Hello Al(l),
I've searched all over google (web, images, groups, even froogle) and I have not found any information suggesting that the materials in my subject line exist in a form other than as a grit or as an exotic coating.
I've tried a local university's library, and amazon.com and found nothing on the topic of making solid parts of HfC, WC, or TaC.
Surely these materials would extend the search for HPHT materials in temperatures at least a thousand degrees higher than what is possible with a cemented carbide like WC.
Do you think these superlative materials be worth the trouble to fabricate?
-Scott