Formation of grain structure and microhardness of Ni3Al intermetallic compound as a result of SHS extrusion

In the work the possibility of improving the strength properties of Ni3Al intermetallic compound by reducing its average grain size was studied using the example of microhardness. The authors investigated the effect of reaction mixture deformation during self-propagating high-temperature synthesis (SHS) on the grain size and microhardness of Ni3Al intermetallic compound. SHS extrusion was carried out on the experimental stand, which allows continuous monitoring of synthesis parameters. It was established that one of the key factors affecting the characteristics of the grain structure and microhardness is degree of the synthesis product deformation. An increase in diameter of the extrusion hole from 3 to 5 mm leads to an increase in the maximum linear displacement of the press plunger due to active output of the material through a hole of the larger diameter. The above assumes a decrease in the material resistance to deformation when pressure is applied and an increase in degree of the material deformation inside the die and its decrease in the extruded material. Furthermore, the average grain size of Ni3Al remaining in the mold volume after synthesis decreases by 40 % (from 7 to 5 μm), and the material that passed through the extrusion hole increases by 2 times (from 3 to 6 µm). Compared to Ni3Al obtained by SHS compaction, the average grain size of the extruded intermetallic compound is 5.6 times smaller (from 17 to 3 μm). A decrease in the average grain size of extruded Ni3Al leads to an increase in microhardness by 600 MPa. The results obtained make it possible to develop recommendations for producing intermetallic compounds and alloys based on them with a fine grain size and high microhardness.