Influence of Tin Additions on the Phase-Transformation Characteristics of Mechanical Alloyed Cu-Al-Ni Shape-Memory Alloy
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BECAUSE of the unique properties of pseudoelasticity, shape-memory effect, and damping capability, Cu-based shape-memory alloys (SMAs) have been widely utilized in numerous practical applications.[1,2] The binary systems of Cu-Zn and Cu-Al are the two primary copper-based alloys that operate in the areas of the b-phase. Undoubtedly, Cu-Al-Ni SMAs are the most-employed alloys when high temperatures are needed.[3] For this reason, they can be used at high transformation temperatures, which are able to work at or perhaps close to 473 K (200 C),[4] which is usually difficult for Cu-Zn-Al and Ni-Ti alloys,[5,6] whose maximum temperatures are approximately 373 K (100 C).[7] The incorporation of a fourth element, for instance, Ti, Zr, Mn, B, Y, or V and rare earths into the ternary Cu-Al-Ni SMAs as a grain refiner may lead to microstructural adjustments in the phase formation, types, and distribution, oppositely to enhance the mechanical
SAFAA N. SAUD and M.N. MOHAMMED, Senior Lecturers, are with the Faculty of Information Science and Engineering, Management and Science University, 40100 Shah Alam, Malaysia, and also with the Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia. Contact e-mail: [email protected] E. HAMZAH, Professor, and H.R. BAKHSHESHI-RAD and T. ABUBAKAR, Senior Lecturers, are with the Faculty of Mechanical Engineering, Universiti Teknologi Malaysia. Manuscript submitted November 30, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
properties of conventionally cast Cu-Al-Ni SMA alloys.[8–11] However, a minor addition was demonstrated to be ineffective in controlling grain growth to an adequate level, while excessive addition tended to change the chemical composition of the alloy, and therefore shift the transformation temperature.[12] Moreover, excessive addition of the alloying element can also form a high volume fraction of precipitates (second-phase particles), which may also affect the mechanical properties.[13] The main issues are to prevent high brittleness in the conventional casting of the ternary and quaternary Cu-Al-Ni alloys and produce a large grain size associated with a high elastic anisotropy, which are categorized as major prohibitive factors that limit their commercial applications.[14–16] In addition, the casting process usually leads to a change in the chemical composition of the alloy, which may cause a shift in the transformation temperatures.[17] Therefore, alternative processing routes that have the ability to control grain size and composition, mechanical alloying (MA) as a powder metallurgy process, were developed.[4,18] These processes are solid-state powder techniques that are widely used to produce refractory metals, dispersion-strengthen alloys, nanocrystalline, and amorphous composite materials.[19–21] A number of researchers have studied the transformation characteristics of Cu-Al-Ni produced by PM, and then sintered using different kinds of sintering techniques.[3,4,13,22–24] Most of these techniques have disadvan
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