Behavior of hydrogen in fracture and friction of metals and alloys

Abstract

The negative effect of hydrogen on the properties of metals and alloys is demonstrated by the results of many studies. However, the mechanism of the behavior of hydrogen in metals still remains unclear. The present work is devoted to the effect of magnetic and electric fields on the diffusion of active hydrogen and to its interaction with impurity elements in metals and alloys in fracture and friction.An increase in the hydrogen content in metals and alloys often leads to substantial worsening of their physical, mechanical, and triboengineering properties and, consequently, to brittle fracture and intense wear of parts even under a meager load. Friction is accompanied by anomalous phenomena, namely, the wear of a steel (or cast iron) part with an elevated hydrogen content turns out to be higher than that of a less hard bronze (or plastic) part operating together with it [1].The harmful effect of hydrogen manifests itself quite vividly in electrolytic hydrogen-charging of a bent steel plate made of a tool steel (Kh6VF) or a corrosion-resistant steel that undergoes brittle fracture (sometimes into three parts) several minutes after the process begins, depending on the degree of deformation. At room temperature such a plate can be in a deformed state for several months and even years without breaking. A deformed steel plate breaks rapidly by a brittle mechanism after its stretched surface is wetted by an electrolyte without passing an electric current.Since the degree of deformation e and the load P acting on the specimen before and after the surface is wetted by an electrolyte (before and after hydrogen absorption) are constant, the development of brittle fracture is obviously caused by an increase in the stresses cr in the specimen to values exceeding the ultimate rupture strength of the material er r due to a reduction in the cross-sectional area of the specimen F, i.e., (or = P/F) > c~ r . Figure 1 presents a comparatively even decrease in the density p of the material over the length of a specimen after a tensile test (by 0.01-0.36% in regions [2][3][4][5][6][7][8] and a jumpwise decrease by a factor of 4.8 -132 (by 1.72%) in the Ukhta Industrial Institute, Ukhta, Russia. fracture zone 9 [2], which is explained by an increase in the porosity of the material.The appearance of pores 0.2 -1.0 I-tm in diameter and even of tube channels 2 to 10-50 lam long, which sometimes merge, forming a scaling system in the surface layer 2 -8 pan deep, has been observed in friction tests of specimens of corrosion-resistant steel 07Khl6N6 [3]. In parts made of steel 45, after operation under wear conditions pores up to 10 pan in diameter and several tens of micrometers long form chains that reach the surface without signs of crack propagation, although in the initial state the material does not have noticeable pores. The marked decrease in the density of the metal in the fracture zone, the changes in the specific elongation and reduction of area, and the proportions of brittle and tough fracture on the surface of specimens, just ...