Patent Publication Number: US-2023138749-A1

Title: Selectively coated gas path surfaces within a hot section of a gas turbine engine

Description:
TECHNICAL FIELD 
     This disclosure relates generally to a gas turbine engine and, more particularly, to a hot section within a gas turbine engine. 
     BACKGROUND INFORMATION 
     A hot section within a gas turbine engine include various hot section components. These hot section components may be exposed to hot gases (e.g., combustion products) flowing through a core gas path extending through the hot section. This exposure to the hot gases may cause the hot section components to thermally expand or contract at different rates, particularly during transient operating conditions. Such differential thermal expansion or contraction may impart internal stresses on the hot section components. There is a need in the art to reduce thermally induced internal stresses within a hot section of a gas turbine engine. 
     SUMMARY 
     According to an aspect of the present disclosure, an apparatus is provided for a gas turbine engine. This gas turbine engine apparatus includes a hot section structure of the gas turbine engine. The hot section structure is configured with a plurality of surfaces respectively forming boundaries of a gas path through the hot section structure. The surfaces include a first surface and a second surface. The hot section structure includes metal and thermal barrier material. The first surface is formed by the metal. The second surface is formed by the thermal barrier material. 
     According to another aspect of the present disclosure, another apparatus is provided for a gas turbine engine. This gas turbine engine apparatus includes a gas path wall forming a peripheral boundary of a gas path within the gas turbine engine. The gas path wall includes a metal body and a thermal barrier coating disposed on the metal body. The metal body forms and is exposed to the gas path along a first portion of the peripheral boundary. The thermal barrier coating forms and is exposed to the gas path along a second portion of the peripheral boundary. 
     According to still another aspect of the present disclosure, another apparatus is provided for a gas turbine engine. This gas turbine engine apparatus includes a first platform, a second platform and a plurality of vanes. The first platform extends axially along and circumferentially about a centerline. The second platform extends axially along and circumferentially about the centerline. The vanes are arranged circumferentially about the centerline. Each of the vanes extends radially between and is connected to the first platform and the second platform. The vanes include a first vane. The first vane is configured with a thermal barrier coating. At least a portion of the first platform adjacent the first vane is configured without a thermal barrier coating. 
     The gas turbine engine apparatus may also include a combustor section and a vane array structure downstream of the combustor section along a gas path. The vane array structure may include the first platform, the second platform and the vanes. 
     The first portion of the peripheral boundary may be upstream of and/or next to the second portion of the peripheral boundary along the gas path. 
     The gas path wall may be configured as or otherwise include an exhaust wall. 
     The thermal barrier material may be or otherwise include ceramic. 
     The first surface may be contiguous with the second surface. 
     The gas path may extend longitudinally through the hot section structure. The first surface may be longitudinally aligned with the second surface. 
     The gas path may extend longitudinally through the hot section structure. The first surface may be laterally aligned with the second surface. 
     At least a portion of the first surface may be upstream of the second surface along the gas path. 
     The gas turbine engine apparatus may also include a combustor section upstream of the hot section structure along the gas path. 
     The hot section structure may be configured as or otherwise include a gas path wall extending along a side of the gas path. The gas path wall may include the first surface and the second surface. 
     The hot section structure may include a vane extending across the gas path. The vane may include the first surface and the second surface. 
     The thermal barrier material may form at least seventy-five percent (75%) of an external surface area of the vane that is exposed to the gas path. 
     The hot section structure may include a gas path wall and a vane projecting out from the gas path wall. The gas path wall may include the first surface. The vane may include the second surface. 
     At least a portion of the first surface may have a straight sectional geometry. At least a portion of the second surface may have a curved sectional geometry. 
     The hot section structure may be configured as or otherwise include a turbine exhaust structure. 
     The hot section structure may be configured as or otherwise include a turbine support structure. 
     The hot section structure may be configured as or otherwise include a vane array structure. 
     The present disclosure may include any one or more of the individual features disclosed above and/or below alone or in any combination thereof. 
     The foregoing features and the operation of the invention will become more apparent in light of the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic sectional illustration of a portion of a hot section of a gas turbine engine. 
         FIG.  2    is a cross-sectional illustration of a vane for a vane array structure of the hot section. 
