Effect Of Electrolysis Process On The Fatigue Performance Of TA15 Powder Metallurgy Titanium Alloy

Titanium alloy has the advantages of high specific strength and excellent corrosion resistance,which has attracted extensive attention of researchers.TA15 titanium alloy is widely used in aerospace due to its high temperature strength,good thermal stability and welding performance.TA15 titanium alloy component obtained by hot isostatic pressing powder metallurgy has good mechanical properties and can even reach the forging level,which is a feasible way to develop and produce products.Electrolysis process is a process in which components are immersed in an acidic solution and remove materials through the driving force of electric current.In the preparation process of powder titanium alloy components,electrolysis is an essential part of the removal of the internal core of titanium alloy components with the complex structure,but the effect of this process on the fatigue performance of the material has not been investigated,and the necessary research data are lacking.To this end,this paper systematically carried out the electrolysis process test,analyzed the effect of the electrolysis process on the composition and tissue of the powder TA15 titanium alloy,and characterized its tensile properties and impact properties,the influence of process parameters on the fatigue performance of materials is mainly studied,which lays a foundation for optimizing electrolysis process parameters and improving the fatigue performance of powder TA15 titanium alloy.The main research contents and results of this paper are as follows:The composition and morphology of the electrolytic surface,microstructure and hydrogen content of the electrolytic sample are analyzed by optical microscope and scanning electron microscope.After electrolysis,the surface color of the sample gradually deepens,from metallic color to black,and finally becomes grey;At the same time,with the extension of electrolysis time,the film gradually thickens,the phenomenon of "powder" appears,and part of the outer film falls off.The energy spectrum analysis of the surface film layer shows that the O-element content in the film layer increase.After electrolysis,the powder TA15 titanium alloy is divided by the equiaxed ? phase and the lamellar phase ? phase distributed inside the powder particles,which is the same as that of unelectrolyzed sample.Under different electrolysis process systems,there is no obvious difference in the microstructure of the sample after electrolysis.For the electrolytic treatment sample,the hydrogen content in the sample increases slightly with the extension of the electrolysis time;With the increase of the electrolysis temperature,the increase of the hydrogen content in the sample increases slightly.For the soaking sample,when the soaking temperature is 30 ?,the hydrogen content in the sample increases slightly with the extension of the soaking time.When the temperature of the soaking solution increases to 40?,the hydrogen content in the sample increases significantly with the extension of the soaking time.The hydrogen content of the surface layer of the sample is higher than that of the core of the sample,and the hydrogen elements is evenly distributed in the core of the sample.Vacuum annealing can effectively remove the hydrogen element in the sample after electrolysis or soaking,reducing it to the standard range.This shows that the increase process of hydrogen element caused by electrolysis or soaking is reversible.Through universal testing machine and scanning electron microscope,the tensile and impact performance of electrolytic samples are analyzed,and the fracture characteristics are observed,at the same time,the effect of vacuum annealing treatment on the tensile and impact properties of the specimens is studied.For electrolytically treated samples,with the extension of electrolysis time,the yield strength and tensile strength of the samples decrease slightly,and the elongation and section shrinkage change little.Increasing the temperature of electrolytic solution has no obvious effect on the tensile properties of the sample.After vacuum annealing,the strength of the sample decreases slightly and the plasticity changes little.For the soaking sample,when the temperature is at 30?,the yield strength and tensile strength of the sample decrease slightly with the extension of soaking time,and the elongation and section shrinkage change little,after vacuum annealing the strength of the sample decreases slightly,and the plasticity changes little;when the temperature is at 40 ?,the yield strength and tensile strength of the sample increased slightly with the extension of soaking time,the elongation and section shrinkage of the sample decreased significantly,and some samples are abnormally broken,with 3 sections broken.after vacuum annealing the strength of the sample decreases slightly,and the plasticity returned to the normal level.The morphology analysis results of the abnormal fracture sample show that the fracture is flush it is a mixed morphology of intergranular fracture,and the fracture source area is rock-like or rock sugar-like,for electrolytically treated samples and soaked samples,with the extension of treatment time,the impact toughness of the samples change very little,and slightly decrease after vacuum annealing.The plastic drop caused by soaking is reversible.Through fatigue performance test and scanning electron microscope,the fatigue life of electrolytic sample under the same stress level is analyzed,and the fatigue limit of the sample is obtained by lifting method,at the same time,the characteristics of fatigue fracture fracture are observed.The fatigue life of electrolytic samples gradually decreases with the extension of electrolysis time.With the increase of the temperature of the electrolytic solution,the reduction rate of the fatigue life of the sample increases.The fracture analysis results show that the fatigue source region of the samples located on the secondary surface of the sample and consists of a series of small facets.Typical fatigue strip characteristics can be observed in the fatigue expansion region of the sample after electrolysis;the morphology of the fatigue extension zone and the transient fracture zone consists of the dimple and the cleavage plane.The electrolytic sample is sandblasted,and then the fatigue test is carried out,the fatigue life is greatly increased.