The addition of alloying element Ta can effectively improve the maximum compressive strength and elongation of the alloys,and change the fracture mode of the alloys.Thus,Co-8.8Al-9.8W-2Ta alloy was taken as the matrix and microalloying with B element and Ce element,prepared eight kinds of alloys with 0.1?0.8 at.%microalloying element content.After solution treatment at 1300°C and aging treatment at 900°C,analyzing alloys from microstructure,element distribution,the secondary phase and microhardness,it will provide some data reference for the further research of alloy.Studying alloys contained B and Ce element found that both the elements hardly effect morphology and volume fraction of strengthening phase,and mainly effect detrimental secondary phases precipitated at grain boundaries.Ce element had no obvious effect on volume fraction of secondary phase,Co₃W,and mainly occurred spheroidization to the secondary phase,and the distribution of secondary phase was the same as that of matrix at the grain boundries.B element effected both category and volume fraction of secondary phase in the alloys,after aging,the main secondary phases of the alloys were Co₃W and Co₇W₆.With the increase of B content,the volume fraction of detrimental secondary phases in the grain boundaries decreased,and no matrix phase precipitated in the grain boundaries.Electron probe microanalysis showed that Ce element uniformly distributed in the alloy,and B element mainly distributed in the secondary phase of grain boundaries region.Some of Ce atoms formed compounds Ce₂Co₁₇ and Al₂Ce₂Co₁₅,and some of B atoms formed Co W₂B₂.Microhardness test showed that:compared with matrix alloy,Co-8.8Al-9.8W-2Ta alloy,the microhardness of alloys were obviously increased after microalloying.The microhardness of Ce-containing alloy increased first and then decreased with the increase of Ce content,the microhardness of 0.4Ce alloy is the highest,while B-containing alloys decreased gradually with the increase of B content.Considering the microstructure and microhardness of the alloys,the addition of B element should be about 0.1 at.%,and the content of Ce element should be about 0.4 at.%.