Selective laser melting-produced Ti6Al4V: Influence of annealing strategies on crystallographic microstructure and tensile behaviour

Ter Haar, Gerrit Matthys (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The ability to manufacture complex shapes and structures with little material waste, among other advantages, makes the metal additive manufacturing technique of Selective Laser Melting a superior manufacturing technique. The titanium alloy, Ti6Al4V, serves as a great material of choice for this manufacturing technique due to its excellent mechanical properties and its biocompatibility. These factors make Ti6Al4V parts produced through SLM highly applicable and valuable in the biomedical and aerospace industries. Due to limited research and development in the field however, part quality in terms of achievable mechanical properties, residual stress and density has been below standard (such as that achieved by wrought Ti6Al4V parts). The study aimed to gain a fundamental understanding of the influence of annealing strategies on the microstructure of SLM-produced Ti6Al4V to improve and optimise the tensile properties of the material. SLM-produced Ti6Al4V tensile samples were subject to various tailored heat treatment strategies. Analysis of microstructure through optical and electron backscatter diffraction allowed for correlations to be made between the annealing strategies and the microstructure as well as between the printing process and the microstructure. Tensile test results of annealed samples show a decrease in tensile strength with an increase in annealing temperature as well as an increase in ductility and stiffness with an increase in annealing temperature. It was found that the fine martensitic (α’) microstructure of the as-built samples decomposes into a dual-phase (α+β) microstructure at ~800 °C, thereby improving ductility and stiffness. An optimal duplex annealing strategy allows for a bi-lamellar microstructure to be formed which allows for a substantial increase in ductility while maintaining a high material strength.

AFRIKAANSE OPSOMMING: Die vermoë om komplekse vorms en strukture te vervaardig met min afvalmateriaal, om slegs een voordeel te noem, maak die metaaltoevoegingsvervaardiging tegniek van Selektiewe Laser Smelting (SLM) ʼn tegniek van voorkeur. Die titanium legering, Ti6Al4V, dien as die materiaal van keuse vir hierdie tegniek as gevolg van sy uitstekende meganiese eienskappe en sy vermoë om suksesvol met biologiese weefsel te integreer. Hierdie faktore maak Ti6Al4V dele geproduseer deur SLM hoogs toepaslik en waardevol in die biomediese en ruimte industrieë. Weens beperkte navorsing en ontwikkeling tot dusver in die gebied, is part kwaliteit, in terme van haalbare meganiese eienskappe, residuele spanning en digtheid, onder standaard (soos wat bereik word deur smee Ti6Al4V dele). Die studie was daarop gemik om 'n fundamentele begrip van die invloed van uitgloeiing strategieë op die mikrostruktuur van SLM-geproduseerde Ti6Al4V te kry, om sodoende die meganiese eienskappe van die materiaal te verbeter en te optimaliseer. SLM-geproduseerde Ti6Al4V trek monsters was onderhewig aan verskeie hitte behandeling strategieë. Ontleding van die mikrostruktuur deur optiese en elektroniese terugstrooiings diffraksie het toegelaat om die uitgloeiing strategieë met die mikrostruktuur te korreleer, asook die SLM-proses met die mikrostruktuur. Trektoetsresultate van uitgegloeide monsters het 'n afname in treksterkte met 'n toename in uitgloeiing temperatuur asook 'n toename in smeebaarheid en styfheid met 'n toename in uitgloeiing temperatuur getoon. Daar is bevind dat die fyn martensitiese (α') mikrostruktuur van die as-vervaardigde monsters ontbind in 'n dubbele-fase (α+β) mikrostruktuur by ~800 ° C, en sodoende verbeter smeebaarheid en styfheid van die materiaal. 'n Optimale dupleks uitgloeiing strategie het toegelaat vir 'n dubbel-lamellêre mikrostruktuur om gevorm te word. Dié mikrostruktuur het 'n aansienlike toename in smeebaarheid getoon, asook ʼn behoud van hoë materiaal sterkte.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102946
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