Discontinuous Precipitation of gamma %26apos; Phase in Ni-Co-Al Alloys

作者：Rojhirunsakool Tana****^*; Nag Soumya; Banerjee Rajarshi

来源：JOM, 2014, 66(8): 1465-1470.

DOI：10.1007/s11837-014-0998-8

Decomposition of nickel-base alloys by precipitation of the gamma%26apos; phase occurs either continuously (homogeneously) or discontinuously. Under certain conditions of solute content and temperature, discontinuous precipitation is observed. Ni-Al-Co alloys have been characterized by coupling atom probe tomography with transmission electron microscopy studies. The primary focus was to investigate the discontinuous precipitation of gamma and gamma%26apos; phases. When subjected to fast quenching after solution treatment, the gamma%26apos; precipitates exhibit a near-spherical shape and monomodal size distribution with an average size of less than 5 nm. After early stage annealing at 600A degrees C for 10 min, discontinuous precipitation nucleated near the grain boundaries while some regions of homogeneous gamma%26apos; precipitates were observed. Discontinuous gamma + gamma%26apos; product was completely transformed throughout the grain after 600A degrees C/1 h. On long-term annealing (600A degrees C/256 h), coarser gamma + gamma%26apos; lamellae products replaced the fine discontinuous products that exhibited after 1 h annealing at 600A degrees C. Equilibrium compositions of the gamma and gamma%26apos; phases were achieved in this coarsening stage. The gamma%26apos; phase has an Al content of 25 at.%, which is consistent with the as-quenched condition where the (Ni + Co)(3)Al stoichiometry is maintained after 600A degrees C/256 h annealing.

• 出版日期2014-8