Microstructure and mechanical properties of γ′ strengthened Co-Ni-Al-W-base ODS alloys

gamma ' precipitates strengthened Co-Ni-Al-W-base ODS alloys, produced by mechanical alloying, are promising high-temperature structural materials. The alloys were found to be composed of gamma/gamma ' two-phase region and discontinuously formed area. The element Ni was effective in enhancing the solubility limit of Al and W within gamma matrix, thus promoting the precipitation of gamma ' phase and restricting the formation of secondary phases, such as Co7W6, Co3W, and AlxCo phases. The flow stress of the alloys was effectively enhanced by the addition of Ni. The peak stress has decreased with increasing deformation temperature. The improved low-temperature strength was mainly attributed to the pining effect of oxide dispersion, gamma ' precipitates and fine-grained structure. The sharp fall in the yield strength in the temperature range of 600-700 degrees C was ascribed to grain boundary sliding, diffusion-controlled void formation, and the formation of shear band. (c) 2012 Elsevier B.V. All rights reserved.