Study On The Microstructure And Property Of High Nb Containing TiAl Alloys Prepared By Reactive Sintering

TiAl-based alloys possess attractive properties, such as low density, high specificyield strength, high specific stiffness and good oxidation resistance, making them a newgeneration of high temperature structural materials. But their room temperaturebrittleness and deficiency in high temperature oxidation resistance above850℃limittheir practical application. Future TiAl-based alloys must exhibit increased hightemperature capabilities with appreciable room temperature ductility, high Nb containingTiAl alloys are the most promising candidates to fulfill these demands.In this paper, massive Nb element is added to TiAl-based alloys to improve theplasticity and high-temperature oxidation resistance. By ways of grading ball milling,vacuum hot pressed sintering, heat-treatment, high Nb containing TiAl alloys have beenprepared, its notional component is Ti-45Al-10Nb(at.%). There are two ways to heat-treatment, one way is homogenizing annealing for30h at800℃, the other is hightemperature heat treatment for20min at1315℃.The microstructure, phase composition,thermal stability of materials at different stages have been observed using metallographicmicroscope, scanning electron microscopy, X ray diffraction and differential thermalanalysis. And room temperature mechanical properties, high temperature mechanicalproperties have been tested, and high-temperature oxidation resistance of alloys whichcontain10%(at.%) and20%(at.%) of Nb element have been analyzed. The correlation ofpreparation technology, microstructure and performance have also been studiedsystematically. The results show that:Results of composite powders by grading ball milling show that particle size andgrain size of composite powders become finer, the average grain size of first grade ballmilled Ti/Al composite powders is5nm. After grading ball milling, particle size ofcomposite powders is fine, the composition is in uniform distribution, compositepowders have lamellar structure, and there is no amorphous phase generated. Differentialthermal analysis shows that grading ball milling decreases reaction temperature of Ti andAl powders.Results of high Nb containing TiAl alloys prepared using Vacuum hot pressedsintering (reaction sintering+high temperature sintering) and heat-treatment show thatthere are TiAl phase、Ti3Al phase、Nb phase and Nb2Al phase in fired billet and heat-treatment billet, among them Nb phase is in uniform distribution. And the higher of heat treatment temperature, Nb element diffuses more sufficiently. Compressive experiment atroom temperature shows that all of the compressive strength, yield strength and maximalcompression ratio of alloys increase remarkably, and billet by high temperature heattreatment possesses optimal mechanical properties, yield strength reaches1052MPa,compressive strength reaches1254MPa, maximal compression ratio reaches20.6%,improving the ductility of alloys.Results of high temperature tensile and high temperature compression tests of firedbillets and heat-treatment billets by homogenizing annealing show that the high er of thetemperature, the strength of alloys is lower, the ductility of alloys is higher. Flowsoftening appears in high temperature tensile and high temperature compression tests at900℃, fired billets have higher high temperature strength than heat-treatment billets, butthe ductility becomes lower.Results of oxidation resistance test show that the high-temperature oxidationresistance of Ti-45Al-10Nb(at.%) alloys is better than Ti-40Al-20Nb(at.%) alloys, on thesurface oxide film of Ti-40Al-20Nb(at.%) alloys, massive Nb element inhibits TiO2particles’ generation.