Investigation Of Thermo-mechanical Treatment, Microstructure And Mechanical Properties Of Ti-47Al-2Cr-2Nb-Y Alloy

Hot deformation and microstructure evolution of as-cast Ti-47Al-2Cr-2Nb-Y alloy were investigated in this present study. And the corresponding results of thermal simulation can be as guidance in canning forging in as-cast Ti-47Al-2Cr-2Nb-Y alloys. Pancakes of TiAl alloys were obtained by canned forging. Microstructures and properties of pancakes are also emphasized and systemically discussed. The as-forged alloy was heat treated and the evolution of microstructure was studied too.The hot deformation results indicated that flow-stress increased as increasing strain rate and felled as temperature increased. The Zener-Hollomon method and hyperbolic sine function were used to study thermal activation energy (Q=419.8KJ/mol.) and their constitutive equation. And the hot processing map was maked developed on the basis of dynamic material modeling. Microstructure observation showed that the deformation is not uniform in different parts of the sample, which is divided into hardly deformed region, large deformation region and medium deformation region. The main crazing manner of sample is inner crazing and cuniform crazing. According to changes in the microstructure appearance of hot pressing sample, the best deformation process is deforming at the temperature of 1200℃and 1250℃with the strain rate 0.01 s-1. we maked the forging process: deformation temperature≥1200℃, strain rate≤0.01s-1.Pancakes of Ti-47Al-2Cr-2Nb-Y alloys were obtained by canned forging, and the phase composition of alloy remainsα2,γ, B2 and YAl2. After the plastic deformation, the amout of lamellar structure disappeared apparently, and grain refinement significant with a size of 10μm. Y-rich phases of YAl2 are broken up or elongated as strap shape after deformation and recrystallization. At room temperature,σs andσb reach 553.3MPa and 568MPa, respectively,δis 0.7%. While at High temperature 800℃and 900℃, the elongation reached 61.7% and 124.3%. with necking phenomenon occuring.From 1340℃to 1400℃of heat treatment experiments of forged Ti-47Al-2Cr-2Nb-Y alloy show that: the content of B2 phase increased and reached maximum at 1370℃and then decreased with increasing temperature. it is full lamellar structure with some residul B2 after heat treated at 1400℃for 20min,with the size of lamaller colony about 150μm ~ 200μm.