{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T17:46:51Z","timestamp":1792086411291,"version":"4.4.0"},"reference-count":36,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2025,5,21]],"date-time":"2025-05-21T00:00:00Z","timestamp":1747785600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Class III Peak Discipline of Shanghai\u2014Materials Science and Engineering (High-Energy Beam Intelligent Processing and Green Manufacturing)"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>The significant phase transformation hysteresis in TiNi alloys limits their performance. To address this, copper (Cu) was added as an alloying element to reduce hysteresis. This study synthesized three compositions of Ti50Ni50\u2212xCux (x = 0, 5, 7 at.%) shape memory alloys (SMAs) via vacuum arc melting to optimize the Cu content. The alloys were homogenized through hot rolling to maintain stable mechanical and shape memory properties. The hot-rolled Ti50Ni45Cu5 alloy demonstrated excellent shape memory behavior, achieving 100% thermal recovery after one cycle at 4% and 6% strain and 99.2% recovery after six cycles at 4% strain. It also exhibited outstanding mechanical performance, with a tensile strength of 900 MPa and 40% elongation. Microscopic analysis using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) revealed that Cu preferentially segregates at grain boundaries, suppressing the formation of the Ti2(Ni,Cu) phase. This moderate segregation, combined with hot rolling, promotes the reprecipitation and uniform distribution of phases, reducing the likelihood of premature fracture caused by stress concentration during deformation. The moderate thickness and uniformly distributed martensite, as well as the Type II twins with strong deformation ability, significantly improved the shape memory properties of Ti50Ni45Cu5. This study provides valuable insights into the microscopic mechanisms influenced by Cu in TiNi alloys and proposes a novel strategy for controlling precipitate phases through adjustments in alloy composition and optimized processing conditions.<\/jats:p>","DOI":"10.3390\/ma18102407","type":"journal-article","created":{"date-parts":[[2025,5,21]],"date-time":"2025-05-21T09:58:22Z","timestamp":1747821502000},"page":"2407","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Influence of Cu on the Mechanical and Shape Memory Properties of TiNi Alloys"],"prefix":"10.3390","volume":"18","author":[{"given":"Luzhou","family":"Dong","sequence":"first","affiliation":[{"name":"Research Center of High-Temperature Alloy Precision Forming, Shanghai University of Engineering Science, Shanghai 201620, China"},{"name":"School of Materials Science and Engineering, Shanghai University of Engineering Science, Shanghai 201620, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Weifang","family":"Mann","sequence":"additional","affiliation":[{"name":"Shanghai Marine Equipment Research Institute, No. 10 Hengshan Rd., Shanghai 200031, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7320-4245","authenticated-orcid":false,"given":"Bo","family":"He","sequence":"additional","affiliation":[{"name":"Research Center of High-Temperature Alloy Precision Forming, Shanghai University of Engineering Science, Shanghai 201620, China"},{"name":"School of Materials Science and Engineering, Shanghai University of Engineering Science, Shanghai 201620, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,5,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6797","DOI":"10.1016\/j.jmrt.2021.11.112","article-title":"Microstructure, shape memory properties, and in vitro biocompatibility of porous NiTi scaffolds fabricated via selective laser melting","volume":"15","author":"Lu","year":"2021","journal-title":"J. Mater. Res. Technol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"3444","DOI":"10.1016\/j.actamat.2010.02.019","article-title":"Influence of Ni on martensitic phase transformations in NiTi shape memory alloys","volume":"58","author":"Frenzel","year":"2010","journal-title":"Acta Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"272","DOI":"10.1016\/j.matchemphys.2013.05.010","article-title":"Influence of the microstructural inhomogeneities on the martensite-to-austenite phase transformation temperatures in TiNiCu-based shape-memory alloys","volume":"141","author":"Haenschke","year":"2013","journal-title":"Mater. Chem. Phys."