Download Corrosion and Material Selection in Biomedical Applications and more Quizzes Engineering in PDF only on Docsity!
how are strength and ductility related
inversely proportionally TERM 2
strain hardening
DEFINITION 2 --the strengthening of a metal by plastic deformation. -- increases line defects --below Tm TERM 3
grain size refinement
DEFINITION 3 --smaller grains, dislocation direction changes --achieved by thermal processing TERM 4
annealing
DEFINITION 4 --slowly cooling material to relieve internal stresses after it was formed. --increases ductility --increased grain size, reduced area of grains --thermodynamically favorable TERM 5
precipitation hardening
DEFINITION 5 --is a heat treatment technique used to increase the yield strength of malleable materials --volume defects --barrier to dislocation
what are the types of forming
--hot working: T>0.3Tm --cold working: T TERM 7
give examples of
shaping
DEFINITION 7 --rolling --forging --extrusion/drawing TERM 8
casting
DEFINITION 8 --Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. --T>Tm --tendency for internal defects --complex shapes --sand casting --investment casting (lost wax) TERM 9
powder processing
DEFINITION 9 --fabrication technique involves the compaction of powdered metal, followed by a heat treatment to produce a more dense piece --method is especially suitable for metals having low ductility, since only small plastic deformation of the powder occurs TERM 10
rapid prototyping/solid
freeform
DEFINITION 10 --similar concept to powder processing --selective laser sintering --complex shapes --kinda like a printer
cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. implanted materals in the body can act as a cathode TERM 17
anode
DEFINITION 17 An anode is an electrode through which electric current flows into a polarized electrical device. implanted materials in the body can act as an anode TERM 18
Galvanic series
DEFINITION 18 The galvanic series (or electropotential series) determines the nobility of metals and semi-metals. while electrically connected, the less noble (base) will experience galvanic corrosion. The rate of corrosion is determined by the electrolyte and the difference in nobility. The difference can be measured as a difference in voltage potential. TERM 19
bio fluids play what role in galvanci corrosion
DEFINITION 19 act as a salt bridge TERM 20
Crevice corrosion
DEFINITION 20 **result of concentration difference of ions or dissolved gases in solution **occurs between two regions of the same piece of metal **region of lower concentration experience corrosion **crevice must be large enough for solution to penetrate **crevice must be small enough for near-stagnant movement of solution, 0.001-0. inches **oxygen depletion leads to oxidation of the metal **reduction occurs at other location of the metal via conduction
possible prevention for crevice corrosion
**use of welds when possible TERM 22
pitting corrosion
DEFINITION 22 Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. ** in metals that are given a protective coating, the metal may not be perfectly coated/ coating may wear off, in which case the imperfection becomes an anode and the rest of the metal becomes a cathode, leading to large pitting TERM 23
intergranular corrosion
DEFINITION 23 is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides. **stainless steel implants rely on chromium oxides to passivate the surface, sometimes the some areas become depleted in Ch when this happens it starts to corrode. Grain boundaries can become depleted to thus causing massive widespread corrosion. **heat treating is used to prevent intergranular corrosion TERM 24
how do you counter act corrosion
DEFINITION 24 **galvanic--proper metal selection **use of noble metals **additional processing: example, heat treatment **coating with polymers or ceramics **passivating oxide layers TERM 25
passivating oxide layer
DEFINITION 25 ????
fretting corrosion
**motion near implant (not loading) **mechanical removal of passivating layer, may be cyclic in nature TERM 32
austenitic stainless steel
DEFINITION 32 used for: temporary implant devices, hip nials and plates, intramedullary pins, hear valves, prosthesis, clips for surgery, and pacemaker electrodes Note: mostly been replaced with cobalt-chrome and titanium alloys due to corrosion resistance TERM 33
stainless steel and corrosion
DEFINITION 33 **iron is very reactive with O2, adding chromium to steel gives stain resistance, chromium combines with O2 in the atmospher to form a layer of chromium oxide, thus creating the "passive film" b/c chromium and O2 atoms are about the same size **composed of: iron 60-65%, chromium 16-20%, nickel 12-14%, molybdenum 2-3%, and other traces TERM 34
cobalt-chromium alloys
DEFINITION 34 advantages: corrosion resistance, smaller grains more strength disadvantages: cost, potential toxicity **composition: Co 59-70%, Cr 27-30%, Mo 5-7% and traces TERM 35
titanium in biomedical
application
DEFINITION 35 anchoring screws, pins and posts for dental implants, knee replacement, and hip replacement
titanium
resistance to corrosion, spontaneous formation in air of highly bio compatible dioxide passivation layer. lower strength than stainless steel, osseointegration thus midigateing need for adhesives TERM 37
osseointegration
DEFINITION 37 the materially is integrated into the bone.
