I know there is a difference in them composition (grade 5 has lower quantity of Fe and O2). And it gives ELI better mechanical properties. But in corrosion terms what is the difference?
The essential difference between Ti-6Al-4V ELI (Grade 23) and Ti-6Al-4V (Grade 5) is the reduction of oxygen content to 0.13% max in Grade 23. This confers improved ductility and fracture toughness, with some reduction in strength. Grade 23 has been widely used in fracture critical airframe structures and for offshore tubulars. Mechanical properties for fracture critical applications can be enhanced through processing and heat treatment.
Obviously, now you can see that the improve mechanical propertiies, especially the ductility and fracture toughness are the dominant reason for the selection.
If you are starting from bar stock, a major issue with Ti-6-4 is the transverse axis properties. These properties are adversely affected by impurities, oxides, etc, which tend to migrate to the centerline during rolling.
Related to this is the fracture toughness of the alloys, which is significantly improved by using the ELI grade. http://www.unitedtitanium.com/ti-6al-4v
This is important for medical implants, because the costs of failure are high. I suspect this is the single biggest reason for using ELI.
The high-cycle fatigue strength (NO CRACKING) is more important for Ti implants than fracture toughness (which actually should not be a selection-limiting factor). Another comment: Ti-6Al-4V is not ideal because of the vanadium content . This is why the Ti-6Al-7Nb alloy has been developed for medical implants (already 40 years ago), since it is bio-compatible. You will find articles about this alloy in the literature.
It is worth repeating that high-cycle fatigue is the most important design criterion for some implants, see the attachment. Fracture toughness is relevant only if there is already a crack - which there shouldn't be! Fatigue cracking should not occur, which is why the fatigue limit in high -cycle fatigue is important. Ideally this should be used with a well-defined safety factor on stress levels. For implants such a safety factor is unlikely to be known, and one has to use 'engineering judgement'. In this respect case histories, as in the pdf attachment, may be helpful for giving guidelines (not well-defined safety factors).
To Dr Russell James Hugh Wanhill
Do you have or know any biocomptibility test result?
by ISO 10993 ?
Sorry, I cannot help you with this. I no longer have the files.
Ti6Al4V ELI (Grade 23) is very similar to Ti6Al4V (Grade 5), except that Ti6Al4V ELI contains reduced levels of oxygen, nitrogen, carbon and iron. ELI is short for “Extra Low Interstitials”, and these lower interstitials provide improved ductility and better fracture toughness for the Ti6Al4V ELI material.
Dear Claudia Rosa Morales Vargas,
*****Ti6Al4V ELI and Ti-6Al-4V (grade 5) both are typically used for medical implants. Ti6Al4V also has numerous applications in the medical industry. The biocompatibility of Ti6Al4V is excellent, especially when direct contact with tissue or bone is required. Ti6Al4V ELI (Grade 23) is very similar to Ti6Al4V (Grade 5), except that Ti6Al4V ELI contains reduced levels of oxygen, nitrogen, carbon and iron. ELI is short for “Extra Low Interstitials”, and these lower interstitials provide improved ductility and better fracture toughness for the Ti6Al4V ELI material. Ti6Al4V ELI (Grade 23) is a special characteristics biomaterial higher in biocompatibility (due to reduced levels of oxygen, nitrogen and iron) compared to Ti6Al4V, Ti6Al4V ELI is chosen ahead of Ti6Al4V.
6Al-4V ELI is one of the most widely used Titanium alloys in the medical industry. It is certified to ASTM F136, and commonly referred to as implant grade 6-4 Titanium. Its properties of biocompatibility, corrosion resistance, high strength, and toughness make it especially suitable for implants and other medical devices.
The main difference between Ti-6Al-4V ELI (Grade 23) and Ti-6Al-4V (Grade 5) is that in ELI (Extra Low Interstitials) the maximum oxygen content is lowered to 0.13%. This gives the material improved fracture toughness. Among it's main uses in the medical industry are Orthopedic implants, Bone and Joint Replacement, Dental root implants, Surgical Clips and Cryogenic Vessels.
6AL-4V ELI is also referred to as Grade 23 Titanium and ASTM F136.
Ashish
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