Field assisted sintering technique .28FAST.29 .2F Direct hot pressing Hot pressing

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figure iii: direct hot pressing


the basic idea of sintering electric current going through mold quite old. resistance heating of cemented carbide powders patented tayler 1933. method undergoing renewed interest. when applying standard (unpulsed) ac or dc current, referred fast direct hot pressing (fast dhp) , common term in many industries. common term rapid hot pressing (rhp) . when applying pulsed dc current, referred spark plasma sintering (sps) . both techniques summarized under generic term field assisted sintering technique (fast) .


the compelling reason shortening cycle time avoid grain growth , save energy. in direct hot pressing, mold directly connected electrical power. resistivity of mold , powder part generates heat directly in mold. results in high heating rates. additionally, leads significant increase in sintering activity of fine metal powder aggregates makes short cycle times of few minutes possible. further, process lowers threshold sintering temperature , pressure compared required in conventional sintering processes. previous 2 methods both closely dependent on intrinsic property of mold material, i.e., thermal conductivity. direct resistance heating, however, heat generated needed.


latest research suggests there no basic difference between sintering pulsed or unpulsed current (sps or fast dhp). in principle same improved sinter results (compared conventional hot pressing) can achieved direct hot pressing techniques, if improvement due in-situ heating of powder. if additional physical effects present, associated electrical current density (which highly dependent on powder type), pulsed current has additional beneficial effects, because during each pulse electrical current density peaks value higher dc current comparable heating power.








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