Evolution of structure, phase composition and microhardness of the near-surface layer of Ni3Al – 30 vol.% TiC composite under the action of low-energy high-current electron beam

Abstract

Using scanning and transmission electron microscopy, X-ray diffraction and indentation tests, westudied the evolution of microstructure, phase composition and microhardness of Ni3Al – 30 vol.%TiC composite fabricated by self-propagating high-temperature synthesis under pressure inducedby low-energy high-current pulsed electron beam irradiation with the surface energy densityof 8 J/cm2 and number of pulses from 10 to 30. It is found that the processing results in the increaseof the yield of the synthesis product Ni3Al and the increase of volume fraction of carbide phase inthe near-surface layer of the composite. Moreover, the refining of titanium carbide particles down toseveral tens of nanometers occurs. The microstrain of crystal lattice increases, and the crystal latticeparameter decreases. As a result, the microhardness of the composite increases by 13%. The physicalfactors causing the above variation of the structure and properties are discussed. The main factordefining the increase of the lattice microstrain is assumed to be ultrafast cooling of the near-surfacelayer due to heat transfer. The preferential evaporation of the matrix caused by the difference in theboiling temperature of Ni3Al intermetallide and titanium carbide may be the reason for the increaseof TiC content in the near-surface layer.