| Title |
Microstructural Evolution in Cast and HIP’ed Ingot Material of Beta Gamma TiAl Alloy by Two Step Cooling |
| Authors |
최광수(Kwangsu Choi); 김정민(Jeong Min Kim); 박준식(Joon Sik Park); 김영원(Young-won Kim) |
| DOI |
https://doi.org/10.3365/KJMM.2018.56.5.335 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
TiAl; colony size; lameller structure; hall petch relation; two step cooling |
| Abstract |
The beta gamma alloys of Ti - 43.8Al - 4Nb - 2Cr - 0.2B - 0.2C at % (9CN) were prepared using induction skull melted (ISM) cast ingots. In order to make a fine fully lamellar structure with some minor phases, two step cooling was performed using two furnaces after heat treatments in the α + β phase region. The heat-treatments produced an ~50 μm fully lamellar structure with α2 / γ + γ + B2 (HIP) → α + β (heating) → α / γ (FL) + γ + B2 → α2 / γ (FL) + γ + B2 phase change. For the two step heat treatment, the specimen was heat treated at 1340 ℃(or 1350 ℃) and transferred to another furnace, which was maintained at 950 ℃, in order to minimize any phase transformations between the temperatures. Fully lamellar specimens with some phases were compression-tested at RT, 700 ℃, 800 ℃, 900 ℃ and 1000 ℃, and showed excellent compressive strength at high temperature. The resultant material property determined via this cooling pr℃ess was superior to that of other materials such as Ni based superalloys or commercial TiAl alloys. The microstructures ass℃iated with the cooling effect were discussed in terms of materials properties and phase transformation. |