Effect of heat treatments on microstructure evolution and mechanical properties of blended nickel-based superalloys powders fabricated by laser powder deposition

详细信息    查看全文

• 作者：Y. Tian^a ; A. Gontcharov^b ; R. Gauvin^a ; P. Lowden^b ; M. Brochu^a ; ^{mathieu.brochu@mcgill.ca" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Nickel-based superalloys ; Laser powder deposition ; Heat treatment ; Microstructure evolution ; Mechanical properties
• 刊名：Materials Science & Engineering A
• 出版年：2016
• 出版时间：30 September 2016
• 年：2016
• 卷：674
• 期：Complete
• 页码：646-657
• 全文大小：6332 K

文摘

Microstructure evolution and mechanical properties of sample produced by laser powder deposition using blended powders of Mar M247 and Amdry DF3 were studied in the as-deposited and heat treated conditions. In the as-deposited condition, continuous (Cr, W) borides and γ-Ni₃B eutectics were observed to segregate in the interdendritic regions. After the two-step aging treatment, the low melting point γ-Ni₃B eutectics re-melted. Small size γ-γ′ eutectics and discrete W borides formed during re-solidification. The γ′ strengthening phase that precipitated out homogeneously in the dendritic cores had an average diameter of 102±26 nm. When annealing was attempted before the aging treatment, both γ-Ni₃B eutectics and the surrounding dendrites re-melted, contributing to the coarsening of the γ-γ′ eutectics and the discrete W borides. Gamma prime precipitates with average diameter of 106±30 nm were observed. This microstructure evolution from the re-melting of γ-Ni₃B eutectics and development of γ-γ′ eutectics eradicated the risk of strain-age cracks during the two tested heat treatments by backfilling. The coarsening kinetics of γ′ precipitates in the two heat treated conditions was modeled and showed a good agreement with the experimental observation. The microhardness results showed that the as-deposited condition possessed the highest hardness attributed to the continuous feature of the secondary phases, while the two heat treated conditions presented similar hardness owing to the similar size and volume fraction of γ′ precipitates. The tensile test results at both ambient and elevated temperatures indicated that the two types of heat treatments increased the tensile properties, especially ductility.