Effect of Directional Solidification on the Structure and Properties of Ni3Al-Based Alloy Single Crystals Alloyed with W, Mo, Cr, and REM

The effect of the solidification gradient (G = 60 and 150 degrees C/cm) at a solidification rate R = 10 mm/min on the structural parameters and the short- and long-term strength characteristics of blade-type single-crystal workpieces made of a heterophase gamma' + gamma VKNA-1V-type gamma'(Ni3Al)-based alloy with low contents of refractory metals is studied. The single crystals have a cellular- dendritic structure: dendrites are heterophase and consist of thin discontinuous nickel-based. solid solution layers between gamma'(Ni3Al)-matrix regions. Primary gamma'-phase precipitates are located in the interdendritic space. An increase in solidification gradient G from 60 to 150 degrees C/cm (by a factor of 2.5) at a solidification rate R = 10 mm/min leads to a decrease in the dendrite arm spacing by similar to 1.5 times, the size of primary gamma'-phase precipitates by 2.5-3 times, and the refinement of.' regions between. layers in dendrite arms and at the periphery of dendrites by 2-3 times. The strength characteristics of the single crystals grown at G = 150 degrees C/cm are higher than those of the single crystals grown at G = 60 degrees C/cm by 10%. An increase in gradient G weakly affects the long-term strength of the single crystals. During long-term high-temperature tests under loading, secondary disperse gamma'(sec) particles precipitate in the discontinuous gamma solid solution layers forming inclusions in two-phase gamma' + gamma dendrites, and the morphology of the gamma layers changes (they become thicker and shorter). The < 111 > VKNA-1V alloy single crystals grown at G = 150 degrees C/cm and R = 10 mm/min have a set of the required properties, namely, a high high-temperature strength over the entire temperature range, moderate high-temperature plasticity, and the absence of the plasticity drop at 800 degrees C (which is characteristic of single crystals with other crystallographic orientations). These properties make < 111 > VKNA-1V alloy single crystals promising for working and nozzle gas turbine engine blades, including the blades in "blisk" assembly units.