Thermoelastic Phase Transformation Research Articles

Microstructure and Magnetic Properties of Fe67.6-Pd32-In0.4 (at.%) Shape Memory Melt-Spun Ribbons.

Fe-~30 at.%Pd is a ferromagnetic shape memory alloy (SMA) with a reversible thermoelastic fcc-fct phase transformation. The advantage of adding a small amount of Indium to Fe-Pd SMAs is, among other things, the upward shift of the transformation temperatures, which allows us to maintain the material in the martensitic state (fct structure) at room temperature. In this work, we study the microstructure and the magnetic properties of nominally Fe67.6-Pd32-In0.4 (at.%) melt-spun ribbons. Energy-dispersive spectroscopy analysis showed a certain level of non-uniformity of Indium distribution in the as-spun ribbon. However, the attempt to homogenize the ribbon by annealing at 1273 K for 120 h resulted in an unfavoured structural change to bct martensite. Magneto strains induced by a 9 kOe magnetic field reached over 400 ppm for certain field orientations, which is around four times more than the magneto strains of near-binary Fe-Pd shape memory alloys.

Design features of drilling equipment elements using materials with shape memory effect

Alloys exhibiting thermoelastic phase transformations are getting more and more used in different industries. This is due to the shape memory effect and pseudo-elasticity (sometimes termed “superelasticity”) they exhibit, which can considerably improve the performance characteristics of various technical systems. One of the highest reliability and durability criterias are applied to equipment for drilling oil and gas wells, and according to this the above-described smart materials and the phenomena they exhibit have been gradually implemented in the oil and gas industry. This article analyzes the developed design of roller cone bits elements and proposes its assembly method, and presents its comparison with currently existing designs. Computational research and computer analysis of a drilling equipment assembly containing parts made of shape memory materials were performed, these studies showed significant advantages of the proposed method.

Структурно-имитационная модель деформирования сплавов с памятью формы. Часть 2. Описание эффекта реверсивной памяти формы

Within the framework of a one-dimensional structural-simulation model for deformation of shape memory alloys during thermoelastic phase transformations, an adequate description of the process of changes in strains during direct transformation under the influence of reverse stresses and the effect of reverse shape memory has been performed

Lüders and Portevin–Le Chatelier processes in austenitic-martensitic TRIP steel

The authors studied the nature of mobile fronts of localized deformation that generate and propagate during deformation of metastable austenitic-martensitic TRIP steel VNS9-Sh along the entire length of the loading curve from the yield point to fracture. A joint research of the nature of the deformation fronts movement and kinetics of the magnetic phase accumulation made it possible to establish that the fronts under consideration are the fronts of the thermoelastic phase transformation of metastable austenite into martensite. This transformation is realized firstly by formation of the Chernov–Lüders bands and then the Portevin–Le Chatelier bands. Both processes are consistent with staging of the deformation curve, which contains a pseudo-plateau, a section with an increasing hardening coefficient, and a section with a decreasing hardening coefficient. It is shown that the deformation-induced phase transformation corresponds to the fronts propagating on the pseudo-plateau and on the section of loading curve with an increasing hardening coefficient. The Portevin–Le Chatelier bands, which are formed in the section of the loading diagram with a decreasing hardening coefficient, are not associated with “austenite-martensite” transformation and have a twin nature. The kinetics of thermoelastic transformation fronts, as well as deformation fronts in materials with a shear mechanism of shaping, can be described in terms of the autowave concept. On the yield plateaus, the phase transformation occurs through generation and propagation of localized plasticity switching autowaves. In the section with an increasing hardening coefficient, it continues through generation and movement of excitation autowaves. The propagation regions of excitation autowaves are limited in the sample space. They are set by the zones of origin and annihilation of primary switching autowaves which were formed on the yield plateau.

Experimental Study and Theoretical Analysis of the Buckling of Titanium Nickelide Plates Induced by the Direct Thermoelastic Phase Transformation under Compressive Loading

Experimental Study and Theoretical Analysis of the Buckling of Titanium Nickelide Plates Induced by the Direct Thermoelastic Phase Transformation under Compressive Loading

Структурно-имитационная модель деформирования сплавов с памятью формы. Часть I. Описание эффекта ориентированного превращения

A one-dimensional structural simulation model for deformation of shape-memory alloys under thermoelastic phase transformations is presented, taking into account the origin and development of martensitic mesoelements during direct transformation and their degradation and disappearance during reverse transformation. An adequate description of the effects of oriented transformation within the framework of the model is given.

