Characterisation of Ti6Al4V (ELI) Powder Used by the South African Collaborative Program in Additive

Conference ProceedingsThe South African Additive Manufacturing Strategy recommends research and development towards “Qualified AM parts for medical and aerospace” as one of the national priorities. In response to this, the national Collaborative Program in Additive Manufacturing includes a sub-programme on “Qualification of Additive Manufacturing of Ti6Al4V for Medical Implants and Aerospace Parts”. This sub-programme entails comprehensive systematic research aimed at establishing a database of material and process data needed for qualification of the AM powders, AM processes and post-process treatments used for medical and aerospace applications. The paper describes the approach taken to characterise the Ti6Al4V (ELI) powder in the as received state and after exposure during repeated AM build cycles, by determining the physical and chemical properties of powder used in two selective laser melting (SLM) machines and a laser engineered net shaping (LENS) machine. Properties of the powder that were determined include the particle size, particle size distribution, morphology, oxygen and nitrogen gas content, and elemental composition. Characterisation techniques employed are Scanning Electron Microscopy, Laser Diffraction, Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), and Inert Gas Fusion. The results of the analyses on as-received powder and powder after exposure to numerous build cycles in the different AM machines are presented and discussed

CHARACTERISATION AND MONITORING OF TI6AL4V (ELI) POWDER USED IN DIFFERENT SELECTIVE LASER MELTING SYSTEMS

Published ArticleThe characterisation and monitoring of Ti6Al4V (ELI) feedstock powder is an essential requirement for the full qualification of medical implants and aerospace components produced in selective laser melting systems. Virgin and reused samples of this powder were characterised by determining their physical and chemical properties through techniques complying with international standards. This paper presents the results obtained for Ti6Al4V (ELI) powder of two different particle size distributions received from the same supplier. The characteristics of these powders after several reuse cycles in two different selective laser melting systems are also presented and discussed

Determination of roll compaction parameters required for high green density, defect free Ti-6Al-4V strips

Abstract: Direct powder rolling (DPR) is an unconventional powder metallurgy technique for fabricating flat mill products. It offers significant cost reduction by using low processing temperatures and reduced fabrication steps compared to ingot metallurgy. Roll compaction is the first stage in the DPR process, hence proper selection of roll compaction parameters is vital for achieving high density defect free (no visible cracks, alligatoring or centre split) green compacts. Unsuitable roll compaction parameters can result in fragile low green density strips which could be difficult to handle during subsequent processing or high green density strips with defects. The focus of this study was therefore, to determine the range of roll compaction parameters required in producing high density, defect free strips. The Ti-6Al-4V strips studied were produced by mixing 150 μm titanium hydride de-hydride powder with a 45 μm 60Al40V master alloy. The powder mix was roll compacted at varying roll gaps and rolling speeds. The compacted strips were evaluated by measuring the green strip density and thickness. It was concluded that for the Ti-6Al-4V powder studied in this work, the preferred roll compaction parameters for achieving high density, defect-free green strips are 0.3 mm to 0.5 mm roll gap with roll speeds from 3 rpm to 10 rpm

A comparative study of oxygen pick-up of TiHDH powder during press and sinter and loose sintering processing

Abstract: Press and sinter is considered to be the most cost effective powder metallurgy process for producing parts. However, loose powder sintering shows to be a more promising cost effective powder metallurgy process as it entails pouring powder into a mould followed by sintering. The differences in their behaviour with respect to densification, maintaining dimensional stability and their oxidation behaviours determine the choice of their industrial applicability. Titanium has a high affinity for oxygen which in turn makes it difficult to process components from powder. It also affects the mechanical properties of products significantly; particularly in applications where ductility is imperative. The focus of this study was therefore to evaluate the oxygen pick-up of the two cost effective powder metallurgy processes (press and sinter and loose sintering). A 100 Mesh TiHDH powder was used for sintering. Sintering was performed at 1500°C for 4 hours. The oxygen contents of the green and sintered compacts were then compared. High oxygen contents were observed in tap density powder and pressed samples. The loosely sintered components showed high oxygen pick-up after sintering while oxygen pickup decreased with increasing pressure in pressed samples. These results show that press and sinter is advantageous over loose sintering where oxygen control is critical

The effect of ternary alloying with vanadium on Ti-Pt shape memory alloys

Ti-Pt alloys have attracted much research due to high transformation temperatures (1050oC) which makes them suitable for high temperature applications in automotive and aerospace industries. The binary alloy exhibits negligible shape memory effect and the amount of platinum (Pt) required to produce this alloy makes it very expensive which limits its practical application and commercialization. Ternary alloying of Ti-Pt could lead to solid solution strengthening and improved shape memory properties. Furthermore, ternary alloying by replacing Pt could reduce the cost of the alloy. However, it could lead to changes in the microstructure, crystal structure, transformation temperatures and transformation temperature hysteresis that would significantly affect the shape memory behaviour of the alloy. This paper investigates the effect of ternary alloying of Ti-Pt with varying vanadium contents (0-18.25 at.%) on the as-cast condition. The effect of ternary alloying on the microstructure, transformation temperature and transformation temperature hysteresis were studied. The Ti50-Pt50-x-Vx (x = 6.25 to 18.25 at.%) alloys were produced by the button arc melting method using elemental powders of titanium, platinum and vanadium. Results showed the formation of martensitic α-Ti50(Pt,V)50 with Ti3Pt, (Ti,V)3Pt, Ti4Pt3-like and oxide phases in Ti-Pt-(V) alloys. The phase transformation temperature of Ti-Pt alloys decreased with increasing vanadium content up to 10.2 at.% V.http://iopscience.iop.org/journal/1757-899Xam2020Materials Science and Metallurgical Engineerin