Effect of vanadium addition on the microstructure and properties of NiCuBSi-WC60 composite coatings deposited by laser direct deposition

Abstract

There is an urgent need to extend the tool life of shield boring machines for complex working conditions. Here, NiCuBSi-WC60 composite coatings with different vanadium contents were prepared by laser direct deposition on the surface of shield boring machine cutter rings, and the influence mechanism of vanadium(V) addition on the microstructure and properties of the coatings was studied. The microstructure of the coatings was analyzed by SEM, XRD, EBSD and TEM to reveal the mechanism of microstructure evolution during laser deposition. The microhardness was tested by Vickers hardness tester, and the wear resistance was tested in practical engineering applications. The results show that the addition of V can promote the formation of W2C and VC, and with the increase of V content, the W2C precipitated in the coating gradually grows and changes from flocculent to plate. The coating containing V mainly consists of Ni(Cu) bonded phase, WC, W2C and VC reinforced phase and Ni10(WC)3 transition phase. HRTEM found that the orientation relationship between W2C and VC interface is W2C (111) // VC (001), W2C [011¯] // VC [11¯0], the angle difference between the Ni(Cu) (111) direction and the Ni10(WC)3 (101¯2) direction is 5.13°, and the lattice mismatch is 12.35%. The average hardness of the coating at the locations without spherical WC particles was statistically analyzed and the highest hardness of 739.90 ± 82.58 HV was found for the coating with 2 wt% V. A small amount of V addition effectively improves the distribution of the reinforcing phase in the coating, thus increasing the wear resistance of the coating. Practical engineering application shows that the wear rate of V-modified NiCuBSi-WC60 coated cutter ring is only 4.6% of that of ordinary 5Cr5MoSiV1 steel ring in the same trajectory line during the boring process of 1521 m in Chengdu sand and pebble strata.