Lecture 3 Flashcards
(22 cards)
Does the alloy composition matter?
Yes - impacts properties
What are some benefits about titanium and its alloys?
Very good
Biocompatible and corrosion resistant
forms passive oxide layer
light
similar properties to bone
Do you need metal ions?
Yes - we have diferent ions in our body (e.g. Mg) but excess is bad
Can metals degrade? If yes, what are some limitations?
Mg alloys might be biodegradable
weaker than other materials but still stronger than ceramics and polymers
For forming interstitial alloys, the atomic size of the alloying element must be what size in comparison to the matrix element?
significantly smaller than the atomic size of the matrix element
Do materials corrode the same in the body and in the air?
No - body is more corrosive
What is the minimum amount of chromium (wt%) needed to impart the ability to form a passive layer for corrosion resistance?
11%
What are some negatives of cobalt alloys?
Difficult to machine and process = high costs
Can metals be porous?
Yes - minimises fibrous tissue encapsulation
Currently hard to manufacture
What are some negatives about titanium?
expensive
not good at wear resistance
easy damage to surface
What are some benefits of platinum alloys?
Metals for electrodes (e.g. stimulating nerves or muscles)
needs low impedance
can be alloyed with iridium
balance of stiffness and flexibility
What are some of the benefits of nitinol? What is it used in?
Alloy of nickel and titanium
better compatibility than ss
shape memory = 2 stable phases
orthopaedic braces, stents etc
When would CpTi be used as compared to Ti-6Al-4V?
CpTi = non load bearing = heart valves, pace makers, dental implants
Ti-6Al-4V = load bearing = all CpTi can do + joints
What are the different types of titanium?
Alpha (HCP) = pure, weaker but more ductile (e.g. aluminium)
alpha-beta = both = stronger and less ductile
beta = good strength but less bone absorption (e.g. silicon or vanadium)
What are some benefits of cobalt-chrome alloys?
Used in joint implants
corrosion resistant = forms oxide layer
mixed with alloys to improve mechanical properties
good wear and fatigue resistance
stronger than titanium and ss
What are some negatives about SS?
leaking chromium or nickel ions = allergic reaction
corrosion resistance isn’t great
fatigue
Why is the austenite phase good?
not magnetic
What are some benefits of SS? What does chromium and nickel do?
Cheap
corrosion resistant
good biocompatibility
common
11% chromium = shiny + thick oxide film
nickel = increased ductility and toughness
What are advantages of metals?
good mech properties
load bearing applications
conductivity
easy to sterilise
manufacture complex shapes
What do alpha and beta stabilisers do to strength and ductility??
strength = enhanced, ductility = reduced
Which Ti alloy generally has the lowest young’s modulus?
beta titanium alloys
What is a criteria where you would pick a metallic material over a polymer or a ceramic?
electrical conductivity
