(W_1‐x,M_x)C carbides with desired combinations of compatible density and properties – A first‐principles study

Abstract

Tungsten monocarbide (WC) is one of the most important components in hard alloys and coatings. 1 WC was originally developed based on the requirement for die materials that were able to withstand severe wear encountered in the drawing of tungsten filaments for light bulbs. However, due to its high brittleness or low fracture toughness, WC was not used widely in industry for a long period. This situation was changed with the invention of cemented carbides, where hard WC particles are embedded in a softer matrix (such as Co or Ni). 2,3 The first WC-Co grades were soon applied in the cutting and milling of cast irons with success. The combination of WC and metallic Co as a binder is a well-modified system, possessing combined high hardness and desired fracture toughness. 4,5 Up to date, WC-containing cement have a wide range of industrial applications. For instance, WC is widely used in cutting tools for machining of metal components in the automotive and/or aerospace industry, used for drilling bits or road headers in the rock tools and mining operation, as well as used as wear-resistant parts in wire drawing dies or punch tools. 6 WC has also been extensively used as a reinforcing phase in protective coatings on soft metal substrates against wear. 7 The coatings containing WC can be made by thermal spraying, spray-fuse, and welding processes. 8,9 Such composite coatings are effective, economic, and flexible for surface protection, which is extensively used in various industrial operations. 6,8,10,11 However, issues exist when making WC composite coatings. For instance, one of the main problems is the inhomogeneity of WC particle distribution in the metal

Densification and Fracture Responses of (Ta1−xWx)C–WC Composites

“…Nominal fracture strengths of TaC ceramics reported in this study and by others [ 19,24,25,29,51,58–63 ] as a function of density, showing density‐dependent and flaw‐dependent strength regimes.…”

“…The fracture strengths of the TaC specimens from this study, 114 ± 10 MPa, are most comparable with 130–150 MPa fracture strengths reported by Shvab and Egorov [ 51 ] because of their similar densities (about 80% of theoretical density). The fracture strengths of the 90(Ta 0.8 W 0.2 )C–10WC composite specimens, 362 ± 31 MPa, are comparable with those of high‐density TaC specimens, [ 29,60–63 ] which exhibit fracture strengths from 280 to 660 MPa. The TaC composite specimens that exhibit fracture strengths greater than 425 MPa correspond to those by Hackett et al [ 60 ] and Liu et al [ 61 ] Hackett et al [ 60 ] experimented with different amounts of TaC, Ta 4 C 3− x , and Ta 2 C present in their composites and found that the increased presence of Ta 4 C 3− x leads to a higher fracture strength but can result in susceptibility to cleavage cracking.…”

Work of Adhesion Analysis for Metal-Substituted W4C4 Carbides in a Cobalt Matrix

“…At x = 0, the structure is unmodified, i.e., without metal substitution, while x = 1 and 2 denote the substitution of W with Cr or Mo by 25 and 50%, respectively. The crystal structures of (W 4– x , M)­C 4 can be found in ref , while the information on crystal structures of HCP and FCC cobalt comes from refs − with electronic configurations of 5d 4 6s 2 , 3p 6 3d 5 4s 1 , 3d 7 4s 2 , 4p 6 4d 5 5s 1 , and 2s 2 2p 2 for W, Cr, Co, Mo, and C, respectively. The valence electrons located in the outermost energy level or shell of an atom can participate in chemical reactions and form bonds with other atoms.…”

“…Christensen et al 45 The density of WC, which is heavier than metals, can be reduced by partially substituting heavy W with metals such as Mo and Cr, while retaining the desired strength. 46 This makes them effective as reinforcements for hardfacing overlays, metalmatrix composites (MMCs) and tool materials, as they can be homogeneously dispersed in the metal matrix. It is, however, unclear if the partially substituted WC has good interfacial bonding with metals such as cobalt, one of the typical metalmatrix materials for hardfacing overlays.…”

“…The density of WC, which is heavier than metals, can be reduced by partially substituting heavy W with metals such as Mo and Cr, while retaining the desired strength . This makes them effective as reinforcements for hardfacing overlays, metal-matrix composites (MMCs) and tool materials, as they can be homogeneously dispersed in the metal matrix.…”