Search

The structure and properties of the hot-extruded Ti–3Al–2.5V pipe 90.0 × 20.0 mm in cross section subjected to vacuum annealing are studied using methods of macro-, micro-, X-ray analyses, tensile and Vickers hardness tests. It is shown that during vacuum annealing within the microstructure there is development of α-phase and formation of a more equilibrium (α + β)-condition compared with the condition after hot extrusion, and these changes are reflected in phase parameters, their volume fraction and chemical composition. It is shown that development of recrystallization processes through a pipe cross section also play a specific role in forming the textural condition in different areas of the cross section (outer surface, 1/2 wall thickness, inner surface of the pipe). It is noted that vacuum annealing facilitates a reduction in the scatter of hardness in a pipe cross section and to formation of the combination of mechanical properties with good ductility and a moderate strength level.

Results are provided for a study of the structure and mechanical properties of alloy AK12 modified with tabletted ultra-finely dispersed modifier based on silicon carbide, introduced “beneath a metal stream” without additional mixing, and in a rotary device. It is established that the optimum method for introducing modifier is that of “beneath a metal stream.” In this case the ultimate breaking strength increases from 110 to 150 MPa, nominal yield strength from 85 to 94 MPa, and relative elongation from 2.3 to 6.2% (metal pouring temperature into a mold 750 °C). Metallographic examination is used to determine the reduction in macro-grain size in test pigs (ingots) by a factor of four compared with control alloys, absence of porosity, and an increase in ingot density from 2.59 to 2.66 g/cm3. Introduction of ultra-finely dispersed modifier based on silicon carbide increases the number of crystallization centers in a 1 kg ingot to 2·1011 units.

Methods of macro- and microstructural, x-ray structural analyses and mechanical tensile tests of the structure and properties of Ti–3Al–2.5V alloy hot-extruded intended for subsequent cold rolling are studied. Hot-extruded pipe is produced according to the scheme: expansion in a vertical press → extrusion in a horizontal press. It is shown that during sleeve expansion structure and phase structure do not change markedly compared with the initial hot-rolled semi-finished product in two-phase (α+β)-region. Hot extrusion in the recommended temperature range provides formation of a sufficiently homogeneous, well worked macro- and microstructure with a tangential basic texture of α-phase. A set of mechanical properties for hot-extruded pipe of alloy Ti–3Al–2.5V required for performing subsequent cold rolling used in the final stages of pipe preparation by TREX technology is provided.

Microstructural methods, thermal analysis, and thermomechanical test methods are used to study the structure and properties of hot-pressed semifinished product of alloy Ti–3Al–2.5V used for developing manufacturing technology for hot-extruded tubes. It is shown that the use of calculation methods for evaluating polymorphic transformation temperature makes it possible to assess the required temperature range with use of a test quenching method. Thermal analysis and laboratory thermomechanical tests are used to determine the temperature range for extrusion in two regions taking account of deformation heating.