Microwave sintering of titanium

Effective sintering of titanium requires the use of a high sintering temperature (>= 1200 degrees C), preferably in high vacuum (< 10(-2) Pa). This confines the heating and cooling rates to similar to 4 degrees C/min because of the limited thermal shock resistance of ceramic tube furnaces. Consequently, it leads to lengthy sintering cycles (10-12 hr). This work presents an assessment of microwave (MW) sintering of titanium. Titanium powders in the size ranges of <20 mu m, 45-63 mu m, and 100-150 mu m were used to make green samples with compaction pressures ranging from 200-800 MPa. Sintering was carried out at 1200 degrees C for 2 hr in a 3 kW MW furnace with a 2.45 GHz multimode cavity under a vacuum of 2-6x10(-3) Pa. The characteristics of MW heating of green titanium samples in vacuum are described in terms of the heating rate, vacuum fluctuations, and sparking discharge. The actual MW heating rate achieved from 350 degrees C to 1200 degrees C was 34 degrees C/min. The attendant densities are comparable to those attained by conventional vacuum sintering. Cross-sectional examinations revealed a fairly uniform pore distribution in MW-sintered samples made from either the coarse or fine titanium powder.