Microstructural Evolution in Novel Suction Cast Multicomponent Ti-Fe-Co Alloys
Abstract
The present work is aimed at understanding the solidification pathways of the Ti-rich Ti-Fe-Co in situ composites consisting of ultrafine eutectic with micron-scale dendrites. The effect of addition of Co in the Ti-rich binary Ti-Fe alloys has been systematically investigated. The series of Ti-Fe-Co ternary alloys i.e., Ti75Fe25- x Co x ( x = 0, 5, 10, 12.5, 15, 20), (Ti70.5Fe29.5)100- x Co x ( x = 0, 2, 4, 6, 8, and 10), Ti70Fe30- x Co x ( x = 0, 5, 10, 15, 20, 25), Ti65Fe35- x Co x ( x = 0, 10, 15, 17.5, 20, 25), and Ti60Fe40- x Co x ( x = 0, 16, 18, 20, 22, 24) are synthesized by arc melting cum suction casting technique under high purity Ar atmosphere to obtain alloy cylinders having diameter ( ϕ) of 3 mm. Detailed X-ray diffraction and electron microscopic (SEM and TEM) study are carried out to identify the phases as well as to monitor the sequence of phase evolution in the ternary alloys. The present study conclusively proves that the Ti65Fe10Co25, Ti70Fe30- x Co x ( x = 10, 20, 25), and Ti75Fe15Co10 alloys show the ternary quasi-peritectic reaction of L + Ti(Co,Fe) → ( β-Ti)ss + Ti2(Co,Fe) at invariant point P (=Ti75.5±0.8Fe6.3±2.1Co18.2±2.7) which is cooperated by means of eutectic reaction of L → ( β-Ti)ss + Ti2(Co,Fe) below P and peritectic reaction L + Ti(Co,Fe) → Ti2(Co,Fe) for Ti65Fe10Co25,Ti70Fe10Co20, and Ti70Fe5Co25 alloys or eutectic reaction L → ( β-Ti)ss +Ti(Co,Fe) for Ti70Fe20Co10, and Ti75Fe15Co10 alloys above the point P. In addition, the peritectic reaction L + Ti(Co,Fe) → Ti2(Co,Fe) plays a significant role in the phase evolution. The microstructural evolution, phase equilibria and solidification pathways have been explained by generating liquidus projection of the investigated alloys. Interestingly, the Co addition leads to the formation of complex Ti2Co phase and significantly affects the compositional stability of TiFe phase. This is found to have significant influence on the microstructural development during suction casting of the investigated alloys.
- Publication:
-
Metallurgical and Materials Transactions A
- Pub Date:
- February 2015
- DOI:
- 10.1007/s11661-014-2675-5
- Bibcode:
- 2015MMTA...46..851S