Effect of the Reverse Thermoelastic Phase Transformation on the Stress of the Onset of a Structural Transformation in Titanium Nickelide

Effect of the Reverse Thermoelastic Phase Transformation on the Stress of the Onset of a Structural Transformation in Titanium Nickelide

Technological aspects of increasing the wear resistance of the working surface of the dump with a modified surface

One of the most common tools used for plowing is the moldboard, which is a curved steel plate at an angle to the furrow wall. So the plow blades work under conditions of abrasive wear and significant static and dynamic loads, while the soil is an aggressive environment, which creates conditions for corrosion damage, so the plow blade as a tillage tool must meet the requirements for wear resistance, corrosion resistance, have high strength characteristics and ensure the preservation shape and size during operation. To improve the operational characteristics and service life of dumps at a low cost, there are various approaches, the general principle of which is based on obtaining layered or matrix-type coatings on the working surface of the dump by various metallization methods. Thus, the creation of a coating of a material with a shape memory effect on the surface of the plow blade will increase the durability and, as a result, the service life. In this case, adhesion is ensured by applying a coating with a gradient in composition along the thickness, changing from the surface of the substrate to the functional wear-resistant layer NiAl/FeMnNiAl from 99/1 to 1/99 with a thickness of 0.2 mm, and the functional wear-resistant layer FeMnNiAl is a material with thermoelastic phase transformation, providing high resistance to abrasive type of wear I=11.4×10-6 g/m3 (with wear rate for steel U10 I=23.3×10-6 g/m3) and corrosion.

On Thermoelastic and Non-Thermoelastic Martensitic Phase Transformations: Coupling of Volume Change and Strain

On Thermoelastic and Non-Thermoelastic Martensitic Phase Transformations: Coupling of Volume Change and Strain

A Review on NiTiCu Shape Memory Alloys: Manufacturing and Characterizations

Shape memory alloys have the thermoelastic phase transformation, known as shape memory characteristics, which make them be used in wide technological applications compared to other alloys. Ni-Ti based SMAs compared to the other families have more applications especially in the biomedical field since they have high biocompatibility, high strain recovery, flexibility, and antirust. In this work, the studies conducted for NiTiCu SMAs were reviewed. Additionally, different manufacturing techniques used by researchers have been explained. Different characteristics of the alloys have been clarified and compared with some other families.

Influence of heat treatment on thermokinetic EMF during reverse phase transition in titanium nickelide

The effect of duration and annealing temperature in the range of 400–800 °C on the thermokinetic EMF value in titanium nickelide, the composition of which is close to the equi-atomic one, at a reverse phase transition was investigated. Thermokinetic EMF was measured directly using a digital millivoltmeter MNIPI V7-72. The phase and elemental composition of the alloy and the kinetics of thermoelastic phase transformations have been checked by X-ray diffraction and calorimetric studies, and X-ray microanalysis. Annealing at temperatures of 500 and 800 °C leads to an increase in the thermokinetic EMF value from 0.22 to 0.25 mV. Removal of the oxide layer from the sample surface annealed at 700 °C for 0.5 h leads to an increase in the thermokinetic EMF value from 0.22 to 0.26 mV for the 1-st thermal cycle. It was found that thermal cycling causes a decrease in the thermokinetic EMF values down to 0.98 mV for the 20th thermal cycle for the samples without an oxide layer and to 0.3 mV for the samples with an oxide layer, respectively. With the increase in annealing time up to 20 h at 700 °C, the decrease in the thermokinetic emf value to 0.16 mV was observed. The thermokinetic EMF value after heat treatment is associated with changes in the physical and mechanical properties of the alloy and characterized by a shift of the characteristic temperatures of the phase transition. The research results are important for understanding the physics of thermoelectric phenomena in shape memory alloys during nonstationary heating and can be used both to control the homogeneity of their physical and mechanical properties and to design smart actuators and sensors, mechanisms of control systems.

