The supersonic flight turns metal bonds weaker.

Above: North American X-15 in wind tunnel test. 

We know that friction weakens materials. Things like metal structures are vulnerable to heat. The reason for that is that metal structures are not solid and homogenous structures. The friction forms heat that destroys the metal structures. In the second image (Image 2),  we can see the aluminum crystalline structure. We can see that those are not in perfect symmetry. But the structure looks a little bit like a diamond (Image 4). That atomic structure makes aluminum very suitable for aviation. The problem is that the real bonds that are marked as grey tubes don't follow the route of the theoretical bonds that are marked by a black dash. If aluminum atoms form the boxes or structures like carbon in a diamond. That makes it stronger. 

Image 2. Crystalline structure of aluminum. 

However the structure can be more effective if those aluminum atoms can form a perfect box structure that continues homogenously over the entire trunk. Things like nanotubes can transport energy out of the structure. The best solution for nanotubes is that they are horizontally through the metal structure. If there are no connection points. That makes energy travel better through those tubes. 

The image 3 shows the problem of energy in the 3D surfaces. We can see that there are potholes in that structure. And that causes energy asymmetry in this lattice. 

The potholes and hills in structure cause differences in energy levels. Make energy travel to the lower energy points. And that forms standing waves that push atoms away. 

There are two ways to make the material strong. One is nanotubes and one is to make metal extremely pure. 

The structure is like boxes. And that allows the metal to dump energy into those boxes. That energy forms a standing wave that breaks the structure sooner or later. The thing that breaks the structure is the reflecting wave from the metal crystal. When we compare that structure with the diamond's carbon structure.

(Image 3) The polarization in lattice. The polarization under laser ray. Tells about the energy levels in the lattice. 

 We can see that the diamond's dodecahedron structure (Image 3)allows energy to travel out from the structure more easily than from the metal. If the energy level in the top carbon is lower than the bottom carbon. That increases the energy flow through a diamond. 

There are small metal crystals and bites of dross in the metal structure. When heat transfers to those structures. It causes standing waves into the layers. When energy travels into those small crystals. They store that energy inside them. Sooner or later. Energy levels in those metal structures turn higher than in the environment. That energy destroys the material structures. 

(Image 4) Diamond crystalline structure. 

We know that. To keep material in its form. There must be someplace. There the material can put that energy. The reason why carbon fiber stands better at supersonic speed is that it is fiber. In supersonic speed the air pressure pushes carbon fiber against the wing. If that fiber goes over the wing it can transport more energy to air. 

The next question is where that energy dump can put that energy. One answer can be the nanodiamonds. That can transport energy out from the metal. Another answer to the heat problem can be nanotubes that can conduct energy out of the structure. The system works that way so that there is a lower energy area behind the aircraft. 

The nanotubes can transport energy out from metal structures if they continue over the entire airplane's body. Things like electron beams can also operate as the thermal pump that transports energy out from the structure. 

 https://interestingengineering.com/innovation/supersonic-speed-weakens-metal-bonds-strength-peaks-at-1060-m-s-study-finds?group=test_b