Large‐Scale Synthesis and Applications of Hafnium–Tantalum Carbides

Abstract

Comprehensive theoretical and experimental studies are performed to discover a new way of synthesis of HfTaC coatings. Here, an evolutionary search for stable crystal structures in the ternary HfTaC system with subsequent selective large‐scale experimental synthesis of coatings using a unique plasma dynamic experimental setup is performed. Optimization of the experimental process allows us to perform selective synthesis of coatings made of hafnium–tantalum carbides with predefined stoichiometry, crystal structure, and properties. Along with more than 70 compounds, the HfTaC system belongs to ternary and quaternary carbides of group IV and V transition metals, and this study opens the door to synthesis of a large number of functional coatings composed of other carbides including high‐entropy carbides.

Prediction of Ta2C‐Type Vacancy‐Layered Structures in the Ternary Hf–Ta–C System

“…Evolutionary algorithms [ 12–14 ] were employed to search for the vacancy‐ordered structures of the ternary Hf–Ta–C system. In addition to the rock‐salt structure, [ 35–37 ] two Ta 2 C‐type structures, HfTa 2 C 2 and Hf 2 Ta 2 C 3 , were found in this work, and their space groups were R‐3m . As shown in Figure 1 , based on the “convex‐hull structure” (when a structure is decomposed to any other structure, the enthalpy becomes positive; thereafter, the structure becomes thermodynamically stable), HfTa 2 C 2 and Hf 2 Ta 2 C 3 are thermodynamically stable at 0 K and ambient pressure.…”

“…[36]. However, the calculated hardness of HfTa 2 C 3 is higher than the experimental value, [36] which is significantly lower than the experimental values. [46,47] In ref.…”

“…[36]. However, the calculated hardness of HfTa 2 C 3 is higher than the experimental value, [ 36 ] which is significantly lower than the experimental values. [ 46,47 ]…”

“…The ternary Hf–Ta–C compounds could be synthesized by plasma dynamic method. [ 36 ] Therefore, at the same experimental conditions with ref. [36], using HfO 2 , Ta 2 O 5 , and C as the raw materials, when the mixture of precursors for the synthesis of ternary Hf–Ta–C compounds is Hf:Ta:C = 1: 2:2 or 2:2:3, maybe HfTa 2 C 2 and Hf 2 Ta 2 C 3 could be synthesized by the plasma dynamic method.…”

“…When the C/N ratio or Hf/Ta ratio was the same, with an increase in the vacancy concentration, the bulk modulus, shear modulus, elastic modulus, and Vickers hardness of the ternary Hf–C–N and Hf–Ta–C compounds decreased (except that the hardness of Hf 6 CN 4 [ x = 1/6] was greater than that of Hf 5 CN 4 [ x = 0]). Kvashnin et al [ 36 ] and Liu et al [ 37 ] investigated the structures of the ternary Hf–Ta–C system and found several vacancy‐ordered structures that all share the rock‐salt structure. In this work, two vacancy‐ordered structures, HfTa 2 C 2 and Hf 2 Ta 2 C 3 , with the Ta 2 C‐type structure are found using the USPEX code, [ 12–14 ] and their mechanical properties are calculated.…”