Twinning and de-twinning in beryllium during strain path changes

Rolled beryllium samples in the form of rectangular parallelepipeds were deformed at strain rates of 0.001/s and 5/s through multiple strain paths. Samples were initially deformed in-plane nominally −0.22 in compression at a rate of 5/s to populate the microstructure with twins and then reoriented and deformed a second time either in the through-thickness direction or the other in-plane direction. The microstructure (texture and internal strain) were monitored through in-situ and ex-situ diffraction measurements using neutron diffraction on the HIPPO diffractometer at LANSCE, and high energy X-ray diffraction on the 1-ID-C beamline at the APS. Twin reversal is observed when the sample is reoriented and deformed a second time in the TT direction. The twin reversal is strain rate independent in contrast to the strong strain rate dependence observed during twinning in beryllium. Deformation twinning is also observed during secondary compression in the second in-plane direction, but from the current data set we cannot determine with certainty if these twins originate from the parent orientation or the twins formed during primary in-plane compression. As a whole, this data set creates a very demanding test for the development of polycrystalline plasticity models of deformation in hexagonal metals.