Patent Number: 
Section: claims

1. A process, comprising:providing a first material having a higher atomic number and a second material having a lower atomic number; anddiffusion bonding the first material and the second material together to form a Z-grade material having:a first layer of the first material;a second layer of the second material; anda third layer, between the first and second layers, consisting of an alloy of the first and second materials, wherein a density of material in the third layer increases along a gradient from the first layer to the second layer, and wherein the third layer is at least 0.5 mil in thickness. 2. The process of claim 1, further comprising, bonding a fourth layer of a third material to the Z-grade material using diffusion bonding, wherein the third material has an atomic number that is less than the atomic number of the first material. 3. The process of claim 2, wherein the diffusion bonding of the fourth layer to the first layer produces a fifth layer between the first and fourth layers, wherein a density of material in the fifth layer increases along a gradient from the first layer to the fourth layer. 4. The process of claim 3, wherein the third material is the same as the second material. 5. The process of claim 4, wherein the diffusion bonding of the fourth layer to the first layer is performed for less time than the diffusion bonding of the first material and the second material. 6. The process of claim 5, wherein the diffusion bonding of the first material and second material comprises vacuum pressing the first and second materials at an elevated temperature. 7. The process of claim 6, wherein when the Z-grade material is warped, further comprising flattening the Z-grade material by vacuum pressing the Z-grade material at an elevated temperature and cooling the Z-grade material under vacuum. 8. The process of claim 7, wherein the elevated temperature is below the melting point of the low atomic number material. 9. The process of claim 8, wherein the thickness of the third layer is at least 10% of the thinner of the first and second layers. 10. The process of claim 9, wherein the third layer is at least as thick as the thinner of the first and second layers. 11. The process of claim 10, wherein the third layer is at least 5 mil in thickness. 12. The process of claim 11, wherein the first material is tantalum and the second material is titanium.