High-temperature Deformation Behaviors Of Bimodal Sized Particulates Reinforced ?TiB+La₂O₃?/Ti Composites

The bimodal sized particulates reinforced?TiB+La₂O₃?/Ti composites have a wide range of potential applications in the aerospace and weapons field due to their high specific strength,high specific modulus,excellent high-temperature durability and good high-temperature resistance.The intense research about high-temperature deformation behavior and microstructural evolution of particle-reinforced titanium matrix composites will greatly promote the development of China's aerospace industry.Thus,in this study we fabricated the?TiB+La₂O₃?/Ti composites using melting-casting and conducted both isothermal compression tests and high-temperature tensile tests in order to study the high-temperature deformation characteristics and microstructural evolution mechanism for?TiB+La₂O₃?/Ti composites.The results indicate that:Firstly,the flow stresses of the composites showed a strong sensitivity to the variation of deformation temperature and strain rate during the isothermal compression tests.The flow stresses increased with decreasing the deformation temperature and increasing the strain rate.The constitutive equations and 2D and 3D processing maps were established using the flow stress data.?TiB+La₂O₃?/Ti composites showed higher flow stresses and activation energies than IMI834 matrix due to the incorporation of bimodal sized reinforcements.The activation energies were calculated to be 752.6kJ/mol in?+?phase region and 185.1 kJ/mol in?phase region.The processing maps showed two stability domain at 900⁹50?/0.01⁰.1 s^-1and 1050¹100?/0.1¹ s^-1 and one instability domain at 850⁹50?/0.1¹ s^-1.Secondly,the microstructural evolution of?TiB+La₂O₃?/Ti composites after isothermal compression tests was observed by OM,SEM,TEM and EBSD methods.The deformation mechanism in the?+?phase region corresponded to continuous dynamic recrystallization?CDRX?of primary?phase and spheroidization of lamellar structure,while the incomplete dynamic recrystallization of primary?grains and dynamic recovery?DRV?in lamellar?phase were observed in the?phase region.The instability phenomenons include TiB breaking,debonding between TiB and matrix and inhomogeneous deformation.Finally,by combining the processing maps and the microstructural observation,the optimal parameters of hot deformation for?TiB+La₂O₃?/Ti composites were determined as the deformation temperature range of 900⁹50?and the strain rate range of0.01⁰.1 s^-1.Thirdly,the micro-sized TiB whiskers and submicro-sized La₂O₃particles played a great role in the microstructural evolution of the composites.Both TiB and La₂O₃ reinforcements can hinder dislocation movement and promote the improvement of flow stress and activation energy for the composites.Apart from these,TiB whiskers can facilitate the generation of dynamic recrystallized?DRXed?grains and are beneficial to the grain refinement.Finally,the high-temperature tensile tests of the composites were performed in order to characterize the superplastic deformation of the composites.The tensile samples exhibited the superplasticity during the tensile temperature range of 875⁹75?and tensile rate range of0.0005⁰.01s^-1.The elongation increased and then declined with increasing both tensile temperature and tensile rate.The dynamic recrystallization was observed at 950?/0.001 s^-1 with the maximum elongation of 213%.