         FIG.  3 A  is a schematic illustration of a portion of a vane array structure during uneven thermal expansion. 
         FIG.  3 B  is a schematic illustration of a portion of a vane array structure during uneven thermal contraction. 
         FIG.  4    is a sectional illustration of a portion of a vane array structure configured with thermal barrier material over a portion of each vane. 
         FIG.  5    is a cross-sectional illustration of a vane of the vane array structure taken along line  5 - 5  in  FIG.  4   . 
         FIG.  6    is a sectional illustration of a portion of the vane array structure configured with the thermal barrier material over an entirety of each vane. 
         FIG.  7    is a schematic sectional illustration of a portion of another hot section of the gas turbine engine. 
         FIG.  8    is a schematic sectional illustration of a portion of the hot section of  FIG.  7    configured with thermal barrier material. 
         FIG.  9    is a schematic illustration of the gas turbine engine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates a hot section  20  of a gas turbine engine. The term “hot section” describes herein a section of the gas turbine engine exposed to hot gases; e.g., combustion products. A (e.g., annular) core gas path  22  of the gas turbine engine, for example, extends longitudinally through the hot section  20  of  FIG.  1   . Examples of the hot section  20  include, but are not limited to, a combustor section, a turbine section and an exhaust section. However, for ease of description, the hot section  20  of  FIG.  1    is described below as a turbine section of the gas turbine engine. The hot section  20  of  FIG.  1    includes one or more rotor assemblies  24 A and  24 B (generally referred to as “24”) and a stationary structure  26 . 
     Each of the rotor assemblies  24  is configured to rotate about a rotational axis  28  of the gas turbine engine, which rotational axis  28  may also be an axial centerline of the gas turbine engine. Each of the rotor assemblies  24  includes a shaft  30 A,  30 B (generally referred to as “30”) and at least a hot section rotor  32 A,  32 B (generally referred to as “32”); e.g., a turbine rotor. The shaft  30  extends axially along the rotational axis  28 . The hot section rotor  32  is connected to the shaft  30 . The hot section rotor  32  includes a plurality of hot section rotor blades (e.g., turbine blades) arranged circumferentially around and connected to one or more respective hot section rotor disks. The hot section rotor blades, for example, may be formed integral with or mechanically fastened, welded, brazed, adhered and/or otherwise attached to the respective hot section rotor disk(s). 
     The stationary structure  26  of  FIG.  1    includes a hot section case  34  (e.g., a turbine case) and a hot section structure  36 . The hot section case  34  is configured to house at least a portion or an entirety of the hot section  20  and its components  24 A,  24 B and  36 . The hot section case  34  extends axially along and circumferentially about (e.g., completely around) the rotational axis  28 . 
     The hot section structure  36  is configured to guide the hot gases (e.g., combustion products) received from an upstream section  37 A of the hot section (e.g., a high pressure turbine (HPT) section) to a downstream section  37 B of the hot section (e.g., a low pressure turbine (LPT) section) through the gas path  22 . The hot section structure  36  of  FIG.  1    is also configured to support one or more of the rotor assemblies  24  within the hot section  20  and its hot section case  34 . The hot section structure  36  of  FIG.  1   , for example, is configured as a support structure such as, but not limited to, a turbine frame structure; e.g., a mid-turbine frame. This hot section structure  36  includes a vane array structure  38  and one or more structural supports  40  and  42 ; e.g., struts, frames, etc. 
     The vane array structure  38  includes a (tubular) outer platform  44 , a (e.g., tubular) inner platform  46  and a plurality of (e.g., stationary) vanes  48 . The outer platform  44  extends axially along and circumferentially about (e.g., completely around) the rotational axis  28  and the structure components  46  and  48 . This outer platform  44  may form an outer peripheral boundary of the gas path  22  through the vane array structure  38 . The inner platform  46  extends axially along and circumferentially about (e.g., completely around) the rotational axis  28 . This inner platform  46  may form an inner peripheral boundary of the gas path  22  through the vane array structure  38 . The vanes  48  are distributed circumferentially about the rotational axis  28  in an annular array radially between the outer platform  44  and the inner platform  46 . Each vane  48  extends radially between and to the outer platform  44  and the inner platform  46 , thereby projecting radially across the gas path  22 . Each vane  48  is (e.g., fixedly) connected to the outer platform  44  and/or the inner platform  46  at a respective end  50 ,  52  of the vane  48 . Each vane  48  may form a side (e.g., an inter-vane) boundary of the gas path  22 . With this arrangement, the hot gases flowing through the gas path  22  within the vane array structure  38  are radially bounded and guided by the outer platform  44  and the inner platform  46  and flow around (e.g., to either side of) each vane  48 ; see also  FIG.  2   . 
