ZrC Layer Research Articles

Understanding the effect of holding time on interfacial microstructure evolution and mechanical properties of Ti3AlC2/Zr-4 brazed joints

In this work, the brazing of Zircaloy-4 (Zr-4) to Ti3AlC2 ceramic was investigated using a Ti–13Zr–21Cu–9Ni (wt.%) amorphous alloy at 930 °C with a holding time of 5–60 min. The typical multilayer structure of the joint was carefully characterized as Ti3AlC2/ZrC/Zr [Ti]ss + [Zr(Ti)]2 [Cu(Ni)]/Zr [Ti]ss/Zr-4. Ti3AlC2 was decomposed into TiCx due to the de-intercalation of Al, and Zr-4 dissolved into the molten amorphous TiZrCuNi fillers to form a Zr-based alloy which reacted with TiCx to form a ZrC particle layer on the Ti3AlC2 side. The microstructures and mechanical properties of the brazed joint were significantly influenced by dwell time, and the underlying evolution mechanisms were addressed based on the considerations of mutual dissolution, diffusion, and reaction among Ti3AlC2, Zr-4, and molten amorphous alloys. With the extension of holding time, the amount of [Zr(Ti)]2 [Cu(Ni)] in the brazed joints decreased gradually, while the ZrC layer thickened with (Ti, Zr)ss formed around the ZrC particles. The maximum shear strength of the joint, with an average strength of 187 ± 34 MPa, was achieved by brazing at 930 °C for 5 min. A detailed fracture analysis was conducted to determine the failure mechanism. This work provides a reference for brazing other MAX phase materials and alloys.

Brazing Zircaloy-4 to Ti3AlC2 using Ti–Zr–Cu–Ni amorphous alloys: Microstructural evolution and mechanical properties

Brazing of Zircaloy-4 (Zr-4) to Ti3AlC2 ceramic was investigated using a Ti–13Zr–21Cu–9Ni (wt.%) amorphous braze alloy (ABA) at temperatures ranging from 840 °C to 990 °C for 5 min. The interfacial reactions of the brazed joint were comprehensively analyzed, revealing a distinct multilayer structure consisting of Ti3AlC2/ZrC/α-Zr(Ti) + [Zr(Ti)]2Cu + [Zr(Ti)]2[Cu(Ni)]/α-Zr(Ti)/α-Zr. The formation of the ZrC carbide particle layer primarily results from the reaction between the molten ABA and decomposed Ti3AlC2 caused by the de-intercalation of Al. Additionally, the dissolution of Zr-4 into the ABA induces an alteration in the composition of the Zr-4/ABA interface, leading to the formation of α-Zr(Ti) isothermal solidification dendrites. The effect of brazing temperature on the mechanical properties of the joint was investigated and detailed fracture analysis was conducted to determine the failure mechanism. The fracture path result indicated that the joint primarily fractured within the ZrC layer due to the mismatch of hardness, rather than within the reticular [Zr(Ti)]2[Cu(Ni)] segregation phase. The maximum shear strength of the brazed Ti3AlC2/Zr-4 joint with an average strength of 187 ± 34 MPa was achieved by brazing at 930 °C for just 5 min. With the increase in brazing temperature, the thickness of the ZrC ceramic layer became thicker in an undulating manner, and the content of Zr-based alloy particles in the ZrC layer increased gradually, resulting in a slight decrease in the bearing capacity of the joint. The presented results provide valuable insights into the microstructural evolution, interfacial reactions, and mechanical properties of the Ti3AlC2/Zr-4 brazed joints using amorphous alloys.

Microstructural evolution in a one-directional phase transforming ultrahigh temperature ceramic laminate composite

A metal-ceramic multilayer composite composed of Zr and ZrC films was magnetron sputter deposited and annealed at 1325 °C to demonstrate its ability to phase transform into a single phase, substoichiometric ultrahigh temperature ceramic carbide. The pre-annealed laminate microstructure comprised columnar grains for both the Zr and ZrC layers, common to thin film deposition. Upon annealing, the diffusion of carbon facilitated the precipitation of multiple equiaxed carbide grains that consumed the former Zr layers. As this carbon diffused from ZrC, it resulted in the carbide undergoing a lattice contraction where the elastic strains facilitated a decohesion between the carbide grain boundaries. This decohesion is shown to be mitigated by increasing the ratio of the initial ZrC layer-to-Zr layer thicknesses. Finally, oxygen, found to be a minor impurity in the ethylene hydrocarbon gas used to reactively deposit ZrC, facilitated irregular zirconia precipitation within the evolving microstructure during the anneal.

