  One of the major barriers in adapting the existing EB-PBF process parameters
to a new powder material system is controlling the preheating conditions such
that every layer of powder results in enough partial sintering to create a
coherent powder cake. To be able to understand the powder sintering process and
adapt it to other materials, we must look at the degree of sintering and the
effective thermal conductivity of the powder bed. An in-depth understanding of
these characteristics will help tailor the preheating conditions and
furthermore, make it easier to remove/de-powder intricate parts after build
completion without compromising the advantages of the preheating phenomenon.
This study evaluates the impact of preheating temperature on the in-situ powder
cake properties. Three different preheat temperatures, 650 {\deg}C, 690 {\deg}C
and 730 {\deg}C, are employed to a Ti-6Al-4V powder cake and in each standalone
build, unique powder-capture artefacts are fabricated to be able to analyze the
in-situ powder cake properties using X-ray computed tomography. An
empirically-derived model for thermal conductivity of the powder cake as a
result of changing the preheating temperatures, was obtained. The results
demonstrated that the effective thermal conductivity of the powder cake at a
given preheating temperature strongly depends on the packing density, contact
size ratio and coordination number. An increase in preheating temperature, lead
to a linear increase in the packing density (from 58.42% to 61.87%), contact
size ratio (from 0.45 to 0.48), coordination number (from 3.36 to 3.58) and the
effective thermal conductivity (from 1.75 W/m/K to 2.11 W/m/K) of the powder
cake.
