Compressive surface layers

Question 1

What causes compressive surface layers? What enhances this effect?

Answer 1

~ developed from spontaneous t–>m transformation of grains near the free surface because of the absence of hydrostatic constraint

~ surface grinding enhances this effect

Question 2

What’s the result of compressive surface layers?

Answer 2

~ squeezes surface cracks, up to doubling the fracture strength of the ceramic

Question 3

How deep can the compressive stresses be?

Answer 3

~ compressive stresses can be generated up to 100um below the abraded surface, mitigating stress intensification for flaws approaching that dimension

Question 4

What is the difference between TZP and PSZ in terms of compressive surface layers?

Answer 4

~ since TZP is composed nearly entirely of metastable tetragonal grains, it enjoys greater surface compression strengthening than PSZ