Nanocrystalline TiAl-V intermetallics hot pressed from mechanically alloyed powders

Jan M. Dutkiewicz ,  Wojciech Maziarz 

Polish Academy of Sciences, Institute of Metallurgy and Materials Sciences (IMIM PAN), Reymonta 25, Kraków 30-059, Poland

Abstract

The TiAl-V alloys compositions were chosen from the gamma-phase stability region up to maximum 20 at. % vanadium. The elemental powders were initially blended to desired composition of Ti-52.7Al-5V, Ti-55.4Al-10V, Ti-57.7Al-15V and Ti-60.4Al-20V (numbers indicate at. %). The milling was performed in a high energy planetary mill Fritsch Pulverisette P/4 resulted in formation of the almost fully amorphous structure after 40 hours. The formation of Al(Ti, V) solid solution was observed after 20 hours of milling. Longer milling caused amorphization of most of the material and formation of metastable phase in the alloy with the highest content of vanadium. TEM observation of powders after 40 hours of milling allowed to identified 50 nm wide nano-layers within individual particles. The origin of layered structure was explained as resulting from the mechanical alloying process, not from the thin foil preparation. The electron diffraction and bright field techniques reveled the amorphous and partially nanocrystalline structure within a milled powders. The local chemical analysis and elemental mapping allowed to show a high homogeneity of individual particles.
Uni-axial hot pressing at 700C under 200 MPa of milled powders allowed to obtain a bulk samples with density of about of 94 % of theoretical one. The X-ray diffraction revealed the two phases γ+α2 structure. TEM studies allowed to identify the nanometer range grains structure with a mean size of about 20-30 nm. The diffraction pattern has shown a ring like pattern without preferred orientation. Some larger grains has shown a parallel aligned defects causing streaks in the diffraction pattern indicating basal Ti3Al plane defects. Their existence indicate disordering within intermetallic grains in spite of 700oC annealing.

 

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Presentation: oral at E-MRS Fall Meeting 2003, Symposium G, by Jan M. Dutkiewicz
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-26 13:02
Revised:   2009-06-08 12:55