Phase transformations in the near contact region are often claimed to play a key role in the overall wear process: amorphization, second phase precipitation, carbide dissolution and martensitic transformations are currently reported. One usually ascribes the origin of such phase transformations to the temperature and pressure excursion at the contact points between the two bodies. However the magnitude of the flash temperature is a matter of debate (at least in metals) and seems to have been overestimated; moreover, the precise effect of a temperature transient is very sensitive to the details of the thermal history: e.g. depending on its time structure, a heat pulse may trigger either amorphization or crystallization, a fact well known in high storage density rewritable optical discs. The question then arises to identify which parameters control the occurrence of a phase transformation under the operating conditions. In the paper the concept of driven alloys is introduced and examples are given for alloys under irradiation or under high energy ball milling. Both natural and computer experiments show that the stationary configuration of the alloy under external forcing depends on the overall temperature, on the ratio of the ballistic to the thermally activated atomic jump frequency, and on the space and time correlation of the ballistic jumps. From the practical point of view, two control parameters are the overall temperature and the intensity of forcing: the latter is the irradiation flux for alloys under irradiation and the momentum transferred to an elementary volume of matter per unit time, under milling. The paper shows how to use these concepts to address the wear rate of train wheels.


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    Title :

    Near surface transformations: an example of driven phase transformations


    Additional title:

    Oberflächennahe Umwandlungen: Ein Beispiel gesteuerter Phasenumformungen


    Contributors:
    Chaffron, L. (author) / Martin, G. (author)


    Publication date :

    2001


    Size :

    10 Seiten, 13 Bilder, 14 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English





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