Mechanical Properties of Ti–6Al–4V Titanium Alloy with Submicrocrystalline Structure Produced by Multiaxial Forging

Abstract

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.

The Aspects of Practical Application of Ultrafine-Grained Titanium Alloys Produced by Severe Plastic Deformation

“…It is noted above that using the method of all-round pressing, formation in titanium alloys of ultrafine-grained structure (size of elements 0.1-0.5 µm) is feasible [5][6][7]11]. In particular, the authors of the given paper applied the above method to form homogeneous ultrafine-grained structure in commercial pure grade titanium and in a range of titanium alloys.…”

“…Thus the formation of ultrafine-grained structure in titanium alloys causes an enhancement in their mechanical properties at room temperature. Moreover, the temperature corresponding to the outset of superplastic flow in such materials is lower by 200-300 K relative to the coarse grained counterparts [6,7,11]. Using the alloy Ti-6Al-4V by way of an example, it was shown in particular that the outset of superplastic flow in a material having ultrafine-grained structure (average size of elements ~0.25 µm) realized at temperatures above 823 К (Fig.…”

“…Several methods are currently employed to form ultrafine-grained structure in metals and alloys. Among the SPD techniques the most perspective and feasible ones are equal-channel angular pressing (ECAP) and all-round pressing [1][2][3][4][5][6]. Thus the use of the former method enables one to attain the true deformation е > 1 within a single pass [1].…”

“…titanium alloys. The method of all-round pressing has been actively developed of late since its application makes feasible formation of ultrafine-grained structure in large-sized billets of metals and alloys, titanium alloys included [5][6][7]. The latter method has two additional advantages in that simple flow sheet is employed and there is no need of press die.…”

Studies on the Superplasticity Effect in UFA: History and Development (In Memory of Prof. O.A. Kaibyshev)

“…For example, forging of various items from the alloy Ti-6Al-4V with a UFG structure is possible at temperatures of 550-750 °C [61][62][63]. At the same time, strength and fatigue characteristics significantly exceed the properties of the alloy with conventional structure and plasticity, and toughness and heat resistance meet the required level [63,64]. Low flow stresses and high elongations provide the possibility of making complex-shape objects by sheet stamping under superplasticity conditions [11,27].…”