Phase formation and properties of vanadium-modified Ni–Cr–B-Si–C laser-deposited coatings

Microstructural design of hardfacing Ni–Cr–B–Si–C alloys

“…However, a major drawback for laser deposition of these alloys is their high cracking susceptibility under the rapid cooling rates of the laser processing [5]. There has been a number of attempts to solve the cracking problem of Ni-Cr-B-Si-C alloys by either reducing the cooling rate of the deposits using preheating and postheating [6][7][8] or increasing the toughness of the alloys by compositional modification [5,6,9,10]. The latter approach, which is more attractive from the practical and economic perspectives, has been concentrated on eliminating or refin-ing the large Cr boride and carbide precipitates by the addition of early transition metals (ETMs) such as titanium (Ti) [9], vanadium (V) [5,6] or tantalum (Ta) [10].…”

“…Toughening of Ni-Cr-B-Si-C alloys by eliminating large Cr-rich precipitates is based on the observation of crack growth in their microstructures. It was shown that Cr borides and carbides such as CrB, Cr 5 B 3 or Cr 7 C 3 act as sites for crack nucleation, as well as being easy routes for crack growth [5,6,11]. The maximum stress (r m ) concentrated at the tip of an individual fractured Cr-rich precipitate can be described by the classical formulation as…”

“…the Gibbs free energy of formation (DG f ) for borides or carbides of that element should be more negative than those of Cr-rich precipitates [5]. Although spontaneous formation (negative DG f ) is a prerequisite for formation of nucleating sites, the lack of microstructural refinement in the Ni-Cr-B-Si-C deposits modified by V [5,6], Ti [9] or Ta [10] raises the question of whether factors other than affinity for B or C play a role in the refinement process.…”

Microstructure and Properties of Laser‐Clad Mo2NiB2 Cermet Coating on Steel Substrate

“…Residual stresses in cermet coatings develop as a result of differences in mechanical and thermal properties of the different phases (matrix and reinforcement in the coating) or layers of materials (coating and substrate). [2,5,[8][9][10][11] A lot of work has been carried out on fabrication of the carbide cermet coating on steel substrate. However, cracking susceptibility of the hardfacing coatings by laser cladding is so high that they cannot be used in reality, especially for cladding of large pieces.…”

“…However, cracking susceptibility of the hardfacing coatings by laser cladding is so high that they cannot be used in reality, especially for cladding of large pieces. [8,11] Ternary boride cermets, consisting of ternary boride as a hard phase and a metallic matrix binder, also have good wear and corrosion resistance, high strength and hardness, and are new wear and corrosion resistant materials. [12][13][14] These are Mo 2 FeB 2 -Fe, Mo 2 NiB 2 -Ni and WCoB-Co cermets.…”