Advanced Alloy Powders for Additive Manufacturing:Application in Orthopedic Implants
Additive Manufacturing(AM)opens lots of possibilities to create completely new designs with complex geometries that meet design requirements.This paper will be focused on mostly titanium based alloys but the ideas presented may be also used for other alloys.While Ti-6,4 is the work horse of AM today due to experience with wrought products and powder availability,alloys with improved properties that are amenable to AM are relatively unexplored.Therefore,it is time to introduce other alloys for AM to complement Ti-6.4.In this paper we will discuss the potential of other alloys suitable for AM as well as several new ideas related to creation of composite parts using either in situ reactions during AM processing or newly designed composite powders.Ti-185(Ti-1Al-8V-5Fe)alloy is a metastable beta-titanium alloy developed in the early 1960s Ti185 has high tensile and shear strengths,which made it an attractive material for fastener applications in the aerospace industry,given its elastic properties and density,it would be also very attractive for automotive spring applications.Despite the advantages of Ti185,the production of this alloy in bulk by conventional ingot processing was not developed because addition of more than 2.5 wt.%of iron to titanium alloys resulted in significant segregation of iron and led to the development of compositional inhomogeneities or beta flecks,which have been shown to be detrimental to the fracture toughness,ductility,and fatigue performance of these alloys.Due to the very small molten volume in AM process,the formation of beta flecks could be potentially suppressed and thus AM may permit the production of Ti 185 parts with attractive mechanical properties.Another group of beta-titanium alloys,for example TNZT(Ti-Nb-Zr-Ta)are very attractive for biomedical applications due to their low modulus of elasticity,which is close to that of the human bone.A series of low modulus beta Ti alloy billets and powders can be produced in commercial quantities using a combination of electron beam melting(EBM)and EIGA inert gas atomization processes.In our study,TNZT alloy powders were deposited using powder bed fusion(EOSINT M290)as well as directed energy deposition(LENS 750).The EOS processed parts were subsequently mechanically tested.Post heat treatments such as stress relief annealing to reduce internal stresses or hot isostatic pressing to remove internal pores were not applied.The as-deposited density can visually be estimated to be > 99.9%.According to EDS study Nb,Zr and Ta are distributed homogeneously throughout the AM deposit.There are no indications of any alloy segregation in the deposit.This shows that the melt generated by the laser rapidly cools down in the powder bed fusion(or selective laser melting,SLM)process.The EOS SLM processed parts yielded dense structures with relatively good surface quality.The mechanical properties of these parts,especially the elongation(24%)along with tensile strength(>500MPa)and modulus of elasticity(~60GPa),are promising for biomedical applications of titanium alloys.The Ti-50%Ta alloys were developed as a potential replacement of the commonly used Ti-6Al-4V alloy in surgical implants due to its better biocompatibility.However,these alloys are very difficult to produce due to significant differences in melting points and densities of Ti and Ta.To achieve complete mutual solubility either arc melting or electron beam melting must be used to prepare Ti-Ta alloy.Atomization process of high melting point Ti-Ta alloys represents another challenge.Published research on 3D manufactured samples used only blended powders of Ti and Ta as a source to produce printed Ti-Ta parts and no Ti-Ta alloy powder was available.The goal our research was to develop manufacturing technique to produce true Ti-Ta alloy powders suitable for additive manufacturing technology.Samples of these alloy powders were obtained by EIGA atomization of powder blended ingots without initial melting: elemental powders were hot isostatic pressed at 180 MPa for 2h in form of ingots suitable for EIGA atomization.Then the Ti-50wt%Ta alloy powder was characterized by optical microscopy(OM),scanning electron microscopy(SEM/EDS),and X-ray diffraction.Results indicate that the homogenization of the beta alloy can be achieved by this novel process,which can be used for other binary or more complex alloys containing high melting point elements.Mechanical tests were made using additively manufactured samples.
beta titanium alloys additive manufacturing
Ivanov Eugene Del-Rio Eduardo Williams J. Banerjee R. Nystr(o)m Maija Kotila Juha
Tosoh SMD Inc,Grove City,OH-43123,USA The Ohio State University,Columbus,OH,USA;Department of Materials Science and Engineering,University Department of Materials Science and Engineering,University of North Texas,Denton,TX USA Electro Optical Systems Finland Oy,Lemmink(a)isenkatu 36,FI-20520 Turku,Finland
国际会议
北京
英文
189-196
2018-09-16（万方平台首次上网日期，不代表论文的发表时间）