Fretting Corrosion

Fretting corrosion is defined as the particular kind of damage which occurs when two surfaces in contact experience slight periodic relative movement. Examples are quoted of its appearance in very diverse circumstances such as press-fitted hubs, riveted structures, and electrical switching gear. It can lead to loss of fit, or seizure, and is a possible source of fatigue cracks. There is as yet no clear indication whether the appearance of cracks in fretted regions is due to the pits formed acting as stress raisers, although their shape could very well produce such an effect, or whether the conditions producing fretting also cause surface fatigue. The amount of damage increases approximately linearly with increasing amplitude of relative motion and increasing normal loading. It also increases as the temperature is lowered or as the atmosphere is more corrosive. The fretting corrosion of steel is reduced in a non-oxidizing atmosphere. There appear to be three possible processes involved: (1) mechanical abrasion by grinding or welding, (2) abrasion by hard particles of oxide, (3) continual mechanical rupture of otherwise protective oxide films. Probably all three mechanisms may be important in different cases, but most of the experimental data for the fretting corrosion of steel is best explained by the third mechanism. Preventive measures are classified according to their effectiveness in ( a) reducing relative movement by increased friction force, such as increased normal load, electroplated metal coatings of high coefficient of friction, elastic inserts, ( b) reducing friction by lubrication or low friction inserts, such as polytetrafluorethylene, ( c) excluding the atmosphere with rubber gaskets or flooding with lubricant, ( d) increasing the abrasion resistance of the surfaces, and ( e) separating the surfaces. It is emphasized that a measure which is a remedy in one case may aggravate the damage in another, indicating the need for careful diagnosis. Foreword By Dr. U. R. Evans On 21st May 1953 a Conference on Service Corrosion Problems was held at the Chemical Research Laboratory, Teddington, Middlesex. This was organized by the Inter-service Corrosion and Electro-deposition Committee—one of the Standing Committees of the Inter-service Metallurgical Research Council. The Conference was attended by representatives of all the Services. In the course of the discussion several speakers emphasized the importance of frettage in Service problems, and expressed a desire for further information on the matter. As a result, the Committee organized on 8th December 1953, a special discussion on the problem of frettage, which was attended by many persons with specialist knowledge of that subject, including four members of the Mechanical Engineering Research Laboratory of the Department of Scientific and Industrial Research, Thorntonhall, Scotland, where frettage research is actively proceeding, and numerous members of Service departments and industrial firms where frettage had caused trouble. The expressions of opinion revealed some diverse points of view and, after the meeting, the author who had been present, performed a real service by re-marshalling the conclusions in logical order and concise form—admirably suited to help those who had attended the meeting. However, it was considered desirable that a longer paper should be produced—suitable for the much wider section of the public which is concerned either with the practical or theoretical aspects of frettage; this would not be restricted to information produced at the meeting, and would make full use of work published, to some extent after the two meetings mentioned above, in the United States of America and on the Continent. The present paper by the author is the result.