High Density Reactive Composite Powders

Tungsten is used by military and civilian organizations as a penetrator and densifier due to its high

density and strength. Tungsten components may be even more attractive in kinetic projectiles if their

rapid oxidation could be triggered by impact. However, igniting tungsten is difficult, probably because

of its high heat capacity and relatively high ignition temperature. This study is aimed to prepare and

characterize composite powders comprising tungsten, titanium, and boron. The targeted density of the

composite material was that of steel, 8050 kg/m3. Both boron and titanium have high heats of

combustion; more importantly, they are also capable of a highly exothermic intermetallic reaction

producing TiB and TiB2. This reaction is expected to be very rapid, and cause fast temperature increase

of composite particles, assisting ignition of tungsten. Further, it is expected that at high temperatures

all metals will proceed to oxidize producing thermodynamically favorable oxides as the final combustion

products. In this study, composite materials were prepared by mechanical milling. In order to achieve

fine mixing, tungsten was first balled milled with boron. Both metals are hard and produce a finely

mixed composite. This composite was then milled with titanium to produce the targeted ternary

compound. SEM imaging showed that the produced powder includes equiaxial fine particles with all

three components mixed on the submicron scale. Particle size distributions were measured using low-

angle laser light scattering. The mean particle size was 11.2 µm and the standard deviation was 1.7 µm.

Differential Thermal Analysis was performed for milled binary B·Ti composite as a reference, and for the

ternary W·B·Ti powders. Results showed an exothermic reaction between boron and titanium occurring

in the temperature range of 700-1400 K. XRD analyses of powders heated to 1400 K confirmed

formation of multiple new phases including all three elements. Powders were fed into a CO2 laser beam

and burned in air. Burn times of the particles and their combustion temperatures were measured.

Results will be presented and discussed in this talk.