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L12 A13Ti-Based Alloys with A12Ti Precipitates-2. Deformation Behavior of Single Crystals
PENNSYLVANIA UNIV PHILADELPHIA
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The operating slip systems and flow behavior of single crystalline Al66.8 Ti 27.4 Fe5.8 two phase L12 Al2 Ti material, was investigated as a function of temperatures using specimens with compressive axes near 011, 113 , 112, 013 and 133. The material shows a very limited compressive ductility, and fracture occurs by cleavage along planes of low indices, such as 011, 001, 013 and 111. Slip occurs exclusively on the octahedral slip systems at low temperatures, and on both octahedral and cube systems at high temperatures. A transition in operating slip systems from octahedral slip to cube slip, similar to the one seen in Ni,Al-type alloys, occurs as the temperature increases and as the orientation of the specimens change from near- 001 to near-111. The transition in slip system is attributed to the hardening effect of the A12Ti precipitates, rather than to the anisotropy of APB energy on cube and octahedral slip planes of the matrix. Because of the large hardening effect of the A12Ti, the two phase material is substantially stronger than single L12 phase materials. The shape but not the level of the flow stress- temperature curve for the two phase material resembles that of the single phase L12 material at low and intermediate temperatures. At high temperatures, however, the flow stress of the two phase material exhibits a sharp decrease, a feature which is not observed in the single phase L12 materials and can be correlated with a continuous dissolution of the A12Ti precipitates at high temperatures.
APPROVED FOR PUBLIC RELEASE