Size Effects in Martensitic Transformations: Poster Session
Program Organizers: Peter Anderson, The Ohio State University

Monday 5:30 PM
July 10, 2017
Room: Crystal Ballroom A
Location: Hyatt Regency Chicago

P1-40: An Assessment of Grain Size Effects on Transformation Temperatures and Hysteresis in Cu-based SMA Tapes Obtained by Melt Spinning: Paulo La Roca1; Lucio Isola1; Cesar Sobrero1; Florencia Giordana1; Analia Roatta1; Philippe Vermaut2; Jorge Malarria1; 1Instituto de Fisica Rosario - CONICET-UNR; 2Ecole Nationale Superieure de Chimie de Paris - Paris-Tech
    We systematically studied the grain size, d, dependence of the shift in transformation temperatures and the widening of the hysteresis in polycrystalline Cu-based shape memory alloy tapes obtained by melt-spinning. Within a phenomenological thermodynamic framework, we analyze changes in the difference in Gibbs free energy between the martensite and the parent phase, which result from contributions of martensite-martensite interface energy, stored elastic energy, and dissipative effects produced by internal friction between mobile interfaces and grain boundaries. Experimental results (Ms vs d, and Hys vs d) are adequately fitted by functions of the characteristic grain size of the specimens, over the range of ~100 µm to ~ 1 µm.

P1-41: Effect of Hydrogen on the Transformation Behavior and Superelasticity of TiNi Binary Alloys with the Coarse-grained and Nanosized Structures: Aleksander Lotkov1; Anatolii Baturin1; Victor Grishkov1; Ivan Rodionov1; Andrey Lider2; 1Institute of Strength Physics and Materials Science of Siberian Branch Russian Academy of Sciences; 2National Research Tomsk Polytechnic University
    On the basis of own results and literature data we analyzed the effect of hydrogen on the superelasticity, temperatures and sequence of martensitic transformations in the binary TiNi based alloys with coarse-grained and nanosized structures. The wires samples have been charged electrolytically with hydrogen in the 0.9% NaCl aqueous solution. It is established that the samples with nanosized structure absorb hydrogen more than twice compared to samples with coarse-grained structure. After hydrogenation of the samples for a long time stored at room temperature to achieve a uniform distribution of hydrogen over the volume of the samples. It is shown that hydrogen absorption leads to a decrease of the temperatures of martensitic transformations (MT) B2RB19` until the complete suppression of MT, at least to the boiling temperature of liquid nitrogen. It is found that hydrogen has a smaller effect on superplasticity of nanostructured samples compared to the coarse-grained materials of the same composition We discuss possible mechanisms of influence of hydrogen on the martensitic transformation and the effect of superelasticity in TiNi based alloys depending on the grain size.

P1-42: Geometrical Evaluation of a Criteria based in Deformation Compatibility for The prediction of the Apparition of Martensite Variants in Shape Memory Alloys: Rodrigo Lechuga Taboada1; Jacinto Cortés Pérez1; Fernando Nestor García Castillo2; Vicente Amigó Borras3; Alberto Reyes Solís1; 1Universidad Nacional Autónoma de Mexico; 2Tecnológico de Estudios Superiores de Chalco; 3Universitat Politčcnica de Valčncia
    This work presents a prediction of the martensite variants formed in some grains with common boundary during the stress induced martensite transformation in a polycrystalline sample of Cu–11.5% wt. Al–0.5%wt. Be shape memory alloy undergoing simple tension. The prediction is based in a criterion who consider parameters widely used in single crystals, such as the crystal orientation and Schmid factor (SF). The displacement vector fields (DVFs) were obtained in the observation system by a mathematical model and were used to distort the boundary of a set of grains. In order to increase the prediction range of the criteria, the inclusion of a comparison between DVFs of high SF variants of two different neighbor grains in order to verify the strain compatibility between their common boundaries is added. The predicted martensite variants in 6 grains located in two different clusters and the experimental observations was compared.