     The outer structural support  40  is connected to the outer platform  44  and the hot section case  34 . The outer structural support  40  of  FIG.  1   , for example, projects radially out from the outer platform  44  to the hot section case  34 . The outer structural support  40  may thereby structurally tie the vane array structure  38  to the hot section case  34 . 
     The inner structural support  42  is connected to the inner platform  46 , and rotatably supports one or more of the rotor assemblies  24 . The inner structural support  42  of  FIG.  1   , for example, includes (or is connected to) a bearing support frame  54 , and projects radially in from the inner platform  46  to the bearing support frame  54 . Each shaft  30 A,  30 B is rotatably supported by a respective bearing  56 A,  56 B (generally referred to as “56”) (e.g., a roller element bearing), which bearing  56  is mounted to and supported by the bearing support frame  54 . The inner support structure  42  may thereby structurally tie the rotor assemblies  24  to the vane array structure  38 . 
     During operation, gas path surfaces of the hot section structure  36  and its vane array structure  38  are exposed to (e.g., in contact with) the hot gases flowing through the gas path  22 . These gas path surfaces include those surfaces which form the boundaries of the gas path  22  within the vane array structure  38 . The gas path surfaces of  FIG.  1   , for example, include a radial inner surface  58  of the outer platform  44 , a radial outer surface  59  of the inner platform  46  and exterior surfaces  60  of the vanes  48 ; see also  FIG.  2   . The hot gas exposure may create relatively large thermal gradients across the vane array structure  38 , particularly during transient operating conditions. For example, a thickness  62  of a sidewall  64  of each vane  48  (see also  FIG.  2   ) may be thinner than a thickness  66  of a sidewall  68  of the outer platform  44  and/or a thickness  70  of a sidewall  72  of the inner platform  46 . Furthermore, while the hot gases flow along the outer platform  44 , the inner platform  46  and the vanes  48 , the hot gases also impinge against a leading edge  74  of each vane  48 . Each vane  48  and its vane sidewall  64  may therefore heat up (or cool down) faster than the outer platform  44  and its outer platform sidewall  68  and/or the inner platform  46  and its inner platform sidewall  72 . This may result in uneven thermal expansion (or contraction) of the structure components  44 ,  46  and  48  as shown, for example, in  FIGS.  3 A and  3 B . 
       FIG.  3 A  illustrates a rapid heating and, thus, thermally induced expansion of an exemplary one of the vanes  48  relative to the surrounding hot section structure  36 .  FIG.  3 B  illustrates a rapid cooling and, thus, thermally induced contraction of an exemplary one of the vanes  48  relative to the surrounding hot section structure  36 . Such uneven thermal expansion (or contraction) of the structure components  44 ,  46  and  48  may impart relatively high internal stresses on the vane array structure  38 , particularly at interfaces (e.g., connections) between the vanes  48  and the outer platform  44  and the inner platform  46 , at an interface (e.g., connection) between the outer platform  44  and the outer structural support  40  and/or at an interface (e.g., connection) between the inner platform  46  and the inner structural support  42 . 
     Referring to  FIGS.  4  and  5   , to reduce thermal gradients across the hot section structure  36  and, more particularly, its vane array structure  38 , thermal barrier material  76  is selectively applied to the hot section structure  36  and its vane array structure  38 . Each vane  48  of  FIGS.  4  and  5   , for example, includes a vane body  78  and a coating  80  of the thermal barrier material  76 ; e.g., thermal barrier coating (TBC). The vane body  78  (as well as bodies of the outer platform  44  and the inner platform  46  of  FIG.  4   ) are constructed from metal  82  such as, but not limited to, a nickel-based alloy; e.g., a nickel-based superalloy such as Inconel 625, Inconel 718, Inconel 792 or Mar-M-247. The thermal barrier material  76  may be a ceramic or other composite material such as, but not limited to, a ceramic oxide; e.g., Al 2 O 3 , SiO 2 , ZrO 2  or yttria-stabilized zirconia (YSZ). 
