|Conductivity (Btu/(hr oF ft))||15||14.4|
There is about a factor-of-two difference in the thermal expansion characteristics between steel and bronze. Depending on the processing details (how well the steel and bronze actually bind together) there will be temperatures low enough that voids will open at the steel-bronze interface, and there will be temperatures high enough that the thermal stress rises above the yield (or ultimate) stress of the metals. The strength properties should show some interesting behavior at elevated temperatures because the bronze will be trying to rip apart the surrounding steel.
One of the things that bothers me about this contest is that they use some youtube videos of test firings of a DMLS chamber, and make it seem like what they are asking the contestants to do will be similar. DMLS is a process that results in a near-net shape part with a homogeneous material that is at least somewhat comparable to normal metal materials that have well characterized properties (especially at the high temperatures and temperature gradients that will be seen in this application, it's safe to assume that these are room temperature properties). Since they are made from a pre-alloyed metal powder, DMLS parts will have none of the CTE mismatch problems described above. As the disclaimer on the Shapeways site indicates: Higher temperatures may significantly change material properties.
There is the significant possibility that this contest will result in a black-eye for additive metal fabrication that is undeserved (FUD fighting is hard enough already). There are additive processes for real, reliable metal materials that are ready for prime-time engineering applications. Shapeway's current metal printing process is not one (though an indirect process based on investment casting could be quite suitable).
for some reason my comment is still in moderation on the Make site:
Update: The Make editor replied to my email inquiry and posted the comment; they posted this one too after a bit of delay.