Study On Strengthening And Corrosion Behavior Of Novel TiZrAlB Alloys

Titanium（Ti）and its alloys are increasingly applied in high-tech and civilian fields owing to their excellent chemical and physical properties,such as low density,high specific strength and good corrosion resistance.Especially in marine and ocean engineering applications,for both the mechanical properties and corrosion resistance constituting significant criteria for metallic material services,Ti alloys show a tremendous application potential.However,traditional Ti alloys could not meet the requirements for these applications which are becoming more and more strict.Based on the performance index of marine structural materials and the existing research results,the alloying element zirconium（Zr）can improve multiaspect properties of the Ti alloy by alloying.In this paper,the relationships between microstructure and strengthening and corrosion behavior inα-type TiZrAlB alloys were studied by optimizing alloy composition,adjusting deformation and heat treatment processes,which promoted the research development of novel structural materials with high strength and corrosion resistant.In the early stages of the study,a series of TiZrAlB alloy ingots were prepared using a vacuum non-consumable electro-arc furnace with a water-cooled copper crucible.As the Zr content increased,the strength and microhardness improved apparently with ductility loss on account of solution strengthening,and the significant refinement caused by Zr addition was also confirmed.After hot-rolling at 930℃and water quenching,the lamellae of some alloys were distorted or broken after rolling,forming large numbers of intragranular dislocations.The microstructure of some alloys was completely filled with acicularα′martensite,and ternary yield strength,ultimate strength and microhardness obviously increased with grain refiment.When Zr content increased to 40 wt.%,alloy revealed the highest yield strength,tensile strength and microhardness of 1388 MPa,1535MPa and 422HV at 6.06%elongation.In comparison,the alloys with identical compositions suggested that hot-rolled alloys did not only exhibit nearly equal elongation with the as-cast alloys but also much higher strength than as-cast alloys.In the middle and late stages of the study,different deformation and heat treatment processes were conducted for the chosen Ti-40Zr-4Al-0.005B（wt.%）through industrial preparation.The experiment results showed that the sizes of these platelet-and lamella-like structures decreased with the density of originalβgrain boundaries as the rolling temperature increased.When rolling at 840℃,the quenched alloys exhibited the highest strength(?_0.2=1121MPa,?_b=1387MPa),and the air-cooled alloys exhibited the higher ductility resulted from grain recovery.In addition,the residualβphase was detected after the thermocompression at 840℃with strain rate of 1×10^-3s^-1.This is because of the dislocations produced by compression provided the diffusion path for Zr and Al elements,and the incubation time of phase transformation was guaranteed by high temperature accompanying with the lower strain rate.In elements rich area,the increased Zr content decreased the phase-transition temperature,and the increased Al content suppressed the martensitic transformation.For the cold-rolled specimens,theαlaths were predominantly parallel to the rolling directions with increased deformation,however,the change of grain size change was not obvious.Furthermore,the 840℃-rolled Ti-40Zr-4Al-0.005B alloys revealed various microstructures after different annealing processes.The mechanical properties were dependent on microstructure type and grain size.The fine basket-weave microstructure exhibited the,the globular structure exhibited the highest ductility with lower strength,and duplex microstructure exhibited the best combination of strength and ductility.The immersion test results showed that corrosion weight loss decreased as the Zr content increased,which indicated the corrosion resistance enhanced with Zr addition.Moreover,the corrosion resistance was not concerned with alloy states i.e.microstructure,it is concerned with alloy composition.The probability of pitting occurring increased with Zr content,however,the Zr addition could accelerate the passivation behavior.Furthermore,the strengthening mechanisms and corrosion behaviors of series TiZrAlB alloys have been also discussed according to the experimental content and results.The research provides a theoretical basis for the application of the novel TiZrAlB alloys.