Measuring Flatness of Ultrafine Machined Copper Disk with Laser Interferometer and Strength of Diffusion Bonding Interface for High-Energy Accelerators

Abstract

This paper describes the relationship between the strength of a joint created by an ultralow-loading diffusion bonding method and the dimension of unit disk parts machined by an ultra precision lathe. Oxygen-free copper disks of 30 mm diameter were machined by an ultra precision lathe, and the roughness, flatness, and undulation of the surfaces were analyzed. After the disks were subjected to an ultralow-loading diffusion bonding process in a vacuum furnace, the tensile test for the bonded joints was conducted. The configuration measurement showed that flatness was on nanometer order and that undulation could be classified as convex, concave, and straight. Regarding the joint strength, a tensile strength of around 200 MPa was obtained by specifying an initial gap at the two bonding surfaces ranging from 0.1 to 0.2 nm, under a bonding temperature of 973 K and a bonding pressure of around 1/1000–1/3000 of the yield stress of copper at that temperature.