It　was　known　for　long　that　Ni-Al　composite　powders　can　be　used　to　deposit　self-bonding　coating　as　a　bond　coat　for　common　ceramic　coatings　due　to　the　exothermic　reaction　between　Ni　and　Al.　However,　it　was　found　that　with　commercial　Ni-Al　composite　powders　with　a　large　particle　size,　it　is　difficult　to　ignite　the　self-propagating　reaction　between　Ni　and　Al　to　form　Ni-Al　intermetallics　by　plasma　spraying.　In　this　study,　Ni-Al　composite　powder　particles　of　different　sizes　were　used　to　prepare　Ni-Al　intermetallics-based　coatings　by　plasma　spraying.　The　dependencies　of　the　exothermic　reaction　between　Ni　and　Al　and　the　coating　microstructure　on　powder　particle　size　and　spray　parameters　were　investigated.　The　phase　composition,　microstructure,　porosity　and　oxide　content　of　the　coatings　were　characterized　by　x-ray　diffraction,　scanning　electron　microscope　and　image　analyzing.　The　results　show　that　particle　size　of　Ni-Al　composite　powders　is　the　dominant　factor　controlling　the　exothermic　reaction　for　the　formation　of　Ni-Al　intermetallics　during　plasma　spraying.　When　the　powders　larger　than　about　50 μm　are　used,　the　reaction　forming　aluminide　cannot　complete　even　by　heating　of　plasma　flame　generated　at　high　plasma　arc　power.　However,　when　smaller　powders　less　than　50 μm　are　used,　the　exothermic　reaction　can　completely　occur　rapidly　in　plasma　spraying,　contributing　to　heating　of　Ni-Al　droplets　to　the　highest　temperature　for　development　of　the　self-bonding　effect.　The　positive　relationship　between　molten　droplet　temperature　and　tensile　adhesive　strength　of　the　resultant　coatings　is　recognized　to　confirm　the　contribution　of　high　droplet　temperature　to　the　adhesive　or　cohesive　strength.　©　2021,　ASM　International.