Corrosion and Material Selection in Biomedical Applications, Quizzes of Engineering

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TERM 1 how are strength and ductility related DEFINITION 1 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 TERM 6 what are the types of forming DEFINITION 6 --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 TERM 21 possible prevention for crevice corrosion DEFINITION 21 **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 ???? TERM 26 role of proteins in corrosion DEFINITION 26 **proteins adsorb to surfaces thus reducing O2 diffusion and increasing corrosion **Metal chelators --example: transferrin --LeChatlier's principle TERM 27 transferrin DEFINITION 27 Transferrin is a blood plasma protein for iron delivery that, in humans, is encoded by the TF gene. TERM 28 LeChatlier's principle DEFINITION 28 ??? TERM 29 role of cells in corrosion DEFINITION 29 **acidification of local microenvironment due to physiological processes **depletion of oxygen due to cellular consumption or reduced diffusion **decrease in passivisation layer thickness **presence of cells increases rate of corrosion TERM 30 stress corrosion cracking DEFINITION 30 **combo of stress and mildly corrosive environment **neither stress nor loading alone can lead to failure **breakdown of passive film through mechanical force leads to cracking/failure **fatigue corrosion due to repeated loading/bending TERM 31 fretting corrosion DEFINITION 31 **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