In-situ synthesis, microstructure, and properties of NbB2-NbC-Al2O3 composite coatings by plasma spraying
Xiaolong Wang, Yong Yang, Shitong Jia, Yanwei Wang, Yu‐duo Ma, Yuhang Cui, Xingyu Wang, Wen‐wei Sun, Liang Wang
Abstract
Abstract The high melting point and strong chemical bonding of NbB 2 pose a great challenge to the preparation of high-density nanostructured NbB 2 composite coating. Herein, we report a novel, simple, and efficient method to fabricate in-situ NbB 2 -NbC-Al 2 O 3 composite coating by plasma spraying Nb 2 O 5 -B 4 C-Al composite powder, aiming at realizing the higher densification and ultra-fine microstructure of NbB 2 composite coating. The microstructure and properties of in-situ NbB 2 -NbC-Al 2 O 3 composite coating were studied comparatively with ex-situ NbB 2 -NbC-Al 2 O 3 composite coating (plasma spraying NbB 2 -NbC-Al 2 O 3 composite powder). The reaction mechanism of Nb 2 O 5 -B 4 C-Al composite powder in plasma jet was analyzed in detail. The results showed that the in-situ nanostructured NbB 2 -NbC-Al 2 O 3 composite coating presented a lower porosity and superior performance including higher microhardness, toughness and wear resistance compared to the plasma sprayed ex-situ NbB 2 -NbC-Al 2 O 3 coating and other boride composite coatings. Densification of the in-situ NbB 2 -NbC-Al 2 O 3 coating was attributed to the low melting point of Nb 2 O 5 -B 4 C-Al composite powder and the exothermic effect of in-situ reaction. The superior performance was ascribed to the density improvement and the strengthening and toughening effect of the nanosized phases. The in-situ reaction path could be expressed as: Nb 2 O 5 + Al → Nb + Al 2 O 3 , and Nb + B 4 C → NbB 2 + NbC.