Preparation And Its Properties Of Ti-22Al-25Nb-2V Alloy By Powder Metallurgy

As a new material that can replace traditional high-density nickel-based superalloy of aerospace industrial aircraft engines,Ti-Al based intermetallic Ti2AlNb based alloys with O phase orthorhombic structure are highly anticipated.However,the phase transformation of Ti2AlNb based alloys is complex and their properties are sensitive to the changes of microstructure.The melting points,vapor pressures and densities of the various elements vary greatly,making it difficult to obtain ingots with accurate composition,uniform composition and compact structure.Preparation of Ti2AlNb based alloys by powder metallurgy due to the designability of its composition,uniform structure and excellent properties are gradually receiving attention.This topic aims to explore the powder metallurgy Ti-22Al-25Nb-2V alloy preparation process route,and the performance of the prepared alloy.Ti-22Al-25Nb-2V alloy was prepared by powder metallurgy method.The influencing factors of pre-alloy densification,microstructure of pre-calcined and reactive sintered alloy and heat-treated alloy were studied by OM,SEM,EDS and XRD Research,and the solid solution-aging treatment of the alloy hardness test and compression experiments.The results show:（1）High aspect ratio of 1:5,1200MPa dwell 10min forming pre-alloy,pre-calcined at 630℃for 4h,then 1000℃high temperature reaction sintering 1.5h alloy have good microstructure.Flakyα₂ phase inlaid in the matrix phase B2,part of the edge by the needle,slab O phase connection,and the matrix phase B2 as a whole,part of the edge directly with the substrate B2 phase closely,in addition to some of the edge of both O phase wrapped with the junction,but also directly with the B2 phase,forming a（α₂+β/B2+O）three phase attached to each other,cross-coexistence of equiaxed tissue.（2）After pre-firing,the internal morphology of the sample is changed from the cross-like structure of the previously dispersed lamellar particles to a consolidated solid.Theα₂ formed by the combination of Ti element particles and Al element particles has a great effect on the growth of the pinned B2 phase,which can effectively prevent grain boundary migration and grain growth and play a role in refining the alloy structure.（3）The microstructure of the alloy after oil cooling treatment at 1100℃for 1.5 h is mainly composed of a large number of lamellarβ/B2 phases,a small amount of equiaxialα₂ phase,and a small amount of precipitated needle-like O phase,and due to the B2 phase grain boundary.With the pinning effect of the sequential B2 phase,the morphology of theβ/B2 phase and theα₂ phase is uniform and the growth is not obvious.The aging process is mainly a process in which needle-like or slat-shaped O phase precipitates from the base phase B2.As the temperature increases,the largest-sized slat-shaped O phase appears at 800℃.When the temperature gradually falls below this temperature,the thickness of the slab-like O phase gradually decreases.（4）With the aging treatment temperature,the relative density of the alloy changes slightly.The vickers hardness gradually decreases and accelerates,the hardness of annealed furnace annealed at 700℃for 12h is 489 HV,and the hardness of annealed at850℃for 12h is 316 HV.The compressive strength and yield strength of the alloy decrease gradually,the compressive strength of the aging sample is the highest,and the compressive strength of the sample is the lowest at 800℃for 12h.