The　evolution　of　mechanical　properties,　namely　Young＇s　modulus,　hardness,　fracture　toughness　and　residual　stresses　of　air　plasma-sprayed　8　wt%　Y2O3-stabilized　ZrO2　thermal　barrier　coatings　(TBCs)　subjected　to　thermal　exposure　at　1100　degrees　C,　was　evaluated　based　on　an　instrumented　indentation　testing　system.　It　is　found　that　the　variation　of　Young＇s　modulus　and　hardness　with　the　increase　of　thermal　exposure　time　can　be　divided　into　two　regimes:　a　rapid　initial　increase,　followed　by　a　more　gradual　increase.　Conversely,　fracture　toughness　decreased　from　the　initial　value　of　1.48-1.05　MPa　m(1/2)　after　350　h,　indicating　the　degradation　of　TBCs.　And　the　corresponding　residual　stress　in　top　coat　varied　from　the　deposition　stress　of　-29.9　MPa　to　a　maximum　of　-56.0　MPa　within　100　h,　and　then　decreased　to　-15.0　MPa　after　350　h.　The　evolution　of　mechanical　properties　was　correlated　with　microstructural　changes　in　the　top　coat.　Microstructure　observations　revealed　that　thermally　grown　oxide　(TGO)　formed　at　the　interface　between　ceramic　coat　and　bond　coat,　and　was　predominantly　comprised　of　Al2O3　layer,　along　with　some　oxide　clusters　of　(Cr,　Al)(2)O-3,　(Co,　Ni)(Cr,　Al)(2)O-4　and　NiO.　The　growth　of　TGO　followed　a　parabolic　law　with　a　rate　constant　of　0.13236　mu　m(2)/h.　After　350　h,　porosity　in　8YSZ　coatings　was　reduced　from　8.39%　to　5.79%　as　a　result　of　activated　diffusion-controlled　sintering.　(C)　2016　Elsevier　Ltd　and　Techna　Group　S.r.l.　All　rights　reserved.