Microwave in metallurgy: A new ERA based on extraordinary discoveries

Microwave energy has been in use for a variety of applications for over 50 years. These applications include communication, food processing, wood drying, rubber vulcanization, medical therapy, polymers, etc. In the last two decades microwave heating has also been applied very effectively and efficiently to heat and sinter many ceramics and other materials. Microwave heating is recognized for various advantages such as: time and energy savings, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. Until recently the use of microwaves in materials processing was confined only to ceramics and composites, but in the last 10 years of work on the interaction of microwaves with matter, the Penn State group has revolutionized the science and the technology of microwave processing by applying it to metallic materials. The advances have been described in terms of sintering of powder metals, metal-ceramic composites, brazing/joining and melting of bulk metals, etc. Many commercial powder-metal components of various alloy compositions including iron and steel, copper, aluminum, nickel, Mo, Co, Ti, W, Sn, etc. and their alloys have also been sintered in microwaves using a 2.45 GHz multimode microwave system, producing better properties than their conventional counterparts. In Japan microwave energy has been applied to make steel from iron ore with substantial energy savings and at least 50% reduction in CO ₂ emission. The implications of these findings are obvious in the field of powder metal technology.