The effect of warm deformation by abc-pressing method on mechanical properties of titanium nickelide

Abstract

Исследовано влияние температуры на предел прочности (σ uts ) и удлинение до разрушения (δ) при растяжении образ-цов никелида титана (50.2 ат.% Ni) с исходной крупнозернистой структурой и структурами после abc-прессования при 873К (сплав 1, истинная деформация е = 2.2) и после прессования с понижением температуры в последователь-ности 873К→673К (сплав 2, е = 4.2). Размер зёрен в образцах сплава 1 (2-40 мкм) меньше, чем в исходных образцах (20-70 мкм). Образцы сплава 2 имели субмикрокристаллическую структуру (зёрна/субзёрна 100-700 нм). Показано, что при охлаждении и нагреве в исходных образцах реализуется мартенситные превращения (МП) В2←→В19ʹ (фазы с кубической и моноклинной структурами, соответственно), а в сплавах 1 и 2 МП протекают в последовательности В2→R→В19ʹ→В2 (R -мартенситная фаза с ромбоэдрической структурой). Завершение МП В19ʹ→В2 в этих образцах происходит при температурах 340-355 К. Растяжение образцов проводили при 293К, 343К и 473К (или 523К), то есть в мартенситной фазе В19ʹ, предпереходной области температур и в В2 фазе. Зависимости «напряжение-деформа-ция», полученные при этих температурах, для всех образцов качественно подобны. В процессе растяжения при 293К и 343К наблюдается площадка псевдотекучести, связанная с переориентацией кристаллитов фазы В19ʹ или форми-рованием деформационной мартенситной фазы В19ʹ. Генерации мартенситной фазы В19ʹ в процессе растяжения при 473К (или 523К) не наблюдается. Показано, что σuts повышается после abc-прессования. Максимум σuts наблюдается в процессе растяжения сплавов 1 и 2 при 293К и 343К (в мартенситной фазе В19ʹ). Наиболее пластичными являются образцы сплава 1 (δ около 80% при 293-343 К). При повышении температуры деформирования до 473К (или 523К) σ uts и δ существенно понижаются (в ~ 2 раза). Ключевые слова: тёплая деформация, никелид титана, механические свойстваThe effect of warm deformation by abc-pressing method on mechanical properties of titanium nickelide The effect of temperature on the ultimate tensile strength (σ uts ) and fracture elongation (δ) under tension of titanium nickelide (50.2 at.% Ni) with initial coarse-grained structure and structures after abc-pressing at 873K (alloy 1, true deformation е = 2.2) and after "step-by-step" pressing at 873K→673K (alloy 2, е = 4.2) are studied. The grain dimensions in the samples of alloy 1 (2-40 μm) are smaller than ones in initial samples (20-70 μm). The structure of alloy 2 is submicrocrystalline (grain/ subgrain dimensions are 100-700 nm). It was found that the martensitic transformations (MT) B2←→B19ʹ had been observed under cooling and heating of initial samples. The sequences of В2→R→В19ʹ→В2 MT were observed in alloys 1 and 2 (R -the rhombohedral martensitic phase). The finish of B19ʹ→B2 MT take place in the temperature range 340-355 K. The tension tests were carried out at temperatures 293K, 343K and 473K (or 523 K), i.e. in the B19ʹ phase, pretransition temperature range and B2 phase, accordingly. The "stress-strain" dependences obtained at these temperatures are quantitavely the same for all

Mechanical Behavior and Structural Characterization of a Cu-Al-Ni-Based Shape-Memory Alloy Subjected to Isothermal Uniaxial Megaplastic Compression

“…It was also shown that warm ECAP, in contrast to other MPD methods that are predominantly deformable by structural mechanism, is most preferable for the formation of a UFG structure, due to the predominance of the dynamic recrystallization mechanism [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. Another similar method of grain-size refinement of the grain structure of titanium alloys is warm abc-pressing [ 52 ]. We have shown that uniaxial hot-pressing can also be effective for refinement of the grain structure in CG copper alloys [ 46 , 49 , 50 ].…”

Crystal Structure Defects in Titanium Nickelide after Abc Pressing at Lowered Temperature

“…The regularities and features of microstructure evolution in TiNi-based alloys under the action of SPD at 623-773 K are studied in a number of works: [9][10][11][12][13][14][15][16][17][18][19][20][21] after ECAP and [4,5,22,23] after abc pressing. The effect of grain-subgrain structure refinement on the mechanical and inelastic properties of these alloys after ECAP was studied in [9][10][11][12][13][14][15][16][17][18][19][20][21] and after abc pressing in [22][23][24][25][26]. It was found that these methods can achieve a refinement of the grain-subgrain structure up to 100-500 nm, depending on the pressing temperature.…”

“…It has also been established that samples of these alloys with an average grain-subgrain structure of 250-300 nm demonstrate an ultimate tensile strength of up to 1200 MPa, and the plasticity reaches 50-60%. In [1,8,14,15,[22][23][24][25]27], the effect of ECAP and abc pressing on the martensitic transformation (MT) temperatures in TiNi-based alloys was studied. The MT temperatures during the cooling and heating of samples of these alloys decrease by 20 degrees or more after ECAP at 623-773 K [1,8,14,15,27], and after abc pressing, they either do not change or change only slightly [22][23][24][25].…”

Effect of abc Pressing at 573 K on the Microstructure and Martensite Transformation Temperatures in Ti49.8Ni50.2 (at%)

“…Research data are also available on the grain-subgrain structure of Ti 49.8 Ni 50.2 specimens exposed to abc pressing (multi-axial forging) with their true strain set from 2.2 to 1.5 or equal to ≈3.6 at each step of the strain temperature successively decreased from 873 K to 573 K [15][16][17][18]. Actually, such pressing conditions mean that each temperature step of abc pressing is applied to specimens with a different initial grain-subgrain structure.…”