Variation of liquation cracking susceptibility for over–aged 247LC superalloy repair weld heat–affected zone

Abstract

In this study, the liquation cracking temperature range (LCTR) of over-aged 247LC superalloy repair welds was quantitatively evaluated using spot-Varestraint testing, especially for application in the repair weld heat-affected zone (HAZ). The metallurgical mechanism of the evaluated liquation cracking susceptibility and variation of the LCTRs of the over-aged 247LC superalloys was clarified by analyzing the microstructural characteristics at the liquation cracking surface, and using thermodynamic calculations. From the spot-Varestraint tests of the over-aged materials, the LCTR was quantitatively evaluated to be 410 and 620 K for the 500 and 1000 h over-aged specimens, respectively. These results demonstrate that the over-aged 247LC superalloys face significant and serious liquation cracking susceptibility in repair weld HAZ. Based on local element distributions at the liquation cracking surface, analyzed by transmission electron microscopy and the Thermo-Calc calculations, the underlying metallurgical mechanism of high LCTRs of overaged materials could be attributed to the precipitation of fine MC and M<sub>6</sub>C carbides during the over-aging treatment. The carbides promote local liquation at the interface between the gamma phase at temperatures lower than the equilibrium solidus (1530 K) of the 247LC. The estimated liquation initiation temperatures at the MC/γ and γ/M<sub>6</sub>C interfaces were 1125 and 1420 K, respectively.

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] .…”