Methods of forming articles including silicon carbide by spark plasma sintering
A method of forming silicon carbide by spark plasma sintering comprises loading a powder comprising silicon carbide into a die and exposing the powder to a pulsed current to heat the powder at a rate of between about 50° C./min and about 200° C./min to a peak temperature while applying a pressure to the powder. The powder is exposed to the peak temperature for between about 30 seconds and about 5 minutes to form a sintered silicon carbide material and the sintered silicon carbide material is cooled. Related structures and methods are disclosed.
1. A method of forming an article including silicon carbide by spark plasma sintering, the method comprising:
providing a powder comprising silicon carbide into a die;
pulsing a direct current through the powder in the die at a current density less than about 0.1 A/mm 2 to heat the powder to a peak temperature of at least about 1,950° C. and form a sintered silicon carbide structure;
exposing the sintered silicon carbide structure to a current density of between about 0.02 A/mm 2 and about 0.08 A/mm 2 while exposing the sintered silicon carbide structure to the peak temperature; and
cooling the sintered silicon carbide structure.
2. The method of claim 1 , further comprising selecting the die to comprise at least one tapered sidewall.
3. The method of claim 2 , further comprising selecting the taper to comprise about a 1° taper.
4. The method of claim 1 , further comprising selecting the die to comprise graphite exhibiting a coefficient of thermal expansion equal to about a coefficient of thermal expansion of the sintered silicon carbide structure within a temperature range of between about 1,950° C. and about 2,100° C.
5. The method of claim 1 , wherein forming a sintered silicon carbide structure comprises forming a silicon carbide structure having a density of about 3.21 g/cm 3 .
6. The method of claim 1 , wherein providing a silicon carbide powder into the die comprises providing the silicon carbide powder into the die substantially free of a lubricant.
7. The method of claim 1 , further comprising selecting the die to comprise isotropic graphite.
8. The method of claim 1 , wherein pulsing a direct current through the powder comprises pulsing the direct current through the powder in cycles, each cycle comprising pulsing the direct current for about 12 milliseconds followed by applying substantially no current for about 6 milliseconds.
9. The method of claim 1 , further comprising after cooling the sintered silicon carbide structure, exposing the sintered silicon carbide structure to the peak temperature again to increase a density of the sintered silicon carbide structure.
10. The method of claim 1 , further comprising after cooling the sintered silicon carbide structure, exposing the sintered silicon carbide structure to the peak temperature again to increase a density of the sintered silicon carbide structure by at least about 0.1 g/cm 3 .
11. The method of claim 1 , wherein forming a sintered silicon carbide structure comprises forming the sintered silicon carbide structure to have a density of at least about 3.178 g/cm 3 .
12. The method of claim 1 , wherein providing a powder comprising silicon carbide into a die comprises providing a powder comprising silicon carbide into a die comprising isotropic graphite having a grain size less than 3 μm.
13. The method of claim 1 , wherein providing a powder comprising silicon carbide into a die comprises providing a powder comprising silicon carbide into a die having a coefficient of thermal expansion between about 4.0 μm/(m·K) and about 5.0 μm/(m·K).
14. The method of claim 1 , wherein providing a powder comprising silicon carbide into a die comprises providing a powder comprising alpha phase silicon carbide into the die.
15. The method of claim 1 , wherein providing a powder comprising silicon carbide into a die comprises providing a powder comprising silicon carbide and boron carbide into the die.
16. The method of claim 1 , wherein providing a powder comprising silicon carbide into a die comprises providing a powder comprising between about 98 weight percent and about 100 weight percent silicon carbide into the die.
17. The method of claim 1 , wherein providing a powder comprising silicon carbide into a die comprises providing a powder into a die having a grain size less than about 3 μm into the die and a bulk density equal to or less than about 1.88 g/cm 3 into the die.