权利要求：
CLAIMS:
1. A method of manufacturing an interlayer comprising a first material and a second material, the method comprising: providing a first surface 301; forming a first structure 302 from the first material on the first surface using an additive manufacturing technique, wherein the first structure comprises at least one surface which is not in contact with the first surface and faces towards the first surface at an angle of less than 90 degrees; forming a second structure 303 from the second material, such that the second structure conforms to the first structure on a side of the first structure opposite the first surface; wherein the first structure and the second structure together form the interlayer, and the first structure and second structure are shaped such that separating the first and second structure requires deforming one or both of the first or second structure.
2. A method according to claim 1, wherein the additive manufacturing technique is a powder bed technique, and comprises: providing a layer of powder of the first material on the first surface; bonding a portion of the layer of powder to form a part of the first structure; providing a further layer of powder on top of the sintered powder; repeating the steps of bonding and providing further layers of powder to form the first structure.
3. A method according to claim 2, wherein the step of bonding the portion of the layer of powder comprises melting or sintering the portion of the layer of powder by providing heat to the powder using a laser or electron beam.
4. A method according to claim 2, wherein the step of bonding the portion of the layer of powder comprises applying a binder to the portion of the layer of powder or selectively curing a binder present in the portion of the layer of powder, and wherein the additive manufacturing technique further comprises sintering the portions of the layers of powder to form the first structure after completion of all steps of binding and providing further layers.
5. A method according to any preceding claim, wherein the first material has a higher melting point than the second material, and wherein the step of forming the second structure comprises providing the second material as a liquid, flowing the second material onto the first structure, and allowing the second material to solidify.
6. A method according to any of claims 1 to 4, wherein the step of forming the second structure comprises providing the second material as a powder, packing the powder on the side of the first structure opposite the first surface, and sintering the powder.
7. A method according to any of claims 1 to 4, wherein the step of forming the second structure comprises providing the second material as a solid, and pressing the second material against the side of the first structure opposite the first surface with sufficient pressure that the second material conforms to the shape of the side of the first structure opposite the first surface.
8. A method according to any preceding claim, and comprising applying a layer of the second material to the side of the first structure opposite the first surface prior to forming the second structure.
9. A method according to claim 8, wherein the layer of the second material is applied by one of: application of a foil of the second material to the surface; physical vapour deposition; or chemical vapour deposition.
10. A method according to any of claims 1 to 4, wherein the second structure is formed during formation of the first structure, by the same additive manufacturing technique as the first structure.
11. A method according to any preceding claim, wherein the first structure is a periodic structure which repeats in at least one direction parallel to the first surface.
12. A method according to any preceding claim, wherein the first structure has a cross section parallel to the first surface which varies such that the cross section of the
first structure decreases monotonically through the thickness of the interlayer from the first surface.
13. A method according to claim 12, wherein the function relating the cross section of the first structure to the depth through the interlayer is one of: a linear function; a sigmoid function; a polynomial function; or a cubic function.
14. A method according to claim 12, wherein the first structure has first, second, third, and fourth average coefficients of thermal expansion, aCTE, defined such that each aCTE is the average coefficient of thermal expansion of the first and second material, weighted by their volume fraction, over one quarter of the thickness of the interlayer; and wherein the first aCTE is defined from the surface of the interlayer opposite the first surface; the second aCTE is defined from the midpoint of the thickness of the interlayer towards the surface of the interlayer opposite the first surface and is less than the first aCTE; the third aCTE is defined from the midpoint of the interlayer towards the first surface and is less than the second aCTE; the fourth aCTE is defined from the first surface and is less than the third aCTE; wherein either: the difference between the first and second aCTE is greater than the difference between the second and third aCTE, and the difference between the second and third aCTE is greater than the difference between the third and fourth aCTE; or the difference between the second and third aCTE is greater than both the difference between the first and second aCTE and the difference between the third and fourth aCTE; wherein each aCTE is related to the volume fraction of the first structure within the interlay
Jer by J the equation k = — — - -(cr£z ),, where k is the volume fraction ^ {CTE^CTE^ {CTE^CTE^
of the first structure within the interlayer, CTEi is the coefficient of thermal expansion of the first material, and CTE2 is the coefficient of thermal expansion of the second material.
15. A method according to any preceding claim, wherein the first structure has a shape which is one of: the locus of points enclosed by a triply periodic minimal surface within the bounds of the interlayer; the locus of points within a fixed distance of a triply periodic minimal surface within the bounds of the interlayer; or the locus of points within a variable distance of a triply periodic minimal surface within the bounds of the interlayer, wherein the variable distance is defined by a function which depends on the position within the interlayer.
16. An interlayer for joining first and second components, the interlayer comprising: first and second surfaces; a first structure formed from a first material, and extending from the first surface, wherein the first structure has at least one surface which is not in contact with the first surface and faces towards the first surface at an angle of less than 90 degrees; a second structure formed from a second material, wherein the second structure extends to the second surface and conforms to the first structure on a side of the first structure opposite the first surface; wherein the first structure and the second structure together form the interlayer, and the first structure and second structure are shaped such that separating the first and second structure requires deforming one or both of the first or second structure.
17. An interlayer according to claim 16, wherein the first structure is a periodic structure which repeats in at least one direction parallel to the first surface.
18. An interlayer according to claim 16 or 17, wherein the first structure has a cross section parallel to the first surface which varies such that the cross section of the first structure decreases monotonically through the thickness of the interlayer from the first surface.
19. An interlayer according to claim 18, wherein the function relating the cross section of the first structure to the depth through the interlayer is one of:
a linear function; a sigmoid function; a polynomial function; or a cubic function.
20. An interlayer according to claim 18, wherein the first structure has first, second, third, and fourth average coefficients of thermal expansion, aCTE, defined such that each aCTE is the average coefficient of thermal expansion of the first and second material, weighted by their volume fraction, over one quarter of the thickness of the interlayer; and wherein the first aCTE is defined from the surface of the interlayer opposite the first surface; the second aCTE is defined from the midpoint of the thickness of the interlayer towards the surface of the interlayer opposite the first surface and is less than the first aCTE; the third aCTE is defined from the midpoint of the interlayer towards the first surface and is less than the second aCTE; the fourth aCTE is defined from the first surface and is less than the third aCTE; wherein either: the difference between the first and second aCTE is greater than the difference between the second and third aCTE, and the difference between the second and third aCTE is greater than the difference between the third and fourth aCTE; or the difference between the second and third aCTE is greater than both the difference between the first and second aCTE and the difference between the third and fourth aCTE; wherein each aCTE is related to the volume fraction of the first structure within the interlay
Jer by J the equation k = — — - -(cr£z ),, where k is the volume fraction ^ {CTE^CTE^ {CTE^CTE^ of the first structure within the interlayer, CTEi is the coefficient of thermal expansion of the first material, and CTE2 is the coefficient of thermal expansion of the second material.
21. An interlayer according to any one of claims 16 to 20, wherein the first structure has a shape which is one of:
the locus of points enclosed by a triply periodic minimal surface within the bounds of the interlayer; the locus of points within a fixed distance of a triply periodic minimal surface within the bounds of the interlayer; or the locus of points within a variable distance of a triply periodic minimal surface within the bounds of the interlayer, wherein the variable distance is defined by a function which depends on the position within the interlayer.