Process of microwave heating of powder materials
A process for heating powder materials by microwave radiation so that heating and sintering or melting progressively and directionally occurs within the powder materials. The process generally entails forming a structure from a powder by arranging the powder in a mass according to size of particles of the powder so that the particles are progressively arranged within at least a region of the mass from smallest to largest. The mass is then subjected to microwave radiation so that the particles within the mass progressively couple with the microwave radiation according to size, the smallest particles coupling first and heating faster than larger particles of the powder, and the largest particles coupling last and heating slower than smaller particles of the powder. As a result of the progressive arrangement of the particles, the mass is progressively and directionally heated by the microwave radiation.
1. A process of forming a structure from at least a first powder of at least a first material, the process comprising:
arranging the first powder in a mass according to size of particles of the first powder so that the particles are progressively arranged within at least a region of the mass from smallest to largest to define a direction of progression through the mass;
subjecting the mass to microwave radiation so that the particles within the mass progressively couple with the microwave radiation according to size, the smallest particles coupling first and heating faster than larger particles of the first powder, and the largest particles coupling last and heating slower than smaller particles of the first powder, such that as a result of the progressive arrangement of the particles the mass is progressively and directionally heated by the microwave radiation in the direction of progression through the mass; and then
interrupting the microwave radiation and allowing the mass to cool and form the structure.
2. The process according to claim 1 , wherein the mass is heated so as to sinter the particles and the mass is a sintered body on cooling.
3. The process according to claim 1 , wherein the mass is heated so as to completely melt the particles and the mass is a solidified body on cooling.
4. The process according to claim 3 , wherein the mass contacts a substrate so that the direction of progression through the mass is away from the substrate, and cooling of the mass is by directional solidification initiating at the substrate so that the mass is progressively and directionally solidified in the direction of progression.
5. The process according to claim 4 , wherein solidification of the mass is epitaxial so that the structure has the same crystallographic characteristics as the substrate.
6. The process according to claim 3 , wherein the first powder is arranged on a substrate and the structure is metallurgically bonded to the substrate as a result of the melting of the particles and cooling of the mass.
7. The process according to claim 6 , wherein the structure metallurgically bonds the substrate to a second substrate as a result of the melting of the particles and cooling of the mass.
8. The process according to claim 6 , wherein the structure is a coating on the substrate as a result of the melting of the particles and cooling of the mass.
9. The process according to claim 6 , wherein the structure is a coating on the substrate as a result of the melting of the particles and cooling of the mass.
10. The process according to claim 6 , wherein the first material and the substrate have substantially the same melting temperature.
11. The process according to claim 10 , wherein the first material and the substrate are superalloys.
12. The process according to claim 3 , wherein the first powder is arranged in a mold and consolidated within the mold while subjected to the microwave radiation to form a powder metallurgy body as a result of the melting of the particles and cooling of the mass.
13. The process according to claim 1 , wherein the first material is a metallic material.
14. The process according to claim 1 , wherein the particles within the mass are progressively layered in the direction of progression through the mass as a function of particle size.
15. The process according to claim 1 , wherein the particles within the mass are progressively graded in the direction of progression through the mass as a function of particle size.
16. The process according to claim 1 , wherein heating of the mass occurs without assistance from convective or radiant heating means.
17. The process according to claim 1 , wherein the first powder of the first material is arranged in the mass along with a second powder of a second material, and the first material has a lower melting temperature than the second material.
18. The process according to claim 17 , wherein the mass is heated so as to melt the particles of the first and second powders, and wherein at least some particles of the second powder are smaller in size than the largest particles of the first powder and melt before the largest particles of the first powder.
19. The process according to claim 1 , wherein the particles are arranged throughout the mass from smallest at one surface of the mass to largest at an opposite surface of the mass, and the mass is directionally heated from the one surface to the opposite surface when subjected to the microwave radiation.
20. The process according to claim 1 , wherein the particles are arranged within the mass from smallest within an interior region of the mass to largest at an exterior surface of the mass, and the mass is directionally heated from the inside out when subjected to the microwave radiation.