NiTi shape memory alloy cellular meshes: manufacturing by investment casting and characterization

Recent studies have shown that conventional meshes comprising pure titanium and its alloys can be used to assist the recovery of bone fractures in various parts of the human body, such as the face, jaw, skull and knee. In anticipation of an improved efficiency for these applications and other applications, this work analyses the thermomechanical behaviour of a type of metallic mesh that is fabricated with NiTi shape memory alloys (SMAs), which are smart metals that exhibit functional properties, such as the shape memory effect (SME) and superelasticity (SE). The development of NiTi SMA meshes with different cell designs, good mechanical strength and recoverable deformation to replace titanium meshes and enhance biomedical applications (as well as applications in other fields) can be considered a current technological challenge. In this framework, this study aims to perform the fabrication and mechanical characterization of NiTi SMA meshes produced by investment casting with three different cell geometries (circular, hexagonal and square) in two states (as cast and heat treated). The obtained results show that the manufactured meshes present functional properties even in the as-cast state, as thermoelastic phase transformation and deformation recovery on the order of 6% is demonstrated. The results show that between the heat treatment and mesh cell geometry, the latter factor is the most influential factor in the mechanical behaviour of the meshes. A brief numerical simulation of the tensile behaviour of the meshes is used to deepen the analysis of the influence of cell geometry on their mechanical behaviour. Overall, as-cast meshes with circular and square cells present a high stiffness under tension and bending. The produced meshes show enough thermomechanical features to enhance biomedical applications. These results support the replacement of conventional titanium alloys, which do not possess functional properties, with NiTi SMAs.

Improving the adhesive strength of coatings from multicomponent materials with thermoelastic phase transformations by external high-energy influences at various processing stages

The paper presents the results of a comprehensive study of the influence of external high-energy ultrasonic and electropulse influences on the adhesive strength of a coating from the material with thermoelastic phase transformations (TEPT) at various processing stages: preparing the base; preparing the sprayed material at the finishing stage after coating. It has been shown that as a result of complex high-energy influences at the processing finishing stage, one observes a distinct fusion of the coating from the material with TEPT (Ni-33%, Ti-49%, Zr -49%) with a base and the absence of the interface, confirmed by electron microscopic studies. The fusion zone is 10-20 μm with the coating thickness of 1 mm; there are practically no coating elements in the base material at the depth of 20 μm. The experimental studies have confirmed an increase in adhesive strength by 1.2-1.5 times up to 130-150 MPa.

Loss of Stability of a Rod from a Shape-Memory Alloy Caused by Reverse Martensitic Transformation

In various formulations (unbound, coupled, and double-coupled) within the framework of the concepts of “Fixed load” and “Variable load”, analytical solutions to the problem of the loss of stability of a pivotally fixed rod made of an alloy with a shape memory, the material of which undergoes inverse thermoelastic phase transformation under the action of constant compression loads in the presence of initial phase — structural compression strains. The formulation of the concept of “Variable load” is justified, within which the solution for the critical length does not depend on the magnitude of the perturbations.

Density functional theory study of TiPd alloying with Os as potential high temperature shape memory alloys

Ti50Pd50 alloy exhibits thermoelastic martensitic phase transformation above 823 K and has the potential for high temperature shape memory material applications. Previous studies showed that this alloy is mechanically unstable with a negative C’ at room temperature. A systematic investigation of the structural, thermodynamic, electronic and elastic properties of TiPdOs is conducted using a first-principles calculation based on density functional theory. The calculated heats of formation show that this compound is thermodynamically stable as Os content is increased. It is found that an increase in Os content stabilizes the TiPd with a positive Cx2032; observed above 18.25 at. %. An increase in Os content results in an increase of the Bulk modulus and Young’s modulus above 18.25 at. %. Anisotropy factor and Vickers hardness are studied and hardness is found to increase with an increase in Os content. The results suggest that the stability of the B2 phase can be significantly enhanced by the addition of Os in TiPd alloy. These findings have important applications for future materials design in aerospace industries.

