Copyright by Stryker



GADS Alloy

The Gas Atomized Dispersion Strengthened (GADS) Vitallium® alloy was developed by Stryker in 1987. It shows a 10% to 36% greater fatigue strength than that of conventional forged Cobalt-Chrome (Vitallium®) alloy while showing equivalent corrosion resistance. GADS alloy is a high strength, corrosion-resistant, high temperature stable and ductile material.

 

Material Properties derives from different manufacturing processes

Standard Cobalt-Chrome:

  • The melting-process of Standard Co-Cr alloy affects its grain structure
  • Standard Co-Cr alloys feature a coarse-grained structure after the regular melting process
  • During forging process great forces are applied on the melted mix and due to its coarse-grained structure, Standard Co-Cr alloy is deforming to some extent and loses part of its original fatigue strength properties

  
   

GADS Vitallium® alloy:

  • Gas atomization is a technique for producing alloy powders having certain powder characteristics such as average particle size, particle size distribution and particle shape
  • Hot Isostatic Pressing (HIP) reduces metal’s porosity and defects by applying an inert gas (isostatic) under elevated heat. This improves metal’s mechanical properties and workability[1]
  • Small amounts of oxides and nitrides produced by gas atomization enhances the retention of Co-Cr’s strength during forging process [2]
  • By forging and rolling GADS alloy powder, a high strength, corrosion-resistant, high temperature stable and ductile material is produced [3]

   

  

Material Properties leading to greater strength

  • Implants forged from GADS Vitallium® alloy develop an exceptionally fine grain structure during exposure to forging temperature compared to standard CoCr alloys
  • The smaller the grains the less deformation and the less losses in material’s properties during forging process
  • The fine grain structure of GADS Vitallium® and its dispersion allows to retain 90% of material’s fatigue properties [4]

                        

   

Increased strength enabling modularity for small implants

  • GADS Vitallium® shows 10% [5] (rotating beam) to 36% [6] (4 point bend test) greater fatigue strength (point at which material begins to have permanent structural damage) than Standard Cobalt-Chrome forging (ASTM F1537 Alloy 1)
  • Thus GADS Vitallium® alloy allows to manufacture necks with thin connexion resulting in modularity even for small implants
  • All Stryker necks are tested according to ISO 7206-6:1992 (Method of Determination of endurance properties of head and neck region of stemmed femoral components)

  

 

                                                                  

   

  

[1 ]  Atkinson, H.V., et. al. Fundamental aspects of hot isostatic pressing: An overview, Springer Boston, Volume 31, Number 12, Boston, 2000

[2  Wang et al., « Dispersion strengthened Cobalt-Chromium-Molybdenum Alloy produced by Gas Atomization », United States Patent, Patent Number: 4,668,290, 1987

[3]  Wang et al., « Prosthesis formed from Dispersion strengthened Cobalt-Chromium-Molybdenum Alloy produced by Gas Atomization », United States Patent, Patent number: 4,714,468, 1987

[4]  Wang, K.K., « For medical implants », The 15th Annual Meeting of the Society for Biomaterials, Lake Buena Vista, Florida USA, 1989

[5] Stryker test report MT94037

[6] Stryker test report MT96055A