With the advent and proliferation of Artificial Intelligence & Machine Learning (AIML) techniques into various fields of science, there have been efforts to accelerate the process of designing, developing & manufacturing new materials thus saving on time & cost. Additionally, the image analysis methods in AIML can help in capturing the nuances of the processing thus enabling the researchers to interface Processing – Structure – Properties of the materials’ systems. The authors have developed an integrated tool, AMDAD, with graphical user interface (GUI) which has all the machine learning operations in one platform starting from data collection, data pre-processing, model fitting, optimization to reading the microstructures.

The ASTM E3097 standard for constant-force thermal cycling provides a useful framework for measuring properties of shape memory alloys relevant to actuation applications, namely transformation strains and transformation temperatures. The standard allows for operator discretion when selecting a heating and cooling rate for the thermal cycling, provided that the specimen temperature is maintained uniformly within ±3°C across the specimen throughout the course of the thermal cycling. With larger test specimens such as dog-bones, for example, this can be ensured via thermocouples affixed to the specimen. Substantial work has been done to quantify the ruggedness of the standard for such specimens. However, it can be difficult to verify specimen temperature in-situ during testing of wire specimens due to their small diameter. Contact methods, such as thermocouples, can be difficult to affix to the specimen due to its small size. It is also difficult to get accurate measurements using contact methods, due to the often- substantial size and mass disparity between the temperature sensor and the wire specimen and the tendency of the temperature sensor to act as a heat sink for the test specimen. Non-contact methods such as infrared (IR) thermography are possible, but not always practical. A high image resolution is crucial for IR measurement of small diameters, and calibration adjustments may be required from one test to the next, depending on surface characteristics and resulting emissive properties, to ensure accurate measurements. For these reasons, one common practice is to thermally cycle the wire specimens by means of a temperature-controlled environment, rather than heating the specimens directly, and change the temperature of the environment at a rate such that the wire specimen remains equilibrated in temperature. It is, therefore, especially important when testing wire according to the E3097 standard for the test operator to understand the potential influence of heating and cooling rates on test results. This work presents results from ASTM E3097 tests performed on various wire diameters using different thermal ramp rates, as well as different testing media.

Additive Manufacturing (AM) gets increasing attention for Nitinol processing for medical devices because it provides the opportunity to circumvent many of the challenges associated with conventional machining of Nitinol as well as the tailoring of patient-specific implants. Frequently used AM techniques for Nitinol are powder-bed technologies such as Selective Laser Melting (SLM) which is a suitable method for creating complex parts. However, functional Nitinol parts are strongly influenced by the powder properties. In particular, the oxygen content is a critical factor when components with medical grade Nitinol are required. Trace amounts of oxygen form an oxide covering the powder surface with a nanometric thickness as well as complex structure and composition due to the high specific surface energy of the powder. The oxide layer is depending on ambient conditions during powder manufacturing as well as powder handling. The present work provides characterization of the oxide layer and the microstructure for a pseudoelastic Ni 50.8 Ti 49.2 Nitinol alloy powder for AM by TEM investigations. Furthermore, for an estimation of the powder oxide layer thickness, the calculated oxide layer thickness resulting from the oxygen content and the particle size is compared with the measured oxide layer thickness by an EDX line-scan.

Nitinol is frequently used as raw material for cardiovascular endoprosthesis, due to their high biocompatibility and properties such as psedoelasticity. Typically, the highest stress/strain that Nitinol based devices undergo occurs during crimping. These mechanical stresses can affect the functional fatigue behaviors. Nitinol devices are crimped to small diameters to deliver to the anatomical location of interest. Thereby, the microstructural and mechanical changes in Nitinol tubes generated by mechanical load conditions are studied, to monitor the pseudoelastic properties as a function of load time. Consequently, a permanent load test is carried out by means of a fixture with parallel clamps, in order to generate deformation of the cross-sectional area of the tube. The procedure consists of deforming 5 mm long samples with 7 mm outer diameter tubes and a wall thickness of 0.5 mm in straight annealed condition at room temperature. For this test, o-shaped samples of single ingot were analyzed. The test was carried out with strains of 2 %, 4 %, 6 % and 8 % to simulate different device crimp strains. Parts were evaluated after time intervals up to six months under load. Afterwards the geometrical changes of the samples were measured. Additionally, the samples were characterized by DSC and XRD measurements.

