Metallic Biomaterials Flashcards
What are the 5 requirements for metallic biomaterials?
- Corrosion resistance
- Biocompatibility
- Suitable mechanical properties
- Fatigue resistant
- Ductile
What effect can Alloying materials have?
o Can confer corrosion resistance (but can also make corrosion more likely, depending on the choice of element)
o Can change the colour of the material
o Can change the character of the material:
e.g. Austen steels are not magnetic like normal steel
What can you coat Cr and Ni with to make them better tolerated? What is the process called?
Coating: Inert Cr2O3 oxide layer
Process: Passivation
What does passivation mean?
Making a material unreactive by adding an oxide layer
What does Young’s modulus refer to?
How hard a material is to deform
What does Yield strength refer to?
The stress at which the material will deform permanently
What does Ultimate Tensile Stress refer to?
The stress at which the material breaks
What is the relevance of Ease of Working?
Very hard materials are difficult to machine and cannot be easily deformed
Good properties are important but what three aspects do these balance against?
Cost
Appearance
Ease of Working
What coating do Cobalt chromium (Co-Cr-Mo) alloys rely on for corrosion resistance?
Cr2O3
Why don’t we use titanium for surfaces?
Release of wear particles
Progressive Degradation
What good properties does Titanium have for implants?
Biocompatibility
Flexible
High tensile strength
- but poor wear resistance
When is Cobalt chrome used?
Specialist applications where high wear resistance is needed e.g., bearing surfaces/dentistry
What is meant by ‘grains’ in metallic structures?
Grains are crystals formed from nucleation points – shape is irregular as crystal growth is inhibited by contact with adjacent crystals
What grain structure gives the best mechanical properties
Small, fine grain structure
