This study takes GTD 111DS material as its subject, and uses heat treatment, overlay welding and laser cladding to propose the condition of recovering the integrity of damaged gas turbine. To do this, damage on the gas turbine’s first stage blade was ...

This study takes GTD 111DS material as its subject, and uses heat treatment, overlay welding and laser cladding to propose the condition of recovering the integrity of damaged gas turbine. To do this, damage on the gas turbine’s first stage blade was divided into material-type and rupture-type degradation. Then, regarding the study on material-type degradation, evaluation was made on the heat treatment condition related to the recovery of the material’s integrity damaged by the operation of the gas turbine. Meanwhile, regarding the study on rupture-type degradation, evaluation was made on the condition related to the recovery of integrity followed by overlay welding and laser cladding. The evaluations were collected to propose an optimal condition of recovering the integrity of damaged gas turbine’s blade, which turned out as below.
1) The heat treatment condition appropriate for recovering the integrity of material-type degradation of nickel based superalloy damaged by the operation of the gas turbine is solution heat treatment and aging treatment after going through hot isostatic pressing (HIP).
2) Overlay welding and pre/post-heat treatments can recover the integrity of the damaged gas turbine blades to a sufficient level. To recover integrity by overlay welding, the cause of rupture-type degradation shall be removed after the operation of the gas turbine. Before WRAP TIG welding, pre-heat treatment of 1,204℃ shall be applied, and after the welding, solution heat treatment of [1,121℃ and 1,204℃] and aging treatment of 843℃ shall be applied. After overlay welding, the influence of HIP seemed to have difficulties in judging whether the treatment took place or not, or the difference cause by the temperature.
3) Since there is a certain relationship between the microstructure and mechanical strength, the difference of qualitative mechanical strength can be forecasted by observing the microstructure. However, in case of dissimilar materials with a base material part and a welding part, such forecast might be incorrect. Thus, the factor deciding mechanical characteristic includes not only the heat treatment or HIP conditions, but also the microstructural difference between the base and welding material.
4) Cavities, caused by the melting bubbles during laser cladding and the hollow powder, remain as deficiency inside the cladding to decrease mechanical strength even after applying post-heat treatment. Although HIP can effectively remove most of the cavities, it didn’t have much effect on removing cavities larger than a certain size.
5) Laser cladding and post-treatment recovered the damaged gas turbine blade to a sufficient level. To recover integrity by laser cladding, the cause of rupture-type degradation shall be removed after the operation of the gas turbine. Then, after cladding with Rene 80 powder, HIP of 1,250℃ shall be applied, as well as solution heat treatment of [1,121℃ + 1,204℃] and aging treatment of 843℃ to see best results.

본 연구에서는 열처리와 육성 용접, 레이저 클래딩을 이용하여 손상된 가스터빈 블레이드의 건전성 회복 조건을 제안하였다. 이를 위하여 가스터빈 1단 블레이드의 손상을 재질형 열화와 균열형 열화로 분류하여, 재질형 열화에 관한 연구에서는 가스터빈 운전에 의해 손 ...

본 연구에서는 열처리와 육성 용접, 레이저 클래딩을 이용하여 손상된 가스터빈 블레이드의 건전성 회복 조건을 제안하였다. 이를 위하여 가스터빈 1단 블레이드의 손상을 재질형 열화와 균열형 열화로 분류하여, 재질형 열화에 관한 연구에서는 가스터빈 운전에 의해 손상된 재질의 건전성 회복에 관련된 열처리 조건을 평가하였다. 또한, 균열형 열화에 관한 연구에서는 균열형 열화 요인을 제거하고 형상을 복원하는 육성 용접과 레이저 클래딩에 따른 건전성 회복에 관련된 조건을 평가하였다. 이러한 평가를 종합하여 손상된 가스터빈 블레이드의 건전성을 회복시키는 최적의 조건을 제안하였다.
레이저 클래딩에 사용되는 많은 파우더들이 개발되고 있으며, 이러한 클래딩부는 클래딩 변수에 따라 다양한 기계적 성질을 나타내게 된다. 따라서 파우더 종류에 따른 클래딩 변수의 영향을 분석하는 것 또한 형상 복원 이외의 클래딩에 의한 표면처리 등에 응용범위가 넓을 것으로 판단된다. 또한, 가스 터빈으로 응용범위가 확대되고 있는 단결정 합금에 관한 레이저 클래딩 방법의 연구도 앞으로 연구되어야 할 주요 과제이다.