Reaction bonded SiC fabrication

Question 1

What is the first step in fabricating RBSiC?

Answer 1

1. a compact is formed with bimodal α-SiC (100um and 10um), carbon (as particles or a thermosetting polymer that polymerizes to leave a carbon char coating the SiC particles), and a polymer binder
   –> well-suited for extrusion or injection molding

Question 2

What is the second step in fabricating RBSiC?

Answer 2

2. the part is heated to remove the binder (thermolysis) and to pyrolyze the carbon containing polymer

Question 3

What is the third step in fabricating RBSiC?

Answer 3

3. It is immersed in molten silicon at 1500C (vacuum or inert atmosphere), Si is then wicked in through open pore channels
   –> Si and C react to form α and β-SiC, with residual porosity, or a dense part is formed with excess silicon filling the void spaces (10-40vol%)
   –> strength is retained up to ~1380C, close to the melting point of Si (1414C)

Question 4

What’s the effect of Al2O3 addition?

Answer 4

~ Al2O3 is poorly wetted by Si, and arrests infiltration and rxn

Question 5

What causes anisotropy in strength?

Answer 5

~ results from alignment of non-equiaxed α-SiC particles along the extrusion direction, or perpendicular to the pressing direction