Effect of temperature dropping during solution treatment in rejuvenation heat treatment on final microstructures of Udimet 520

Abstract

Udimet 520 is a low precipitation hardened nickel-based superalloy, which is made to be turbine blades at high temperature. After long-term service, the microstructure of the turbine blades could be degraded, then the mechanical properties are worse than the new ones. The rejuvenation heat treatment of degraded turbine blades, which are made of cast Udimet 520, is following by solution treatment at 1,121ºC / 4 hours and then double aging processes, which include primary aging at 843 ºC / 24 hours and secondary aging at 760 ºC / 16 hours, respectively.However, in practical reheat treatment processes, the temperature during solution treatment can be dropped by error or malfunction of heating furnace because the furnace has to be operated at very high temperature for long time. Simulating this effect, the droppings of temperature during solution treatment are chosen and performed for 3 levels; 840 ºC, 800 ºC and 760 ºC, which could happen in practical working then heated up again immediately to solution temperature level. The maximum number of temperature dropping during the single solution treatment is up to 3 times. Received results show that the effect of temperature dropping during solution treatment has influenced on the final rejuvenated microstructures slightly due to the alloy is low precipitation behavior.