TY - JOUR

T1 - Functional and structural fatigue of titanium tantalum high temperature shape memory alloys (HT SMAs)

AU - Niendorf, T.

AU - Krooß, P.

AU - Batyrsina, E.

AU - Paulsen, A.

AU - Motemani, Y.

AU - Ludwig, A.

AU - Buenconsejo, P.

AU - Frenzel, J.

AU - Eggeler, G.

AU - Maier, H. J.

N1 - Funding information: Financial support by the Deutsche Forschungsgemeinschaft (DFG) within the Research Unit Program “Hochtemperatur-Formgedächtnislegierungen” (Contract nos. NI1327/3-1 ; MA1175/34-1 ; FR2675/3-1 and LU1175/11-1 ) is gratefully acknowledged. P.M. Kadletz is thanked for providing the data from X-ray diffraction.

PY - 2014/10/22

Y1 - 2014/10/22

N2 - Due to their high work output and good mechanical properties, actuators made from shape memory alloys (SMAs) are used in numerous applications. Unfortunately, SMAs such as nickel-titanium (Ni-Ti) can only be employed at temperatures up to about 100°C. Lately, high-temperature shape memory alloys (HT SMAs) have been introduced to overcome this limitation. Ternary systems based on Ni-Ti have been intensively characterized and alloys are available that can operate at elevated temperatures. However, these alloys either contain substantial amounts of expensive noble elements like platinum and palladium, or the materials are brittle. The titanium-tantalum (Ti-Ta) system has been developed to overcome these issues. Binary Ti-Ta provides relatively high MS temperature combined with excellent workability, but it suffers from fast cyclic degradation. By alloying with third elements this drawback can be overcome: The ternary Ti-Ta-Al alloy shows overall promising properties as will be shown in the present work. In-situ thermo-mechanical cycling experiments were conducted and allowed for evaluation of the factors affecting the functional and structural fatigue of this alloy. Functional fatigue is dominated by ω-phase evolution, while structural fatigue is triggered by an interplay of ω-phase induced embrittlement and deformation constraints imposed by unsuitable texture. In addition, a concept for fatigue life extension proposed very recently for binary Ti-Ta, is demonstrated to be also applicable for the ternary Ti-Ta-Al.

AB - Due to their high work output and good mechanical properties, actuators made from shape memory alloys (SMAs) are used in numerous applications. Unfortunately, SMAs such as nickel-titanium (Ni-Ti) can only be employed at temperatures up to about 100°C. Lately, high-temperature shape memory alloys (HT SMAs) have been introduced to overcome this limitation. Ternary systems based on Ni-Ti have been intensively characterized and alloys are available that can operate at elevated temperatures. However, these alloys either contain substantial amounts of expensive noble elements like platinum and palladium, or the materials are brittle. The titanium-tantalum (Ti-Ta) system has been developed to overcome these issues. Binary Ti-Ta provides relatively high MS temperature combined with excellent workability, but it suffers from fast cyclic degradation. By alloying with third elements this drawback can be overcome: The ternary Ti-Ta-Al alloy shows overall promising properties as will be shown in the present work. In-situ thermo-mechanical cycling experiments were conducted and allowed for evaluation of the factors affecting the functional and structural fatigue of this alloy. Functional fatigue is dominated by ω-phase evolution, while structural fatigue is triggered by an interplay of ω-phase induced embrittlement and deformation constraints imposed by unsuitable texture. In addition, a concept for fatigue life extension proposed very recently for binary Ti-Ta, is demonstrated to be also applicable for the ternary Ti-Ta-Al.

KW - Beta titanium alloy

KW - In-situ characterization

KW - Martensitic transformation

KW - Microstructure

KW - Shape memory effect

KW - Thermo-mechanical cycling

UR - http://www.scopus.com/inward/record.url?scp=84910093396&partnerID=8YFLogxK

U2 - 10.1016/j.msea.2014.10.038

DO - 10.1016/j.msea.2014.10.038

M3 - Article

AN - SCOPUS:84910093396

VL - 620

SP - 359

EP - 366

JO - Materials Science and Engineering A

JF - Materials Science and Engineering A

SN - 0921-5093

ER -