Study on the Heat Treatment Improvement of Directionally Solidified High Entropy Ni-based Superalloy

• Main Authors: Po-Chung Yen, 顏柏充
• Other Authors: Sheng-Rui Jian
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/x9wt7w

碩士 === 義守大學 === 材料科學與工程學系 === 104 === In this study, nickel (Ni) as a base, by adding about ten elements and through software calculation, three kinds of nickel-based high-entropy superalloys were designed, namely, HESA-A only adds 2wt.% tantalum and no niobium, while HESA-C only adds 2wt.% of niobium and no tantalum, whereas HESA-B is added to each of tantalum and niobium with 1wt.%. Through different heat treatment temperatures and changes in the added element, microstructures are inspected and mechanical properties are investigated. The study found that after 1210C solution heat treatment, strengthening phase γ'' has almost dissolved back to γbase phase, in addition hardness values exceed 400HV for both aging heat treatments at 900C single aging and 900C/750C double aging, where the hardness value of 900C/750C double aging is the highest one, nevertheless the γ'' volume fraction of it is also the highest one. From the differences of added elements due to the alloy design of three nickel-based high-entropy superalloys, tantalum content of HESA-A carbides is 48.81wt.%, tantalum and niobium contents of HESA-B carbides are respectively 27.82wt.% and 20.81wt.%, niobium content of HESA-C carbides is 47.78 wt.%. From the partition analysis of element concentration between γ'' and γ, because of adding 1wt.% more tantalum and no niobium, HESA-A shows higher content of tantalum in γ'' phase than that of HESA-B, and HESA-C also shows higher content of niobium in γ'' phase than that of HESA-B because of adding 1wt.% more niobium but no tantalum. Furthermore, tungsten in HESA-C moves to the γ base phase because of adding 2wt.% niobium but no tantalum, whereas tungsten remains in the γ'' phase in both cases of HESA-A and HESA-B.