Mechanical and Functional Behavior of High-Temperature Ni-Ti-Pt Shape Memory Alloys

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 47; no. 4; pp. 1587 - 1599
• Main Authors: Buchheit, Thomas E., Susan, Donald F., Massad, Jordan E., McElhanon, James R., Noebe, Ronald D.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.04.2016; Springer Nature B.V; ASM International
• Subjects: Alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Failure; High temperature; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Materials Science; Mechanical properties; Mechanical testing; Metallic Materials; Metallurgy; Microstructure; Nanotechnology; Nickel base alloys; Recovery; Shape memory alloys; Strain; Structural Materials; Surfaces and Interfaces; Thin Films; Transformations; Shape Memory; Shape Memory Alloy; Shape Recovery; Martensite; Austenite
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-016-3324-y

A series of Ti-rich Ni-Ti-Pt ternary alloys with 13 to 18 at. pct Pt were processed by vacuum arc melting and characterized for their transformation behavior to identify shape memory alloys (SMA) that undergo transformation between 448 K and 498 K (175 °C and 225 °C) and achieve recoverable strain exceeding 2 pct. From this broader set of compositions, three alloys containing 15.5 to 16.5 at. pct Pt exhibited transformation temperatures in the vicinity of 473 K (200 °C), thus were targeted for more detailed characterization. Preliminary microstructural evaluation of these three compositions revealed a martensitic microstructure with small amounts of Ti 2 (Ni,Pt) particles. Room temperature mechanical testing gave a response characteristic of martensitic de-twinning followed by a typical work-hardening behavior to failure. Elevated mechanical testing, performed while the materials were in the austenitic state, revealed yield stresses of approximately 500 MPa and 3.5 pct elongation to failure. Thermal strain recovery characteristics were more carefully investigated with unbiased incremental strain-temperature tests across the 1 to 5 pct strain range, as well as cyclic strain-temperature tests at 3 pct strain. The unbiased shape recovery results indicated a complicated strain recovery path, dependent on prestrain level, but overall acceptable SMA behavior within the targeted temperature and recoverable strain range.