EFFECT OF HEATING ON THE STRUCTURE AND MECHANICAL PROPERTIES OF THE INTERMETALLIC Ni<sub>3</sub>Al, OBTAINED BY SPARK PLASMA SINTERING
This paper deals with influence of annealing at temperatures of 800, 900 and 1000 °C on the structure and mechanical properties of the monophasic intermetallic Ni<sub>3</sub>Al and with addition of 0.1wt.% B obtained by spark plasma sintering technology. The powders of nickel, aluminum and boron were mechanically activated before sintering. The relative density of the samples is in the range 97-99% of the theoretical density of nickel aluminide. Using scanning electron microscopy, the authors determined that heating of the samples obtained by sintering a mixture of a mechanically activated nickel alumina without and with 0.1wt.% B powders particles in the structure of the material increases the number of intermetallic Ni<sub>3</sub>Al cubic crystal form, surrounded by a viscous solid γ-phase solution. The highest value of the microhardness (6840 MPa) recorded in compacts of Ni<sub>3</sub>Al after annealing at 900 °C. At an annealing temperature of 1000 °C, begins the process of coagulation Ni<sub>3</sub>Al particles. After annealing at 1000 ° C the hardness of the test samples is reduced. The hardness of the nickel aluminide is reduced to 6370 MPa. A similar dependence of the microhardness is observed for a sample of nickel aluminide modified by boron. The highest level of microhardness of the material is 5440 MPa while heating to 900 ° C.