fig1 shows a gas turbine 1 with a flow duct 5 extending along an axis 3 and having an annular cross section for a working medium m . a number of blade stages are arranged in the flow duct 5 . in particular , a second guide blade stage 9 is arranged downstream of a first guide blade stage 7 along the axis 3 . furthermore , a second moving blade stage 13 is arranged downstream of a first moving blade stage 11 . the guide blade stages 7 , 9 in this case have a number of guide blades 21 arranged annularly on a peripheral turbine casing 15 and extending radially into the flow duct 5 . a moving blade stage 11 , 13 in this case has a number of moving blades 23 arranged annularly on an axial turbine rotor 19 and extending radially into the flow duct 5 . the flow of a working medium m is in this case generated in the form of a hot gas by a burner 17 . correspondingly to the annular cross section of the flow duct 5 , a number of such burners 17 are arranged around the axis 3 in an annular space not shown in the cross - sectional drawing of fig1 . a guide blade 21 and a moving blade 23 are shown diagrammatically in fig1 . a guide blade 21 has a blade tip 27 arranged along a blade axis 25 , a blade leaf 29 and a platform region 31 . the platform region 31 has a platform 33 extending transversely with respect to the blade axis 25 and a blade foot 35 . a moving blade 23 has a blade tip 37 arranged along a blade axis , a blade leaf 39 and a platform region 41 . the platform region 41 has a platform 43 extended transversely with respect to the blade axis 45 and a blade foot 47 . the platform 33 of a guide blade 21 and the platform 43 of a moving blade 23 thus form in each case part of a boundary 49 , 51 of the flow duct 5 for the working medium m which flows through the gas turbine 1 . the peripheral boundary 49 is in this case part of the peripheral turbine casing 15 . the rotor - side boundary 51 is in this case part of the turbine rotor 19 rotating when the gas turbine 1 is in the operating state . as indicated diagrammatically in fig1 and shown in detail in fig2 , in this case the platform 33 of a guide blade 21 and the platform 43 of a moving blade 23 are formed by sheet metal parts fixed to the blade leaf 29 , 39 . fig2 shows , to represent a platform region 31 , 41 , a platform region 61 . the first turbine blade 63 and second turbine blade 65 , shown in fig2 , in this case represents a first guide blade 21 of a first guide blade stage 7 and a second guide blade 21 , arranged directly axially downstream of this , of a second guide blade stage 9 . the first turbine blade 63 and the second turbine blade 65 also represent a first moving blade 23 , shown in fig1 , of the first moving blade stage 11 and a second moving blade 23 , directly arranged axially downstream of this , of the second moving blade stage 13 . preferably , however , the turbine blades 63 , 65 are guide blades . the first turbine blade 63 has a blade leaf 69 depicted in truncated form . the second turbine blade 65 in this case has a blade leaf 67 depicted in truncated form . in the case of the first turbine blade 63 and of the second turbine blade 65 , the platform region 61 has formed in it , at the foot of the blade leaf 67 , 69 , a platform 71 which extends transversely with respect to the blade axis 73 , 75 . in this case , the platform 71 is formed , on the one hand , by a first resilient elastic sheet metal part 79 shown in the first blade 63 and , on the other hand , by a second sheet metal part 77 shown in the second blade 65 . the first resilient elastic sheet metal part 79 is fastened to a first abutment 83 on one side of the blade leaf 69 , this side being shown in the case of the first turbine blade 63 . the second resilient elastic sheet metal part 77 is fastened to a second abutment 81 on the other side of the blade leaf 67 , this side being shown in the case of the second turbine blade 65 . the fastening may take place , for example , by welding or soldering and is in this case leak tight . the first abutment 83 and the second abutment 81 are in each case designed in the form of a groove , into which in each case the first resilient sheet metal part 79 and the second sheet metal part 77 butts in each case with its edge ending at the blade leaf 69 or at the blade leaf 67 . furthermore , the second resilient elastic sheet metal part 77 is held at a further abutment 85 of the second turbine blade 65 . in the present embodiment , the second sheet metal part 77 is attached to the abutment 85 . alternatively or additionally , the second sheet metal part 77 could also engage behind the further abutment 85 . the latter case applies to the first resilient elastic sheet metal part 79 of the first turbine blade 63 , which sheet metal part is held jointly with the second sheet metal part 77 at the further abutment 85 of the second turbine blade 67 . for this purpose , the first resilient elastic sheet metal part 79 engages loosely behind the further abutment 85 . the further abutment 85 is designed in the form of a bearing support for holding the second sheet metal part 77 and the first resilient elastic sheet metal part 79 and thus forms , on its side facing the first resilient