Heat Treatment Method of a Ni-Based Superalloy for Wave-Type Grain Boundary and a Ni-Based Superalloy Produced Accordingly

Abstract

The present invention suggests a method of heat treatment of a Ni-based superalloy that improves resistance against creep, fatigue and stress corrosion cracking while being economical and easy, and a Ni-based superalloy produced by using the same. The method and the superalloy of the present invention include solution treatment at the high temperature region during a heat treatment process after manufacturing or final cold working fabrication. Immediately following the solution treatment, the material is slowly cooled at 1˜15° C./minute down to the intermediate temperature region for aging treatment. After the slow cooling stage, aging treatment is directly performed by holding it at the intermediate temperature region for the prescribed time. Lastly, the aging treatment is followed by air-cooling stage.

1 . A heat treatment method of a Ni-based superalloy for wave-type grain boundary in heat treatment stage after producing or processing a Ni-based superalloy, comprising:
 a solution treatment process at the high temperature region;   a slow cooling process at 1˜15° C./minute down to the intermediate temperature region for direct aging treatment after the solution treatment;   an aging treatment process by holding it for the prescribed time at the intermediate temperature region for the aging treatment immediately after the slow cooling process; and   an air-cooling process after the aging treatment.   
   
   
       2 . The heat treatment method of the Ni-based superalloy according to  claim 1 , wherein the slow cooling process comprises,
 a stage in which incomplete wave-type grain boundaries form at some of flat grain boundaries formed during the solution treatment process; and   a stage in which the incomplete wave-type grain boundaries grow into stable wave-type grain boundaries, incomplete wave-type grain boundaries form at the flat grain boundaries, and planar carbides begin to precipitate at the wave-type grain boundaries.   
   
   
       3 . The heat treatment method of the Ni-based superalloy according to  claim 2 , wherein aging treatment process is characterized by that;
 most of the incomplete wave-type grain boundaries transform into stable wave-type grain boundaries; and   the precipitated carbides form incoherent interfaces by growing into planar shapes towards the opposite grain while being coherent with one grain constituting the wave-type grain boundary.   
   
   
       4 . The heat treatment method of a Ni-based superalloy for wave-type grain boundary according to  claim 1 , wherein the solution treatment is processed at 1000˜1200° C. during the solution treatment time, and the aging treatment is processed at 700˜900° C. during the aging treatment time. 
   
   
       5 . A Ni-based superalloy for wave-type grain boundary wherein wave-type grain boundaries are included and the planar carbides are placed at the grain boundaries away from one another. 
   
   
       6 . The Ni-based superalloy according to  claim 5 , wherein the carbides create a coherent interface with one grain with the above grain boundary, and make an incoherent interface by growing toward the opposite grain. 
   
   
       7 . The Ni-based superalloy for wave-type grain boundary according to  claim 5 , wherein the array of incoherent interfaces of the planar carbides formed at the wave-type grain boundaries is zigzag pattern.