Possible Wave Processes Controlling the Growth of Martensite Crystals at B2-B19, B2-B19' and B2-R Transformations

Кащенко, М. П.; Чащина, В. Г.

doi:10.4028/www.scientific.net/msfo.81-82.3

Cited by 4 publications

(4 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This fact can be explained taking into account that dislocations play an important role in martensite nucleation [33] and that tilt and twist grain boundaries produce edge and screw dislocations, respectively. Edge dislocations are more efficient in martensite nucleation because they produce favorable stress fields [22,33]. Along with the direct B2 → B19' transition, in both bi-crystals, FMT occurs also through the formation of IP (B2 → IP → B19'), while RMT is one-step transition B19' → B2.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, it is important to differentiate FMT that is associated with the appearance of IP, through the B2 → IP transition, (FMT-1) and FMT which is characterized by nucleation of the monoclinic phase via B2 → B19' and / or IP → B19' (FMT-2). It is believed that, along with the mentioned IPs, there are other IPs that can be observed during FMT [22].…”

Section: Modelingmentioning

confidence: 99%

See 1 more Smart Citation

Martensitic phase transformation in NiTi bi-crystals with symmetric ∑25 twist and tilt grain boundaries

Babicheva¹,

Gunderov²,

Stolyarov³

et al. 2018

LoM

View full text Add to dashboard Cite

NiTi alloys attract a lot of attention of researchers for a number of reasons; among them are their practical importance and challenges for theoretical understanding. The most exciting feature of these alloys is the shape memory effect due to the martensitic transformation at temperatures close to the room temperature. There exist many factors affecting the transition temperatures in such materials, such as a deviation from stoichiometric composition, dislocation density, grain size, and the type of grain boundaries. The latter factor is one of the less explored, and we are aware of just a few studies in this direction. In the present work, molecular dynamics simulations are carried out to reveal the effect of symmetric tilt and twist grain boundaries in bi-crystals with nanosized grains on the forward and reversed martensitic transformations during cooling down from the austenite B2 phase and subsequent heating up from the martensite B19' phase. Phase composition, elastic strain components, relative change of volume, potential energy per atom, and shear stresses are calculated and analyzed as the functions of temperature. It is found that the type of grain boundaries in the bi-crystals strongly affects the transition temperatures. Start and finish temperatures of the forward and reverse martensitic transformations are much lower in the bi-crystal with twist grain boundaries as compared to that having tilt grain boundaries. Overall, the simulation results of this study are in a good qualitative agreement with the available experimental data. NiTi сплавы привлекают большое внимание исследователей по ряду причин; среди них их практическая ценность и сложность для теоретического понимания. Наиболее выдающаяся особенность таких сплавов это эффект памя-ти формы, который обусловлен мартенситным превращением, протекающим при температурах близких к комнат-ной. Существует множество факторов влияющих на температуру фазового перехода в этих материалах, например, отличие химического состава сплава от стехиометрического, плотность дислокаций, размер кристаллитов и тип границ зерен. Последний фактор, из перечисленных, наименее изучен, и мы осведомлены только о нескольких ра-ботах, посвященных этому вопросу. В данной работе проведено моделирование методом молекулярной динамики с целью изучения вопроса влияния симметричной границы наклона и кручения в нанокристаллических бикристал-лах на прямой и обратный мартенситные переходы при охлаждении с аустенитной B2 фазы и последующем нагреве с мартенситной B19' фазы. Определены и проанализированы фазовый состав, компоненты упругой деформации,

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Modelingmentioning

confidence: 99%

Martensitic phase transformation in NiTi bi-crystals with symmetric ∑25 twist and tilt grain boundaries

