EFFECT OF ELECTRIC CURRENT ON THE PRODUCTION OF NiTi INTERMETALLICS VIA ELECTRIC-CURRENT-ACTIVATED SINTERING

This study focuses on investigating the fabrication of in-situ intermetallic NiTi composites from a powder mixture containing the mass fractions 50 % nickel powder and 50 % titanium powder. The elemental powders were mixed in the stoichiometric ratio corresponding to the NiTi intermetallic molar proportion of 1 : 1, ball-milled and uniaxially compressed under a pressure of 170 MPa. Sintering was then carried out for 15 min in a steel mold using the electric-current-activated sintering method. Electric-current values of 1000 A, 1300 A and 2000 A were used for the sintering while keeping the voltage in the range of 0.9 V to 1.2 V. The phases in the samples were analyzed with XRD and their Vickers hardness was measured as (701 +/- 166) HV0.05. Energy dispersive X-ray spectroscopy carried out with a scanning electron microscope (SEM-EDS) showed that the microstructures of the samples consist of different phases such as Ti, Ni2Ti3, NiTi2, Ni3Ti and TiO2 as a function of electric current. The XRD analysis also supported the SEM-EDS results. The nano-indentation technique was used to determine the elastic modulus of different phases