Coherent　nanoprecipitates　formed　at　early-stage　decomposition　in　a　number　of　body-centered-cubic　(BCC)　Fe-based　alloys　with　nonmagnetic　solute　have　been　found　to　strengthen　their　magnetostriction　significantly.　Despite　that　the　differences　in　structure　and　properties　between　equilibrium　and　metastable　states　have　been　well　recognized　in　an　extensively-studied　system　Fe-Ga,　however,　a　non-equilibrium　time-temperature-transformation　(TTT)　diagram　for　manipulating　the　intermediate　nanoprecipitates　towards　further　enhancing　magnetostriction　is　still　lacking.　By　systemically　investigating　the　time-　and　temperature-dependent　early-stage　phase　transformations　of　the　magnetostriction-peak　composition　alloy　Fe73Ga27,　a　non-equilibrium　TTT　diagram　and　the　corresponding　time-temperature-property　(TTP)　relation　were　successfully　determined　in　this　work.　A　nose　temperature　(the　optimum　temperature　with　maximal　nucleation　rate)　of　∼400　°C　to　produce　face-centered-tetragonal　(FCT)　L60　nanoprecipitates　was　determined　in　the　diagram.　Above　the　nose　temperature,　the　L60　nanoprecipitates　grow　much　faster　and　become　incoherent　rapidly,　characterized　by　their　enlarged　tetragonality　c/a　towards　the　equilibrium　face-centered-cubic　(FCC)　L12　phase.　Below　the　nose　temperature,　the　L60　nanoprecipitates　grow　much　slower　and　keep　coherent　with　the　BCC　matrix　over　a　wide　aging　time　range,　but　the　low　atomic　diffusion　rate　and　the　coherent　elastic　energy　produce　extra　hexagonal　omega　nanoprecipitates　at　the　phase　transformation　front.　Based　on　the　non-equilibrium　TTT　diagram,　the　optimally-aged　random　polycrystalline　alloy　with　coherent,　dense　and　fine　L60　nanoprecipitates　can　exhibit　magnetostriction　as　large　as　180　ppm,　nearly　3　times　of　that　of　the　solution-treated　counterpart.　Consequently,　this　work　not　only　provides　a　processing　base　for　enhancing　magnetostriction　of　Fe-Ga　alloys,　but　also　may　offer　important　guidance　to　tailor　the　microstructure　of　other　nanoprecipitates-bearing　alloys　with　similar　diffusion-controlled　phase　transformation.　©　2022　Acta　Materialia　Inc.