Thermophysical Properties of Laser-Sintered Zr-ZrB2 Cermets

Abstract

Thermophysical properties between 293 and 1863 K were investigated for laser-sintered Zr-ZrB 2 cermets containing 30, 50, and 70 wt% Zr. The measured values of coefficient of thermal expansion of Zr-ZrB 2 cermets were larger than the predicted values due to the effect of Zr-O solid solution, which was formed during laser sintering. The order-disorder phase transition of Zr-O solid solution resulted in the sharp increase in heat capacity between 625 and 675 K. Thermal conductivities were calculated from measured densities, heat capacities, and thermal diffusivities. Thermal diffusivities at 473 K were 14.0, 12.2, and 8.0 mm 2 /s for 30Zr-ZrB 2 , 50Zr-ZrB 2 , and 70Zr-ZrB 2 , respectively. Thermal conductivities at 473 K were 38, 31, and 20 W . (m . K) À1 for 30Zr-ZrB 2 , 50Zr-ZrB 2 , and 70Zr-ZrB 2 , respectively. Electron contribution to thermal conductivity of the 70Zr-ZrB 2 cermet was determined using electrical resistivity measurements, which shows that total thermal conductivity mostly came from the electron contribution at high temperatures (1073-1473 K) while the phonon contribution was very small.

Heating rate effects on the thermal and mechanical properties of ZrB2

“…The thermal diffusivity of ZrB 2 has been measured by a number of researchers. 7,8,20,31,32 Typically, thermal diffusivity is measured by the laser flash technique, and values >0.25 cm 2 /s have been reported at room temperature for ZrB 2 -based materials. 7,29,31 However, the values are sensitive to changes in processing conditions (e.g., impurities, additives, densification time and temperature, etc.)…”

“…Thus, changes in thermal conductivity were attributed to changes in thermal diffusivity. The thermal diffusivity of ZrB 2 has been measured by a number of researchers 7,8,20,31,32 7,29,31 .…”

“…29,30 The physics of resin flow into a mold under pressure is similar to the seepage problem and so similar approaches have been used also to model the flow of resin into a mold containing fiber mats. 23,[31][32][33][34][35][36][37][38] The models are used in these cases to determine the resin flow front and mold filling times corresponding to different infiltration conditions.…”

Elevated temperature electrical resistivity measurements of zirconium diboride using the van der Pauw Method

“…× 0.10 cm thick, by surface grinding (FSG‐3A818; Chevalier, Santa Fe Springs, CA) and cylindrical grinding (608 Plain Grinder; Crystal Lake Grinders, North Fork, CA). Measured electrical resistivities were adjusted for porosity using the empirical relation in Equation where ρ e,exp , ρ e,ZrB2 , and ρ e,p are the electrical resistivities for the experimental measurements, ZrB 2 phase, and porosity, respectively, and ν p represents the volume fraction porosity.…”

“…Measured electrical resistivities were adjusted for porosity using the empirical relation in Equation (5). 35 where ρ e,exp , ρ e,ZrB2 , and ρ e,p are the electrical resistivities for the experimental measurements, ZrB 2 phase, and porosity, respectively, and ν p represents the volume fraction porosity. Equation (5) has been rewritten with inverse resistivities, in place of the conductivities, and ρ e,p −1 was assumed to be zero (i.e., pores have electrical conductivity of zero or infinite electrical resistance).…”