Machinability of Cu-Al-Mn Shape Memory Alloys

Abstract

Cu-Al-Mn (CAM) shape memory alloys (SMA) are cost effective, have a high low-cycle fatigue life and superelastic limit, and a wide temperature application range compared to other types of SMAs. These characteristics of CAM SMAs have resulted in an increased research interest in their use in civil engineering applications, particularly as reinforcement in concrete structures, and dampers in steel structures. However, these applications could require machining of the CAM SMA bars for connecting with other structural elements. This study presents the methods and results of the first systematic research on the machinability of CAM SMAs. The key machinability characteristics of CAM SMAs, such as chip formation, cutting temperature, tool wear, workpiece surface roughness and diameter deviation were studied and compared with conventional NiTi SMAs, and commonly used steel: mild steel (MS) and 304 stainless steel (SS). Effects of a wide range of cutting parameters, such as cutting speed ranging from 15 to 120 m/min, feed rate ranging from 0.1 to 0.2 mm/rev, and depth of cut ranging from 0.5 to 1.5 mm, were investigated. The results from this study demonstrated that the tool wear from machining CAM SMAs was close to that of SS and slightly higher than that from machining MS but much lower than of that from machining NiTi SMAs. In all the cases considered here, the tool wear from machining CAM SMAs was found to be 0.6 to 1.8 times that from machining SS, 0.8 to 2.4 times that from machining MS, and 1/7 to 1/21 times that from machining NiTi SMAs. After a continuous machining test with a total cutting length of 4.5 m, the nose wear of machining CAM SMAs was found to be 1.6 times that of machining MS, and the average flank wear of machining CAM SMAs was found to be three times that of machining MS; the diameter deviation (relative diameter difference with the first sample) of CAM SMAs was only 10 mm larger than that of MS.