Effect of heat treatment on the microstructures and hardness of Ti-48Al-xCr alloys
Microstructural developement during continuous cooling (0.245oC/min to 500oC/min) from the α-Ti phase region and subsequent annealing treatment, 1450oC (15minutes) 1250oC (1 hour) has been investigated using Ti-48Al, Ti-48Al- 2Cr, Ti-48Al-4Cr and Ti-48Al-8Cr (at. %) alloys. In the Ti-48Al alloys...
Saved in:
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
2012
|
| Subjects: | |
| Online Access: | http://eprints.utm.my/id/eprint/28953/5/FarizaMohamedJamilMFKM2012.pdf |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | Microstructural developement during continuous cooling (0.245oC/min to
500oC/min) from the α-Ti phase region and subsequent annealing treatment, 1450oC
(15minutes) 1250oC (1 hour) has been investigated using Ti-48Al, Ti-48Al-
2Cr, Ti-48Al-4Cr and Ti-48Al-8Cr (at. %) alloys. In the Ti-48Al alloys and Ti-48Al-
2Cr, nearly fully lamellar transform fully lamellar with the lamellar grain size and
lamellar spacing decrease as the cooling rates increases. At slowest cooling rates, a
small amount of Widmanstatten-lamellar structure observed appears to be
intermediate between the lamellar structure. Meanwhile, addition of chromium up to
4%, at any cooling rates the lamellar grain size remain unchanged. But the formation
of β phase is increases at fastest cooling rate (oil quenched). This is due to the
precipitation of the β phase at grain boundaries during heat treatment and insufficient
time to dissolve to α and γ phase due to fast cooling. Slowest cooling rates (furnace
cooled) all β phase completely dissolved as the following transformation β α + γ
α2+ γ. The study revealed at 8% of Chromium slowest and fastest cooling rates
shows large portion of β phase at precipitated at grain boundaries but at intermediate
cooling rates the β phases seem disappeared or dissolved. Microhardness analysis
shows that several factors significantly increase the hardness value of Ti-48Al alloys
which is the evolution of α2-volume fraction, high cooling rates and smallest lamellar
spacing. |
|---|