     The thermal barrier coating  80  of  FIGS.  4  and  5    is applied to an exterior of the respective vane body  78 , and may cover at least a major portion of the vane exterior. The thermal barrier coating  80  of  FIG.  4   , for example, (e.g., completely) covers an intermediate coated region  84  of the vane exterior with a spanwise height  86  (e.g., radial height) of at least seventy-five percent (75%) of an overall spanwise height  88  (e.g., radial height) of the respective vane  48  between the platforms  44  and  46 . The coated region height  86 , for example, may be greater than eighty or ninety percent (80-90%) of the vane height  88 . The coated region height  86  of  FIG.  4   , however, is less than the vane height  88  to provide one or more un-coated end regions  90 A and  90 B (generally referred to as “90”). Referring to  FIG.  5   , the coated region  84  may also extend (e.g., completely) around an outer perimeter of the respective vane  48 . The thermal barrier coating  80  may therefore (e.g., completely) form the leading edge  74 , a trailing edge  92  and lateral sides  94  of the respective vane  48  within the coated region  84 . The thermal barrier material  76  may thereby form at least seventy-five percent (75%) of an external surface area of the vane  48  that is exposed to the hot gases flowing through the gas path  22 . The thermal barrier material  76 , for example, may form more than eighty or ninety percent (80-90%) of the external surface area. 
     The thermal barrier material  76  of  FIGS.  4  and  5    forms a coated vane surface  96 . This coated vane surface  96  is an exterior gas path surface of the vane  48 ; e.g., a segment of the vane exterior surface  60  of  FIG.  1   . The coated vane surface  96  forms a boundary of and is directly exposed to the hot gases within the gas path  22 . 
     Referring to  FIG.  4   , each end region  90  may be configured without any thermal barrier material. The metal  82  of the vane body  78  may thereby form one or more uncoated vane surfaces  98 A and  98 B (generally referred to as “98”). Each uncoated vane surface  98  is an exterior gas path surface of the vane  48 ; e.g., a segment of the vane exterior surface  60  of  FIG.  1   . Each uncoated vane surface  98  forms a boundary of and is directly exposed to the hot gases within the gas path  22 . Each uncoated vane surface  98 A,  98 B of  FIG.  4    extends between and is contiguous with coated vane surface  96  and the respective platform surface  58 ,  59 . 
     The outer platform  44  and/or the inner platform  46  may also be configured without any thermal barrier material. The metal  82  of the outer platform  44  may thereby form at least a portion or an entirety of the outer platform inner surface  58 . The metal  82  of the inner platform  46  may similarly from at least a portion or an entirety of the inner platform outer surface  59 . 
     With the foregoing arrangement, the thermal barrier coating  80  of  FIGS.  4  and  5    insulates the hot gases flowing though the gas path  22  from the underlying metal  82  of the respective vane body  78  in the coated region  84 . Thermal expansion (or contraction) of the underlying metal  82  of the respective vane body  78  in the coated region  84  may thereby be slowed to more closely match the thermal expansion (or contraction) of the metal  82  of the outer platform  44  and/or the thermal expansion (or contraction) of the metal  82  of the inner platform  46 . This may reduce thermal gradients across the vane array structure  38  and, thus, reduce internal stresses on the vane array structure  38 . 
     In some embodiments, referring to  FIG.  6   , the thermal barrier coating  80  and the associated coated region  84  may extend spanwise (e.g., radially) to the outer platform  44  and/or the inner platform  46 . The coated vane surface  96  thereby extends between and is contiguous with the outer platform inner surface  58  and the inner platform outer surface  59 . The thermal barrier coating  80  of  FIG.  6   , for example, completely covers the exterior of the vane body  78 . 
     In some embodiments, referring to  FIGS.  4  and  6   , each coated vane surface  96  may be longitudinally (e.g., axially along the rotational axis  28 ) aligned with and overlap one or more uncoated gas path surfaces of the hot section structure  36 ; e.g., the surfaces  58 ,  59 ,  98 A and/or  98 B. Each coated vane surface  96  may also (or alternatively) be laterally (e.g., circumferentially about the rotational axis  28 ) aligned with and overlap one or more uncoated gas path surfaces of the hot section structure  36 ; e.g., the surfaces  58 ,  59 ,  98 A and/or  98 B. 
