Special Features of Deterioration and Structure of the Surface Layers of Molybdenum and Metal Materials Under Dry Slidin
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CONDENSED-STATE PHYSICS SPECIAL FEATURES OF DETERIORATION AND STRUCTURE OF THE SURFACE LAYERS OF MOLYBDENUM AND METAL MATERIALS UNDER DRY SLIDING WITH ELECTRIC CURRENT M. I. Aleutdinova and V. V. Fadin
UDC 669.017.3
The possibility is considered of increasing the electrical conductivity of the electrical contact under dry sliding with current density exceeding 100 A/cm2 by means of application of a molybdenum counterbody. It is shown that sliding of tungsten and a sintered metal composite against molybdenum is characterized by low electrical conductivity and low wear resistance of the contact. It is shown that a change in the contact pressure in the range of 0.02–0.13 MPa and a change in the sliding velocity in the range of 5–10 m/s yields no significant increase in the electrical conductivity and the wear resistance of the contact. The x-ray analysis shows the absence of equilibrium oxides on the sliding molybdenum and tungsten surfaces. Nonequilibrium chemical compounds are also formed during friction. The formation of the transfer layers and their deterioration due to contact adhesion are established. The stress relaxation by the mechanism of low-cycle fatigue in the surface layer is considered as a main reason for fast deterioration of the surface layer and high wear intensity. These data on the structure of the surface layers and the unsatisfactory characteristics of the contact suggest the impossibility of significant improvement of the sliding parameters with current collection against molybdenum and inexpediency of its application as a counterbody under these conditions. Keywords: structure and phase composition of the surface layer, viscous plastic flow in the transfer layer, deterioration and wear of the sliding surface, sliding electric contact, electrical conductivity of the sliding contact.
INTRODUCTION It is well known [1] that high electrical conductivity and high wear resistance are the most important characteristics for exploitation of a sliding electrical contact. These target parameters of the tribosystem with current collection depend on many input parameters: pressure, sliding velocity, interface geometry, composition of the surrounding medium, initial structure of materials, etc. Generally, the high wear resistance (that is, the high strength of the working layer) is determined by the high resistance of the surface structure to the action of external friction and electric current. Previously, the natural increase was noted in the wear resistance of different metal composites and metals with increasing electrical conductivity of the contact during dry sliding against a steel counterbody with current density higher than 200 A/cm2 [2]. As a rule, the electrical resistance of the contact between two metals can be calculated from the Holm formula r = 0.25(ρ1 + ρ2)/a·n, where ρ1 and ρ2 are the specific electrical resistances of the contact materials, a is the average radius of contact spots, and n is the number of contact spots [3]. It then follows that the high electrical conductivity of the con
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