Evaluation of two-step transformation in Ni-rich titanium-nickel alloys using thermal and internal friction analyses

The use of Ti-Ni memory alloys covers several fields of application such as medicine, dentistry, actuators, sensors among others. Because of the thermomechanical behavior of these materials, they are an object of continuous studies and their properties are related to the occurrence of thermoelastic martensitic phase transformations. The thermal analyzes were performed using dilatometry and differential scanning calorimetry to determine the temperatures that occurred transformations during the cooling and heating, as well as to evaluate the influence of the thermal treatments performed by dilatometry. The thermomechanical behavior was also evaluated by the internal friction that measured behavior damping considering the structural and microstructural changes. The calorimetry measurements indicated suppression of the R phase through decomposition of precipitates of Ti3N4after the thermal treatments, that were corroborated by dilatometry and microhardness. This phase was also studied by the technique of internal friction, which showed that the mechanical damping coefficient increased as a function of temperature, due to the movement of the defects induced by tension. Keywords: Ti-Ni, shape-memory effect, internal friction, dilatometry, calorimetry.

Technological aspects of improving adhesion of TiNiZr coating materials with thermoelastic phase transformations formed by high-velocity oxygen-fuel spraying

The authors discuss technological aspects of increasing the adhesion of coatings made of materials with thermoelastic phase TiNiZr transformations formed by high-velocity oxygen-fuel spraying (HVOF) with a steel base by means of using a combined method, including HVOF and electromechanical treatment (EMT). The authors presented the results of the structure and elemental composition of the surface-modified layer before and after high-frequency impulse action in the EMT process and established new possibilities of modification of the structure and properties. It is shown that in the optimal modes of EMT, the fusion zone of the coating and the base is 10-20 microns. The authors designed the statistical models of technological process, which allowed defining fusion depth and diameter of a contact core depending on technological modes of EMT, as well as a current density and frequency or pulse duration. Adhesion tests according to State Standard 98844-99 showed that the strength of the coating with the base reaches (0.3-0.4) from the tensile strength of the base, depending on the depth and size of the fusion zone. It is recommended to perform additional thermomechanical processing to ensure the functional properties of materials with shape memory effect in the TiNiZr surface layer.

Solution of The Double-Coupled Problem of Buckling of a Shape Memory Alloy Rod Due to The Direct Thermoelastic Phase Transformation

Problems of the stability of a shape memory alloy rod during the direct martensitic phase transformation under constant compressive loading are solved taking into account the effect of stresses on the phase transition and the effect of the phase transition on the temperature regime using various statements. A comparison of the results of the obtained solutions is made.

THERMOKINETIC EMF IN SHAPE MEMORY ALLOYS UNDER THERMOELASTIC PHASE TRANSFORMATIONS

It is known that thermokinetic EMF occurs in homogeneous materials when the heating zone moves along a conductor. The obligatory occurrence of this kind of EMF is associated with phase transformations that proceed in a local heat-affected zone, for example, iron undergoes an allotropic transformation at 700–800 °C. It is natural to assume that this phenomenon can be observed in shape memory alloys under thermoelastic phase transformation that takes place at much lower temperatures. The studies presented here showed that the thermokinetic EMF appearance in titanium nickelide alloys is possible during the movement both of the heating zone (reverse phase transformation) and of the cooling zone (direct phase transformation). The physical justification for the EMF appearance is provided, according to which thermokinetic EMF is initiated as a result of a potential difference between the areas of direct and reverse phase transformations that occur due to the temperature influence along the TiNi wire sample. The paper also considers the thermokinetic EMF appearance in an amorphous–crystalline thin ribbon of Ti50Ni25Cu25 when a high-temperature local heating zone moves along it. This phenomenon is associated with the process of crystallization of material, i. e., amorphous to a crystalline state transition. Thermokinetic EMF also occurs when the interface between the amorphous and crystalline phases is heated locally. In this case, the thermokinetic EMF appearance is associated with a potential difference between the regions and similar to thermokinetic EMF occurring in the thermocouple. Studies on the thermokinetic EMF appearance due to the temperature effect on shape memory alloys during thermoelastic phase transformations allows one to more fully understand the thermokinetic EMF phenomenon. The results can find practical application in non-destructive testing of physical-mechanical properties of these alloys and as energy sources.

Connected and Doubly Connected Buckling Problems for Shape Memory Alloys

The models and methods of studying the buckling of shape memory alloy (SMA) elements that is caused by a forward thermoelastic phase transformation under a constant load are analyzed. The singly and doubly connected formulations of the corresponding problems are considered in terms of the concepts of a fixed load and a variable load concept. The critical parameters are shown to be minimal for the singly connected formulation at a variable load. The conclusions are illustrated by the example of solving the problem of buckling the Shanley column on SMA rods.