Vladimir A. Andreev

The effect of rotary swaging (RS) at room temperature and subsequent annealing at 350 °C on the microstructure, mechanical properties, and fatigue strength of Cu–35.8%Zn two-phase brass was studied. A structure with grains of α and β′ phases elongated along the deformation direction was formed after RS. It was also shown that subgrains of 200–300 nm in size, shear bands 100–200 nm wide, and deformation twins 10–30 nm wide were formed inside the α-phase grains. RS caused the increase in the yield stress (YS) from 93 ± 4 to 717 ± 6 MPa and the ultimate tensile strength (UTS) from 332 ± 2 to 744 ± 19 MPa with a decrease in ductility (El) from 71.0 ± 2.0 to 10.3 ± 1.7%. The fatigue limit also increased from 240 to 415 MPa after RS. Subsequent annealing at 350 °C induced recrystallization of the α-phase with the formation of equiaxed grains 2.2–3.6 µm in size, which resulted in a decrease in UTS to 462–466 MPa and an increase in ductility to 44–45%. Extending the annealing time to 4 h did not affect the strength and ductility values of the alloy.

The effect of thermomechanical processing (TMP) parameters on the structural-phase evolution and properties of Ni-enriched Ti–50.8 at.% Ni shape memory alloy was investigated. Compression deformation was performed at T = 300–500 °C, accompanied by the development of dynamic aging (DA) processes, to true strains of e = 0.5–1.3, followed by post-deformation static aging (SA) at 430 °C for 1 and 10 h. The structural-phase state and properties were characterized using optical and transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, and Vickers hardness measurements. The results confirmed that DA processes were activated during compression but proved insufficient for pronounced Ti₃Ni₄ precipitate growth compared with SA. The temperature range of 430–500 °C promoted the most intensive DA processes and facilitated ultrafine-grained structure formation. The processing route combining DA at 500 °C with short-term SA (1 h) resulted in the finest precipitates of Ti₃Ni₄ phase and most homogeneous substructure. These findings demonstrate that the proposed TMP strategy enables effective tailoring of precipitate dispersion, evolution of transformation temperatures and mechanical properties (hardness), providing a viable manufacturing pathway for tailoring TiNi SMA performance in advanced biomedical and engineering applications.

Introduction. Ti-Ni based shape memory alloys (SMAs) are functional materials that find widespread practical application in engineering and medicine. Functional properties of Ti-Ni based alloys are sensitive to the chemical composition. To develop alloys with specific properties, ternary SMAs are being actively developed. For example, TiNiHf ternary alloys are characterized by a high-temperature shape memory effect. Today, there is a demand for SMAs used in the production of functional elements with a response temperature of more than 120 °C. These alloys must also have sufficient ductility to obtain deformed semi-finished products for the subsequent manufacture of heat-sensitive functional elements. Also among the current issues of developing the practical application of TiNiHf alloys is the lack of technological schemes for obtaining semi-finished products from TiNiHf SMAs. The purpose of this work is study the feasibility of conducting deformation processing of the studied TiNiHf alloys with a high-temperature shape memory effect and to identify the relationships between phase composition and mechanical characteristics and the applied processing method. In this work, the possibility of producing sheets and rods from TiNiHf alloys with 5 and 10 at.% Hf and 50.0 at.% Ni by longitudinal rolling, caliber rolling, and rotary forging was investigated. The research methods were: X-ray analysis, differential scanning calorimetry, and measurement of Vickers hardness. Results and discussion. It was found that the TiNiHf alloy with 10 at.% Hf has insufficient ductility. From the alloy with 5 at.% Hf, blanks in the form of sheets and rods of various sizes were obtained by using longitudinal rolling and rotary forging processes. It was shown that hot deformation allows increasing the hardness of the studied TiNiHf alloy with 5 at.% Hf compared to the cast state, from 232 HV to 242–264 HV. Cold deformation leads to a significant increase in hardness values up to 362–394 HV. Characteristic temperatures of the forward and reverse martensitic transformation are quite stable. The obtained results indicate the potential of using longitudinal rolling and rotary forging to obtain semi-finished products of TiNiHf alloys with 5 at.% Hf and to improve the functional and mechanical properties of the alloy after smelting.

A review has been conducted to determine current research directions in three-high rolling and piercing of steel billets. The billets are made of carbon, low-, medium-, and high-alloy steels. Investigations related to billet fracture processes are important. Fracture is found to be both ring-shaped and axial. Results on qualitative and quantitative estimation of a microstructure and the influence of three-high screw rolling on mechanical properties are presented. A submicron structural state has been achieved in a number of works; an increase in yield strength and tensile strength and a decrease in relative elongation have been detected in all studies. Some works detected the influence of three-high screw rolling on impact toughness. Compared to rolling, piercing has been studied much less frequently. The change in the grain size across the wall thickness and the changes in the hardness and the mechanical properties are investigated.

Предложен способ деформационно-термической обработки, основанный на ротационной ковке и обеспечивающий получение длинномерных заготовок из сплава Al – 2 % (масс.) Cu – 2 % (масс.) Mn. Проведена ротационная ковка сплава при 200 °C (после выдержки 10 – 15 мин) и последующий отжиг в интервале температур 250 – 450 °C. Исследована структура алюминиевого сплава в разных состояниях, измерена микротвердость по Виккерсу, проведены статические испытания образцов на растяжение. С использованием ротационной ковки получены длинномерные заготовки, обладающие высокой прочностью в сочетании со значительной пластичностью (предел текучести выше 300 МПа, относительное удлинение 13 %), а также высокой термической стабильностью (до 350 °C) без дополнительного введения в сплав циркония.