Ar-ion- and electron-irradiated ZrC layers in ZrC-SiC-coated surrogate TRISO fuel particles

Surrogate tristructural isotropic (TRISO) particles, including ZrC and SiC layers, were manufactured through fluidized-bed chemical vapor deposition and irradiated. ZrC layers exhibited C/Zr atomic ratio of 0.95 without distinct crevices at interfaces in microscopy, but underwent significant microstructural changes post-irradiation. Defects included black dots and Frank loops, with increasing irradiation doses augmenting their area fractions. Frank loop density reduced at 9.4dpa due to the formation of fewer, fully circular loops. The ZrC hardness and modulus rose by 25% and 26% following Ar-ion irradiation at 9.4dpa, linked to the formed defects and implanted Ar ions. Electron irradiation expanded the defect-prone zone up to 100nm from the ZrC grain boundary and led to ZrO2 formation. ZrC grains recrystallized post electron irradiation at 700 °C, causing initial grain decomposition, amorphization, and nanocrystal formation. These nanocrystals, formed at 3.3dpa, closely aligned with ZrC diffraction patterns with no preferred orientations.

Modulation of particle residence time in powder size-dependent ZrC coating on carbon-carbon composite with vacuum plasma spray

Recently, carbon-carbon (C/C) composites have been widely employed in various application fields due to their exceptional properties, but their oxidation at relatively low temperature around 500 °C poses a challenge to be used in high-temperature conditions. To address the drawback, the coating of ultra-high temperature ceramic (UHTC) layer on the C/C composites has been suggested as one of promising solutions. However, the quality of UHTC coating layers obtained through vacuum plasma spraying (VPS) is heavily influenced by the size of the introducing raw powders to coat the layers. Therefore, we investigated the size effects of ZrC powders in the range of (10–50) μm, one of UHTCs, to optimize the coating quality. By modulating process conditions, the coating quality with thick ZrC layer having lower porosity was obtained when using the powder around 34 μm. From the results, we found the gas residence time related to the particle velocity in the plasma flame is one of key parameters to be modulated by VPS operational parameters, which could improve the quality of the coating layer even for large powder cases.

Comparison of thermal-hydraulic calculation in 100 MWt thorium-based HTGR using SiC and ZrC TRISO coated fuel particle

The High-Temperature Gas-cooled Reactor (HTGR) uses Tri-structural Isotropic (TRISO) coated fuel, the first barrier to fission products with unique ruggedness. One of the layers of TRISO is a SiC layer, which maintains the fuel's dimensional stability and mechanical integrity and acts as a fission product barrier. At extremely high temperatures, the SiC layer in the TRISO coating system tends to decompose, vaporizing silicon elements and forming a porous carbon structure. The weakness of the SiC layer leads to more expensive and difficult maintenance processes. ZrC is considered the primary alternative to replace the SiC layer due to its superior stability at high temperatures and more resistance to fission products especially palladium. Previous research has shown that from a neutronic perspective, the performance of ZrC and SiC layers is equally good with insignificant differences. The following research step analyzes the temperature distribution in the hot spot channel of the fuel and the overall core using both types of layers. The temperature analysis is essential to ensure that the maximum fuel temperature during normal operation does not exceed the thermal design target of 1495 °C. This research also simulates the temperature of both layers above the fuel design limit of 1600 °C. In addition to thermal–hydraulic analysis, calculations were also conducted to determine the coolant pressure drop caused by friction, elevation and form. The calculation showed that the peak temperature value during normal operation for TRISO with SiC and ZrC layer is below the thermal design target value. Both temperatures are not significantly different, with the TRISO (ZrC) temperature being higher during normal operation and the TRISO (SiC) temperature being higher during accident/high-temperature conditions. The pressure drop profile indicates that both coated fuel particles do not exhibit significant differences.