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"2029","DOI":"10.1016\/S1003-6326(13)62692-8","article-title":"Phase transformation and damping behavior of lightweight porous TiNiCu alloys fabricated by powder metallurgy process","volume":"23","author":"Jiang","year":"2013","journal-title":"Trans. Nonferrous Met. Soc. China"},{"key":"ref_5","first-page":"959","article-title":"Cu-content dependence of shape memony characienistics in TiN-cu aloys. MatelTrans","volume":"31","author":"Nam","year":"1990","journal-title":"JLM"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"148","DOI":"10.1016\/0921-5093(95)09801-1","article-title":"Cyclic stress-strain characteristics of Ti-Ni and Ti-Ni-Cu shape memory alloys","volume":"202","author":"Strnadel","year":"1995","journal-title":"Mater. Sci. Eng. A"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"20","DOI":"10.1016\/j.intermet.2014.04.013","article-title":"An investigation on the crystal structures of Ti50Ni50\u2212xCux shape memory alloys based on density functional theory calculations","volume":"53","author":"Gou","year":"2014","journal-title":"Intermetallics"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"32","DOI":"10.1016\/j.jmbbm.2013.01.014","article-title":"Study of thermomechanical treatment on mechanical-induced phase transformation of NiTi and TiNiCu wires","volume":"21","author":"Shahmir","year":"2013","journal-title":"J. Mech. Behav. Biomed. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"032001","DOI":"10.1088\/2631-7990\/acc7d9","article-title":"Laser powder bed fusion additive manufacturing of NiTi shape memory alloys: A review","volume":"5","author":"Wei","year":"2023","journal-title":"Int. J. Extrem. Manuf."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"2064","DOI":"10.1016\/S1003-6326(23)66244-2","article-title":"Effect of rolling temperature and reduction on brick-and-mortar Ti2Ni\/TiNi composite","volume":"33","author":"Jia","year":"2023","journal-title":"Trans. Nonferrous Met. Soc. China"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"205","DOI":"10.1016\/j.jmst.2021.06.019","article-title":"Simultaneous enhancement of mechanical and shape memory properties by heat-treatment homogenization of Ti2Ni precipitates in TiNi shape memory alloy fabricated by selective laser melting","volume":"101","author":"Lu","year":"2022","journal-title":"J. Mater. Sci. Technol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"600","DOI":"10.1016\/j.matpr.2022.10.225","article-title":"Investigation of some thermomechanical processing effects on the structure and properties of a TiNiCu shape memory alloy","volume":"72","author":"Popa","year":"2023","journal-title":"Mater. Today Proc."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Villa, F., Nespoli, A., Passaretti, F., and Villa, E. (2021). Microstructural and Thermo-Mechanical Characterization of Cast NiTiCu20 Shape Memory Alloy. Materials, 14.","DOI":"10.3390\/ma14143770"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"147920","DOI":"10.1016\/j.msea.2025.147920","article-title":"Enhanced strength-ductility synergy in ferrous medium-entropy alloys via single-step hot rolling","volume":"926","author":"Liao","year":"2025","journal-title":"Mater. Sci. Eng. A"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1058","DOI":"10.1016\/j.scib.2021.02.032","article-title":"Dislocations across interphase enable plain steel with high strength-ductility","volume":"66","author":"Zhang","year":"2021","journal-title":"Sci. Bull."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1428","DOI":"10.1016\/j.jmrt.2022.07.146","article-title":"Role of Nb on the phase stability and morphology of Ti\u2013Ni\u2013Cu\u2013Nb alloys","volume":"20","author":"Silva","year":"2022","journal-title":"J. Mater. Res. Technol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"4925","DOI":"10.1016\/j.matdes.2011.05.051","article-title":"A comparative study of Ni\u2013Ti and Ni\u2013Ti\u2013Cu shape memory alloy processed by plasma melting and injection molding","volume":"32","author":"Gonzalez","year":"2011","journal-title":"Mater. Des."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Cascadan, D., and Grandini, C.R. (2020). Effect of Oxygen in the Structure, Microstructure and Mechanical Properties of Ti-xNi (x = 5, 10, 15 and 20 wt%) Alloys. Metals, 10.","DOI":"10.3390\/met10111424"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"502","DOI":"10.1016\/S1003-6326(18)64683-7","article-title":"Microstructure and superelastic properties of free forged Ti\u2013Ni shape-memory alloy","volume":"28","author":"Bahador","year":"2018","journal-title":"Trans. Nonferrous Met. Soc. China"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"116617","DOI":"10.1016\/j.actamat.2020.116617","article-title":"Giant hardening response in AlMgZn(Cu) alloys","volume":"206","author":"Stemper","year":"2021","journal-title":"Acta Mater."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"012067","DOI":"10.1088\/1742-6596\/430\/1\/012067","article-title":"Local crystal structure of TiNiCu shape memory alloys","volume":"430","author":"Menushenkov","year":"2013","journal-title":"J. Phys. Conf. Ser."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"168664","DOI":"10.1016\/j.jallcom.2022.168664","article-title":"Microstructures and mechanical behavior of Ti-(38+x)Ni-12Cu (at%) (x=0\u223c3) alloys","volume":"938","author":"Kim","year":"2023","journal-title":"J. Alloys Compd."