Composition Optimization,Structure And Properties Of TiZr-based Alloy

Because of possessing high specific strength,high fatigue strength,good resistance to crack expansion and excellent corrosion resistance,Ti and its alloys are widely used in the aerospace,marine and biomedical industries.Meanwhile Zr and its alloys are widely used in the nuclear,acid and chemical industries,which are attributed to their small neutron absorption area,strong irradiation resistance,oxidation resistance and low coefficient of thermal expansion.With the advancement of aerospace exploration,titanium and zirconium alloys have been widely used in the aerospace industry.However,the harsh spatial environment more demanding requirements for space materials and moving parts.In this paper,TiZr-based alloys with different compositions are prepared by using a non-vacuum melting furnace with the objective of developing new space structure materials.The phase transformation,tissue evolution and strengthening mechanism of TiZr-based alloys are systematically investigated by deformation and heat treatment processes.In this paper,according to the influence of alloying elements on the phase composition,a series of(100-x)(Ti50Zr)x Cr(x=0,1,2,3,4.5,9,13,wt.%)alloys and(100-y)(Ti50Zr5Cr)y Al(y=1,2,3,5 wt.%)alloys are prepared using a non-vacuum melting furnace with Ti50Zr alloy as the base alloy.The results show that the phase composition in the alloy gradually changes with the increase of Cr element content,i.e.,?+????+?????+Zr Cr₂ phase.The phase composition in the alloy is a single?phase when the addition of Cr element is between 2wt.%?5 wt.%.Due to the element Cr addition into(100-x)(Ti50Zr)x Cr,the?-phase grain size of the casted alloys is refined.When the Cr concent was 5 wt.%,the comprehensive mechanical properties of the alloy obtained,i.r.,(compressive yield strength of 909 MPa,maximum compressive strength of 1710 MPa,and compressive strain of 42.0%).To further improving the mechanical properties of the alloy,Al as alloying element is added into the TiZr5Cr alloy.The results show that the phase composition of the alloy was a single?-phase after the Al addition less 3 wt.%,and the Ti₃Al intermetallic compound appeared in the alloy when the Al content reached upto 5 wt.%.The grain size of the?-phase is further refined with the increase of Al content.The strength of the alloy gradually increased with the increase of Al element,and the comprehensive mechanical properties of the alloy are optimized when the addition of Al element was 2 wt.%.The compressive yield strength,maximum compressive strength and compressive strain were 952 MPa,1837 MPa and 46.6%,respectively,and the microhardness value was 315 HV0.2.The strengthening mechanisms of Cr and Al elements on TiZr-based alloys are fine grain strengthening and solid solution strengthening.This paper is designed to eliminate coarse primary grains in cast alloys and optimize the mechanical properties of the alloy.The(100-x)(Ti50Zr)x Cr(x=1,2,3,4,5 wt.%)alloy and(100-y)(Ti50Zr5Cr)y Al(y=1,2,3,4 wt.%)alloy are rolled in multiple passes at 950°C,and the final deformation of all composition alloys exceeded 75%.The evolution of the organization and mechanical properties of the alloys with different compositions under the same deformation process is investigated,and the results show that in the hot-rolling state(100-x)(Ti50Zr)x Cr alloy,the phase composition of the alloy changed from??+?phase to a single?phase with the increase of the Cr element content.The higher the content of Cr elements in the alloy,the more complete the dynamic recrystallization process at the grain boundaries.The comprehensive mechanical properties of the TiZr5Cr alloy under the hot-rolling state reach the optimum,which yield strength,tensile strength elongation and microhardness 845 MPa,867 MPa,4.4%,and283 HV0.2,respectively.The fracture mode of the(100-x)(Ti50Zr)x Cr alloy after hot-rolling was all present as brittle fracture.In the hot-rolling state TiZr5Cry Al alloy,the alloy phase composition of each component consists of a single?-phase.With the increase of Al element content,the?-phase grains gradually tend to be equiaxed.The comprehensive mechanical properties of the hot-rolling TiZr5Cr2Al alloy are optimal,and the microhardness,yield strength,tensile strength and elongation of 308 HV0.2,934 MPa,974 MPa and 6%,respectively.The fracture mode of(100-y)(Ti50Zr5Cr)y Al alloys under the hot-rolling state is mixed of ductile fracture and brittle fracture.To further optimize the effect of deformation process on TiZr5Cr2Al alloy,the deformation process of hot rolling+cold rolling is used.The results show that when the cold deformation is small,the alloy shows a single?phase,and when the cold deformation increases,a small amount of?"martensite phase appears.The alloy with a total deformation of 70%for hot rolling+cold rolling has the best comprehensive mechanical properties with yield strength of 885 MPa,tensile strength of 944 MPa,elongation of 8.1%,and microhardness of 329 HV0.2.The phase transformation patterns in TiZr-based alloys are investigated by a series of heat treatment processes.Among them,the cast(100-x)(Ti50Zr)x Cr(x=3,3.5,4,4.5,5 wt.%)alloy is subjected to solid solution treatment at 800°C,the hot-rolling(100-y)(Ti50Zr5Cr)y Al(y=1,2,3,4 wt.%)alloy is subjected to solid solution treatment at 850°C,and the hot-rolling TiZr5Cr3Al and TiZr5Cr4Al alloys are subjected to 600,800 and 1000°C The annealing treatment is carried out at 600,800 and 1000.The results show that the phase composition of TiZr-based alloys after solid solution treatment is composed of a single?-phase.The solid solution treatment caused the disappearance of grain boundary coarsening in the hot-rolling(100-y)(Ti50Zr5Cr)y Al alloy and the growth of equiaxed organization and?grains at the grain boundaries.The relative content of?-phase gradually increases with the increase of annealing temperature for TiZr5Cr3Al and TiZr5Cr4Al alloys,and a small amount of?-phase and?-phase appears in the alloys.The microhardness of TiZr5Cr3Al alloy tends to decrease and then increase as the annealing temperature increases,while the microhardness of TiZr5Cr4Al alloy tends to decrease gradually.