Effect of Nano CeO 2 Addition on the Microstructure and Properties of a Cu-Al-Ni Shape Memory Alloy
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COPPER-BASED alloys are given more attention because of their low cost and commercially attractive practical application with respect to Ni-Ti-based shape memory alloys (SMAs). A prospective application of copper-based SMAs is as sensors and actuators, where their pseudo-elastic properties can be fruitfully exploited. There are a broad range of copper-based alloys that show the shape memory effect (SME) and some other properties depending upon their alloying elements: Cu-Zn-Al alloys, which are known for their high transformation temperature; Cu-Al-Mn-based alloys that show high ductility; Cu-Al-Ni alloys that show high-temperature stability; and SMAs that can only be used up to 473 K (200 °C). Pseudo-elasticity and shape memory properties are attributed to these alloys from reversible and diffusionless thermoelastic martensitic transformations.[1] Only within a certain range of compositions do Cu-Al-Ni alloys show SME, which usually varies from 11 to 14 wt pct aluminum and 3 to 5 wt pct nickel with the balance copper. In spite of the advantages of Cu-Al-Ni SMAs, they are still not attractive commercially and have limited application due to their poor workability and susceptibility to brittle intergranular cracks.[2] Processing of this alloy through
ABHISHEK PANDEY, Scientist, ASHISH KUMAR JAIN, Junior Project Fellow, SHAHADAT HUSSAIN, Ph.D. Research Scholar, and RUPA DASGUPTA, Senior Principal Scientist, are with the Department of Materials Design and Processing, CSIR-Advanced Materials Processes and Research Institute, Bhopal, 462026, India. Contact email: [email protected] V. SAMPATH, Professor, is with the Department of Metallurgical and Materials Engineering, IIT Madras, Chennai, India. Manuscript submitted October 27, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
the conventional casting process causes course grain structure, due to which brittleness is introduced and increases further with thermomechanical treatment, which is the essential step to impart SME. Coarse grains contribute to poor mechanical properties, whereas fine grains are responsible for improved mechanical properties.[3,4] However, fine grain structure is limited to the powder metallurgy (PM) route, as it is difficult to maintain the fine grains during casting. Through the PM route, it is possible to obtain fine-structured material with improved mechanical properties, but the PM route also has its limitations. For example, it is difficult to attain 100 pct density through PM route processing; repeatability is a major concern; and, above all, large scale production is still a challenge. However, many researchers have shown that it is possible to attain fine grains with improved mechanical properties via the casting route by using different materials as alloying elements or grain refiners.[5–9] In a similar attempt, the present article concentrates on studying the effect of different quantities of nano ceria (CeO2) particles added to act as grain pinners on the microstructure, hardness, phase precipitation by X-ray diffraction (XRD) technique, an
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