Evaluation of Liquation Cracking Susceptibility of CM247LC Superalloy Repair Welds via Pre-Weld Varestraint Test

Abstract

In this study, the liquation cracking susceptibility in the heat-affected zone of CM247LC superalloy gas turbine blades during repair welding was quantitatively evaluated using a newly developed pre-weld Varestraint test method. The repair welding geometry was replicated through Varestraint tests for the pre-weld bead. The liquation cracking susceptibility, that is, the liquation cracking temperature range (LCTR), could be evaluated through temperature visualization at the time of crack formation during the Varestraint test. The LCTR of CM247LC alloy repair welds (heat-affected zone of the second layer weld) was 280 K. Compared to the LCTR of as-cast (620 K) and aged (65 K) CM247LC, metallurgical mechanisms for controlling the LCTR of repair welds were examined based on the microstructural characterization and Scheil’s solidification calculations for the pre-weld. The LCTR of the CM247LC alloy repair weld was influenced by the MC carbide fraction and the segregated concentration of trace and impurity elements, such as B and S in pre-weld solidification path. A process design capable of reducing the fraction of MC carbides and solidification segregation of trace impurity elements is required. Based on the experimental and theoretical results, the proposed modified Varestraint testing method for dissimilar welds is expected to analyze the solidification cracking behavior effectively in manufacturing high-soundness CM247LC superalloy welds.

Strategy of Suppressing the Solidification Cracking Susceptibility of 247LC Superalloy Weld Metals using Commercial Ni-Based Fillers

“…본 연구에서 주목하고 있는 블레이드 소재 는 일방향응고용 247LC 초내열합금으로, 해당 소재는 용접 고온균열(응고 및 액화균열)에 취약한 소재로 잘 알려져 있다 6,7) . 본 저자는 247LC 초내열합금 용접부 의 응고 및 액화균열 민감도 최소화를 위한 용접야금학 적 인자 규명에 대한 다양한 선행연구 결과를 보고한 바 있다 4,5,[7][8][9][10][11] . 가스텅스텐아크용접(Gas Tungsten Arc Welding, GTAW)을 이용한 Varestraint 시험으로부터,…”

Solidification Crack Free Welding Strategy via Ultra High Precision Laser Scanning at a Single Grain of Directionally Solidified and Single Crystal Superalloys

“…대한용접․접합학회지 제41권 제4호, 2023년 8월 255 향응고 및 단결정 니켈계 초내열합금을 기반으로 한 각 종 고부가 소재부품의 제조기술 국산화 연구개발이 활 발하게 진행되고 있다. 해당 부품(예: 가스터빈 블레이 드, 베인 등)들은 신품 제조 [1][2][3][4] 및 유지보수 [5][6][7] 시 용 접 및 적층제조 공정의 적용이 필수적이며, 따라서 용 접 야금학적 현상의 이해를 바탕으로 한 용접 건전성 확보는 해당 부품의 성능, 내구성과 직결되는 주요 핵심 공정기술이다. 하지만 일방향응고 및 단결정 초내열합 금들은 용접 시 고온균열이 발생하는 난용접(Difficultto-weld) 소재들로 잘 알려져 있어, 용접 건전성 확보 에 상당한 어려움이 있다 1,6,[8][9][10] .…”