Transient liquid phase, pressureless joining of aluminum nitride components
A monolithic, substantially hermetic joining or bonding of two or more aluminum nitride (“AlN”) ceramic components is made by promoting transient liquid phase sintering near the contact areas between the components. In a first approach, AlN particles are combined with a rare earth oxide sintering additive such as yttrium oxide (Y 2 O 3 ) in a joining paste can be applied between the joining surfaces of fired ceramic preformed components prior to final firing to weld the components together. In a second approach, the additive is added to green mixture, and the components having different shrinkage aspect ratios are mated and cofired in an atmosphere containing a partial pressure of the additive. The additive encourages wetting and diffusion of the liquid phases present on the surfaces of ceramic interface particles in the contact areas during final firing.
1. A process for joining ceramic components, said process comprising:
selecting at least two green state aluminum nitride (AlN) particle components having different aspect ratios,
and containing an amount of a transient liquid phase inducing additive comprising a first rare earth oxide in a concentration of about 1-5% by weight of the AlN present,
each of said components having a contact area shaped and dimensioned to intimately contact the contact area of an other of said components when said components are matingly contacted to one another;
placing said components in mating contact in a substantially contained atmosphere;
co-heating said components to a form a transient liquid phase along said contact areas for about 60 to 300 minutes;
allowing a vaporized amount of said first rare earth oxide to form in said substantially contained atmosphere, wherein said vaporized amount has a partial pressure of no more than about 1.0 atmosphere, thereby substantially pressurelessly inhibiting further vaporization of said transient liquid phase during said co-heating; and,
cooling said components to room temperature.
2. The process of claim 1 , which further comprises pressing said areas together during said co-heating.
3. The process of claim 2 , wherein said pressing comprises applying a pressure of at least 0.75 to 3.0 grams per square centimeter.
4. The process of claim 2 , wherein said pressing comprises:
orienting said components in a top and bottom orientation;
sprinkling a lubricating thin layer of AlN particles upon an exposed top surface of a first of said components, said exposed top surface being located apart from said contact areas; and,
placing a weight on top of said layer.
5. The process of claim 1 , wherein said atmosphere has a total pressure of no more than about 1.0 atm.
6. The process of claim 1 , wherein said first rare earth oxide is taken from a group consisting of yttrium oxide and oxides of the lanthanum rare earth series.
7. The process of claim 1 , wherein said aluminum nitride particles comprise at least 1% by weight oxygen.
8. The process of claim 1 , wherein said co-heating comprises raising the ambient temperature to between about 1780° C. and about 1840° C.
9. The process of claim 1 , wherein a linear shrinkage differential between said contact areas is between about 1 and 5% for a set of items identical to said components and sintered separately according to said co-heating step.
10. The process of claim 1 , which further comprises:
metallizing an exposed surface of at least one of said components after said cooling.
11. The process of claim 1 , which further comprises:
bonding a body to an outer surface of at least one of said components after said cooling, wherein said body comprises pathways selected from the group consisting of: electronic pathways; process gas pathways; temperature adjusting fluid pathways; vacuum channel pathways; and, combinations thereof.