Atmospheric corrosion of magnetic-film structures
- PDF / 817,007 Bytes
- 4 Pages / 594 x 774 pts Page_size
- 53 Downloads / 230 Views
(a)
(b) Fig. 3--Typical fractographic features near the fracture origin. (a) o- = 1100 MPa, N; = 1.78 x 105, "short life" group specimen. (b) o- = 925 MPa, NI = 7.40 x 106, "long life" group specimen,
prove the fatigue properties of carburized steel with surface structure anomalies. 2
cially known. Their compositions are described in detail by the American Aluminum Association and the American Society for Metals, respectively. The AA5086 is composed primarily of aluminum with 3.5 to 4.5 wt pct magnesium. Other metallic components exist as impurities or additives for corrosion resistance, e.g., 0.2 to 0.7 pct manganese. The HAYNES-188 is a higher temperature alloy containing primarily 20 to 24 pct chromium, max 3 pct iron, 20 to 24 pct nickel, 13 to 16 pct tungsten, and the balance cobalt. The AIMg substrates are initially machined, one side at a time, on a high-speed, diamond-tooled precision lathe to achieve a required substrate thickness, surface finish, and flatness. Their sides are arbitrarily called A and B such that the B side is the last side to face the lathe's chuck. All the above metallic layers were dc (magnetion) sputtered, with the exception of the FeCoCr (42.5/ 42.5/15 wt pct) film which was vacuum evaporated. The disks were simultaneously sputtered on both of their sides. However, great care was taken in the sputtering and evaporation to have equal deposition rates and times so that layers of equal thickness were produced. The HAYNES-188 was chosen on the basis of its bulk hardness value and its corrosion resistance. The function of such an undercoat is to supply the disk substrate with sufficient hardness to withstand intermittent recording headdisk contact during computer file operation. It will be seen that the primary corrosion mechanism of this disk structure will be the electrochemical (galvanic) interaction between the relatively thick HAYNES-188 underlayer and the A1Mg structure. To study the corrosion of such a thin film structure, it was exposed to a laboratory test chamber. Due to the corrosion resistance, passivity, of this HAYNES alloy, surface examination of this (polished) material after exposure to such corrosion chamber gases showed undetectable activity. This corrosion chamber has a well-controlled Table I.
Thin Film Disk Structure
REFERENCES
A machined A1Mg (AA5086) substrate 4 p.m of polished HAYNES alloy #188 0.035/xm of an FeCoCr magnetic film 0.075/xm of a rhodium overcoat
1. Takeshi Naito, Hideo Ueda, and Masao Kikuchi: Metall. Trans. A, 1984, vol. 15A, pp. 1431-36. 2. Masao Kikuchi, Hideo Ueda, Keisuke Hanai, and Takeshi Naito: Advances in Surface Treatments, Pergamon Books Ltd., Oxford, England, 1985, vol. 3, pp. 69-74.
S.K. DOSS and G.A. CONDAS are Advisory Engineers with IBM Corporation, 5600 Cottle Road, San Jose, CA 95193. Manuscript submitted March 7, 1986.
158--VOLUME 18A, JANUARY 1987
METALLURGICALTRANSACTIONS A
composition that is described in the literature. 2 The electrochemical (corrosive) reaction of two metals is reflected in the separation in the ga
Data Loading...
