SMA based high damping composite materials; microstructural characterization

In the last years absorption of vibration energy by mechanical damping have attracted much attention in several fields like vibration reduction in aircraft and machinery industries, nano-scale vibration isolations in electronic industry, vibration damping in civil engineering, etc. For structural applications, materials that combine a high damping capacity and high stiffness at moderate temperatures are required, but unfortunately this combination is not frequent. Usually, the most used high-damping materials are based on polymers due to their viscoelastic behaviour. However, polymeric materials typically show a low elastic modulus and are not stable at relatively low temperatures (≈ 323 K). Therefore, alternate materials for damping applications are needed. Metallic materials, which originally exhibit better mechanical properties (higher modulus and thermal stability) than polymers, with similar damping properties were proposed to replace polymeric ones. In particular, shape memory alloys (SMAs), thanks to the dissipative hysteretic movement of interfaces (martensite variant interfaces, twin boundaries) under external stresses, have found practical applications as high-damping metals.
Against this background, a completely new approach was applied to produce high-damping materials with relatively high stiffness. Cu-Al-Ni shape memory alloy powders were embedded with metallic matrices of pure In, a In-10 wt.% Sn alloy and In-Sn eutectic alloy. The production methodology is briefly described. A thorough characterization of the composites microstructures properties was carried out applying optical and scanning and transmission electron microscopy. A good particle distribution of the Cu-Al-Ni particles in the matrices was observed. Intermetallic phases were formed during the composite production. The nucleation of martensite at the interface between a Cu-Al-Ni particle and the matrices confirmed a strong interaction at the interfaces. The crystallographic structure of all phases was determined by electron diffraction. The methodology introduced provides versatility to control the temperature of maximum damping by adjusting the shape memory alloy composition.