A Novel Powder Metallurgy Processing Approach to Prepare Fine-Grained Cu-Al-Ni Shape-Memory Alloy Strips from Elemental
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SHAPE-memory alloys (SMAs) have received a considerable amount of attention in recent decades because of their viability of potential applications in a variety of areas including automotive, aerospace, and biomedical applications.[1–5] As a result, several types of SMAs, such as Ni-Ti-based, Cu-based, and Fe-based alloys, have been developed according to specific requirements.[1–6] Among these SMAs, Cu-based shape-memory alloys have been considered a potential material for applications such as high-damping capacity material, sensors, and actuators. In particular, Cu-Al-Ni alloys have been found suitable for high-temperature applications because of their high thermal stability at increased temperatures, i.e., above 373 K (100 °C).[4–8] However, the Cu-Al-Ni alloys prepared by conventional casting method suffered with the problem of severe brittleness as a result of large grain sizes (up to several millimeters) coupled with large elastic anisotropy.[6,9,10] Hence, several attempts were made to enhance the ductility of conventionally cast Cu-Al-Ni alloys through S.K. VAJPAI, Research Scholar, R.K. DUBE and S. SANGAL, Professors, and P. CHATTERJEE, Graduate Student, are with the Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India. Contact e-mail: [email protected] Manuscript submitted September 13, 2011. Article published online February 10, 2012 2484—VOLUME 43A, JULY 2012
grain refining by addition of a fourth element, such as Ti, Zr, Mn, B, Y, V, and rare earths.[11–19] The grain size of the resulting Cu-Al-Ni alloys was found to lie in the range of 100 to 800 lm. The grain refinement via alloying additions exhibited improvement in the mechanical properties of the Cu-Al-Ni alloys. However, the mechanical properties of these alloys were still unsatisfactory for most practical applications. A few attempts have been made to prepare finegrained Cu-Al-Ni alloys, with a grain size less than 100 lm, via different powder metallurgy routes. These routes were based on the Cu-Al-Ni alloy powder that was prepared by either inert gas atomization process or mechanical alloying of elemental powders in a highenergy ball mill under inert gas atmosphere. The consolidation of these powders was carried out by sintering, hot pressing, hot isostatic pressing, hot extrusion, hot swaging, hot-densification rolling, or a combination of these. One important feature of the Cu-Al-Ni SMAs produced by powder metallurgy routes was that the products had a fine grain size vis-a`-vis those produced from the liquid metallurgy route. As a result, near fulldensity powder metallurgy Cu-Al-Ni SMAs exhibited superior mechanical properties. There have been some attempts to prepare finegrained Cu-Al-Ni alloys starting with inert gas atomized prealloyed powders.[20–25] It was found that the Cu-AlNi SMA prepared from inert gas atomized powders exhibited superior mechanical properties compared with METALLURGICAL AND MATERIALS TRANSACTIONS A
conventionally cast material. However, only a few
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