As a new category of ultra-high temperature ceramics (UHTCs), multi-anionic highentropy (HE) carbonitride UHTCs are expected to have better comprehensive performances than conventional UHTCs. However, how to realize the green and low-cost synthesis of high-quality multi-anionic HE carbonitride UHTC powders and prepare bulk ceramics with excellent mechanical properties still faces great challenges. In this work, a green, low-cost and controllable preparation process of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)CxN1-x powders is achieved by a sol-gel combined with carbothermal reduction/nitridation method for the first time. The as-synthesized (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)CxN1-x powders possess high compositional uniformity and controllable particle size. In addition, the obtained bulk ceramics prepared at 1800 ℃ exhibit a superior fracture toughness of 5.39±0.16 MPa•m 1/2 , high nanohardness of 35.75±1.23 GPa, elastic modulus of 566.70±8.68 GPa and flexural strength of 487±41 MPa. This study provides a feasible strategy for preparing high-performance HE carbonitride ceramics in a more environmentally friendly and economical manner.
Iron-based specimens with boronized layers were prepared by boriding at 800 ℃, 900 ℃ and 1000 ℃ for 3, 5, and 7 hours, respectively. The thickness, microstructure, surface roughness, friction, and wear performance were studied. Results showed that the process parameters such as temperature, the time of boriding have remarkable impact on the thickness of the boronized layer. Dual-phase was generated at 1000 ℃ which lead to increased brittleness, lower surface hardness, and decreased adhesion to the substrate. Compared with specimens boronized at 1000 ℃ and 800 ℃, the surface structure of the boronized layer of specimens boronized at 900 ℃ is denser and uniform, the wear track is not damaged. The average friction coefficient and mass loss by wear of specimens boronized at 900 °C are smaller than that of boronized at 1000 ℃ and 800 ℃, indicating that specimens borided at 900 ℃ behave excellent friction and wear performance.
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