MSE 230 - Week 9

What are ferritic stainless steels?

Greater than 13 wt% Cr

BCC structure that makes it magnetic

Strengthened by cold work, cannot be heat treated

What are martensitic stainless steels?

Less than 13 wt% Cr due to C being added in the alloy

High yield strength

Good corrosion resistance

What are austenitic stainless steels?

Added Ni, with 18 wt% Cr

corrosion resistant, high ductility, expensive

cannot be heat treated

What are cast irons?

More carbon, lowering melting temperature

Easy for molding and applications

What are superalloys?

High Ni content, good oxidation resistance

Control microstructure to improve performance and longevity

Cuboidal precipitates within the superalloy microstructure

What are the primary bonds in ceramics?

Covalent and ionic

T/F: Ceramics are typically more complex than metals due to atomic sizes and electrical charges.

True!!!

What are the three ceramic unit cells? Describe em.

1. Rocksalt in FCC

   1. NaCl, MgO

2. CsCl in BCC

   1. TaN, Cu, Zn

3. Perovskite - 3 elements

   1. BaTiO3, Pb, ZrO3

What is the radius rule?

R of cation / R of anion → predicting the coordination geometry

Why do ceramics have a low K_IC?

They have sessile dislocations, so there is no local plastic deformation at the crack tip. This leads to the ceramic unable to compensate for stress amplification.

For the slip to occur, bonds must be broken so like charges must come into contact.

How do you measure the strength of a ceramic?

3 vs. 4 point bending test!

σ_f = 3FL/2bd² or σ_f = 3FD/bd²

What is the effect on porosity on the strength?

σ_f = σ_o exp(-np)

Reduces cross-sectional area and adds stress concentration which locally amplifies stress