MICROSTRUCTURE EVOLUTION AND INTERFACIAL FORMATION MECHANISM OF WIDE GAP BRAZING OF DD5 SINGLE CRYSTAL SUPERALLOY

Abstract

Ni-based single-crystal superalloy DD5 has excellent high temperature properties, which is the preferred raw material for aero-engine turbine blade in recent year. In this research, DD5 superalloy was brazed by different contents of Ni-Co-Cr-W-B+DD99 mixed powder filler alloy. The microstructure evolution and interfacial formation mechanism of DD5 superalloy brazing joint were analyzed by SEM and EPMA. The mechanical properties of joint after solid solution treatment and aging treatment were tested. The results show that g-Ni primary phase formed firstly in the Ni-Co-Cr-W-B/DD99 interface during the brazing process, and then B element segregated and precipitated to fine granular M3B2 type boride. The residual liquid phase solidified and formed lastly to the M3B2 phase, g+g′ eutectic phase and g-Ni+Ni3B+CrB eutectic phase during cooling. With increasing the ratio of DD99 in mixed powder filler alloy, the low melting point eutectic phase and borides in the joint decrease and the uniformity of composition and microstructure of joint improve. When the ratio of DD99 increased to 70% (mass fraction) in the mixed powder filler alloy, it can be observed that element of B diffused to DD99 additive powder which result*国家自然科学基金项目51401210和51331005以及国家高技术研究发展计划项目2014AA041701资助 收到初稿日期: 2015-12-03,收到修改稿日期: 2016-04-17 作者简介:孙元,女, 1980年生,副研究员 DOI: 10.11900/0412.1961.2015.00622 第875-882页 pp.875-882