Relationships between processing, structure and properties at Ti-6Al-4V parts made by powder injection molding

RELATIONSHIPS BETWEEN PROCESSING, STRUCTURE ANDPROPERTIES AT Ti-6Al-4V PARTS MADE BYPOWDER INJECTION MOLDING(M.Sc. Thesis)Yaşar ÇAKARGAZI UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYMay 2006ABSTRACTIn this study, the characterization of Ti-6Al-4V parts made by powder injectionmolding (PIM) were carrried out. Ti-6Al-4V PIM parts were produced byusing blended elemental and prealloyed approaches. Powder blends consisted ofpure, gas atomized powder and 60Al/40V master alloy mix in the formerapproach; and prealloyed gaz atomized Ti6Al4V powder in the secondapproach. Powder feedstocks were prepared from these powder blends with theaddition of a binder mix comprimising 25 % polyethylene, 15 % paraffin wax, 5% stearic acid, PIM parts were produced at IFAM, Bremen by mixing,granulation, injection moulding, debinding, and sintering. PIM?ed and deboundgreen samples were sintered at different temperatures, times and atmospheres,and were cooled to room temperature with different rates and atmospheres todetermine the best possible processing conditions.For this purpose in the first part of the investigation, the characterization of Ti-6Al-4V parts, sintered at 1250ºC for 0,2,4 hours and 1300ºC for 2 hours incovered-uncovered conditions followed by vacuum cooling to room temperaturewere carrried out. After determination of the best possible sintering practice,the second step was carried out. In this stage, samples were cooled to roomtemperature, by argon and interrupped cooling in addition to vacuum cooling.The aim in this second stage was to determine the best possible coolingcondition to room temperature. In the final stage, TiH2 additions in amounts of10-30 % were made to blended elemental feedstocks to study their influence inthe microstructure and properties of Ti-6Al-4V PIM parts. In the experimentalpart of the current investigation, chemical analysis of as-received powders,determination of mechanical properties and SEM fracture surface examinationof tensile test samples were carried out.In addition to these, some samples were analyzed chemically by EnergyDispersive X-Ray Microanalysis and structurally analyzed by X-Ray difractionto determine the level of interstitial elements contaminations and resultingphase (precipitate) formations. As a result of the current investigation, it wasfound and concluded that sintering at 1250ºC for 4 hours under protectiveatmosphere (i.e, under Ar-flushed vacuum atmosphere) of Ti-6Al-4V PIMparts prepared from powder feedstocks made up of prealloyed (PA) Ti6Al4Vpowder mixes (without any TiH2 addition) with binder compound followed bycooling to room temperature under Ar gas was best in terms of microstructuresand properties expected for application conditions. Ideal microstructure was theone with low porosity and with thin widmantatten α plates, no equi-exed αplates around pores and no formation of α-case in the surface of the PIM parts.Ideal mechanical properties were high yield and ultimate tensile strength,acceptible level hardness and elongation, low brittleness, high elastic modulusfor rigicity when the material had high % of theoretical density, low level ofporosity and interstitial element (O and N) contamination, together with lowtitanyum nitrür (TiN0,3) formation.Science code : 710.1.092Key Words : Titanium and Ti-6Al-4V, Powder Injection Molding (PIM),Powder Metallurgy, CharacterizationPage Number : 147Adviser : Prof. Dr. Sedat ÖZB LEN