The effect of microstructure and strain rate on the 25 °C and 700 °C compression deformation behavior of powder metallurgy processed Ti-45Al-2Nb-2Mn (at.%)-0.8 TiB2 (vol%) alloy

Highlights: • The near fully-lamellar microstructures exhibited higher strengths than the duplex microstructure. • For all the strain rates and temperatures examined, the near fully-lamellar microstructures exhibited higher strengths than the duplex microstructure. • The activation volume, which ranged between 0-100b³ (b is the Burger's vector), was found to be inversely proportional to the flow stress at 700 °C. This dependence was shown to be qualitatively consistent with the assumption that dislocation glide is controlled by the thermally activated overcoming of forest junctions. • The RT deformation was considered to be controlled by dislocation glide, while at elevated temperature, the likely thermally activated process controlling dislocation glide was associated with the forest junctions acting as pinning points. The effect of microstructure and strain rate on the room-temperature (RT) and 700 °C compression deformation behavior of a powder metallurgy processed γ-TiAl intermetallic alloy, Ti-45Al-2Nb-2Mn (at.%)-0.8 (vol%) TiB₂, was investigated. Samples were heat-treated to obtain a duplex two-phase α₂+γ microstructure and two nearly fully-lamellar α₂+γ microstructures with different lamellar spacings and γ-phase volume fractions. Compression experiments were performed to a minimum deformation of 10% true strain under strain rates of 10⁻², 10⁻³, 10⁻⁴, and 10⁻⁵ s⁻¹. The compression strength, strain rate sensitivity, colony size, interlamellar spacing, and microhardness were dependent on microstructure. The nearly fully-lamellar microstructures exhibited higher compression strengths than the duplex microstructure for all the testing conditions. The strain rate sensitivity index (m), tended to increase with increasing temperature, and for the 700 °C deformation, m increased with increasing true strain. The apparent activation volumes, decreased with increasing true strain at 700 °C. Scanning electron microscopy observations showed that cracking preferentially occurred within the γ phase and the extent of cracking increased with increased temperature, strain, and strain rate. Overall, the RT deformation was considered to be controlled by dislocation glide, while at elevated temperature, the likely thermally activated process controlling dislocation glide was associated with the forest junctions acting as pinning points.