Production of TiAl sheet by cold-rolling

在室温下生长和轧制了具有近似化学计量组成的TiAl的多合成孪晶（PST）。在不断裂的情况下所能达到的最大总厚度减少取决于相对于轧制平面和轧制方向的层状取向。当试样取向使平行于板层边界的剪切变形在轧制过程中起作用时，它的作用使试样变长，这样的试样可以轧制到厚度减少约50%。研究了TiAl冷轧PST晶体的恢复和再结晶行为。发现显微硬度的变化发生在两个阶段，与还原量无关；第一阶段与位错密度的降低有关，第二阶段与轧制过程中TiAl片层中引入的变形孪晶的退火有关。然而，发现再结晶模式的变化取决于厚度的减少量。在轧制厚度减少20%以下的试样中，硬度完全恢复，并保留了层状组织。提出了一种解释PST TiAl冷轧至低于20%时异常再结晶行为的机制。在本研究的后期，发现PST TiAl中发生了环境脆化。然后，进行了合金化的尝试，以减少环境对延性的影响。与二元PST晶体相比，Cr、Mo、V或Mn改性的PST TiAl在延展性方面的环境损失较小。Cr的加入对TiAl的环境脆化有明显的抑制作用。最近，我们证实了cr改性的PST TiAl可以比二元PST TiAl更容易地冷轧到50 w的厚度。

Polysynthetically twinned (PST) crystals of TiAl with a nearly stoichiometric composition have been grown and rolled at room temperature. The maximum total reduction in thickness which is attainable without fracture depends on lamellar orientation with respect to the rolling plane and rolling direction. When specimens are oriented such that shear deformation parallel to the lamellar boundaries is operative during rolling and its operation causes lengthening of specimens, such specimens can be rolled up to about 50 % reduction in thickness.The recovery and recrystallization behavior of cold-rolled PST crystals of TiAl was also investigated. The change in microhardness was found to occur in two stages regardless of the amount of reduction ; the first sage associated with the decrease in dislocation density and the second stage related with the annealing-out of deformation twins introduced in TiAl lamellae during rolling. However, the recrystallization mode was found to vary depending on the amount of reduction in thickness. In specimens rolled to less than 20 % reduction in thickness, th full recovery in hardness occurs preserving the lamellar structure. A mechanism is proposed to interpret the unusual recrystallization behavior of PST TiAl cold-rolled to less than 20 %.At the later stage of this research, environmental embrittlement was found to occur in PST TiAl. Then, alloying attempts were made to reduce the environmental loss in ductility. The Cr, Mo, V or Mn modified PST TiAl was found to show a small environmental loss in ductility as compared with the binary PST crystals. In particular, the addition of Cr is effective in reducing environmental embrittlement of TiAl. Recently, we confirmed that the Cr-modified PST TiAl can be cold-rolled to 50 w reduction in thickness much more easily than the binary PST TiAl.