Optimization of 200 MWt HTGR with ThUN-based fuel and zirconium carbide TRISO layer

Abstract TRISO fuel particle using ZrC has better strength and resistance to high temperatures than SiC. Previous studies show that the ZrC layer, as a substitution of SiC within the TRISO layer of coated fuel particles, has an insignificant difference in the performance of the neutronic aspect. Further neutronic studies are required to obtain the best combination of thorium-based fuel with ZrC coating for HTGR. This study analyzed the neutronic performance of three types of thorium-based fuels, oxide, carbide, and nitride, for HTGR. The reactor design refers to the High-Temperature Test Reactor with some axial and radial fuel configuration adjustments. This reactor is designed to operate at 200 MWt and has been modified to use a ZrC layer as a substitute for the SiC layer on the coated fuel particles. The neutronic study is carried out using SRAC2006 code with JENDL 4.0 nuclear data library. Neutronic parameters analyzed include multiplication factor, power peaking factor, and neutron spectrum. Neutronic analysis results show that thorium nitride fuel’s multiplication factor (k eff) is better than other compared fuel types with k-eff 1.050, higher than thorium carbide, 1.004. At the same time, thorium oxide has been sub-critical. The power-peaking value of all materials is close to the ideal peaking value that is one. Other neutronic aspects, such as the neutron spectrum for three compared fuel types, have a similar trend.

Enhanced Ti3AlC2/Zircaloy-4 interfacial bonding by using copper as an interlayer

We propose a novel strategy for the high-strength joining of Ti3AlC2 and Zircaloy-4 by introducing copper as an interlayer. The interfacial microstructure reveals spontaneously formed Cu–Zr eutectic liquid phase wet Ti3AlC2 ceramic, generating a ZrC layer instead of brittle ZrxAly at the interface, enhancing the Ti3AlC2/Zircaloy-4 joint strength.

Melt/solid interaction and melt super-saturation effect on the microstructure asset of ultra-refractory composites prepared by reactive melting infiltration

The reactions occurring between a Zr2Cu melting phase and possible compounds intended for use in ultra-refractory ceramic matrix composite, i.e. SiC, TiB2 and ZrB2 are first explored through sessile drop tests, confirming a promising infiltration capability of the melt. Then, a multiphasic ultra-high temperature ceramic matrix composite was prepared by reactive melt infiltration (RMI), using a TiB2-coated carbon fiber preform infiltrated with Zr2Cu at 1500 °C which resulted in the precipitation of ZrB2 and ZrC sub-micrometric faceted grains and a general damage of both fiber and fiber coating, which were penetrated by the melt. Then, to decrease the RMI process temperature down to 1200 °C and limit the fiber damage degree, a second composite was prepared by introducing an additional ZrB2-B infiltration step. Although processing at 300 °C lower, notable alteration of the fiber occurred upon reaction with the Zr2Cu melt and developed a ZrC layer around them, but still allowing pull-out. In addition, the local B-rich environment promoted the development of a dual-phase microstructure within the matrix composed of new sub-micrometric grains and of larger ZrB2 grains, partially dissolved in the melt and re-precipitated acquiring a nano-sized lamellar eutectic structure. The combination of factors on multiple scale length, from the micro- of the fiber to the nano-of the lamella, seems to provide synergistic reinforcing phenomena and thus could be a valuable approach to develop materials for extreme environments.

Carburization Kinetics of Zircalloy-4 and Its Implication for Small Modular Reactor Performance.

Carburization of cladding materials has long been a concern for the nuclear industry and has led to the restricted use of high-thermal conductivity fuels such as uranium carbides. With the rise of small modular reactors (SMRs) that frequently implement a graphite core-block, carburization of reactor components is once more in the foreground as a potential failure mechanism. To ensure commercial viability for SMRs, neutron-friendly cladding materials such as Zr-based alloys are required. In this work, the carburization kinetics of Zircaloy-4 (Zry-4), for the temperature range 1073-1673 K (covering typical operating temperatures and off-normal scenarios) are established. The following Arrhenius relationship for the parabolic constant describing ZrC growth is derived: Kp (in μm2/s) = 609.35 exp(-1.505 × 105/RT)). Overall, the ZrC growth is sluggish below 1473 K which is within the operational temperature range of SMRs. In all cases the ZrC that forms from solid state reaction is hypo-stoichiometric, as confirmed through XRD. The hardness and elastic modulus of carburized Zry-4 are also examined and it is shown that despite the formation of a ZrC layer, C ingress in the Zry-4 bulk does not impact the mechanical response after carburization at 1073 K and 1473 K for 96 h.

