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金属学报  2016, Vol. 52 Issue (4): 455-462    DOI: 10.11900/0412.1961.2015.00399
  论文 本期目录 | 过刊浏览 |
铸造镍基高温合金中初生MC碳化物的退化过程和机理*
孙文,秦学智,郭建亭,楼琅洪,周兰章
中国科学院金属研究所, 沈阳 110016
DEGENERATION PROCESS AND MECHANISM OF PRIMARY MC CARBIDES IN A CAST Ni-BASED SUPERALLOY
Wen SUN,Xuezhi QIN,Jianting GUO,Langhong LOU,Lanzhang ZHOU
Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
全文: PDF(1328 KB)   HTML
摘要: 

采用OM, SEM和TEM及其HAADF模式下的元素面扫描, 研究了一种铸造镍基高温合金长期时效期间初生MC碳化物的分解反应过程、形式及机理.结果表明, 在长期时效过程中, 初生MC分解反应分为3个阶段: MC+γM6C + γ′, MC+γM6C + M23C6+γ′MC+γM6C + M23C6+η.HAADF模式下对分解区域进行元素面扫描, 浓度梯度显示初生MC分解实际上是元素在初生MC和γ基体之间的互扩散交流过程, 分解产物中的C主要来源于初生MC, Ni, Al和Cr来源于γ基体, 而Ti, W和Mo不仅源于γ基体也源于初生MC. 合金具有较高的Ti+Nb+Ta+Hf原子分数和(Ti+Nb+Ta+Hf)/Al原子比是初生MC分解过程中析出η相的必要条件, 而其析出的数量与初生MC的分解程度有关, 分解程度越高, 析出数量越大.

关键词 铸造镍基高温合金长期时效初生MC退化机制    
Abstract

Primary MC carbide is one of the most important phases in cast Ni-based superalloys. During long-term thermal exposure, the primary MC carbide is not stable and tends to degenerate, exhibiting various degeneration reactions, such as MC+γM6C+γ′, MC+γM6C + M23C6+ γ′ and MC+γM6C + M23C6+η. It is widely known that the degeneration of primary MC carbide has obvious influence on the microstructural evolutions of superalloys, including coarsening of γ′ phase, coarsening of grain boundaries and precipitation of topologically close-packed (TCP) phase, and consequently the mechanical properties of alloys. Much research work has focused on the degeneration mechanism of primary MC carbide during long-term thermal exposure, however, it is not very clear so far. In this work, a cast Ni-based superalloy is fabricated and thermally exposed at 850 ℃ for 500~10000 h in order to study the degeneration mechanism of primary MC carbide. The degeneration of primary MC carbide is observed by OM, SEM and TEM. High-angle annular dark field (HAADF) mode of TEM is used to clearly observe the degeneration of primary MC carbide and the element distribution in the degeneration areas. The results show that the primary MC degeneration is an inter-diffusion process which occurs between the primary carbide and the γ matrix. During the degeneration, C is released from the primary carbide, Ni, Al and Cr are provided by the γ matrix, while Ti, W and Mo come from both primary MC and γ matrix. The precipitation of η phase is determined by the atomic fraction of Ti+Nb+Ta+Hf and atomic ratio of (Ti+Nb+Ta+Hf)/Al and its amount is affected by the degeneration degree of primary MC carbide. The higher the degeneration degree, the larger the tendency for the precipitation of the η phase.

Key wordscast Ni-based superalloy    long-term thermal exposure    primary MC carbide    degeneration mechanism
收稿日期: 2015-07-17     
基金资助:*国家自然科学基金项目51001101和国家能源局项目NY20150102资助

引用本文:

孙文,秦学智,郭建亭,楼琅洪,周兰章. 铸造镍基高温合金中初生MC碳化物的退化过程和机理*[J]. 金属学报, 2016, 52(4): 455-462.
Wen SUN, Xuezhi QIN, Jianting GUO, Langhong LOU, Lanzhang ZHOU. DEGENERATION PROCESS AND MECHANISM OF PRIMARY MC CARBIDES IN A CAST Ni-BASED SUPERALLOY. Acta Metall Sin, 2016, 52(4): 455-462.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2015.00399      或      https://www.ams.org.cn/CN/Y2016/V52/I4/455

图1  热处理态合金中初生MC碳化物的SEM像和EPMA分析
图2  热处理态合金中初生MC碳化物的SEM和TEM像
Phase Cr Fe Ni Mo W Al Ti Nb
MC 2.6 - 5.0 13.6 31.1 - 43.0 4.7
γ' 9.9 11.7 67.1 0.9 2.0 2.4 6.1 -
M6C 12.7 10.0 15.1 24.4 37.8 - - -
M23C6 68.7 3.2 5.0 10.6 12.6 - - -
η 4.5 2.7 68.5 1.5 1.0 3.9 17.0 0.9
表1  初生MC分解区域中各相的化学成分
图3  850 ℃时效1000 h合金中初生MC分解的BSE像、TEM像、HAADF像和M6C的EDS分析
图4  在850℃时效6000 h合金中初生MC的BSE像和EPMA分析
图5  在850 ℃时效10000 h合金中初生MC退化的SEM像、HAADF像和反应区中各相的SAED谱
图6  图5b Area 1中正在退化中的初生MC的HAADF像与周围γ基体之间的元素分布图
图7  图5b Area 2中正在退化中的初生MC与周围γ基体之间的元素分布图
Alloy
Atomic fraction / % Atomic ratio of (Ti+Nb+Ta+Hf)/Al η phase precipitation D
Al Ti Nb Ta Hf Ti+Nb+Ta+Hf
K444 6.80 5.50 0.12 - 0.13 5.75 0.85 Yes High
K446 3.46 2.92 0.69 - - 3.61 1.04 No Low
K452 5.22 4.11 0.15 - - 4.26 0.82 Yes High
K465 11.89 3.41 0.69 - - 4.10 0.35 No Low
GTD-111 6.66 5.69 0.01 0.90 - 6.60 0.99 Yes High
IN738 7.32 3.91 0.74 0.38 - 5.03 0.69 Yes High
A0[20] 3.60 3.03 0.72 - - 3.75 1.04 No Low
Present alloy 3.92 4.23 0.06 - - 4.29 1.10 Yes High
A7[20] 4.12 4.15 0.07 - - 4.22 1.02 Yes High
A8[20] 3.88 4.04 0.07 - - 4.10 1.06 Yes High
表2  镍基高温合金的化学成分与初生MC退化及η相析出的关系
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