Creep induced precipitation of the (Cr,Mo)5B3-type boride in γ/γ′ eutectic of a Ni-based superalloy.

Boron segregation and boride formation at grain boundaries are generally accepted in Ni-based superalloys. However, the addition of boron was found to result in the formation of a high density of nanosized M 5 B 3 (where M is a mixture of Cr, Mo) particles in γ/γ′ eutectics of a Ni-based superalloy during high-temperature creep in this work. M 5 B 3 phase precipitated at γ/γ′ eutectics keeps a well-defined orientation relationship with the eutectics, which is [001] γ/γ′ //[001] M5B3 , (020) γ/γ′ //(130) M5B3. And these nanosized borides could block dislocation slip, result in stress concentration surrounding γ/γ′ eutectics and facilitate crack initiation at γ/γ′ eutectic/matrix interface during the creep at high temperatures. • The structrural characteristic of γ/γ′ eutectics in a crept polycrystalline superalloy was analyzed. • High density of nano-sized M 5 B 3 -type boride precipitated at γ/γ′ eutectic regions was observed. • Nanosized borides can aggravate the deformation incompatibility of γ/γ′ eutectics during high temperature creep. [ABSTRACT FROM AUTHOR]