Fabrication, mechanical and thermal properties of al-alloy reinforced with NiTi shape memory alloy composites (SMACs)

ABSTRACT

In the present research NiTi (Nitinol) particulates were dispersed in aluminum alloy (LM 13) by melt deposition technique followed by hot extrusion.  The size of the particles dispersed varies from 50-80 nm and amount of addition varies from 3 to 15 wt.% in steps of  3%.  Microstructural studies of the shape memory alloy composite developed indicate that there is uniform distribution of the reinforcement in the matrix alloy with significant grain refinement and retention of residual porosity. 

It is  observed that composites developed are plastically deformed at low temperature (-50 deg C), and upon exposure to  temperature (120 deg C)will return to their shape prior to the deformation.  This behavior observed varies for different composites developed i.e., their transformation temperature varies as dispersoid content in the composite varies.

Mechanical properties (at room temperature) reveal that presence of  NiTi particulates has improved significantly the strength and hardness with slight  reduction in ductility as compared against the matrix alloy.  Fractography of the specimens showed that the fracture behavior of  matrix alloy has changed from ductile intergranular mode to cleavage mode of fracture.  Results of the thermal and electrical tests on the composites developed indicate that, thermal conductivity  and electrical resistance both decreased with increase in reinforcement content.  As far as thermal conductivity is concerned, the matrix alloy has the higher thermal conductivity.    But increase in NiTi particle content might lead to an increase of phonon scattering, which will reduce the thermal conductivity of the SMAC.