factors affecting diffusion rates 1.concentration gradient—driving force 2.diffusing species &...

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).