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Research has demonstrated that the formation of a bulk ultrafine‐grained (UFG) structure in metals and alloys through severe plastic deformation (SPD) enables increasing of their strength properties and decreasing of the temperature range of superplasticity. Designers and process engineers generally show a great interest in such materials because the development of mechanical engineering industries places ever‐increasing demands on the performance properties of commercial alloys, especially for parts operating under extreme conditions. One of the approaches for a comprehensive enhancement of the performance characteristics of structural materials is a combination of a UFG structure in the bulk of a material, providing an increase in strength, and an additional surface modification providing resistance to erosion and corrosion damage. As a result, a set of material service properties can be enhanced, which is difficult to achieve through only metal nanostructuring or only surface modification. This approach has been demonstrated through an example of UFG titanium alloys produced by SPD, including those with nanostructured multilayer TiVN coatings of different “architectures.” Accordingly, herein, the trends, problems, and prospects of surface modification for the innovative application of structural UFG titanium alloys in advanced mechanical engineering are examined.

This work studies a near-surface layer microstructure in Ti-6Al-4V alloy samples subjected to plasma electrolytic polishing (PEP) and subsequent high-energy ion implantation with nitrogen (II). Samples with a conventional coarse-grained (CG) structure with an average α-phase size of 8 μm and an ultrafine-grained (UFG) structure (α-phase size up to 0.35 μm) produced by equal channel angular pressing were used in the studies. Features of phase composition and substructure in the thin surface layers are shown after sequential processing by PEP and II of both substrates with CG and UFG structures. Irrespective of a substrate structure, the so-called “long-range effect” was observed, which manifested itself in enhanced microhardness to a depth of surface layer up to 40 μm, exceeding the penetration distance of an implanted ion he. The effect of a UFG structure on depth and degree of surface hardening after PEP and ion-implantation is discussed.

A comparative investigation of mechanical properties of Ti–6Al–4V titanium alloy with coarse-grained (400 m), microcrystalline (10 µm) and submicrocrystalline (0.4 µm) structures in the temperature range 20–500°C has been carried out. The submicrocrystalline structure was obtained by multiaxial isothermal forging. The alloys with the coarse-grained and microcrystalline structures were used in a heat-strengthened condition. The microstructure refinement increases both the strength and fatigue limit of the alloy at room temperature by about 20%. The strength of the submicrocrystalline alloy is higher than that of the microcrystalline alloy in the range 20 - 400°C. Long-term strength of the submicrocrystalline specimens below 300°C is also considerably higher than that of the other conditions. However, the creep strength of the submicrocrystalline alloy is slightly lower than that of the heat-strengthened microcrystalline alloy already at 250°C. The impact toughness in submicrocrystalline state is lower especially in the samples with introduced cracks. Additional surface modification of submicrocrystalline alloy by ion implantation gives a considerable increase in the fatigue limit. Advantages of practical application of submicrocrystalline titanium alloys produced by multiaxial isothermal forging have been evaluated.