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

Abstract

The emerging reduction technologies for titanium from ore produce powder instead of sponge. Conventional methods for sintering and melting of titanium powder are costly, as they are energy intensive and require high vacuum, 10-6 Torr or better, since titanium acts as a getter for oxygen at high temperature, adversely affecting mechanical properties. Other melting processes such as plasma arcs have the additional problem of electrode consumption, and direct induction heating of the titanium powder is problematic. Microwave sintering or melting in an atmospheric pressure argon gas environment is potentially cost effective and energy efficient due to the possibility of direct microwave heating of the titanium powder augmented by hybrid heating in a ceramic casket. We are investigating this approach at the Naval Research Laboratory using an S–Band microwave system. The experimental setup and the results of melting and sintering experiments will be described including a rough estimate of energy usage.

Microwave Heating, Isothermal Sintering, and Mechanical Properties of Powder Metallurgy Titanium and Titanium Alloys

“…[20] Fortunately, the use of MW susceptors such as SiC can significantly enhance the heating efficacy. [21][22][23][24][25] Three mechanisms have been proposed to account for the effectiveness: heat radiation from the MW susceptors at low temperatures, the transformation of the MW-inert TiO 2 film on each Ti powder particle to oxygen-deficient MW-absorbing Ti oxides, and the volumetric heating of Ti powder particles by eddy currents. [25] However, the consistency and capabilities of MW heating of titanium powder remain largely unknown.…”

Powder metallurgy of titanium – past, present, and future

“…However, the heating of Ti by microwaves tends to be erratic [229]. For this reason, several studies have utilised microwave susceptors, such as SiC sample holders, to produce predictable and consistent heating of Ti powders [218][219][220]222,[224][225][226]. It has also been reported that TiH 2 is capable of being heated by microwave radiation without susceptors [230,231] to produce small CP-Ti samples with improved density and mechanical properties compared to those produced from metallic Ti powder [228].…”

“…There have been several studies on the heating susceptibility of Ti powders to microwave radiation [215][216][217][218][219], the densification and microstructure of microwave-sintered Ti [218][219][220][221][222][223][224][225][226][227][228], and the resulting mechanical properties [218,220]. However, the heating of Ti by microwaves tends to be erratic [229].…”

Effect of Microwave Sintering Parameters on the Physical and Mechanical Properties of Pure Ti and Blended Elemental Ti Alloys

“…Early research on MWS of metal powders such as Cu, Al, Fe and Co are available [4][5][6]. Recently research was also found on MWS of Ti, TiH2 and pre-alloyed Ti6Al4V powders [7][8][9][10][11][12][13]. These works made a significant contribution in improving the MW furnace design, which increased the sintering efficiency and consequently proved the advantages of MWS metallic materials, such as shorter processing time, enhanced densification and improved mechanical properties.…”