Turbine blade platform with steam as well as air cooling

The air and steam cooled platform (4) of a turbine blade (1) has the air cooling forming an open circuit and the steam cooling forming a closed circuit. The platform is air-cooled in an outer region (28) and steam-cooled in an inner region (25). The outer and inner regions of the platform are cooled by impingement cooling by way of impingement cooling inserts.