NiCoCrAlY　and　CoNiCrAlY　bond　coats　used　for　thermal　barrier　coatings,　as　well　as　8　wt%　Y2O3-stabilized　ZrO2　(8YSZ)　ceramic　top　coat,　were　air　plasma　sprayed　on　Inconel　718　superalloy　and　then　subjected　to　thermal　exposure　at　950,　1050　degrees　C　in　air.　The　microstructural　evolution　and　oxidation　behaviour　of　bond　coats　were　comparatively　studied　using　scanning　electron　microscopy　(SEM)　and　energy　dispersive　spectroscopy　(EDS).　The　results　show　that　the　diffusion　of　Al　is　the　key　factor　causing　the　microstructural　changes,　resulting　in　three　zones　in　the　bond　coats:　outer　beta-depleted　zone　(OBDZ),　inner　beta-depleted　zone　(IBDZ)　and　beta-left　zone　(BLZ).　The　thickness　of　BLZ　decreases　with　the　increasing　of　the　heating　time　or　temperature.　NiCoCrAlY　bond　coat　with　higher　Al　content　presents　lower　beta-depletion　rate　and　smaller　Al　interdiffusion　coefficient,　and　the　oxide　scale　is　predominantly　composed　of　Al2O3　whereas　in　the　CoNiCrAlY　coating,　large　amount　of　non　alpha-alumina　oxides　have　been　found,　resulting　in　the　larger　oxidation　constant　at　the　stable　oxidation　period　and　higher　micro-crack　density　at　the　8YSZ/TGO　interface　and　8YSZ　coating.　The　results　reveal　that　NiCoCrAlY　bond　coat　presents　better　characteristics　of　oxidation　resistance　and　crack　resistance　when　used　for　thermal　barrier　coatings.