Study Of Corrosion And Tribocorrosion Behavior Of Ti15Mo Alloy Fabricated By Selective Laser Melting

Ti15Mo alloys are often used as a biomaterial in biomedical fields such as medical devices,dentistry and orthopedics because of its matching mechanical properties with human bone,excellent corrosion resistance,wear resistance and outstanding biocompatibility.At present,the processing efficiency and material utilization rate of traditional processing technology are relatively low,and some parts with complex structures are difficult to process.In this paper,selective laser melting(SLM)was used to produce Ti15Mo alloy,and the anisotropy of electrochemical behavior,wear behavior and tribocorrosion behavior of the SLM processed Ti15Mo alloys with different building directions(0°,45°and90°)were measured to investigate the dependence on the microstructure.Finally,the effects of different heat treatment process on microstructure and properties of SLM processed Ti 15Mo alloy were discussed.The main research contents are as follows:(1)The microstructure of SLM-fabricated Ti-15Mo alloy on different directions displays obvious distinction.A small amount of ω phase can be observed in 0° sample,which is no detected in 45° sample and 90° sample.From the grain point of view,the average grain sizes increase in the order:0°→ 45°→ 90°.The equiaxed grains with less grain size deviations are observed in 0° plane,while for the 45° plane and 90° plane are the mixed microstructure of equiaxed and columnar crystals.The grains on the 0° plane are mainly oriented along(001)texture orientation while for 90° plane are mainly oriented along(111)texture orientation.(2)The anisotropy of electrochemical behavior,wear and bribocorrosion behavior of SLM processed Ti15Mo alloy in Hank’s solution was studied.The corrosion resistance of the three samples in Hank’s solution shows in the following order:0°>45°>90°.The refined grain size and high grain boundary density of 0° sample could make the passive film generate quickly,since they make the surface more active.The 90° sample has a higher molten boundary density than the other two samples,which leads to the decline of the corrosion resistance of the alloy.Because of the higher surface energies,the(001)texture orientation in the surface shows a better corrosion resistance than(111)texture orientation.The wear resistance of the samples formed in different building directions under two different conditions was ranked as follows:0°>45°>90°.While the ω phase can be one of the critical factors to lead the anisotropic bribocorrosion resistance due to their high hardness.The fine grain strengthening is also suitable for the tribocorrosion behavior.The finer gain size can result in the higher tribocorrosion resistance.(3)The effects of different heat treatment temperatures and different cooling rates on the microstructure of SLM-formed Ti15Mo alloy were investigated.The contents of α-phase andβ-phase in the SLM processed Til5Mo alloy obtained under different heat treatment conditions were different.With the increase of heat treatment temperature,the content of α-phase in the alloy decreased;the faster the cooling rate,the more β phase content in the alloy.The samples obtained from the furnace cooling heat treatment at 750℃ had the most α-phase content,and the alloy samples obtained from the water quenching heat treatment at 750℃ had the smallest average grain size.(4)The effects of different heat treatment conditions on the electrochemical behavior,wear behavior and tribocorrosion behavior of SLM processed Ti15Mo alloy are explained from the perspective of microstructure.As the smaller the grain size,it is easier to form a dense passivation film and enhance the corrosion resistance of the alloy.Therefore,the best corrosion resistance among the four groups of samples is the sample obtained by water cooling after holding at 750℃ for 1 hour.The wear resistance of the alloy is mainly influenced by the content of α-phase,as the hardness of α-phase is higher than that of β-phase,the more the content of αphase in the alloy,the better the wear resistance.The strengthening of the alloy by grain refinement is also applicable to the corrosive wear behavior.Under dry and corrosive wear conditions,the samples obtained by heat treatment with furnace cooling at 750℃ have better wear resistance.