Precipitation stability and micro-property of (Nb, Ti)C carbides in MMC coating

Abstract

Multiple particles reinforced composite coatings have been noticed by many researchers due to its excellent wear resistance. In this work, (Nb,Ti)C multiple carbide reinforced Fe matrix composite coating was prepared. The microstructure and phase structure of the coatings were analyzed by scanning electron microscope (SEM) equipped with an energy-dispersive spectroscopy (EDS), X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The stability, mechanical parameters (Elastic modulus, Bulk modulus and Shear modulus), hardness, brittleness, bonding structures of (Nb,Ti)C and misfit between carbide and Fe matrix were calculated by first principles method. The experimental results show that, core-shell (Nb,Ti)C can be observed in Ti-1 (0.52 wt.% Ti) coating and compared to Ti-0 (0 wt.% Ti), the morphology of carbides in Ti-1 coating is improved. The calculation results show that, the lattice constants, formation energy of (Nb,Ti)C (Nb0.75Ti0.25C, Nb0.5Ti0.5C and Nb0.25Ti0.75C) and misfit between carbide and Fe matrix are decreased with the decrease of Ti content in the carbide. Moreover, the hardness and brittleness of (Nb,Ti)C carbides are increased. The Nb-C covalent bonds in (Nb,Ti)C carbides act as a dominant factor for their high hardness.

Microstructure and wear resistance of (Nb,Ti)C carbide reinforced Fe matrix coating with different Ti contents and interfacial properties of (Nb,Ti)C/α-Fe

“…The average amount of primary carbide in the coatings is about 0.35, 0.48 and 0.53 per square micron, respectively. The Gibbs free energy of TiC is lower than that of NbC [6,30], and the element Ti is believed to improve the precipitation ability of primary NbC carbide [8], therefore the amount of primary carbides are increased with the increase of Ti contents. However, the increase in the amount of primary carbides will decrease the content of elements Nb, Ti and C in the molten pool, which may be the reason why the size of carbides are decreased with the increase of Ti content.…”

“…Based on our previous work, the matrix in the coatings is the martensite (α-Fe), and the carbide are mainly connected with α-Fe, therefore, (Nb,Ti)C/α-Fe interface was selected in this work. The element compositions of (Nb,Ti)C carbide have been reported [7,8], in which, element Ti is rich in the core area of the carbide and element Nb is rich in the part of carbide near the matrix. Therefore, the combination of (Nb,Ti)C with α-Fe was calculated using the interface model of Nb0.75Ti0.25C with α-Fe.…”

“…And they found that the wear resistance of coating withTi/Nb=1 is the best. It can be learnt from our previous work [8,9]that, element Ti can improve the hardness of carbide and decrease the misfit between carbide and matrix. Besides, it can also change the morphology of carbide by changing the precipitation order of carbide and matrix.…”

Micro-properties of (Nb,M)C carbide (M= V, Mo, W and Cr) and precipitation behavior of (Nb,V)C in carbide reinforced coating

“…Our previous studies [12] have investigated the strengthening mechanism of (Nb, Ti)C carbide composite coatings, and we found that the addition of Ti can increase the hardness of carbides, reduce the mismatch between them and the matrix, and promote the formation of primary granular carbides, which are beneficial to the wear resistance of coating. Elements V, Mo, W and Cr are also MC type carbide forming ones, and their formation ability are weaker than that of Nb.…”

Decision Support System in the Field of Defects Assessment in the Metal Matrix Composites Castings

“…This definition describes an ideal composite material with a perfect structure. Real composite materials generally have imperfect structures-composite materials contain various defects [1,2,[4][5][6][7][8][9][10][11][12], especially when considering cast composites. Castings feature a specific structure that is related to the course of the manufacturing process [13][14][15][16][17][18][19][20][21][22][23][24].…”