Single crystal component and a method of heat treating a single crystal component

Abstract

A single crystal component comprising a first region and a second region. The component comprising a nickel base single crystal superalloy having a gamma phase matrix and gamma prime phase precipitates distributed in the gamma phase matrix. The first region of the component comprises a bi-modal distribution of gamma prime phase precipitates in the gamma phase matrix and the second region of the component comprising a uni-modal distribution of gamma prime phase precipitates in the gamma phase matrix. The uni-modal distribution of gamma prime phase precipitates consisting of primary cuboidal gamma prime phase precipitates and the bi-modal distribution of gamma prime phase precipitates consisting of primary cuboidal gamma prime phase precipitates and secondary spherical gamma prime phase precipitates and/or cuboidal gamma prime phase precipitates whereby the first region of the component has enhanced resistance to low cycle fatigue and the second region of the component has enhanced resistance to creep deformation.

1 . A single crystal component comprising a first region and a second region, the component comprising a nickel base single crystal superalloy having a gamma phase matrix and gamma prime phase precipitates distributed in the gamma phase matrix, wherein the first region of the component comprising a bi-modal distribution of gamma prime phase precipitates in the gamma phase matrix and the second region of the component comprising a uni-modal distribution of gamma prime phase precipitates in the gamma phase matrix, the uni-modal distribution of gamma prime phase precipitates consisting of primary cuboidal gamma prime phase precipitates and the bi-modal distribution of gamma prime phase precipitates consisting of primary cuboidal gamma prime phase precipitates and secondary spherical gamma prime phase precipitates and/or cuboidal gamma prime phase precipitates whereby the first region of the component has enhanced resistance to low cycle fatigue and the second region of the component has enhanced resistance to creep deformation. 
   
   
       2 . A single crystal component as claimed in  claim 1  wherein the primary cuboidal gamma prime phase precipitates in the second region of the component have edge lengths within the range 200 to 700 nm. 
   
   
       3 . A single crystal component as claimed in  claim 2  wherein the primary cuboidal gamma prime phase precipitates in the second region of the component have edge lengths within the range 250 to 500 nm. 
   
   
       4 . A single crystal component as claimed in  claim 1  wherein the volume fraction of primary cuboidal gamma prime phase precipitates in the second region of the component is at least 50 vol %. 
   
   
       5 . A single crystal component as claimed in  claim 4  wherein the volume fraction of primary cuboidal gamma prime phase precipitates in the second region of the component is at least 60 vol %. 
   
   
       6 . A single crystal component as claimed in  claim 5  wherein the volume fraction of primary cuboidal gamma prime phase precipitates in the second region of the component is 70 vol %. 
   
   
       7 . A single crystal component as claimed in  claim 1  wherein the gamma channel widths between the gamma prime phase precipitates in the second region of the component is within the range 10 to 100 nm. 
   
   
       8 . A single crystal component as claimed in  claim 7  wherein the gamma channel widths between the gamma prime phase precipitates in the second region of the component is within the range 30 to 60 nm. 
   
   
       9 . A single crystal component as claimed in  claim 1  wherein the primary cuboidal gamma prime phase precipitates in the first region of the component have edge lengths within the range of 200 to 700 nm. 
   
   
       10 . A single crystal component as claimed in  claim 9  wherein the primary cuboidal gamma prime phase precipitates in the first region of the component have edge lengths within the range of 250 to 500 nm. 
   
   
       11 . A single crystal component as claimed in  claim 1  wherein the secondary spheroidal and/or cuboidal gamma prime phase precipitates in the first region of the component have edge lengths within the range of 1 to 50 nm. 
   
   
       12 . A single crystal component as claimed in  claim 11  wherein the secondary spheroidal and/or cuboidal gamma prime phase precipitates in the first region of the component have edge lengths within the range of 5 to 20 nm. 
   
   
       13 . A single crystal component as claimed in  claim 1  wherein the secondary spheroidal and/or cuboidal gamma prime phase precipitates in the first region of the component are contained within the gamma channels between the primary cuboidal gamma prime phase precipitates. 
   
   
       14 . A single crystal component as claimed in  claim 1  wherein the component is a turbine blade comprising a root, a shank, a platform and an aerofoil. 
   
   
       15 . A single crystal component as claimed in  claim 14  wherein the first region comprises the root and the shank and the second region comprises the platform and the aerofoil. 
   
   
       16 . A single crystal component as claimed in  claim 15  wherein turbine blade comprises a shroud and the second region comprises the platform, the aerofoil and the shroud. 
   
   
       17 . A single crystal component as claimed in  claim 1  wherein the nickel base single crystal superalloy comprises a 3 rd , 4 th  or a 5 th  generation single crystal superalloy. 
   
   
       18 . A method of heat treating a single crystal component comprising a first region and a second region, the method comprising heat treating the component to produce primary cuboidal gamma prime precipitates in a gamma phase matrix in the first region and the second region, heat treating the component to produce secondary gamma prime phase precipitates in the first region. 
   
   
       19 . A method as claimed in  claim 18  wherein the method comprises solution heat treating the component, primary ageing the component and secondary ageing the component wherein the primary ageing of the component comprises cooling the first region of the component at a lower cooling rate than the cooling rate of the second region of the component during the cooling from the primary ageing temperature of the primary ageing heat treatment to room temperature. 
   
   
       20 . A method as claimed in  claim 18  wherein the method comprises solution heat treating the component, primary ageing the component and secondary ageing the component wherein the secondary ageing of the component comprises heating the second region of the component to a temperature above the solvus temperature of the fine secondary gamma prime precipitates while heating the first region of the component to a temperature below the solvus temperature of the fine secondary gamma prime precipitates during the secondary ageing heat treatment. 
   
   
       21 . A method as claimed in  claim 19  comprising providing insulation on the first region of the component during the primary ageing heat treatment or providing insulation on the first region of the component during the cooling part of the primary ageing heat treatment to reduce the cooling rate of the first region of the component after the primary ageing heat treatment. 
   
   
       22 . A method as claimed in  claim 19  comprising heating the first region of the component to further reduce the cooling rate of the first region of the component after the primary ageing heat treatment. 
   
   
       23 . A method as claimed in  claim 19  comprising submerging the first region of the component in a molten salt bath maintained at an elevated temperature to reduce the cooling rate of the first region of the component. 
   
   
       24 . A method as claimed in  claim 19  comprising directing a cooling fluid onto the surface of the second region of the component to reduce the cooling rate of the first region of the component relative to the cooling rate of the second region of the component. 
   
   
       25 . A method as claimed in  claim 20  comprising heating the second region of the component to the temperature above the solvus temperature of the fine secondary gamma prime precipitates to dissolve them. 
   
   
       26 . A method as claimed in  claim 20  comprising providing insulation on the second region of the component and locally heat treating the first region of the component to precipitate secondary gamma prime phase precipitates while the insulation maintains the second region of the component at a temperature below the secondary gamma prime solvus so that secondary gamma prime phase precipitates are not formed in the second region of the component. 
   
   
       27 . A method as claimed in  claim 18  comprising heating the whole of the component during part of the primary heat treatment, secondary heat treatment and coating heat treatment step and controlling the heating such that different temperature gradients are produced in the first region and the second region of the component.