The　studies　are　focused　on　the　complexions　in　the　WC-Co　cemented　carbides,　which　represent　the　phase-like　interfacial　state　at　the　WC/Co　interfaces.　A　series　of　experiments　were　designed　to　investigate　the　formation,　growth　and　transformation　behaviors　of　the　complexions.　It　was　found　that　the　complexions　with　cubic　structure　can　be　stabilized　by　quenching　or　by　dissolution　of　specific　elements　added　in　form　of　carbides　as　grain　growth　inhibitors.　The　characteristics　and　stabilization　conditions　of　the　complexions,　as　well　as　their　influences　on　the　interfacial　structures　and　mechanical　properties　of　the　cemented　carbides,　were　studied　in　detail　for　additions　of　various　inhibitors　such　as　VC,　Cr3C2,　TiC,　TaC　and　NbC.　The　results　disclose　that　the　existence　of　complexions　is　dominated　by　their　formation　energy　and　misfit　at　the　interface　between　the　complexion　and　WC.　The　stabilization　of　complexions,　on　one　hand,　inhibits　WC　grain　growth　effectively,　on　the　other　hand　separates　the　bonding　of　WC　and　Co,　thus　causes　decrease　of　the　resistance　against　intergranular　fracture　of　the　cemented　carbides.　It　is　proposed　that　tailoring　the　stability　of　complexions　by　matching　inhibitor　and　carbon　content　can　lead　to　both　the　high　fracture　toughness　and　high　strength　of　the　cemented　carbides.　(C)　2018　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.