     In some embodiments, each coated vane surface  96  may be upstream of at least a portion (or an entirety) of one or more uncoated gas path surfaces of the hot section structure  36 ; e.g., the surfaces  58  and  59 . Each coated vane surface  96  may also or alternatively be downstream of at least a portion (or an entirety) of one or more uncoated gas path surfaces of the hot section structure  36 ; e.g., the surfaces  58  and  59 . 
       FIG.  7    illustrates another hot section  20 ′ of the gas turbine engine. This hot section  20 ′ may be configured as a turbine exhaust section of the gas turbine engine. The hot section  20 ′ of  FIG.  7    includes a hot section structure  36 ′ (e.g., a duct) with a plurality of gas path walls such as an inner wall  100  and an outer wall  102 . 
     The inner wall  100  extends longitudinally between and to an upstream end  104  and a downstream end  106 . The inner wall  100  includes an upstream segment  108 , a downstream segment  109  and an intermediate segment  110 . 
     The inner wall upstream segment  108  is disposed at the inner wall upstream end  104 . The inner wall upstream segment  108  of  FIG.  7   , for example, extends substantially axially along the rotational axis  28  from the inner wall upstream end  104  to the inner wall intermediate segment  110 . This inner wall upstream segment  108  may be parallel with the rotational axis  28 , or at least a (e.g., downstream) portion of the inner wall upstream segment  108  may have a slight slope with a radial rise to an axial run of less than, for example, 0.15; e.g., less than 0.1. The radial rise to the axial run, of course, may alternatively be greater than 0.15 in other embodiments; e.g., between 0.15 and 0.3. At least a (e.g., upstream) portion (or an entirety) of the inner wall upstream segment  108  may have a straight sectional geometry when viewed, for example, in a reference plane parallel with the rotational axis  28 . At least a (e.g., downstream) portion (or an entirety) of the inner wall upstream segment  108  may also or alternatively have a slightly curved sectional geometry when viewed, for example, in the reference plane. 
     The inner wall downstream segment  109  is disposed at the inner wall downstream end  106 . The inner wall downstream segment  109  of  FIG.  7   , for example, extends substantially radially inward from the inner wall downstream end  106  to the inner wall intermediate segment  110 . This inner wall downstream segment  109  may be perpendicular to the rotational axis  28 , or at least a (e.g., upstream) portion of the inner wall downstream segment  109  may have a slight slope with a radial rise to an axial run of greater than, for example, 4; e.g., greater than 6. The radial rise to the axial run, of course, may alternatively be less than 4 in other embodiments; e.g., between 2 and 4. At least a (e.g., downstream) portion (or an entirety) of the inner wall downstream segment  109  may have a straight sectional geometry when viewed, for example, in the reference plane. At least a (e.g., upstream) portion (or an entirety) of the inner wall downstream segment  109  may also or alternatively have a slightly curved sectional geometry when viewed, for example, in the reference plane. 
     The inner wall intermediate segment  110  is arranged and extends longitudinally between the inner wall upstream segment  108  and the inner wall downstream segment  109 . This inner wall intermediate segment  110  provides a transition (e.g., a turning segment) between the inner wall upstream segment  108  and the inner wall downstream segment  109 . At least a portion or an entirety of the inner wall intermediate segment  110 , for example, has a curved sectional geometry when viewed, for example, in the reference plane that transitions from the substantially axial trajectory of the inner wall upstream segment  108  to the substantially radial trajectory of the inner wall downstream segment  109 . 
     The outer wall  102  extends longitudinally between and to an upstream end  112  and a downstream end  114 . The outer wall  102  includes an upstream segment  116 , a downstream segment  117  and an intermediate segment  118 . 
