| Ti-48Al-2Cr-2Nb（T4822 for short）,as a cast Ti Al alloy,has low density,good high-temperature oxidation resistance,and good mechanical properties at high temperatures,making it a broad application prospect in high-temperature applications.However,the microstructure of the cast T4822 alloy is composed of very large grains（lamellar clusters）,resulting in relatively low tensile ductility of the alloy and anisotropy of mechanical properties.Therefore,grain refinement is essential.Based on the above background,this article takes T4822 alloy as the research object and prepares two alloys,T4822-0.1B4C and T4822-0.2B4C.The alloys are subsequently subjected to different heat treatment processes,and the solidification structure transformation and crystallinity of the alloys in the as-cast and different heat treatment processes are processed.The mechanism of grain refinement,mechanical properties at room temperature and high temperature,and creep resistance have been systematically studied.The main research contents and conclusions are as follows:The results of the study of as-cast T4822-0.1B4C and T4822-0.2B4C alloys show that the two as-cast alloys are mainly composed ofγphase andα2 phase,which are near-lamellar structures.The borides precipitated by adding 0.1at.%B4C alloy are mostly strip-shaped,while adding 0.2at.%B4C alloy borides are smaller in size,mainly short rods and rods.T4822-0.2B4C alloy has better comprehensive properties.The high temperature strength at 800°C is 484MPa.Compared with room temperature tensile strength,the strength is significantly improved,and the high temperature strength of T4822-0.1B4C alloy is more stable.The T4822-0.1B4C alloy does not show an obvious accelerated creep stage,and the T4822-0.2B4C alloy has better creep resistance,and the fracture has an obvious tendency to toughen.Therefore,the T4822-0.2B4C alloy was further modified by heat treatment.Three different heat treatment processes are used:α+γdual-phase zone heat treatment,αsingle-phase zone heat treatment and cyclic heat treatment.The results show that the heat treatment holding time of T4822-0.2B4C alloy in theα+γdual-phase zone increases,and the lamella spacing is higher than that of the as-cast state.As the alloy increases,the microstructure obtained is a typical dual-state structure,which has a certain effect on improving the high-temperature plasticity of the alloy,and the fracture surface has an obvious tendency to toughen.When the alloy is heat-treated in theαsingle-phase region,the grain size is finer than that of the as-cast alloy,and the ratio of lamellae is significantly increased.The high temperature strength and plasticity are improved,and the creep resistance is significantly improved.The T4822-0.2B4C alloy was subjected to cyclic heat treatment,and it was found that heat treatment of different cycles has different effects on the structure and properties of the alloy.The heat treatment of the alloy 4 cycles has a high temperature strength of558 MPa at 800℃,which is 74 MPa higher than that of the as-cast alloy.At the same time,the creep of the alloy is Performance is improved.The steady-state creep rate of heat treatment for 6 cycles is reduced by about 61%compared with the as-cast alloy,and the creep rupture time is about 39.8%longer than that of the as-cast alloy.The creep resistance is significantly improved. |
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