Unveiling interfacial structure and improving thermal conductivity of Cu/diamond composites reinforced with Zr-coated diamond particles

To overcome the drawback of weak interface bonding in diamond particles reinforced Cu matrix (Cu/diamond) composites, we prepared the Cu/Zr-diamond composites via a gas pressure infiltration method with Zr coatings with thicknesses from 47 nm to 430 nm on diamond surfaces. The scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) analyses reveal that during preparation the gradual transformation of metallic Zr to ZrC occurs through the diffusion of C atoms, and the crystallographic orientation relationship between diamond and ZrC is characterized as (1¯11)diamond//(1¯11)ZrC and [110]diamond//[110]ZrC. The formed ZrC layer between diamond and Cu can bridge the large gap of acoustic impedance and greatly strengthen the interface bonding, and a maximal thermal conductivity of 735 W m−1 K−1 is achieved with the thickness of the interfacial ZrC layer of 50 nm (corresponding to Zr-coating thickness of 47 nm). However, with increasing the thickness of the interfacial ZrC layer, the composite thermal conductivity decreases attributed to the intrinsic low thermal conductivity of ZrC and the interface de-bonding with the large ZrC layer thickness. This study accurately establishes the relationship between interfacial structure and thermal conductivity and provides guidance for the interface design in Cu/diamond composites.

Discussion on structural parameters of the multilayer ZrC/TaC coatings based on stress analysis and ablation behaviors

The multilayer ZrC/TaC ablation resistant coatings with different layers were designed and fabricated on the SiC coated carbon/carbon composites by plasma spraying. Based on stress distribution and ablation performance under heat flux of 2.4 MW/m2, structural parameters of the multilayer ZrC/TaC coatings (total thickness d, number of layers n and thickness ratio R) were discussed and optimized. When R was equal to 1 and d was ~300 μm, the multilayer ZrC/TaC coating with three layers (n = 3) exhibited moderate stress distribution and the best ablation resistance, induced by the ZrC anti-scouring layer with sufficient thickness and effective crack deflection at the interface. The optimized structural parameters for multilayer ZrC/TaC system are considered as follows: (i) the larger d value was beneficial to reducing the residual thermal stress during ablation process; (ii) d/n for the ZrC layer was between 100–150 μm, while d/n for the TaC layer was between 40–100 μm.

High temperature reaction of multiple eutectic-component system: The case of solid metallic Zr and molten stainless steel-B4C

The eutectic melting, one of the fundamental phenomena in high temperature reactions involving liquid phases, is a primitive but important subject for both scientific and industrial fields associated with metallurgy. The present study aims at revealing the formation and reaction mechanisms of the multiple eutectic-component system consisting of solid metallic Zr and molten stainless steel-boron carbide (SS-B4C) by combining multiple analytical methods (i.e. powder X-ray diffraction (PXRD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and dynamic secondary ion mass spectrometry (D-SIMS)) with thermodynamical consideration. The results indicate that the solidified Zr-SS-B4C mixture is composed of major phases of (Fe,Cr)2Zr, (Fe,Cr,Ni)2Zr, (Ni,Fe)Zr2, ZrB2, and a minor phase of ZrC. The results also reveal that the eutectic melting between solid metallic Zr and molten SS-B4C can be described as the combination of diffusion kinetics and thermodynamic stability. That is, the initial formation of ZrC and ZrB2 layers at the reaction interface significantly retards the diffusion of other SS-B4C components (i.e. Cr, Fe, and Ni) into solid metallic Zr.

