Precipitation Behavior And Mechanical Properties Of Aged Ti₂AlNb-based Alloys Prepared By Spark Plasma Sintering

Based on ordered orthorhombic?O?phase,Ti₂AlNb-based alloys have been used in the aircraft engine due to their outstanding creep resistance,strong plasticity,and high-temperature oxidation resistance.The microstructure and properties of Ti₂AlNb-based alloys were determined by the preparation paths.Powder metallurgy could overcome the shortcomings of smelting and forging technology,including fluctuation of properties and waste of alloys.Hence,it is essential to study the microstructure and properties of the alloys by modifying the sintering method and heat treatment process of the Ti₂AlNb-based alloys.In this study,the precipitation behavior of O phase of powder metallurgic Ti₂AlNb-based alloys was first investigated bysintering and coolingin different phase region.According to the phase and microstructure transformation,the aging treatment was carried out in the B2+O phase region.The phase transformation and microstructure evolution during aging were studied,and theprecipitation behavior of O phase was also clarified.Finally,the powder was pretreated to study the effect of pretreatment on the precipitation behavior of O phase.The conclusions can be summarized as follows.?1?B2+O Widmanstatten structure was constructed by high-temperaturesintering,and the hardness of the alloys was improved.For the alloys treated in the non-single-phase region,the refinement of O-phase lath is conducive to the hardness.?2?When the sample was furnace cooled from the single B2 region,?₂ phase was completely solved in the matrix.Complete B2+O structure was therefore obtained,and the alloyexhibited the highest Vickers hardness.?3?Ti₂AlNb-based alloys,spark plasma sintered in the?₂+B2+O phase region,was aged in the B2+O phase region.The microhardnessof the aged alloyswas improved.With the elevated aging temperature,the variation tendency of the hardness was in agreement with thatof the O-phase content.The hardness is determined by the O phase content and the dimension of the O laths.?4?Ti₂AlNb-based alloys aged at 800 ? contained complete B2+O Widmanstatten structure with finely dispersed B2 particles,resulting inthe most favorable hardness performance.The fine B2 particles were generated due to the decomposition of equiaxed O-phase grains and the solution of B2 laths in the O-phase matrix.?5?The microstructure of the spark plasma sintered alloys depends largely on the shape and size of the pre-alloyed powder.Aging regulated the reversible transformation of B2?O.Uniform and refined B2+O Widmanstatten structure provided effective precipitation strengthening,bringing about favorable mechanical properties with Vickers hardness of 448±9 HV,ultimate tensile strength of 730 MPa,and elongation of0.43%.