The effect of heat treatment variables on the phase transformations at 1,420 C in Ti-48Al and Ti-48Al-2Mn-2Nb alloys

Journal Article · Fri Dec 01 04:00:00 EST 1995 · Acta Metallurgica et Materialia

DOI:https://doi.org/10.1016/0956-7151(95)00119-G· OSTI ID:178009

Ramanujan, R V ^[1]

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1. Bhabha Atomic Research Centre, Bombay (India). Metallurgy Div.

The effect of heat treatment variables such as initial microstructure, isothermal reaction time and cooling rate on the phase transformations occurring at 1,420 C in Ti-48Al and Ti-48Al-2Mn-2Nb alloys was studied. The main effect of the initial microstructure, which comprised either lamellae of {alpha}{sub 2} and {gamma} or equiaxed {gamma} grains, was to alter the kinetics, through a change in the chemical driving force of the phase transformations. Therefore, the equiaxed {gamma} grains transformed to {alpha} much faster than the lamellar structure and in the initially lamellar structure, growth of {alpha} resulted in the delineation of the initial dendritic structure formed during solidification. The effect of the rate of cooling from the heat treatment temperature on the final morphology of these alloys was drastic and resulted in a change in morphology from lamellar grains obtained on furnace cooling to a feathery and mottled morphology obtained on water quenching. TEM analysis of water quenched Ti-48Al-2Mn-2Nb revealed complex morphologies including a structure which consisted of equiaxed {gamma} grains and residual {alpha}{sub 2} and abutting colonies of {gamma} and {alpha}{sub 2}. Based on the TEM results, the early stages of formation of {gamma} from {alpha} were studied and mechanisms of nucleation and growth discussed. The relative importance and the coexistence of massive and martensitic transformation products is also discussed.

• OSTI ID: 178009
• Journal Information: Acta Metallurgica et Materialia, Journal Name: Acta Metallurgica et Materialia Journal Issue: 12 Vol. 43; ISSN 0956-7151; ISSN AMATEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
COOLING
CRYSTAL-PHASE TRANSFORMATIONS
GROWTH
LAMELLAE
MANGANESE ALLOYS
MARTENSITE
MICROSTRUCTURE
MORPHOLOGY
NIOBIUM ALLOYS
NUCLEATION
REACTION KINETICS
TITANIUM ALLOYS
TRANSMISSION ELECTRON MICROSCOPY