Radical surgical intervention for chest wall tumors is typically accompanied by the lesion of osteochondral structures and the appearance of complex post-resection defects, which result in functional and aesthetic impairment. After extensive resection of the chest wall, it is vitally important that it be simultaneously repaired, including restoring the osteochondral framework and the integrity of the integumentary tissues as well as maintaining the anatomical and physiological volume of the mediastinum and the pleural cavities. Porous and solid Nitinol implants and their successful deployment in surgical treatments have encouraged insights for immediate and delayed osteoplasty in cancer patients. The novel aspect of this work consists in this surgical method of post-excision defect repair is performed using a proprietary approach and customized NiTi-based implants. The results indicate that the suggested surgical approach and tactics using one-step repair are one of the promising techniques even though the case is aggravated with extensive chest wall lesions. The approach can be performed safely and can be recommended as a routine procedure with a high success rate. Combined Nitinol implants seem to be very good reinforcing biomaterials that enabled the reliable repair of thoracic post-excisional defects of various sizes with good functional, clinical, and cosmetic outcomes.

The continuous rolling of Nitinol alloys is a metalworking process with the ability to produce large quantities of sheet with uniform properties for the use in actuation applications in motion systems with cyclic loads. Great advantages of continuous rolling in comparison with other manufacturing methods are the cold work and heat treatment steps and their ability to influence the properties of the product and keep them in a very tight window over the width and the length of the process. Those tightly controlled properties are key-requirements to use the continuous rolled Nitinol material for subsequent automated processes like stamping in progressive dies or deep- drawing. It is also required for efficient reel-to-reel laser or EDM cutting. The primary objective of this work is to evaluate and obtain the properties of Nitinol continuously flat-rolled sheets and optimization of the process parameters by fatigue evaluation.

Elastocaloric cooling has emerged as a promising alternative to traditional vapor-compression refrigeration. Attempts to develop elastocaloric devices have been made in recent years, with substantial achievements in realizing large temperature span and high coefficient of performance (COP). Moreover, miniaturization of these devices will be highly beneficial in commercializing the elastocaloric cooling. In this work, the authors report a bending approach to induce the phase transformation of NiTi sheet with advantages of low force actuation and high temperature change, while performances of elastocaloric air cooler based on the bending mode are demonstrated and analyzed.

TiNi-based wire is widely used in the manufacture of surgical implants and designs due to its biocompatibility and ability to undergo viscoelastic deformation with tissues, withstanding millions of deformation cycles without destruction. TiNi is a self-passivating material, as it forms a complex surface oxide layer that protects the material from corrosion and is itself biocompatible. The functional properties of TiNi wire are determined by the structure, composition, and thickness. The purpose of this work is to study the deformation behavior of thin TiNi wires depending on the thickness. TiNi wires of different thicknesses (40, 60, 90 µm) were tested by uniaxial tension to rupture and in the load-unload cycle (5 cycles). The results found that All TiNi wires exhibit the effect of superelasticity at a relative strain of 5-7%. With an increase in the wire thickness from 40 to 90 µm, the values of the martensitic shear stress increase from 450 to 1200 MPa and the tensile strength increases from 1300 to 3150 MPa.

In this work, a new method of processing shape memory alloys was utilized to understand the effects of disrupting the martensitic long range order and forming amorphous nanodomains with martensitic short range order. Based on the obtained results, strain glass alloy states were analyzed and confirmed using various characterization methods to determine trends and compare two alloys, Ni 49.5 Ti 50.5 and Ni 50.8 Ti 49.2 . For Ni 49.5 Ti 50.5 a 33% thickness reduction was required to obtain a cold work-induced strain glass state, while for Ni 50.8 Ti 49.2 a 24% reduction was required.

A promising elastocaloric cooling technology (one of the solid-state cooling technologies) does not require any potentially harmful vaporous refrigerants. Its basic working principle, the martensitic transformation and its reverse transformation of shape memory alloys (SMAs) such as NiTi, NiTiCu, and NiFeGaC is one of the first-order non-diffusible phase transitions between a high-temperature phase (the austenite phase) of a B2 cubic structure and a low-temperature phase (the martensite phase) of a B19′ monoclinic structure. This paper investigates the compression behaviors of different NiTi regenerator structures through fatigue tests. An optimized 3-layer sample shows promise to be used in elastocaloric cooling prototypes and gives insight into the structural optimization of regenerators.