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Effect of Ti$_2$Pd(Ni) on the Transformation Behavior in Sputtered Ti-rich TiNiPd Shape Memory Alloys
Authors:
Lars Bumke,
Niklas Wolff,
Lorenz Kienle,
Eckhard Quandt
Abstract:
TiNiPd based shape memory alloys (SMAs) share similar microstructural features as TiNiCu-based SMAs known for their exceptional resistance to functional fatigue due to their high crystallographic compatibility, nanometer sized grains and coherent precipitates, making them an ideal system to further explore the critical factors influencing cyclic stability. In this study, we investigate the effect…
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TiNiPd based shape memory alloys (SMAs) share similar microstructural features as TiNiCu-based SMAs known for their exceptional resistance to functional fatigue due to their high crystallographic compatibility, nanometer sized grains and coherent precipitates, making them an ideal system to further explore the critical factors influencing cyclic stability. In this study, we investigate the effect of heat treatments (500 °C, 600 °C, 700 °C and 800 °C) on the cyclic stability and microstructure of free-standing, magnetron-sputtered Ti$_{53.6}$Ni$_{35.2}$Pd$_{11.2}$ films. All heat treatments promote the formation of Ti$_2$Pd(Ni) precipitates and result in a similar grain size (~1-4 $μ$m). Lower heat treatment temperatures improve the cyclic stability of the stress induced transformation while reducing transformation temperatures and latent heat. Temperature dependent X-ray diffraction reveals a complex microstructure for the martensite phase with Ti$_2$Pd(Ni), Ti$_2$Ni(Pd), TiNiPd(B2), B19/B19$'$ and R-phase. The thermal phase transition changes from a distinct 1st order to a 2nd order like transition, accompanied by increasing amount of remanent austenite and R-phase, with nearly no change for the sample heat treated at 500 °C. In situ stress dependent X-ray diffraction demonstrates a significant difference between the temperature and stress induced phase transformation for this heat treatment. The observed semi crystalline microstructure, featuring nano domains of Ti$_2$Pd(Ni) precipitates in the sample heat-treated at 500 °C, leads to a mixture of long range martensitic and strain glass transition. This study highlights the impact of heat treatment and microstructure on the phase transformation behavior and functional fatigue in Ti-rich TiNiPd alloys.
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Submitted 1 May, 2025;
originally announced May 2025.
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Composition Design of Shape Memory Ceramics based on Gaussian Processes
Authors:
Ashutosh Pandey,
Justin Jetter,
Hanlin Gu,
Eckhard Quandt,
Richard D. James
Abstract:
We present a Gaussian process machine learning model to predict the transformation temperature and lattice parameters of ZrO$_2$-based ceramics. Our overall goal is to search for a shape memory ceramic with a reversible transformation and low hysteresis. The identification of a new low hysteresis composition is based on design criteria that have been successful in metal alloys: (1) $λ_2 = 1$, wher…
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We present a Gaussian process machine learning model to predict the transformation temperature and lattice parameters of ZrO$_2$-based ceramics. Our overall goal is to search for a shape memory ceramic with a reversible transformation and low hysteresis. The identification of a new low hysteresis composition is based on design criteria that have been successful in metal alloys: (1) $λ_2 = 1$, where $λ_2$ is the middle eigenvalue of the transformation stretch tensor, (2) minimizing the max$|q(f)|$, which measures the deviation from satisfying the cofactor conditions, (3) high transformation temperature, (4) low transformational volume change, and (5) solid solubility. We generate many synthetic compositions, and identify a promising composition, 31.75Zr-37.75Hf-14.5Y-14.5Ta-1.5Er, which closely satisfies all the design criteria based on predictions from machine learning. However, differential thermal analysis reveals a relatively high thermal hysteresis of 137°C for this composition, indicating that the proposed design criteria are not universally applicable to all ZrO$_2$-based ceramics. We also explore reducing tetragonality of the austenite phase by addition of Er$_2$O$_3$. The idea is to tune the lattice parameters of austenite phase towards a cubic structure will increase the number of martensite variants, thus, allowing more flexibility for them to accommodate high strain during transformation. We find the effect of Er$_2$O$_3$ on tetragonality is weak due to limited solubility. We conclude that a more effective dopant is needed to achieve significant tetragonality reduction. Overall, Gaussian process machine learning models are shown to be highly useful for prediction of compositions and lattice parameters, but the discovery of low hysteresis ceramic materials apparently involves other factors not relevant to phase transformations in metals.