Effects of Zr element on the microstructure and mechanical properties of B4C/Al composites fabricated by melt stirring method

In this study, the addition of Zr element (K2ZrF6) was employed to improve the wettability, inhibit the serious chemical reaction of B4C to Al, and uniformly disperse the B4C particles in the Al melt, during the fabrication of B4C/Al composites via melt stirring method. And the particle distribution, interface microstructure and mechanical properties of the fabricated composites were further investigated. The metallography observation shows that the B4C particles could be effectively introduced to the Al melt with the addition of Zr element, while there were few B4C particles observed in the composites without Zr addition. The XRD analysis indicates that the ZrB2 and ZrC peaks arise with the addition of Zr, where the ZrB2 and ZrC have better chemical stabilization and wettability than the B4C ceramic particles. The SEM, EDS, TEM and SAED analysis shows that the ZrB2 and ZrC interface layer with a thickness of about 200–350 nm on the B4C surface was formed, which could avoid the serious chemical reaction and improve the wettability of B4C to Al, simultaneously. In addition, the easy introduction of B4C particles to the Al melt with K2ZrF6, the formation mechanism of ZrB2 and ZrC layer, and mechanical properties of the composites were also discussed.

Wearable thermoelectric 3D spacer fabric containing a photothermal ZrC layer with improved power generation efficiency

Harvesting energy directly from the body heat has been suggested as an effective way to realize sustainably and uninterruptedly wearable power supply. However, the low temperature gradient (ΔT) between the human body and the environment has limited the power generation efficiency. In this study, the photothermal-thermoelectric 3D spacer fabric (ZrC-PPSF) was prepared by coating a thin zirconium carbide/polyurethane (ZrC/PU) photo-thermal layer on the poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS)/spacer fabric (SF) thermoelectric composite (PPSF). By utilizing the excellent photo-thermal conversion of ZrC and the thermal insulation performance of PPSF, a larger ΔT was generated and maintained, so as to enhance the power generated and efficiency. The effects of ZrC concentration, SF thickness and optical power density on the photo-thermal efficiency and voltage generated were studied. When the ZrC concentraiton is 1.5 wt%, the ΔT increases form 67.5 °C to 179.3 °C under the optical power density of 500 mW/cm2. Regardless of sunny and cloudy day, a larger ΔT can be generated. Based on this, a flexible and wearable wristband containing 30 ZrC-PPSF units was prepared. Encouragingly, the voltage generated by the wristband under the sunshine is almost 11 times the voltage generated indoors. Under the optical density of 100 mW/cm2 for 800 min, the highest voltage generated by the wristband is 9.11 mV, much higher than the 3.12 mV generated without light. All the results demonstrate that it is a very effective and simple method to improve the thermoelectric power generation efficiency by photo-thermal conversion. The wearable TE device prepared in this study is especially suitable for outdoor application, and provide continuous and stable energy for the wearable electronics.

Graphite phases in chemical vapour deposited grown ZrC/graphite layers

The graphitic phases detected in chemical vapour deposited (CVD) ZrC layers were characterized by glancing angle X-ray diffraction. The layers were deposited at different temperatures ranging from 1250 to 1450°C in steps of 50°C. The precursors used were ZrCl 4 and CH 4 in the presence of hydrogen and argon. A total of seven graphitic phases were detected, five of which have been reported in the literature. However, two new hexagonal graphitic phases, P-6m2 (187) and P-62c (190), were also detected. It is proposed that the appearance of these two (new) phases was due to the influence of impurities in the growth region on the growth kinetics. A comprehensive phase identification process was followed to index all observed diffraction lines, followed by Rietveld analysis, to report on phase composition and crystalline properties. A distinct increase in overall graphite phase composition is observed at the higher CVD temperatures, which confirms the impact from graphitization.

Study of the microstructure and thermomechanical properties of Mo/graphite joint brazed with Ti–Zr–Nb–Be powder filler metal

