Texture evolution of niobium, aluminum, and titanium in Ti-Al-Nb composites processed by accumulative roll bonding
Multilayered Ti/Al/Nb composites were produced by the accumulative roll bonding (ARB) process utilizing pure Ti, Al and Nb element sheets. Up to four cycles of ARB were applied to the composites. The microstructure and texture evolution of the elemental Nb, Al and Ti phase was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Nanoindentation was performed as well. Nb and Ti layers necked and fractured as the number of ARB passes increased. After four ARB cycles, a nearly homogeneous distribution of Nb and Ti layers in an Al matrix was achieved. The as-received Nb sheet exhibited a fully lamellar structure and had a strong cold rolling texture. After subjecting to ARB, slight grain refining was observed and the high angle grain boundary (HAGB) fraction was increased. The intensity of the α-fiber texture was weakened while that of the γ-fiber texture was strengthened during ARB. The texture evolution was attributed to partial recrystallization during the ARB process as a result of adiabatic heating. In the Al phase, grain refinement occurred with increased ARB cycles as a result of the increased fraction of HAGBs. Strong recrystallization texture occurred for samples subjected to increased ARB cycles as a result of the adiabatic heating produced. The shear bands at the Ti/Al interface reduced the intensity of the cold rolling fiber textures of Al. There was no evidence of shear component from the orientation distribution function (ODF) results. Twinning was observed in the Ti phase for all stages of deformation but had little influence on microstructure. Grain refinement was achieved as a result of the accommodating of shear bands to the limited slip system of Ti. Recrystallization occurred at higher ARB cycles as a result of adiabatic heating. The Schmid factor shows that Basal and prismatic slip systems dominate at low ARB cycles, while at higher deformation, the first-order and second-order pyramidal slips are active.