Babicheva¹,

Gunderov²,

Stolyarov³

et al. 2018

LoM

View full text Add to dashboard Cite

show abstract

“…It is believed that, along with the rhombohedral R or orthorhombic B19 intermediate phases (IPs), there are other IPs that can be observed during MT [45]. In this study, forward MT (FMT) is associated with the formation of the B19' martensite phase on cooling either directly from the austenite phase (B2→B19'), or from IP (IP→B19'), or from mixture of B2 and IP, and by analogy, the generation of B2 phase from B19' and / or IP during heating is attributed to the reverse MT (RMT).…”

Section: Modelingmentioning

confidence: 99%

Effect of grain boundary segregations on martensitic transformation temperatures in NiTi bi-crystals

2019

View full text Add to dashboard Cite

NiTi alloys are very important in a number of applications since they demonstrate shape memory effect, which is due to the martensitic phase transition with the transition temperatures close to the room temperature. Many factors affect transition temperatures of the alloy, including a variation of its chemical composition and thermo-mechanical treatment, which affects grain size, dislocation density, and other crystal structure parameters. It is well-known that the chemical composition of the alloys in grain boundaries can differ significantly from that in the bulk due to segregation of certain elements from the matrix to the grain boundaries. The effect of grain boundary segregations on the martensite transformation temperatures is still poorly understood. In the present molecular dynamics study, the possible effect of segregation of Ti or Ni atoms along Σ25 tilt grain boundary on the forward and reverse martensitic transformations is analyzed. The segregation is simulated by replacing the monoatomic Ti or Ni layer in the grain boundary with Ni or Ti layer, respectively. The results are compared to the case of no segregations. We analyze the initial relaxed and thermalized structures of the bi-crystals in austenite state as well as the temperature dependencies of potential energy per atom and volumetric dilatation. It is found that segregations may significantly decrease the start and finish temperatures of the martensitic transformation, and this effect is more pronounced for segregations of Ni.

show abstract

“…In the case of shape memory alloys (SMA) the level of threshold deformations is lower than in the case of γ-α MT. However, as the analysis shows [7], the observed morphological features of martensite crystals in alloys based on titanium nickelide can be unambiguously compared by the NCs for all variants of martensitic transformations. This result testifies to the possibility of using the concept of heterogeneous nucleation.…”

Section: Introductionmentioning

confidence: 97%

Nucleation centers for martensite with habitus {110} in the shape memory alloys

Кащенко

Чащина

2022

IOP Conf. Ser.: Mater. Sci. Eng.

View full text Add to dashboard Cite

The dynamic theory of martensitic transformations (MT) considers the formation of habit planes of martensite crystals as a consequence of the propagation of a controlling wave process (CWP). The general ideology makes it possible, by comparing the observed habits with calculations of the elastic fields of defects (as a rule, dislocations), to identify nucleation centers. In a number of cases (In-Tl alloys, Ni50Mn50 alloys, Heusler alloys …) under MT in the shape memory alloys, {110} habits are observed (in the basis of the initial cubic phase), which often have a fine twin structure with twin boundaries of the same type. This highly symmetric structure is described by the CWP containing longitudinal waves (both relatively long-wavelength ℓ and short-wavelength s) propagating along the 4-order symmetry axes. In this paper, it is shown that such habits are associated with rectilinear segments of dislocation loops with directions Λ along <001> and Burgers vectors along <010> (or <110>) orthogonal to Λ, both for sliding and for prismatic loops. The tetragonality, the relative volume change during the MT, and the dependence of the start temperature M s on changes in the concentration of alloy components are also briefly discussed.

show abstract

Possible Wave Processes Controlling the Growth of Martensite Crystals at B2-B19, B2-B19' and B2-R Transformations

Cited by 4 publications

References 27 publications

Martensitic phase transformation in NiTi bi-crystals with symmetric ∑25 twist and tilt grain boundaries

Martensitic phase transformation in NiTi bi-crystals with symmetric ∑25 twist and tilt grain boundaries

Effect of grain boundary segregations on martensitic transformation temperatures in NiTi bi-crystals

Nucleation centers for martensite with habitus {110} in the shape memory alloys

Contact Info

Product

Resources

About