Study On TiAl Based Alloys Prepared By Grading Ball Milling And Vacuum Hot-Pressed Sintering Process

TiAl-based alloys become a very potential high-temperature structural material because of its high specific strength, high specific stiffness and good high temperature performance. By now, the poor ability of room-temperature deformation and the weakness of high temperature oxidation resistance restrict the applications of TiAl-based alloys, the TiAl-based alloys containing high Nb show a much better general performance which earns people's attention.By grading ball milling and vacuum hot-pressed sintered technology, high-Nb TiAl alloy were prepared. In order to improve the alloy's high temperature performance and improve the alloy's brittleness at room temperature, in this artical,high levels of Nb element(20at.%) are added, at first, grading ball milling is applied with elemental powders(TiAl high-energy ball milling+Nb-TiAl low-energy ball milling), and then milling powders are sintered with vacuum heating-press sintering process(low temperature reactive sintering+high temperature sintering), finally high Nb containing TiAl alloys with ductile Nb phase are prepared. The main contents are as follows:The research of grading high-energy ball milling process is investigated. According to the rule for the impact of grinding process on powers, Ti/Al composite powders are prepared by first-rank high energy ball milling, Nb-TiAl compound powders are prepared by secondary low energy ball milling, Parameters'changes in behavior of milling process are studied, such as particle morphology size, grain, composition, thermal stability and so on.by observing the Photos of the morphology and analyzing the composition of powders, the change mechanism of particle morphology in milling process is defined; observed by TEM, microscopic change mechanism in powders is verified; by XRD and DTA analysis, the thermal stability of milling powders is analyzed to provide the basis for the subsequent sintering process.through grading ball milling process, TiAl compound powders that finally obtained are fine and uniform, Nb elemental particles uniformly distributed and occurs only minor changes in morphology of Nb-TiAl compound powder.The research of vacuum hot-pressed sintered technology is investigated. According to generation characteristics of TiAl intermetallics, we adopted vacuum hot-pressed sintering process (620℃low temperature reactive sintering+1200℃high temperature sintering), the bulks of high Nb containing TiAl alloys with high density are prepared. By XRD analysis, the phase compositions of the alloy are determined. By metallographic observation and SEM, the microstructures of alloy are analyzed; by compression test at room temperature, deformation performance of alloy at room temperature is tested. In order to compare with the vacuum hot-pressed sintered technology, pressure sintering in air is also tried, through analyzing corresponding performance, the facts that the bulks which are hot pressed in the air have severe oxidation are found, which lead to dense block can't be made, resulting in poor performance.