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Submitted 4 April, 2026; v1 submitted 2 April, 2025;
originally announced April 2025.
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In-situ compression and shape recovery of Ceramic single grain micro-pillar
Authors:
Justin Jetter,
Eckhard Quandt
Abstract:
Most ceramic materials are known for high fracture toughness while reacting highly brittle to physical deformation. Some advancements were made by utilizing the transformation toughening effect of Yttria-doped Zirconia. However, finding a ceramic material demonstrating an effect analogous to the Shape Memory Effect (SME) in certain metals, that also allows for superelastic responses, remains a cha…
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Most ceramic materials are known for high fracture toughness while reacting highly brittle to physical deformation. Some advancements were made by utilizing the transformation toughening effect of Yttria-doped Zirconia. However, finding a ceramic material demonstrating an effect analogous to the Shape Memory Effect (SME) in certain metals, that also allows for superelastic responses, remains a challenge. The underlying mechanism for SME and superelasticity is based on crystallographic variations within the material's grains, requiring sophisticated electron microscopy techniques for direct observation. The combination of a scanning electron microscope (SEM) with focused ion beam (FIB) milling, a Kleindiek Nanotechnik GmbH micro-manipulator with a 1.5 $μ$m diamond tip, and the ability to achieve in-situ heating up to 450 °C on a Kleindiek heating stage provides a robust platform for the preparation, deformation, and heating of micro-pillars made from ceramic materials. This setup enabled us to conduct detailed studies on the Zirconia-based ceramic, observing permanent deformation exceeding 4% strain, followed by shape recovery at 370 °C. The paper provides outlines the key experimental steps that facilitated these observations.
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Submitted 2 April, 2025;
originally announced April 2025.
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Theory of Intermediate Twinning and Spontaneous Polarization in Ferroelectric Potassium Sodium Niobate
Authors:
Georgios Grekas,
Patricia-Lia Pop-Ghe,
Eckhard Quandt,
Richard D. James
Abstract:
Potassium sodium niobate is considered a prominent material system as a substitute for lead-containing ferroelectric materials. It exhibits first-order phase transformations and ferroelectricity with potential applications ranging from energy conversion to innovative cooling technologies, thereby addressing important societal challenges. However, a major obstacle in the application of potassium so…
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Potassium sodium niobate is considered a prominent material system as a substitute for lead-containing ferroelectric materials. It exhibits first-order phase transformations and ferroelectricity with potential applications ranging from energy conversion to innovative cooling technologies, thereby addressing important societal challenges. However, a major obstacle in the application of potassium sodium niobate is its multi-scale heterogeneity and the lack of understanding of its phase transition pathway and microstructure. This can be seen from the findings of Pop-Ghe et al. (Ceram Int 47(14):20579-20585, 2021, https://doi.org/10.1016/j.ceramint.2021.04.067) which also reveal the occurrence of a phenomenon they term intermediate twinning during the phase transition. Here, we show that intermediate twinning is a consequence of energy minimization. We develop a geometrically nonlinear electroelastic energy function for potassium sodium niobate, including the cubic-tetragonal-orthorhombic transformations and ferroelectricity. The construction of the minimizers is based on compatibility conditions which ensure continuous deformations and pole-free interfaces. These minimizers agree with the experimental observations, including laminates between tetragonal variants under the cubic to tetragonal transformation, crossing twins under the tetragonal to orthorhombic transformation, intermediate twinning and spontaneous polarization. This shows how the full nonlinear electroelastic model provides a powerful tool in understanding, exploring, and tailoring the electromechanical properties of complex ferroelectric ceramics.
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Submitted 13 March, 2025; v1 submitted 3 February, 2023;
originally announced February 2023.