Sample preparation and microstructural characterization of the gamma titanium aluminide Ti-48Al-2W-0.5Si

Preparing samples that faithfully reveal all microstructural features in gamma-TiAl-base alloys for both optical and scanning electron microscope studies is fraught with difficulties. This study demonstrates that satisfactory results can be obtained through mechanical grinding, polishing, and proper etching. A preparation recipe is presented. Nine lots of investment-cast gamma-TiAl material with the nominal composition of Ti-48Al-2W-0.5Si have been characterized through optical and scanning electron microscope examinations. The study shows that a small depletion in Al content has a large effect on the microstructure. The duplex microstructure with a lamellar alpha(2)/gamma colony size of about 500 mu m and a large percentage of single-phase gamma grains as large as 200 mu m is altered to a coarse, nearly lamellar microstructure with a colony size as large as 5000 mu m and a small percentage of small single-phase gamma grains in the colony boundaries. (C) Elsevier Science Inc., 1997.