In-situ SEM and TEM tensile observations of novel Co-Al-W-Mo-Ta-B-Ce alloys with a coherent γ-CoSS/γ’-Co3(Al,W) microstructure at room temperature

Abstract

Slip band-grain boundary interactions of γ’-Co3(Al,W)-strengthened Co-9Al-4.5W-4.5Mo-2Ta-0.02B-(0.01, 0.1)Ce alloys (referred to as 0.01Ce alloy and 0.1Ce alloy, respectively, hereafter) were investigated in-situ using SEM and TEM. For the 0.01Ce alloy with a γ/γ’-Co3(Al, W) coherent microstructure, the {1 1 1}<1 1 0> dislocations initiate in the γ channels and subsequently cut into the neighbouring γ’ phase. A low-angle grain boundary (LAGB) is necessary for the slip band transfer mechanism. The slip bands transfer through the LAGB when the alignment factor M>0.8 with the incoming easy-slip system and the Schmid factor >0.3 on the outgoing slip system. The high-angle grain boundaries (HAGBs) usually have a low M value and the incoming slip bands are blocked at the HAGBs without transfer; instead, independent slip systems with the highest Schmid factor in the neighbouring grain are activated. The plastic deformation of the γ/γ’-Co3(Al,W) microstructure and the slip band-grain boundary interactions lead to an elongation of 16.4% of the 0.01Ce alloy. With some Co3W precipitates at the grain boundary of the 0.1Ce alloy, the slip bands bypass, cut through, or sometimes are arrested by the precipitates, resulting in a low elongation of 2.1% and a mixed dimple and cleavage failure.