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Amorphous CR(80)B(20) and CR(60)B(40) Extremely High Corrosion Resistant Alloys

IP.com Disclosure Number: IPCOM000051872D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Kateley, W: AUTHOR [+4]

Abstract

In general, some improvement in the corrosion resistance of a metal alloy system results if it can be made amorphous. It is not considered to be a major effect. We have found that the corrosion resistance of pure chrome can be improved by a factor of 35,000 (see table below) by the addition of small amounts of boron to make it amorphous. This improvement persists down to at least 40 atomic percent boron. If the Cr-B alloys are annealed into a microcrystalline state, we see similar high corrosion resistance. When annealed to the microcrystalline state, the Cr(80)B(20) (amorphous) becomes chrome with boron interstitials. This makes the corrosion resistance even more remarkable considering that we are merely going from pure crystalline chrome towards a slightly expanded chrome lattice with boron interstitials.

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Amorphous CR(80)B(20) and CR(60)B(40) Extremely High Corrosion Resistant Alloys

In general, some improvement in the corrosion resistance of a metal alloy system results if it can be made amorphous. It is not considered to be a major effect. We have found that the corrosion resistance of pure chrome can be improved by a factor of 35,000 (see table below) by the addition of small amounts of boron to make it amorphous. This improvement persists down to at least 40 atomic percent boron. If the Cr-B alloys are annealed into a microcrystalline state, we see similar high corrosion resistance. When annealed to the microcrystalline state, the Cr(80)B(20) (amorphous) becomes chrome with boron interstitials. This makes the corrosion resistance even more remarkable considering that we are merely going from pure crystalline chrome towards a slightly expanded chrome lattice with boron interstitials. Composition Structure Corrosion Rate* Cr(80) B(20) Amorphous 0 Cr(80) B(20) Microcrystalline 210 Cr(80) B(20) Crystalline 4x10/4/ Cr (bulk) Large Crystals 7x10/6/ *Corrosion rate in A/day for samples immersed 5 days in concentrated HCL in order of increasing grain size.

We therefore conclude on the basis of this and some additional data (see table above) that by making the grain size extremely small or nonexistant (amorphous) a large improvement in the corrosion resistance results. The larger grains present edges, peaks, amorphous grain boundaries and different crystal facets which favor different oxide formation kinetics with an associated variation in thickness and density. This results in defects that are preferentially attacked.

It appears that the corrosion resistance of any metal that passivates (valve metals) spontaneously can be improved substantially by making the material microcrystalline or amorphous. This means that when it is desirable to maintain the characteristics, such as hardness, conductivity, etc., of a specific metal, one can make a major improvement in its corrosion resistance by adding a small, good glass-forming element, such as boron, and then annealing the sample only enough to cause the formation of a microcrystalline structure. For example amorphous C...