P1-43: Microstructure, Martensitic Transformation and Mechanical Properties of Ultrafine-grained TiNiNb Alloy: Yunxiang Tong1; Guang Chao. Wang1; Feng Chen1; Bing Tian1; Li Li1; 1Harbin Engineering University
    In present work, microstructure, martensitic transformation and mechanical properties of ultrafine-grained TiNiNb alloy were investigated as a function of processing parameters. The results show that the grain size of TiNiNb alloy was reduced to about 200-300 nm after pressing for eight passes, irrespective of processing route. Ms temperature decreases with increasing pass number. After the samples in martensitic state were deformed, their reverse transformation proceeded into a multiple-stage manner upon first heating. The as-ECAP processed sample showed a much wider transformation hysteresis than that of initial alloy. This is ascribed to the enlarged strength mismatch between matrix and beta-Nb phase. The yield strength of ultrafine-grained TiNiNb alloy were obviously improved as compared to initial alloy. The results may provide guideline on the further optimization of TiNiNb alloys.

P1-44: Research for Phase Transformation of Magnetic Shape Memory Alloy Particles: Bing Tian1; Yunxiang Tong1; Feng Chen1; Li Li1; Yufeng Zheng1; 1Harbin Engineering University
    The martensitic transformation of magnetic shape memory alloy particles is critical for the performance of the composites with magnetic shape memory alloy particles and ductile matrix. In this investigation, the ternary NiMnGa particles and quaternary NiCoMnIn particles are prepared by ball milling and post-annealing. It was found that the martensitic transformation of both particles after ball milling disappeared due to the deterioration of high ordered Heusler structure. Post annealing at temperatures of 873~1173K was effective in restoring the martensitic transformation of NiMnGa particles but difficult to retrieve that of NiCoMnIn particles. The procedure of ball milling and post-annealing refined grain size of these alloys, therefore the martensitic transformation of quaternary NiCoMnIn alloy could be more sensitive to grain size of the particles than that of ternary NiMnGa alloy, which resulted in the disappearance of martensitic transformation of NiCoMnIn particles after even a high temperature post-annealing.

P1-45: Temperature Dependent Indentation Response of NiTi-based Shape Memory Alloys: Peizhen Li1; Haluk Karaca1; Yang-Tse Cheng1; 1University of Kentucky
    The indentation response of conventional NiTi, high temperature NiTiHf and high strength NiTiHfPd shape memory alloys were investigated by instrumented indentation over a range of temperature (25 to 340 °C) using a spherical indenter (tip radius, r = 25 µm). Change of indentation hardness, contact modulus, and work recoverable ratio were revealed as functions of temperature, applied load, composition and orientation. The findings were compared with compression results. It was revealed that transformation temperatures can be determined from the changes in work recovery and they are consistent with the values obtained from mechanical tests. Moreover, it will be shown that indentation response can be used to determine the deformation mechanism such as martensite reorientation, superelasticity and plastic deformation.

P1-46: Ultra-low Stiffness in Martensitic Nanostructures through Landscape Engineering: Sam Reeve1; Yang Wang1; Karthik Guda Vishnu1; Alejandro Strachan1; 1Purdue University
    We utilize free energy landscape engineering to develop novel properties in composite nanostructures consisting of both martensitic and non-martensitic metals. In this example, we use large-scale molecular dynamics (MD) simulations of epitaxially integrated martensitic Ni63Al37 and non-martensitic NiAl, chosen because of the specific overlap in their energy landscapes. We aim to utilize not the stable (martensite) or metastable (austenite), but the unstable region in between, stabilized by the non-martensitic phase. Analytical combination of the landscapes for each individual component predicts an extended flattened stable region, indicating low stiffness. We confirm this with MD simulations of core/shell nanowires and laminates, reaching stiffness as low as 4 GPa while retaining full strength. We have additionally shown tunability of the stiffness, transformation temperature, and transformation strain. Continuing, nanostructures could be designed using landscape engineering for numerous properties from purposeful mechanical anisotropy to martensitic behavior from non-martensitic components.