Softening mechanism in high-temperature nickel alloys subjected to thermomechanical treatment in long-term high-temperature tests

Abstract

It is known that in high-temperature tests the rate. of softening in nickel alloys after termomechanical treatment (TMT) is higher than after the standard heat treatment (SHT). For low-alloyed alloys of the ÉI437B type this is associated with the development of recrystallization at operating temperatures of 650 – 750°C. Complexly alloyed high-temperature nickel alloys are characterized by a higher content of the y'-phase, a wide range of the double-phase (γ+ γ′)-state, and, as a consequence, a considerably higher recrystallization temperature compared to alloy ÉI43B7. However, these alloys often lose strength after TMT more intensely than after SHT. The causes of this phenomenon have not been determined so far. This investigation is devoted to the solution of this problem.