A two-step carbothermal reduction process produced zirconium carbide particles with less aggregation and smaller ZrC grains than those produced by one-step reduction. Reduction at 1500 degrees C for 10 min (1st step) and then at 1300 degrees C for 30 min (2nd step) produced significantly smaller agglomerations (1-8 mu m) and particles (33 nm) than those produced using other reduction processes, which were 2200 mu m and >1 mu m, respectively. The first high-temperature step allowed effective reduction, while the subsequent cooler step inhibited grain growth and agglomeration. The resulting ZrC particles showed a stoichiometric composition of ZrC0.97 through control of the carbon content. A sintered W-ZrC composite made using the two-step-reduced ZrC was harder and showed a more homogeneous dispersion of ZrC in the tungsten matrix than a composite made using one-step sintered ZrC. (C) 2015 Elsevier B.V. All rights reserved.

The microstructures and properties of W-ZrC composites prepared in situ were compared with those of conventionally prepared W-ZrC and W-(Zr, W) C. In situ preparation led to an ultrafine microstructure with a homogeneous dispersion of ZrC, while the other composites showed microstructures similar to each other. The composite of W containing 30 vol.% (Zr-0.88 W-0.12) C showed an excellent flexural strength of similar to 1425 MPa at 1000 degrees C. It also showed an excellent flexural strain of 0.051 at 1400 degrees C, which was obtained by using a maximum displacement of 2.41 mm. Those values have never been reported previously. A similar W composite, in situ W-10 vol.% ZrC, demonstrated a flexural strength of 1324 MPa and a displacement of 0.9 mm under similar conditions. The results of this study are discussed in terms of microstructure and phase stability. (C) 2014 Elsevier B.V. All rights reserved.

Powders of W-ZrC and W-Zr(CN) were carbothermally synthesized in situ from milled mixtures of graphite, WO3 and ZrO2. The thermal stability of Zr(CN) in a W matrix was simulated and compared with that of ZrC in W in terms of free energy change and carbide coarsening. Carbon and nitrogen had high mutual affinity in Zr(CN) of B1 crystal structure, which led their activity curves to exhibit strong negative deviation from ideal mixing behavior. Zr(CN) was more stable than ZrC up to 2075 K; however, a microstructural study showed that it became less stable than ZrC at around 1975 K. This result is attributed to the decreasing thermodynamic stability of ZrN with increasing temperature. Other transition metal carbonitrides containing group 4-6 elements are expected to show similar coarsening behaviors at high temperatures. (C) 2015 Elsevier B.V. All rights reserved.

Partially solutionized carbide cermets (PSCs) were prepared for cutting tool applications by replacing a portion of Ti(CN) with (Ti0.88W0.12) C or (Ti0.88W0.12)(C0.7N0.3) in a conventional Ti(CN)-based cermet. The PSC containing (Ti0.88W0.12) C exhibited high fracture toughness with no loss of hardness. The elimination of Ti(C0.7N0.3) cores in the microstructure reduced the strain at the core/rim interfaces, leading to the increase in fracture toughness. The PSC containing (Ti0.88W0.12) C showed coherent relationships at the core/rim and rim/binder interfaces, contributing to the improved mechanical properties. In contrast, nitrogen in (Ti0.88W0.12)(C0.7N0.3) resulted in a different microstructure and properties. The major factors determining the mechanical properties of the cermets are discussed in terms of the carbide/binder interfaces and the thermal stability of the added carbides. (C) 2015 Elsevier B.V. All rights reserved.

Highlights • The addition of (Ti0.88W0.12)C significantly improved the toughness of cermets. • The ceramic particles in the cermets exhibited {111} plane faceting. • The coherency state at the core/rim/binder interfaces led to high toughness. • The thermal stability of constituents and nitrogen in the system are the main causes. Abstract Partially solutionized carbide cermets (PSCs) were prepared for cutting tool applications by replacing a portion of Ti(CN) with (Ti0.88W0.12)C or (Ti0.88W0.12)(C0.7N0.3) in a conventional Ti(CN)-based cermet. The PSC containing (Ti0.88W0.12)C exhibited high fracture toughness with no loss of hardness. The elimination of Ti(C0.7N0.3) cores in the microstructure reduced the strain at the core/rim interfaces, leading to the increase in fracture toughness. The PSC containing (Ti0.88W0.12)C showed coherent relationships at the core/rim and rim/binder interfaces, contributing to the improved mechanical properties. In contrast, nitrogen in (Ti0.88W0.12)(C0.7N0.3) resulted in a different microstructure and properties. The major factors determining the mechanical properties of the cermets are discussed in terms of the carbide/binder interfaces and the thermal stability of the added carbides. Graphical abstract

Ti(CN)-based cermet is a potential alternative to WC-Co for cutting applications. We attempted to improve the mechanical properties of Ti(CN)-based cermets by adding (Ti0.88W0.12)C and (Ti0.88W0.12)(C0.7N0.3). The (Ti0.88W0.12)C phase decreased the number of Ti(CN) cores more effectively than (Ti0.88W0.12)(C0.7N0.3) and thus improved toughness was obtained. The binder phase fractions were altered substantially by the kind of carbides. In particular, the presence of N in (Ti0.88W0.12)(C0.7N0.3) increased the binder fractions and refined the microstructure of Ti(CN) cermets significantly. However, the increase in the binder faction provided a limited improvement in toughness in the systems of study. (C) 2015 Elsevier B.V. All rights reserved.