     The outer wall upstream segment  116  is disposed at the outer wall upstream end  112 . The outer wall upstream segment  116  of  FIG.  7   , for example, extends substantially axially along the rotational axis  28  from the outer wall upstream end  112  to the outer wall intermediate segment  118 . This outer wall upstream segment  116  may be parallel with the rotational axis  28 , or at least a (e.g., downstream) portion of the outer wall upstream segment  116  may have a slight slope with a radial rise to an axial run of less than, for example, 0.15; e.g., less than 0.1. The radial rise to the axial run, of course, may alternatively be greater than 0.15 in other embodiments; e.g., between 0.15 and 0.3. At least a (e.g., upstream) portion (or an entirety) of the outer wall upstream segment  116  may have a straight sectional geometry when viewed, for example, in a reference plane parallel with the rotational axis  28 . At least a (e.g., downstream) portion (or an entirety) of the outer wall upstream segment  116  may also or alternatively have a slightly curved sectional geometry when viewed, for example, in the reference plane. 
     The outer wall downstream segment  117  is disposed at the outer wall downstream end  114 . The outer wall downstream segment  117  of  FIG.  7   , for example, extends substantially radially inward from the outer wall downstream end  114  to the outer wall intermediate segment  118 . This outer wall downstream segment  117  may be perpendicular to the rotational axis  28 , or at least a (e.g., upstream) portion of the outer wall downstream segment  117  may have a slight slope with a radial rise to an axial run of greater than, for example, 4; e.g., greater than 6. The radial rise to the axial run, of course, may alternatively be less than 4 in other embodiments; e.g., between 2 and 4. At least a (e.g., downstream) portion (or an entirety) of the outer wall downstream segment  117  may have a straight sectional geometry when viewed, for example, in the reference plane. At least a (e.g., upstream) portion (or an entirety) of the outer wall downstream segment  117  may also or alternatively have a slightly curved sectional geometry when viewed, for example, in the reference plane. 
     The outer wall intermediate segment  118  is arranged and extends longitudinally between the outer wall upstream segment  116  and the outer wall downstream segment  117 . This outer wall intermediate segment  118  provides a transition (e.g., a turning segment) between the outer wall upstream segment  116  and the outer wall downstream segment  117 . At least a portion or an entirety of the outer wall intermediate segment  118 , for example, has a curved sectional geometry when viewed, for example, in the reference plane that transitions from the substantially axial trajectory of the outer wall upstream segment  116  to the substantially radial trajectory of the outer wall downstream segment  117 . 
     The hot section structure  36 ′ (e.g., the duct) is connected to one or more external (e.g., support) structures  120  and  122  at (e.g., on, adjacent or proximate) the inner wall downstream end  106  and the outer wall downstream end  114 . The gas path walls  100  and  102  provide a thermal buffer between the gas path  22  extending longitudinally through the hot section structure  36 ′ and the external structures  120  and  122 . The hot section structure  36 ′ and its gas path walls  100  and  102  may thereby heat up (or cool down) quicker than the external structures  120  and  122 , particularly during transient conditions. This may result in the hot section structure  36 ′ pushing radially outward against the external structures  120  and  122  where the gas path walls  100  and  102  heat up quicker than the external structures  120  and  122 , or pulling radially inwards against the external structures  120  and  122  where the gas path walls  100  and  102  cool down quicker than the external structures  120  and  122 . Such uneven thermal expansion (or contraction) of the components  36 ′,  120  and  122  may impart relatively high internal stresses on the hot section structure  36 ′, particularly at an interface (e.g., connection) between the inner wall  100  and the external structure  120  and/or at an interface (e.g., connection) between the outer wall  102  and the external structure  122 . 
     Referring to  FIG.  8   , to reduce thermal gradients across the hot section assembly, thermal barrier material  124  is selectively applied to the hot section structure  36 ′ and its gas path walls  100  and  102 . Each gas path wall  100 ,  102  of  FIG.  8   , for example, includes a wall body  126 ,  128  and a wall coating  130 ,  132  of the thermal barrier material  124 ; e.g., inner wall thermal barrier coating (TBC). The wall body  126 ,  128  is constructed from metal  134  such as, but not limited to, a nickel-based alloy; e.g., a nickel-based superalloy such as Inconel 625, Inconel 718, Inconel 792 or Mar-M-247. The thermal barrier material  124  may be a ceramic or other composite material such as, but not limited to, a ceramic oxide; e.g., Al 2 O 3 , SiO 2 , ZrO 2  or yttria-stabilized zirconia (YSZ). 
