comparison of conventional and microwave sintering of metal solids
Author: langfeng1 Time: 2017-05-09
Figure 2 compare the thermal profiles of the compacts for both solid-state and super-solidus sintering heated in conventional and microwave furnaces. It is interesting to note that both straight and YAG-added 316L compacts couple with microwaves and get heated rapidly. In the case of microwave heating, temperature could only be measured from 700C onward. However, it takes about 5.5 minutes to heat the compacts from room temperature to 700C. The overall heating rate in the microwave furnace was around 45C /min. Taking into consideration the slow heating rate (5C/min) and isothermal holds at intermittent temperatures in the conventional furnace, there is about a 90 pct reduction in the process time during sintering of stainless compacts in the microwave furnace.
Microwave heating in a metallic material, such as stainless steel, is different than that observed in dielectric materials (mostly ceramics). Because they are good conductors , no internal electrical field is induced in metals. The induces electrical charge remains at the surface of the sample; hence, microwave heating is restricted only to the metal surface. This depth of penetration of microwaves in meals, also know s skin depth, typically varies between 0.1 and 10um and is inversely related to the electrical conductivity. For metallic systems, as the resistively increases with the increase in temperature, the skin depth too increase.