Titanio Gr 5 ELI (Gr 23)
The best material for long lasting implant prosthetic results
Titanium grade 23, generally known as titanium grade 5 ELI (Extra Low Interstitial), is the titanium alloy (Ti6Al4V) currently used in the production of “Easy Grip®” implants and abutments. For many years T.F.I. System srl has adopted this alloy in place of titanium grade 4 CP (Commercially Pure) for its characteristic properties that we briefly list below:
Titanio Gr 5 ELI
(Gr 23)
The best material for long lasting implant prosthetic results
Titanium grade 23, generally known as titanium grade 5 ELI (Extra Low Interstitial), is the titanium alloy (Ti6Al4V) currently used in the production of “Easy Grip®” implants and abutments. For many years T.F.I. System srl has adopted this alloy in place of titanium grade 4 CP (Commercially Pure) for its characteristic properties that we briefly list below:
Hardness
The 6% aluminium presence increases hardness, reduces specific weight and improves the elasticity modulus "E". Furthermore, association with aluminium and vanadium reduces thermal conductivity by about 50%, but above all increases wear resistance by the same percentage.
Surface resistance
The Ti6Al4V ELI titanium alloy is an alpha-beta alloy, i.e. it contains both alpha stabilising (aluminium and oxygen) and beta stabilising elements (vanadium); this type of alloy may be surface treated in order to increase friction corrosion resistance.
Friction wear resistance
Here is an excerpt from the “titanium” page in Wikipedia: “it has the property of being biocompatible, with surface porosity similar to human tissue, so that it is physiologically inert. For this reason, the Ti6Al4V ELI titanium alloy is used in hip and knee prosthetic components. However, due to the high friction coefficient it is never used as a component for articular joints." Unfortunately, titanium surfaces obtained from turning commercially available bars have a relatively low friction wear resistance. In particular, titanium surfaces in mutual contact between them or with other metals are damaged quickly due to rubbing or friction (the so-called fretting corrosion). Surfaces may therefore completely seize up even with a light load and small relative movement.
This situation is due to adhesive wear, in which microscopic asperities on the metal surfaces come into contact with each other as a result of relative sliding and tend to weld together, forming a bond that may have greater tensile strength than the underlying metal; the fracture, then, occurs at one of the asperities, causing a transfer of metal from one surface to another; the residues thus formed give rise to the accelerated wear that occurs in titanium.
In view of this, it is essential to adopt appropriate solutions in order to use titanium in conditions in which wear might be a problem.
Fatigue resistance
The complex manner in which the microstructure and morphology contribute to changing the properties of the material, call for the fatigue behaviour to be generally assessed experimentally on a case by case basis, depending on requirements. In general it can be stated that all changes which result in an increase of the yield strength also lead to an improvement in fatigue resistance. Another key factor is the state of surfaces, whose poor finish is conducive to the onset of cracks, which may then propagate by fatigue even at very low loads. That is why we pay special attention to surface treatments.
Fracture toughness
The Ti6Al4V ELI alloy (titanium grade 5 ELI), is used for those applications requiring very high fracture toughness (for example hip prosthesis). This titanium alloy is treated with a particular process to reduce interstitial elements (ELI process), which significantly improves K values (effort which the material is able to withstand in the event of cracks), making it possible to reach values even twice as high as those of the simple Ti6Al4V alloy with normal levels of oxygen.
Breaking strength
Grade 5 ELI titanium has a value of 830 MPa, compared to 550 MPa for titanium grade 4.
Yield strength
Grade 5 ELI titanium has a value of 760 MPa, compared to 480 MPa for titanium grade 4.
Resistance to crack propagation
The natural formation of some surface defects is often originated by lathe methods, operation to be deemed necessary to achieve the desired processing result (thread start, grooves, etc.). Such surface defects are often the cause of cracks, generated following fatigue strain of the piece.
The "Friction Fit" and "Surface Treatments" sections deal in depth with the development of methods that lead to considerably increase this type of resistance for the products of our “Easy Grip®” implant line.
Here we will just say that to reduce this phenomenon,
TFI System srl uses CNC (numerical control) lathes equipped with expensive additional items such as internal and external tourbillonage, indispensable to perform internal and external threads, reducing to a minimum the surface defects in question.
