me 370/570 materials science and engineering-i chapter xiv...

1Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

ME 370/570Materials Science and Engineering-I

Chapter XIV

• Instructor: Dr. R. Srinivasan• Mechanical and Materials

Engineering Dept.



Processing of Ceramics• Ceramic materials fall into some broad categories

– Glass – transparent, hard – amorphous– Clay products – used for everyday applications – dinnerware,

sanitary ware etc.– Refractory products – thermal insulation– Abrasives– Cements– Advanced ceramics

• Processing methods depend on the type of ceramic• Other than glass, most ceramics are high melting and cannot be

mechanically deformed. Therefore processes applied to metals cannot be used.

• These ceramics generally start of as powders.• Glass can be melted, and is soft and deformable at high temperatures



Glass is produced by mixing components and heating to a high temperature that allows the components to melt and mixMixing and cooling is controlled to prevent gas bubbles



“Super cooled liquid”AmorphousNon-crystalline



• Non crystalline ceramics can be modeled as viscous liquids

• The viscosity is a measure of the shear stress required to maintain a certain gradient of velocity.

( )dv/dyτ

η =• 1 Poise (P) = 1 dyne-s-cm-2

• 10 P = 1 Pa-s

Viscosity changes with temperature



Important temperatures are identified by the viscosity:•Strain point•Annealing point•Softening point•Working point•Melting point



•Tensile stresses cause fracture•When you bend an object, the tensile stress is greatest on the surface•Thermal tempering introduces a compressive residual stress on the surface



Steps in making ceramic products

• Material preparation– Mixing with binders: wet or dry– Sometimes with water to make a slurry

• Forming– Giving the ceramic its basic shape

• Dry pressing, isostatic pressing, hot pressing, slip casting, extrusion

• Thermal processing– Drying and binder removal (< 300°C)– Sintering: solid state diffusion at high temperature causes

binding• Small particles disappear, larger particles grow.

– Vitrification: Glassy coating that fills up cracks and pores



Slip Casting



“Green” compact is then sintered



Some particles have bonded together but there are pores between others.



These materials have high thermal insulation. They are used as furnace liners



Advanced Ceramics• Advanced ceramics are generally highly purified compounds

which are used by themselves, or in combination with other pure compounds– Si3N4, SiC, ZrO2, BN, Al2O3, MgO

• Properties are more controlled• Drive for high temperature engines requires materials that will

work at higher temperatures• Special insulating ceramics for the Space Shuttle• Corrosion resistance• Suitable electrical properties

Processing of CeramicsSteps in making ceramic productsAdvanced Ceramics

me 370/570 materials science and engineering-i chapter xiv...

Documents