     The inner wall thermal barrier coating  130  of  FIG.  8    is applied onto the inner wall body  126  along the inner wall segments  109  and  110 . This inner wall thermal barrier coating  130  thereby extends longitudinally along the inner wall body  126  from the inner wall upstream segment  108  to the inner wall downstream end  106 . The thermal barrier material  124  of  FIG.  8    forms a coated inner wall surface  136 . This coated inner wall surface  136  is a gas path surface of the inner wall  100 . The coated inner wall surface  136  forms a boundary of and is directly exposed to the hot gases within the gas path  22 . 
     The inner wall upstream segment  108  of  FIG.  8    is configured without any thermal barrier material. The metal  134  of the inner wall body  126  may thereby form an uncoated inner wall surface  138 . This uncoated inner wall surface  138  is a gas path surface of the inner wall  100 , which is upstream and contiguous with the coated inner wall surface  136 . The uncoated inner wall surface  138  forms a boundary of and is directly exposed to the hot gases within the gas path  22 . 
     The outer wall thermal barrier coating  132  of  FIG.  8    is applied onto the outer wall body  128  along the outer wall segments  116 - 118 . This outer wall thermal barrier coating  132  thereby extends longitudinally along the outer wall body  128  from the outer wall upstream end  112  to the outer wall downstream end  114 . The thermal barrier material  124  of  FIG.  8    forms a coated outer wall surface  140 . This coated outer wall surface  140  is a gas path surface of the outer wall  102 . The coated outer wall surface  140  forms a boundary of and is directly exposed to the hot gases within the gas path  22 . 
     With the foregoing arrangement, the thermal barrier coatings  130  and  132  of  FIG.  8    insulate the hot gases flowing through the gas path  22  from the underlying metal  134  of the inner wall  100  and the outer wall  102 . Thermal expansion (or contraction) of the underlying metal  134  of the respective gas path wall  100 ,  102  where coated may thereby be slowed to more closely match the thermal expansion (or contraction) of metal of the respective exterior structure  120 ,  122 . This may reduce thermal gradients across the hot section assembly and, thus, reduce internal stresses on the respective gas path wall  100 ,  102 . 
       FIG.  9    is a schematic illustration of a gas turbine engine  142  which may include one or more of the hot sections  20  and/or  20 ′. This gas turbine engine  142  includes a compressor section  144 , a combustor section  145 , a turbine section  146  and an exhaust section  147 . The gas path  22  extends longitudinally sequentially through the compressor section  144 , the combustor section  145 , the turbine section  146  and the exhaust section  147  from an upstream engine inlet  148  to a downstream engine exhaust  150 . During operation, air enters the gas turbine engine  142  and the gas path  22  through the engine inlet  148 . This air is compressed by the compressor section  144  and directed into the combustor section  145 . Within the combustor section  145 , the compressed air is mixed with fuel and ignited to produce the hot gases; e.g., combustion products. These hot gases are directed out of the combustor section  145  and into the turbine section  146  to drive compression within the compressor section  144 . The hot gases then flow through the exhaust section  147  and are exhausted form the gas turbine engine  142  through the engine exhaust  150 . 
     The gas turbine engine  142  may be configured as a geared gas turbine engine, where a gear train connects one or more shafts to one or more rotors. The gas turbine engine  142  may alternatively be configured as a direct drive gas turbine engine configured without a gear train. The gas turbine engine  142  may be configured with a single spool, with two spools, or with more than two spools. The gas turbine engine  142  may be configured as a turbofan engine, a turbojet engine, a turboprop engine, a turboshaft engine, a propfan engine, a pusher fan engine or any other type of gas turbine engine. The gas turbine engine  142  may alternative be configured as an auxiliary power unit (APU) or an industrial gas turbine engine. The present disclosure therefore is not limited to any particular types or configurations of gas turbine engines. 
     While various embodiments of the present disclosure have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the disclosure. For example, the present disclosure as described herein includes several aspects and embodiments that include particular features. Although these features may be described individually, it is within the scope of the present disclosure that some or all of these features may be combined with any one of the aspects and remain within the scope of the disclosure. Accordingly, the present disclosure is not to be restricted except in light of the attached claims and their equivalents.