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"174937","DOI":"10.1016\/j.jallcom.2024.174937","article-title":"Nanoscale-precipitate-strengthened (Ni,Cu)-rich TiNiCu shape memory alloy with stable superelasticity and elastocaloric performance","volume":"997","author":"Hsu","year":"2024","journal-title":"J. Alloys Compd."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"143346","DOI":"10.1016\/j.msea.2022.143346","article-title":"Improvement in the superelasticity of a Ti\u201335.5Ni\u201315Cu (at.%) alloy using Ti(Ni, Cu)2 phase","volume":"847","author":"Shim","year":"2022","journal-title":"Mater. Sci. Eng. A"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"116595","DOI":"10.1016\/j.actamat.2020.116595","article-title":"Segregation and precipitation stabilizing an ultrafine lamellar-structured Al-0.3%Cu alloy","volume":"206","author":"Shuai","year":"2021","journal-title":"Acta Mater."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"451","DOI":"10.1007\/s11665-020-05415-3","article-title":"Effect of Various Thermal Treatments and Cu Contents on Precipitation Mechanism, Martensitic Growth, and Cold Workability of Ti50Ni50-xCux Ternary Shape Memory Alloys","volume":"30","author":"Haq","year":"2021","journal-title":"J. Mater. Eng. Perform."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"98","DOI":"10.1016\/j.jmapro.2019.11.003","article-title":"Thermo mechanical analyses and characterizations of TiNiCu shape memory alloy structures developed by laser additive manufacturing","volume":"48","author":"Shiva","year":"2019","journal-title":"J. Manuf. Process."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"109326","DOI":"10.1016\/j.triboint.2024.109326","article-title":"Analyzing the effect of the mechanical stability of residual austenite on the wear performance","volume":"192","author":"Zhu","year":"2024","journal-title":"Tribol. Int."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"120885","DOI":"10.1016\/j.actamat.2025.120885","article-title":"Austenite residual stress and lath martensite variant selection in low carbon steels","volume":"289","author":"Kumar","year":"2025","journal-title":"Acta Mater."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Costanza, G., Tata, M.E., and Libertini, R. (2016, January 14\u201318). Effect of temperature on the mechanical behaviour of ni-ti shape memory sheets. Proceedings of the TMS Annual Meeting and Exhibition, Nashville, TN, USA.","DOI":"10.1007\/978-3-319-48254-5_52"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"166275","DOI":"10.1016\/j.jallcom.2022.166275","article-title":"Shape memory effect in TiNi single crystals with thermal-induced martensite transformation or strain glass transition","volume":"922","author":"Timofeeva","year":"2022","journal-title":"J. Alloys Compd."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"49","DOI":"10.1016\/j.pmatsci.2017.03.003","article-title":"Deformation physics of shape memory alloys\u2014Fundamentals at atomistic frontier","volume":"88","author":"Chowdhury","year":"2017","journal-title":"Prog. Mater. Sci."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1016\/j.matdes.2016.07.057","article-title":"Interface stress evolution of martensitic transformation in MnCu alloys: A phase-field study","volume":"109","author":"Cui","year":"2016","journal-title":"Mater. Des."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"119418","DOI":"10.1016\/j.actamat.2023.119418","article-title":"Unleashing multi-scale mechanical enhancement in NiTi shape memory alloy via annular intra-laser deposition with homogenized Ti2Ni nanoprecipitates","volume":"262","author":"Yi","year":"2024","journal-title":"Acta Mater."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"178450","DOI":"10.1016\/j.jallcom.2025.178450","article-title":"In-situ TEM study on the effect of dislocations on phase transformation and cycling behaviors of laser powder bed fused TiNi alloy","volume":"1013","author":"Zhang","year":"2025","journal-title":"J. Alloys Compd."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"2006","DOI":"10.1016\/j.jmrt.2024.08.030","article-title":"Effect of heat treatment processes on the microstructure and mechanical properties of 00Cr13Ni5Mo super martensitic stainless steel (SMSS)","volume":"32","author":"Zhu","year":"2024","journal-title":"J. Mater. Res. Technol."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/18\/10\/2407\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T17:36:36Z","timestamp":1760031396000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/18\/10\/2407"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,5,21]]},"references-count":36,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2025,5]]}},"alternative-id":["ma18102407"],"URL":"https:\/\/doi.org\/10.3390\/ma18102407","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,5,21]]}}}