Airfoil assembly with spacer and tie-spar

1. An airfoil assembly comprising:

at least one airfoil that has a hollow interior;

first and second platforms between which the airfoil is disposed;

at least one tie-spar that extends along an axis through the first platform, the hollow interior of the airfoil, and the second platform, and there is a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction; and

at least one spacer portion arranged on the tie-spar, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D such that the spacer portion maintains the tie-spar under tension and clamps the first and second platforms on the airfoil, wherein the spacer portion extends into the hollow interior of the airfoil.

2. The airfoil assembly as recited in claim 1 , wherein the spacer portion has an aspect ratio of length-to-width of greater than one, with the length being along the axial direction and the width being perpendicular to the axial direction.

3. The airfoil assembly as recited in claim 1 , wherein each of the first and second platforms extends partially in the hollow interior of the airfoil.

4. The airfoil assembly as recited in claim 1 , wherein the spacer portion includes a central through-hole, through which the tie-spar is received, and a majority of the length of the tie-spar is within the through-hole.

5. The airfoil assembly as recited in claim 1 , wherein the spacer portion is outboard of the first and second platforms with respect to the hollow interior of the airfoil.

6. The airfoil assembly as recited in claim 1 , wherein the at least one spacer portion includes two spacer portions, one of which is located near a first end of the tie-spar and the other of which is located near a second opposed end of the tie-spar.

7. The airfoil assembly as recited in claim 1 , wherein the hollow interior of the airfoil has multiple cavities, and the at least one tie-spar includes multiple tie-spars that extend, respectively, through the multiple cavities.

8. The airfoil assembly as recited in claim 1 , wherein there is an annular clearance gap between an exterior of the tie-spar and an interior of the spacer portion.

9. The airfoil assembly as recited in claim 8 , wherein the exterior of the tie-spar and the interior of the spacer portion each include a thermal barrier coating.

10. The airfoil assembly as recited in claim 1 , wherein the airfoil is free of direct contact with the first and second platforms.

11. The airfoil assembly as recited in claim 1 , further comprising a baffle in the hollow interior of the airfoil and through which the tie-spar extends.

12. The airfoil assembly as recited in claim 11 , wherein the baffle extends from the hollow interior of the airfoil to an attachment portion external of the hollow interior.

13. The airfoil assembly as recited in claim 1 , further comprising a clip that abuts a bearing face of the tie-spar and a surface of the spacer portion to lock the tie-spar under tension.

14. The airfoil assembly as recited in claim 13 , wherein the clip has spaced-apart arms.

15. The airfoil assembly as recited in claim 14 , wherein the spaced-apart arms have interior surfaces that are slanted.

16. The airfoil assembly as recited in claim 15 , wherein the clip has a recess at a base of the spaced-apart arms and the tie-spar includes an enlarged end that is received into the recess to lock the clip and the tie-spar together.

17. The airfoil assembly as recited in claim 16 , wherein the enlarged end has sloped bearing surfaces that engage the interior surfaces of the spaced-apart arms that are slanted.

18. The airfoil assembly as recited in claim 1 , further comprising a classified spacer mounted on the tie-spar.

19. The airfoil assembly as recited in claim 18 , wherein the classified spacer is an end cap mounted on an end of the tie-spar.

20. The airfoil assembly as recited in claim 1 , wherein the airfoil includes a radial wall that has protruding radial arms that partially extend around one of the first and second platforms.

21. A gas turbine engine comprising:

an airfoil assembly that includes:

at least one airfoil that has a hollow interior;

first and second platforms between which the airfoil is disposed;

at least one tie-spar that extends along an axis through the first platform, the hollow interior of the airfoil, and the second platform, and there is a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction; and

at least one spacer portion arranged on the tie-spar, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D such that the spacer portion maintains the tie-spar under tension and clamps the first and second platforms on the airfoil, wherein the spacer portion extends into the hollow interior of the airfoil.

22. A method for making an airfoil assembly, the method comprising:

arranging at least one tie-spar to extend along an axis through a first platform, a hollow interior of an airfoil, and a second platform, there being a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction; and

maintaining the tie-spar under tension to clamp the first and second platforms on the airfoil by using at least one spacer portion arranged on the tie-spar, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D to maintain the tie-spar under tension and clamp the first and second platforms on the airfoil, wherein the spacer portion extends into the hollow interior of the airfoil.

23. The airfoil assembly as recited in claim 1 , wherein the first and second platforms are formed of a superalloy and the at least one airfoil is formed of is a refractory metal-based alloy or ceramic-based material, and further including cobalt spacers between the first and second platforms and the at least one airfoil such that the at least one airfoil is free of direct contact with the first and second platforms.

24. The airfoil assembly as recited in claim 23 , wherein the superalloy is a nickel-based alloy and the at least one airfoil is formed of the refractory metal-based alloy, and the refractory metal-based alloy is a molybdenum-based alloy.