Deformations of advanced metallics alloys
The work is focused on the study of the mechanisms of deformation acting at the microscale on a g-TiAl alloy in a broad range of temperatures up to 750°C. These intermetallics are very attractive for aerospace applications due to their increased thrust-to-weight ratios and improved efficiency under aggressive environments at temperatures up to 750°C. For that reason, they are projected to replace the heavier Ni-base superalloys currently used for low pressure turbine (LPT) blades manufacturing.
With the aim of developing a multiscale model of the polycrystalline g-TiAl alloy under study we have first analyzed the behavior of single colonies as a function of layer orientation and the influence that the operative deformation mechanisms have on the mechanical response of the material at the microscale. This has been achieved through compression tests carried out on micropillars (MPs) representative of the behavior of single colonies at lamellar angles, FL, close to 0°, 45° and 90°.
Our results yield to an observed softening when FL≈45° (see Fig. 1), this arises from the operation of longitudinal systems (which are those presenting their plane and direction of slip/twinning parallel to the interfaces, and thus barriers to dislocation motion are considered to be low). For FL≈0° and FL≈90° (where mixed and transversal systems are activated respectively) results show higher yield values. For the case of FL≈0° the observed strengthening might arise from the interaction between the plane of slip of mixed systems and the lamellar interfaces. While for the case of FL≈90° the high yield values are likely be promoted by a contribution of both the high interaction between transversal systems of deformation with the lamellar interfaces and the low SF associated to these systems at this loading mode in the undeformed configuration.
Complementary, our results are validated with numerical simulations following a crystal plasticity approach. This allowed us to confirm experimental evidence and to define a CRSS for each mode of deformation matching the values measured through traces analysis on the MPs after compression.
HR-SEM micrograph of a compressed MP with L=45 (a). CPFEM simulation of a deformed MP showing deformation concentrated in a slip band (b). Experimental and simulated strain-stress curves representative of a MP at a soft loading mode (c).