elastic sheet metal part 79 , a sealing surface which serves as an abutment for the first resilient elastic sheet metal part 79 . a boundary 87 of the flow duct 5 is formed in the way outlined above between the first turbine blade 63 and the second turbine blade 65 by the first resilient elastic sheet metal part 79 of the first turbine blade 63 and by the second sheet metal part 77 of the second turbine blade 65 , the boundary 87 being continuous . thus , the use of a thin - walled platform 71 which is not load - bearing for producing the boundary 87 in the form of a second sheet metal part 77 and of a first resilient elastic sheet metal part 79 makes it possible at the same time for the sheet metal parts 77 , 79 to act as a sealing element . a sealing element of this type is at the same time sufficiently flexible to allow relative movement of the adjacent first turbine blade 63 and second turbine blade 65 , and nevertheless has a sufficient sealing action . this avoids the need for a sealing element , such as would have been necessary for the sealing off of parting planes in the case of hitherto conventional platforms lying opposite one another . potentially high - risk , structurally and thermally unfavorable reception structures of such a sealing element are consequently avoided . in the embodiment shown here , the platform 71 largely manages on its rear side 89 without a supporting structure or a load - bearing platform wall arrangement . instead , on the rear side 89 , a first cooling space 93 and a second cooling space 91 are formed , which make it possible to cool the platform 71 optimally in the region between the second turbine blade 65 and the first turbine blade 63 . thus , a platform edge design which is otherwise normally complicated to configure can , in connection with the further abutment 85 , have a simpler configuration without any thermally high - risk region . to assist the cooling in the cooling spaces 91 , 93 , the carrying structure 95 , 97 of the turbine blades 65 , 63 which starts from the foot of the blade leaf 67 , 69 is continued with an optimized configuration toward the blade foot 35 , 47 in fig1 . the sealing action , provided particularly at the further abutment 85 , of the second sheet metal part 77 and of the first resilient elastic sheet metal part 79 arises , depending on the type of operation of the first turbine blade 63 and of the second turbine blade 65 , preferably in the form of a guide blade 21 shown in fig1 or , if appropriate , also in the form of a moving blade 23 shown in fig1 . during the rotary operation of a turbine blade 65 , 63 in the form of a moving blade 23 on a turbine rotor 19 , to be precise , a centrifugal force acting from the foot of the blade leaf 67 , 69 in the direction 99 of the blade leaf 67 , 69 is generated as a result of rotation . a pressure drop , in the case of a guide blade 21 , also occurs in addition . it is also conceivable that the first resilient elastic sheet metal part 79 lies sealingly against the further abutment 85 by means of a prestress self - generated by the first resilient elastic sheet metal part 79 . the pressing force generated by the pressure drop can thereby be intensified . during the operation of a turbine blade 65 , 63 in the form of a guide blade 21 , shown in fig1 , on a peripheral turbine casing 15 , a pressure drop from the foot of the blade leaf 67 , 69 in the direction 99 of the blade leaf 67 , 69 is generated from the rear side 89 of a platform 71 by a cooling medium . the direction 99 of an abovementioned centrifugal force for a moving blade 23 also the direction 99 of the pressure drop for a guide blade 21 are identified in fig2 by an arrow . depending on the design of the turbine blade 67 , 69 as a moving blade 23 or as a guide blade 21 , therefore , the platform 71 in the form of the resilient elastic sheet metal parts 77 , 79 is pressed against the further abutment 85 by means of the centrifugal force or by means of the pressure drop . in this way , the sheet metal parts 77 , 79 of the platform 71 are fastened by centrifugal force or fastened by pressure and at the same time deploy their sealing action and separating action between the flow duct 5 , acted upon by hot gas , and the rear side 89 , acted upon by cooling medium , of the platform 71 . in summary , in order to configure a boundary 87 of a flow duct 5 of a gas turbine 1 as simply as possible , in the case of a turbine blade 63 , 65 with a blade leaf 67 , 69 arranged along a blade axis 73 , 75 and with a platform region 61 which , arranged at the foot of the blade leaf 67 , 69 , has a platform 71 extending transversely with respect to the blade axis 73 , 75 , it is proposed that the platform 71 be formed by a sheet metal part 77 , 79 fixed to the blade leaf 67 , 69 . this also applies to a gas turbine 1 with a flow duct 5 extending along an axis 3 of the gas turbine 1 and having an annular cross section for a working medium m , and with a second blade stage 9 , 13 arranged downstream of a first 7 , 11 along the axis 3 , a blade stage 7 , 9 , 11 , 13 having a number of annularly arranged turbine blades 63 , 65 extending radially into the duct 5 , according to the above concept .