Recent Advances in Microwave and Millimeter-Wave Processing of Materials

Abstract

We are using 2.45 GHz (S-Band) microwave systems and an 83-GHz, gytrotron-based, millimeter-wave beam system in material processing and other areas. We use one 2.45 GHz system in preparation of nanophase metals, metal mixtures and metal oxides, via the patented continuous microwave polyol process, with potential for large scale, low cost production. Of interest are precious metals, mixtures of magnetic and nonmagnetic metals, and mixed metal oxides for ceramic precursors. The other S-Band systems are used to develop repair techniques for ceramic matrix composites where the repairs are heated to 200-1000°C. A portable, battery-powered system is being developed for field repairs, and promises to be much more practical than alternative approaches (e.g., heating blankets). The 83-GHz system is being used in rapid sintering of polycrystalline ceramic materials intended for use in high power solid state lasers, where the requirement if for sintering to transparency with high optical quality and good lasing efficiency. Transparent Yb-doped yttria has been produced with hybrid conventional/millimeter-wave sintering of nanophase powders, as well as theoretically dense YAG. Another application for the millimeterwave beam system is in consolidation and bonding of hard coatings to light alloys, such as SiC on titanium, where the beam system allows heating of the coating to very high temperatures without overheating the metallic substrate. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, where the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition. Results for these various areas will be presented and discussed.

Processing of Titanium and its Alloys by Microwave Energy

“…The Naval Research Laboratory has been investigating the use of several different microwave and millimeter-wave systems in material processing for over a decade [4][5][6][7]. Here we address cost reductions achievable by microwave sintering of low-cost titanium metal/alloy powders compacted into complex near-net shapes.…”

Microwave Sintering and Melting of Titanium Powder for Low-Cost Processing

“…This reduces the power needed and processing time for a considerable energy savings. We have been investigating the application of microwave and millimeter-wave processing to ceramic and metallic materials at the Naval Research Laboratory (NRL) for a number of years [2][3][4]. This paper presents our initial experimental results for titanium processing based on an S-Band microwave system in which titanium powder compacts are melted or sintered in a ceramic crucible [5].…”