Formation of Residual Stresses during Discontinuous Friction Treatment

The tool with grooves on its working surface is used to improve the properties of the strengthened layer. This allows us to reduce the structure’s grain size and increase the thickness of the layer and its hardness. Mineral oil and mineral oil with active additives containing polymers are used as a technological medium during friction treatment. It is shown that the technological medium used during the friction treatment affects the nature of the residual stresses’ distribution. Thus, when using mineral oil with active additives containing polymers, residual compressive stresses are more significant in magnitude and depth than when treating mineral oil. The nature of the residual stresses diagram depends on the treated surface’ shape. After friction treatment of cylindrical surfaces, the highest compressive stresses near the treated surface decreases with depth. And after friction treatment of flat surfaces near the treated surface, the compressive stresses are small. They increase with depth, pass through the maximum, and then decrease to the original values. The technological medium used during friction treatment affects residual stresses in the grains and in the crystal lattice.

THE INFLUENCE OF NANOSTRUCTURING FRICTION TREATMENT ON MICROMECHANICAL AND CORROSIVE CHARACTERISTICS OF STABLE AUSTENITIC CHROMIUM-NICKEL STEEL

Friction treatment is an effective method to increase the strength and wear resistance of austenitic chromium-nickel steels. Previously, the authors identified that the high level of mechanical properties of metastable austenitic steels is achieved at the intensive development of deformation γ→α'-transformation. However, the presence of deformation martensite in the austenitic steel structure can negatively affect its anti-corrosion properties. The search for ways to improve the strength characteristics of stable austenitic chromium-nickel steel while maintaining high resistance to corrosion destruction is the up-to-date line of research. In this paper, to evaluate the mechanical properties of 03Cr16Ni14Mo3Ti steel in the hardened condition and after friction treatment, the authors applied the technique of measuring the hardness using the restored print and the method of instrumental micro-indentation, which allows recording the indenter loading and unloading diagrams. The corrosion failure resistance of steel was studied in general corrosion tests. The authors compared the corrosion rate of austenitic steel after grinding, electropolishing, and friction treatment; using scanning electron microscopy and optical profilometry, studied steel surfaces subjected to these treatments and determined their roughness. Nanostructuring friction treatment provides surface hardening of stable austenitic steel up to 570 HV 0.025. The study showed the high efficiency of friction treatment application to increase the strength characteristics and resistance of steel surface layer to elastic and plastic deformation. The authors identified that austenitic steel is characterized by similar corrosion rates km=(3.26–3.27)∙105 (g/cm2∙h) after electrolytic polishing (the structure of large-crystal austenite) and after frictional treatment (sub-micro/nanocrystalline austenite structure), while mechanical grinding leads to a twofold increase in the corrosion rate of 03Cr16Ni14Mo3Ti steel due to the occurrence of microcracks and metal breakouts on the polished surface. The research justified the determining role of the quality of the surface formed by various treatments (roughness, the presence of continuity defects) in ensuring the corrosion resistance of stainless steel.

Softening Behaviors of Severely Deformed Zn Alloy Studied by the Nanoindentation

Zamak 3 alloy treatment by sliding-friction treatment (SFT) was investigated by nanoindentation to explore the influence of microstructure and strain rate on nanoscale deformation at room temperature. The results show that obvious material softening occurs in the ultrafine-grained (UFG) Zn alloy and strain-hardening happens in the twinning-deformed layer, respectively. It can be concluded that almost constant values of V in the UFG Zn alloy contribute to the dislocations moving along the grain boundary (GB) not cross the grain interior. In the twinning-deformed layer, the highly frequent dislocation–twinning boundary (TB) interactions are responsible for subsequent inverse Cottrell–Stokes at lower stress, which is quite different from dislocation–dislocation reaction inside the grain in their coarse-grained (CG) counterpart.