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Fabrication of Source Material for Rod-Fed Evaporation

IP.com Disclosure Number: IPCOM000042599D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Kwong, AF: AUTHOR [+4]

Abstract

A technique has been developed for the fabrication of rod evaporation source material of a ternary alloy, used in electron beam evaporation for deposition of the magnetic recording media of controlled composition and thickness on a thin film disk. The technique is a combination of vacuum casting pure metals, followed by a proprietary thermomechanical treatment of the alloy, and a special vacuum heat-treatment prior to machining to final shape. It allows for control of the film composition within Å1.0 weight percent for each alloy component even though the alloy constituent metals may have substantially different vapor pressures at temperatures incurred during casting or thermomechanical treating. Furthermore the volume of rod material is homogeneous with respect to composition and oxide dispersion.

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Fabrication of Source Material for Rod-Fed Evaporation

A technique has been developed for the fabrication of rod evaporation source material of a ternary alloy, used in electron beam evaporation for deposition of the magnetic recording media of controlled composition and thickness on a thin film disk. The technique is a combination of vacuum casting pure metals, followed by a proprietary thermomechanical treatment of the alloy, and a special vacuum heat-treatment prior to machining to final shape. It allows for control of the film composition within Å1.0 weight percent for each alloy component even though the alloy constituent metals may have substantially different vapor pressures at temperatures incurred during casting or thermomechanical treating. Furthermore the volume of rod material is homogeneous with respect to composition and oxide dispersion. The fabrication process consists of the following steps: 1. Starting material of the alloy constituent elements in the proper proportions is induction melted under vacuum. The purity of the starting material is 99.9% or better. 2. The melt charge is cast under vacuum in a clean cylindrical mold to form an ingot nominally 2.75" in diameter and 20.0" long. The ingot is slow cooled under vacuum. 3. The 2.75" x 20" ingot is rotary forged (swaged) at a temperature in the range 550-625OEC. This thermomechanical treatment results in a rod about 236" long, which is subsequently cut into 16" lengths (with the two end sections discarded as scrap). 4. The 16" rods are stress relief annealed at 1175OEC for one hour under vacuum (backfilled with argon). 5. The annealed rods are given a best effort straightening treatment. 6. The straightened 0.80" x 16" rods are centerless ground to the final diameter. 7. The ground 16" long rods are cut into two equal lengths nominally 8" long. This process is compared with a previous process which was found to result in rod material showing inferior evaporation behavior. The old process steps were as follows: 1. Induction melting (under vacuum) of the starting material constituents in the proper proportions. Starting material purity is 99.9% or better. 2. Casting of the melt charge under vacuum into cylindrical molds 0.850" in diameter and 16" long. Slow cooling under vacuum followed. 3. Centerless grinding of the 16" x 0.850" diameter rods to the final diameter. 4. Cutting of the 16" x 0.750" rods into two 8" lengths. The advantages of the new process as compared to the old process are directly attributable to the fact that the new process uses oversize vacuum castings which are sized by subsequent thermomechanical treatments. The desirable features of rods made by the new process are as follows: A. Contamination of the rod material may be minimized. Vacuum casting oversize ingots minimizes contamination by decreasing the surface area to volume...