Factors affecting diffusion rates
1. Concentration Gradient—driving force
2. Diffusing species & host material
3. Temperature
Diffusing Host Metal T(oC) D (m2/s)speciesFe -Fe (BCC) 500 3.0 x 10-21
Fe -Fe (BCC) 900 1.8 x 10-15
Fe -Fe (FCC) 500 1.1 x 10-17
Fe -Fe (FCC) 900 7.8 x 10-16
Which diffuses faster?A.Fe through -Fe at 500oCB.Fe through -Fe at 900oCC.Fe through -Fe at 500oCD.Fe through -Fe at 900oC
How does
diffusion affect material
properties?
Brass =Alloy of Copper and Zinc
Bras
sCopp
erZinc
Brass = Stronger than either Copper or ZincExplanation in Chapter 7
City Steel Heat Treating Co.
Solid Diffusion Hardening:Case Hardening Hard Case w/ tough core
Low-C Steels (> 0.30% C):
Carburizing,
Nitriding,
Carbonitriding
Carburized depth of 0.030” to 0.050” in 4 hours @ 1700°F
What happens in the case: Steel = C + Fe
• Add more C to the outer surface.
• Interstitial C imposes lattice strains in Fe
• Strains near dislocations can bind atoms and reduce deformation (see Ch. 7)
Carburizing—Solid Diffusion process
Begin at 1:35–2:40
YouTube: Vacuum Carburizing and Heat treating
Composition & processing affect material properties
Section 6.1-6.3Mechanical Properties of
Metals:
Elastic Deformation:
Stress-Strain behavior
Mechanical Properties:How will the object respond to an applied load (force)?
• Stiffness
• Ductility
• Strength
• Toughness
• Hardness
Tension
Compression
Shear
Tensile Test
Tensile Test
Tensile Test
Ductile Failure: Tensile Test of AlMgSi alloy
Brittle Failure: Tensile test of Nodular Graphite Cast Iron
Principles of
Stress and
Strain
What is it good for?
• Normalize tensile tests• Measure intensity of a load
Stress is used to:
The
Ultimate Chair Cushion
Design
Types of Deformation
•Elastic•Plastic
Elastic
Deformation:
Recoverable
Elastic
By Design
Elastic deformation of Metals
Motorcycle
Shock absorber
http://upload.wikimedia.org/wikipedia/commons/thumb/1/10/R75-rear-shock.jpg/220px-R75-rear-shock.jpg
Elastic deformation of Ceramics
Fiber optic cable
Elastic deformation of Polymers
Shooting a
rubber band
http://rickischultz.files.wordpress.com/2009/09/rubber-band.jpg
Elastic deformation of Composites
Carbon-fiber
prosthetic legs
http://info.rogersathletic.com/get-strong/bid/62010/Muscle-Tendon-Springs
Elastic deformation of Composites
Diving Board
Elastic deformation of Composites
Diving Board
Quantifying Elastic
Deformation
Hooke’s Law
• Elastic deformation–Recoverable:
= E
• Stiffness – E – resistance to elastic deformation
Brittle Failure: Tensile test of Nodular Graphite Cast Iron
YouTube
REAL Golf Ball hitting steel in slow motion by the USGA - YouTube
Comparison of E values
Plastic
Deformation:
Permanent
plastic (adj.)
1630s, "capable of shaping or molding"
from L. plasticus, from Gk. plastikos "able to be molded, pertaining to molding,"
plastic (adj.)
Main modern meaning, "synthetic product made from oil derivatives," first recorded 1909, coined by Leo Baekeland (see bakelite).
Picked up in counterculture slang as an adj. meaning "false, superficial" (1963).
Mechanical Property:Elasticity–recoverable deformation
Paper clip under normal use
Mechanical Property:Plasticity—permanent deformation
Paper clip
under abuse
Plasticity by design
Radial profile segments
Plasticity by accidentStreet lamp damaged during storm
(Brid
gepo
rt,
CN
)
Formed by plastic deformation;Behaves elastically
Binder Clip
Plastic deformation of Metals–Spring shape
Elastic deformation: Shock absorbers
Springs absorb shock transmitted from road to vehicle.
Plastic Deformation
• Plastic deformation – Permanent
• Yielding – onset of plastic deformation
• Yield strength – Stress at yield (specified amount of strain).