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 micro scope studies is fraught with difficulties. This study demonstrates th at satisfactory results can be obtained through mechanical grinding, p olishing, and proper etching. A preparation recipe is presented. Nine lots of investment-cast gamma-TiAl material with the nominal compositi on of Ti-48Al-2W-0.5Si have been characterized through optical and sca nning electron microscope examinations. The study shows that a small d epletion in Al content has a large effect on the microstructure. The d uplex microstructure with a lamellar alpha(2)/gamma colony size of abo ut 500 mu m and a large percentage of single-phase gamma grains as lar ge 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 sma ll single-phase gamma grains in the colony boundaries. (C) Elsevier Sc ience Inc., 1997.