Chromium carbide micro-whiskers: Preparation and strengthening effects in extreme conditions with experiments and molecular dynamics simulations

Abstract

The rod-like Cr3C2 micro-whiskers were successfully synthesized from chromic oxide and blank carbon as reaction sources and halide salts and nickel as catalysts by using a carbothermal reduction method assisted with high energy milling and liquid phase catalysis. The optimal preparing condition was to calcine the mixture of Cr2O3:C:NaCl:KCl:Ni ​= ​1:8:0.4:0.4:0.3 (mole ratio) at 1300 ​°C for 2h without other post-treatments. The growth of Cr3C2 micro-whiskers was based on S-L-S mechanism that the brief reaction process of Cr2O3+C→Cr7C3→Cr3C2 occurred in molten catalyst liquids. Besides, the deficiency of carbon led to the generation of Cr7C3 particles, and its excess could induce the formation of coral clusters. The obtained Cr3C2 whiskers were not oxidized in air atmosphere at temperature lower than 1000 ​°C, and a thin Cr2O3 coating which prevented further oxidation gradually formed on the outside of whiskers from 1000 to 1200 ​°C. In addition, the bonding strength of heat resistant adhesive was increased by 16–28% from 500 to 1500 ​°C after adding Cr3C2 whiskers, which was mainly attributed to the pull-out mechanism, whereas the added carbon fibers were completely oxidized and left many sags in adhesive structure, thus severely decreasing the strength. Molecular dynamics simulations with the tersoff forcefield were carried out to facilitate fundamental understanding of the micro-whiskers growing in preferred directions. Combined with theoretical and experimental studies, this work significantly expands the design space and motivates future efforts in exploring the emerging applications of the mechanical properties of Cr3C2 whiskers in severe occasions.