Phase transformation and segregation to lattice defects in Ni-base superalloys

International audienceNanostructural features of nickel-base superalloys as revealed by atom probe field ion microscopy (APFIM) and atom probe tomog. (APT) are reviewed. The more salient information provided by these techniques is discussed through an almost exhaustive anal. of literature over the last 30 years. Atom probe techniques are shown to be able to measure the compn. of tiny g' ppts., a few nanometers in size, and to reveal chem. order within these ppts. Phase sepn. kinetics in model NiCrAl alloys was investigated with both 3DAP and Monte-Carlo simulation. Results are shown to be in good agreement. Plane by plane anal. of '001' planes of Ni3Al-type g' phase makes it possible to est. the degree of order as well as the preferential sites of various addn. elements (Ti, Cr, Co, W, Ta, Re, Ru, etc.) included in superalloys. Clustering effects of Re in the g solid soln. were also exhibited. Due to its ultrahigh depth resoln., the microchem. of interfaces and grain boundaries can be characterized on an at. scale. Grain boundaries in Astroloy or N18 superalloys were found to be enriched in B, Mo, and Cr and Al depleted. [on SciFinder (R)