Microstucture and hardness of copper based shape memory alloys with fourth alloying elements

Abstract

Many potential applications of Cu based shape memory alloys (SMAs) are restricted due to the brittleness of the material. This research was conducted to enhance the mechanical properties of the Cu based SMAs. The research examined the effects of adding the fourth alloying elements, i.e., Boron (B), Cobalt (Co) and Titanium (Ti) on the microstructures and mechanical properties of the Cu based SMAs. The fabrication of Cu-Al-Ni alloys with these fourth alloying elements was carried out using a casting method. Several characterization tests were conducted to identify the effects of the fourth alloying elements using Scanning Electron Microscope (SEM), Optical Microscope, and Vickers hardness test. From the microstructural observation, it was found that the grain sizes of these alloys were refined with the addition of the fourth alloying elements. The addition of B shows the most fined grain size. The SEM results indicate that the microstructures consisted of two types of martensite, which were β1with an 18R structure, and ..1 with a 2H structure. The 1, looking like parallel martensite morphologies, are known as lamella structures. This type of lamella morphologies has also grown into grain. The β1 phase is typically formed with self accommodating groups in two different morphologies, plates and needles. The precipitation existed in the structure known as ..2, which also existed and acted like barriers in the grain boundaries. ..2 precipitates can be found in grain boundaries and in between structure β1 and ..1. The addition of the fourth alloying elements shows an increment in the hardness of the alloys in which the addition of Ti element demonstrates the highest hardness value.