Antiphase boundary strengthening in a single crystal nickel-base superalloy

An investigation has been made into strengthening mechanism in a single crystal nickel-base superalloy DD8 by transmission electron microscopy. The results show that the stress rupture strength of the alloy increase with the decrease of misfits, and the antiphase boundaries (APBs) formed in the ordered γ' phase, rather than the misfits, play a dominate role in strengthening the single crystal Ni-base superalloy DD8. There are three kinds of mechanisms for forming the APBs which are observed in the present materials. One is mis-arrangement of the local ordered atoms in the γ' phase due to the local strain; the second arises from the 1/2(110) dislocations cutting into the γ' phase, and the third is the formation of the APBs induced by the 1/2(110) matrix dislocation network. The formula for the contribution of the antiphase boundary energy to the strength of the alloy is presented.