Properties of TiAl sheet pack-rolled at temperatures below 1000°C

Abstract

TiAl alloy specimens with microcrystalline (MC, grain size is 5 µm) and submicrocrystalline (SMC, grain size is 0.4 µm) structures were successfully pack-rolled to sheet with a thickness down to 0.4 mm in the temperature ranges of 800°C to 1000°C and 900°C to 1000°C, respectively. An 18/10 stainless steel was used as a rather inexpensive can material for pack-rolling. Unidirectional rolling and bidirectional cross-rolling were used. Because of a wider temperature range for pack rolling and a lower cost for production of the alloy preforms, the microcrystalline structure was found to be a better microstructural condition for the TiAl sheet rolling. The sheet produced by unidirectional rolling had an anisotropy of mechanical properties, i.e., strength was smaller and elongation larger in the rolling direction than in a transverse direction. The anisotropy decreased when the rolling temperature increased. The bidirectional rolling led to in-plane isotropic properties of the sheet. The produced sheet showed elongation of about 3 pct at room temperature, brittle-to-ductile transition in the temperature range of 750°C to 850°C, and superplastic behavior in the temperature range 900°C to 1000°C.