Spark plasma sintering and structural analysis of nickel-titanium/coconut shell powder metal matrix composites

Spark plasma sintering eliminates the need for metal removal processes, which can enhance productivity and make possible the fabrication of materials impossible to get from a melt. In this study, elemental powders of titanium, nickel, and finely pulverized coconut shell powder (CSP) were prepared as a metal matrix composite using the powder metallurgy method. The concentration of CSP organic reinforcement was set at 1, 3, and 5 wt% to the nickel content, while titanium amount was fixed all through. The mild-milled powders were sintered at 850 °C at 10-min dwelling time, 50 MPa and 100 °C/min heating rate. The samples were analyzed using a scanning electron microscope with an energy dispersive X-ray (SEM-EDX) spectrometer, optical microscope, X-ray diffractometer (XRD), and Vickers microhardness tester. Chemical analysis showed the formations of phases consisting of major Ti-rich and Ni-rich compounds with TiNi3 intermetallic boundary layer. Sparse distributions of oxides and ceramic compound phases were also detected. Structural analysis indicates a decrease in crystallite size, D (45.50 to 33.58 nm), and a corresponding increase in lattice strain (0.344 to 0.429%) with organic reinforcement additions. Microstructural analysis indicates an increase in grain densification with CSP reinforcement, and this agrees with the evaluated densification and microhardness properties.