| β titanium alloy exhibit high specific strength,excellent corrosion and high temperature resistance and good biocompatibility.Therefore,this class of alloy has been widely used in aerospace,military industry,biomedicine and other industries.βtitanium alloy prepared by ingot metallurgy has been successfully applied,but the effect of titanium alloy in subsequent machining is not ideal due to its low thermal conductivity.Powder metallurgy technology can improve material utilization.However,the problem of easily introducing impurity oxygen into powder metallurgy has not been properly solved.In this paper,Ti-18Nb(at.%)alloy was prepared by powder metallurgy net forming technology,and the oxygen content of the alloy was controlled by pre oxidation.The effects of oxygen content on the microstructure,tensile mechanical properties and compressive superelasticity of Ti-18 Nb alloy were studied,and the mechanism was analyzed.The oxygen content of the alloy was controlled at a low level by high vacuum sintering,and the hole defects in the sintered alloy was improve by hot isostatic pressing(HIP).The phase composition and mechanical properties of thermal equilibrium state with furnace cooling and metastable state with solution treatment were studied.The evolution behavior of microstructure and the corresponding plastic deformation mechanism during tensile were discussed.The main results of this paper are as follows:Ti-18Nb-(0.7,1.5,2.0 at.%)O alloys with different oxygen contents were prepared by powder metallurgy.The mechanical behavior of sintered alloys with different oxygen content showed little difference.The overall performance was brittleness and the strength was close.The ductility of solution treated alloy is better than that of sintered alloy.With the increase of oxygen content,the strength of the alloy was improved,but the plasticity decreased.And the existence of oxygen will inhibit theβ→α’’ phase transformation.Stress induced α’’ phase transformation occured in the compression deformation of solution treated alloys with different oxygen content at room temperature.After compression and unloading with different deformation,they all showed obvious superelasticity.With the increase of strain,residual strain appeared.When the loading strain is 5%,the recoverable strains of Ti-18Nb-0.7O,Ti-18Nb-1.5O and Ti-18Nb-2.0O alloys with oxygen content were 2.9%,3.2% and3.5% respectively.With the increase of oxygen content,the recoverable strain increased.The higher oxygen content increased the slip critical stress of β phase,reduced the density of residual dislocations after deformation,and improved the recoverable strain.The fully dense Ti-18 Nb alloys were prepared by high vacuum sintering and HIP.The oxygen content was as low as 0.18 wt.% The tensile elongation of the samples cooled with the furnace after HIP was only 1%,while the elongation of the samples after solution treatment was as high as 22%.The stress induced α’’ phase transformation occured in the two different samples had been proved by EBSD,TEM and other technical.But stress induced α’’ phase transformation provided limited plasticity for the alloy cooled with the furnace..While stress induced α’’ phase transformation provided good plasticity for the alloy after solution treatment.In addition,low oxygen content was also an important factor for good plasticity of the alloy.The effects of different oxygen content on the microstructure and mechanical properties of the alloy was discussed in this research.It is found that the existence of oxygen has a great influence on the mechanical properties and phase composition of the alloy.This study will provide a theoretical basis for the design and preparation ofβ titanium alloy prepared by powder metallurgy,and lay a foundation for the engineering of this kind of alloy. |
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