Microstructure and Mechanical Properties Evolution of High-Temperature Titanium Alloys with In Situ Synthesized TiB Whiskers

Microstructures, mechanical properties and fractural characteristics of boron-containing titanium alloys are carefully investigated. Strengthening mechanism, recrystallization mechanism and fractural mechanism are revealed. Above 90% equiaxed alpha grains are acquired in TA6.5-0.2B, and almost all grains transform to equiaxed morphology in TA6.5-0.4B. TiB whiskers exhibit nearly oriented arrangement, and its contents increase with increasing boron additions. TiB whiskers impede moved dislocations and stimulate dynamic recovery and recrystallization of alpha grains. More whiskers provide more sufficient motivation for recrystallization. Room-temperature strengths increase with increasing boron contents, while elongations decrease. 650 degrees C strengths also increase, continuously, while elongations increase firstly and then decrease. Strengths gradually decrease with increased tensile temperatures, and elongations increase, continuously. When temperatures are higher than 600 degrees C, decreasing rates of strengths are higher than that at temperatures lower than 600 degrees C. Elongations show contrary evolution laws comparing with strengths. Decreased strengths and increased elongations are mainly ascribed to the softening of matrix and grain boundary sliding, and more significant with increased tensile temperatures. At room temperature, grain refinement strengthening, load transferring strengthening, dislocation strengthening and thermal mismatch strengthening increase with increased boron contents. At 650 degrees C, most important mechanism for enhancement of strengths is load transferring strengthening.