Methods of manufacturing diffusion bonded products and products manufactured by such methods

1. A method of diffusion bonding a first member and a second member to each other, comprising:

providing a first joint portion and a second joint portion on the first member and the second member, respectively,

fitting the first and second joint portions to each other with a predetermined interference, such that the first and second joint portions press against each other with a predetermined pressing force in a fitted state, and

thereafter heating the first and second members under a condition substantially without oxygen, and without applying any additional force to the first and second joint portions, so that the first and second joint portions are diffusion bonded to each other.

2. A method as in claim 1 , wherein at least one of the first and second members is made of titanium-based material, and the first and second members are heated within a vacuum furnace.

3. A method as in claim 2 , wherein the titanium-based material is titanium alloy.

4. A method as in claim 1 , wherein the materials of the first and second members are chosen from a group consisting of titanium alloy, steel and ceramic.

5. A method as in claim 1 , wherein the fist and second joint portions comprise a convex joint portion and a concave portion, respectively.

6. A method as in claim 5 , wherein the first and second joint portions are fitted to each other by press fitting.

7. A method as in claim 5 , wherein the first and second joint portions are fitted to each other by a shrink fitting utilizing heat.

8. A method as in claim 5 , wherein the fist and second joint portions are fitted to each other by an expansion fitting utilizing heat.

9. A method as in claim 5 , wherein the first and second joint portions comprise a tapered hole and a projection that has a configuration conforming to the tapered hole, respectively.

10. A method of manufacturing an engine valve, wherein the engine valve includes a valve shaft and a valve head, comprising:

providing a first joint portion and second joint portion on the valve shaft and the valve head, respectively,

fitting the first and second joint portions to each other with a predetermined interference; and

thereafter heating the valve shaft and the valve head under a condition substantially without oxygen, so that the first and second joint portions are diffusion bonded to each other.

11. A method as in claim 10 , wherein at least one of the valve shaft and the valve head is made of titanium-based material, and the valve shaft and the valve head are heated within a vacuum furnace.

12. A method as in claim 11 , wherein the titanium-based material is titanium alloy.

13. A method as in claim 10 , wherein the materials of the valve shaft and the valve head are chosen from a group consisting of titanium alloy, steel and ceramic.

14. A method as in claim 10 , wherein one of the first and second joint portions comprises a convex portion and the other of the first and second joint portions comprises a concave portion.

15. A method as in claim 14 , wherein the first and second joint portions are fitted to each other by a press fitting.

16. A method as in claim 14 , wherein the first and second joint portions are fitted to each other by a shrink fitting utilizing heat.

17. A method as in claim 14 , wherein the first and second joint portions are fitted to each other by an expansion fitting utilizing heat.

18. A method as in claim 14 , wherein one of the first and second joint portions comprises a tapered hole and the other of the first and second portions comprises a projection that has a configuration conforming to the tapered hole.

19. A method as in claim 10 , wherein the valve shaft has a tubular configuration.

20. A method as in claim 10 , wherein the engine valve further includes a shaft end member.

21. A method as in claim 20 , further including:

providing a third joint portion and a fourth joint portion on the valve shaft and the shaft end portion, respectively, wherein the first joint portion and the third joint portion are disposed opposite to each other; and

joining the third and fourth joint portions to each other.

22. A method as in claim 21 , wherein the third and fourth joint portions are diffusion bonded to each other at the same time that the first and second joint portions are diffusion bonded to each other.

23. A method as in claim 21 , wherein the materials of the valve shaft, the valve head and the shaft end member are chosen from a group consisting of titanium alloy, steel and ceramic.

24. A method as in claim 21 , wherein the third and fourth joint portions are friction bonded to each other.

25. A method of manufacturing an engine valve, wherein the engine valve includes a valve shaft and a shaft end member, comprising:

providing joint portions on the valve shaft and the shaft end member, respectively,

fitting the joint portions to each other with a predetermined interference, such that the first and second joint portions press against each other with a predetermined pressing force in a fitted state; and

thereafter heating the valve shaft and the shaft end member under a condition substantially without oxygen, and without applying any additional force to the first and second joint portions, so that the joint portions are diffusion bonded to each other.

26. A method as in claim 25 , wherein at least one of the valve shaft and the shaft end member is made of titanium-based material, and the valve shaft and the shaft end member are heated within a vacuum furnace.

27. A method as in claim 25 , further including cutting the valve shaft to a predetermined length with reference to a joint point between the valve shaft and the shaft end portion.