GB2073254A

GB2073254A - Ion implanting metal coated ferrous surfaces

Info

Publication number: GB2073254A
Application number: GB8111040A
Authority: GB
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1980-04-09
Filing date: 1981-04-08
Publication date: 1981-10-14
Also published as: GB2073254B

Abstract

The wear and/or corrosion resistance of ferrous materials, is improved by coating with a layer of tin, cobalt, silver or gold, and then subjecting the coated surface to bombardment with ions of a light species so as to cause the coating metal to migrate into the said surface of the body. The preferred ions are N<+>, B<+>, C<+>, Ne<+>.

Description

SPECIFICATION Improvements in or relating to the improvement of the wear and corrosion resistance of ferrous materials The invention relates to the improvement of the wear and corrosion resistance of ferrous materials.

Ferrous materials can wear by a process including the formation of iron oxides which are not strongly adherent to the unoxidised portion of the material and readily are removed by abrasion.

It is known to improve the wear and corrosion resistance of metal bodies by forming layers of oxidation-resistant coatings on the metal bodies.

However, sometimes the coatings themselves may not adhere strongly to the surface they are to protect.

According to the present invention there is provided a process for improving the wear and/or corrosion resistance of ferrous materials, comprising the operations of coating a surface of a body of ferrous material which is likely to be subject to wear and/ar corrosion with a layer of tin, cobalt, silver or gold, and then subjecting the coated surface to bombardment with ions of a light species so as to cause the coating metal to migrate into the said surface of the body.

For the purposes of this specification, the term "light" refers to an ion species the mass of which is insufficient to cause a harmful degree of sputtering of the surface under treatment during the ion bombardment. The preferred ion species are N+, B+, C+ or Ne+.

The initial coating can be formed by any convenient process, for example, sputtering, ion plating, ion bombardment, vacuum deposition or electroplating.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a diagrammatic representation of the stages of preparation of an embodiment of the invention, and Figure 2 shows the friction force and wear characteristics of iron surfaces which have, and have not, been treated according to the present invention.

Referring to Figure 1, a central region 1 of an iron specimen in the form of a flat disc 2 of 25 mm diameter was subjected to bombardment through a mask 3 by a beam 4 of Sn+ ions. The Sn+ ions had an energy of 200 keV, and the bombardment was continued until a dose of 5 x 1016 ions per cm2 had been implanted. The implanted region 1 of the disc 2 was then subjected to further bombardment by a beam 5 of N+ ions. The N ions had an energy of 400 keV, and bombardment was continued until a dose of 4 x 1017 ions per cm2 had been implanted. The N+ ions were not confined to the central region 1 of the disc 2.

The wear characteristics of the disc were then determined by means of a standard technique (not illustrated) in which a loaded pin carried on a hinged arm was brought to bear on the disc while it was rotated. The pin which was of 1 mm diameter also was made of pure ion. It was brought to bear on both treated and untreated regions of the disc 1 with a load of 25N. The frictional force and the rates of wear were measured for both the treated and untreated regions of the disc. In order to minimise the effects of abrasive wear, the surface under test was continuously washed with a mixture of 61% wt paraffins, 20% wt napthenes and 19% wt aromatics (white spirit).

The pin was first brought to bear on an untreated region of the disc and appropriate measurements taken. The test was then repeated on the implanted region of the disc.

A series of tests showed that both the wear rate and the friction force were independent of the relative velocity between the pin and disc for the range 40-60 cm/sec. The results are shown in Figure 2.

The wear rate is expressed in terms of a dimensionless wear parameter Kv which is defined by the relation Kv = Vp/x.A where Vp is the volume of material removed from the pin, x is the sliding distance and A is the apparent area of contact between the pin and the disc. The slope of the arm vertical displacement trace is thus a direct measure of the value of the parameter Kv. In Figure 2, the upper trace in each part of the figure represents the frictional force on the pin, and the lower trace represents the vertical displacement as the pin/disc combination wears. Part (a) of Figure 2 shows the results for the untreated area of the disc. It can be seen that throughout the test the friction force remains constant, as does the wear rate, its value being 2.1 x 10-8. Part (b) of Figure 2 shows the results for the treated area of the disc.Although the general results are similar, it can be seen that after a time the wear rate decreases and reaches a constant value of about 2.7 x 10-10, that is, some two orders of magnitude less than that for the untreated region of the disc.

The friction force shows some anomalous behaviour during the transition stage of the wear rate, but it stabilises again at about the same value as for the unimplanted region of the disc.

Wear measurements under the same conditions were performed on discs which had been implanted with lower doses of tin. No noticeable improvement was found with doses as low as 1 x 1016 Sn+ ions per cm2. The wear performance improved with dose, reaching an approximately constant value at a dose of 1 x 1016 Sn+ ions per cm2. A sample which was coated with an evaporated layer of tin which was not subsequently subjected to ion bombardment showed no improvement over an untreated specimen.

In addition to the discs, some pure iron foils were first electropolished and then annealed at 8000C for an hour before being implanted with tin ions over half their area under the same conditions as the discs. These samples were then oxidised in a furnace with a constant flow of dry oxygen at a temperature of 5000 C. The oxide films on the treated and untreated regions of the foils were then analysed by measuring the amount of oxygen present in the respective area of the samples by means of the 160 (d, p,) 170 nuclear reaction at 800 keV using a 5 MeV Van de Graaff accelerator.

The protons p, produced in the reaction were detected by a surface barrier silicon detector placed at 1 600 with respect to the incident deuteron beam.

The results for the oxidation experiment were obtained by inspection with the 1 mm diameter dueteron beam at several points on the implanted and unimplanted areas of the same face of the iron foils. The oxygen take-up of the implanted areas was much lower than that of the unimplanted areas. After exposure to oxygen for 10 min at 5000C, the oxygen take-up in the implanted areas was only 0.18 of that in the unimplanted areas of the foils.

For the convenience the invention has been described with reference to pure iron specimens.

The benefits of the invention however extend to iron alloys such as tool steels, and is expected to be particularly beneficial to steels which are required to operate at elevated temperatures.

Claims

1. A process for improving the wear and/or corrosion resistance of ferrous materials, comprising the operations of coating a surface of a body of ferrous material which is likely to be subject to wear and/or corrosion with a layer of tin, cobalt, silver or gold, and then subjecting the coated surface to bombardment with ions of a light species so as to cause the coating metal to migrate into the said surface of the body.

2. A process according to claim 1 wherein the light ions are N+, B+, C+ or Ne+.

3. A process according to claim 1 or claim 2 wherein the layer of tin, cobalt, silver or gold is deposited by a vapour phase deposition technique.

4. A process according to claim 1 or claim 2 wherein the layer of tin, cobalt, silver or gold is deposited by means of electroplating.

5. A process according to any preceding claim wherein the ferrous body is coated with a layer of tin prior to bombardment with the light ion species so as to cause the tin to migrate into the said surface of the body.

6. A process according to claim 5 wherein the layer of tin is deposited by means of ion bombardment, and then subjected to bombardment by N+ ions.

7. A process according to claim 6 wherein a dose of at least 1 016 Sn+ ions per cm2 of the surface of the body is implanted.

8. A process substantially as hereinbefore described with reference to the accompanying drawings.