The aim of this work was to braze molybdenum and graphite with Ti–40Zr–8.5Nb–1.5Be filler metal in order to demonstrate the possibility of its application for X-ray tube target brazing, further to investigate the joint microstructure using energy-dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), X-ray diffraction (XRD), and electron microscopy as well as to conduct shear and unbrazing tests. It is shown that the brazed joint consists of matrix from β-(Ti, Mo) solid solution, mixed ZrC and TiC carbide layers at the braze/graphite interface, and beryllides TiBe2 and MoBe2 located at the grain boundaries of β-(Ti, Mo). The presented data made it possible to propose a brazed joint formation mechanism and explain the concentration of beryllides at the grain boundaries during brazing, as well as the mixed carbide layer formation from the side of the graphite. The mechanical tests showed that Mo/graphite brazed joints have a shear strength of at least 28.0 ± 0.9 MPa. However, sample failure occurred through the graphite due to the graphite surface mechanical treatment and the presence of a ductile β-Ti phase in the joint. The evaluation of joint thermal properties was performed using unbrazing tests. The unbrazing temperature was 1882 °C, which was caused by formation of refractory phases during brazing. The microstructure study shows that unbrazing occurs through the β-(Ti, Mo) phase with grain boundaries and beryllides eutectic melting.

First-principles studies on behaviors of He impurities in d-MAX phase Zr3Al3C5

Understanding helium (He) incorporation into materials is essential to estimate the material performance in a nuclear environment for the fabrication of nuclear devices. The effect of helium irradiation on Zr 3 Al 3 C 5 was studied by using the first-principles method. It is found that the He interstitial atoms tend to situate in the Al-C layers in Zr 3 Al 3 C 5 . The calculation of defect formation energy shows that the defects at the Zr sites are the most difficult to form, while vacancies at the Al and C sites are more ready to form in Zr 3 Al 3 C 5 . The numbers of He atoms that can be trapped by an Al(2) and a C(3) vacancy are seven and three, respectively, which show that Al vacancies have a stronger ability to trap He atom than C vacancies. The migration of He in Zr 3 Al 3 C 5 is also investigated. The results indicate that He impurity atoms migrate more easily along the c-axis than in the a-b basal plane in the Al-C layer. The diffusion barrier of He atom from the Al-C into the Zr-C layer is determined to be 3.13 eV. The results imply that the Al-C layers tend to be disordered while the Zr-C layers exhibit good tolerance of damage under He irradiation. Additionally, we also studied the stress-strain relationships of Zr 3 Al 3 C 5 under tensile and shear loading, with the ideal tensile strength and shear strength of Zr 3 Al 3 C 5 predicted.

Influences of the ZrC coating process and heat treatment on ZrC-coated kernels used as fuel in Pu-burner high temperature gas-cooled reactor in Japan

ABSTRACT The concept of Pu-burner high temperature gas-cooled reactor (HTGR) has been proposed to more safely reduce the amount of recovered Pu. In the Pu-burner HTGR concept, coated fuel particles with ZrC-coated yttria-stabilized zirconia containing PuO2 (PuO2-YSZ) kernels are employed for very high burn-up and high nuclear proliferation resistance. The role of ZrC layer is that of oxygen getter. CeO2-YSZ kernels were fabricated to simulate the PuO2-YSZ kernel and coated with a ZrC layer. In this study, we clarified that both Ce-rich grains and Zr-rich grains were densely distributed in surface regions of the as-fabricated CeO2-YSZ kernel. However, we have already clarified that the surface region of the CeO2-YSZ kernel coated with a ZrC layer was porous and mainly consisted of Zr-rich grains. These experimental results confirmed that Ce-rich grains were selectively corroded during the ZrC coating process. Then, the chemical stability of Zr-rich grains would be higher than that of Pu-rich grains. Thus, it would be more difficult to extract Pu from PuO2-YSZ kernels (in which almost all grains are Zr-rich) than from PuO2-YSZ kernels (in which many Pu-rich grains are included). Influences of the sintering of fuel compact on the microstructure of the ZrC-coated CeO2-YSZ kernel is also reported.

Mechanism of Incongruent Reactions Between Zr-Cu Melts and Solid Tungsten Carbide

The incongruent reactions between Zr-Cu melts and WC solid were studied. Mo was used as a tracer to track the movement of “heavy” W atoms during the incongruent reaction. In separate experiments, dense polycrystalline plates and porous preforms of W0.9Mo0.1C were reacted with Zr2Cu and Zr14Cu51 melts at 1200 °C, 1300 °C and 1600 °C for 15 minutes. The microstructure of the reactive interfaces was studied using scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The change of microstructure and chemical composition at the reactive interface was observed as a function of temperature, Zr content in the melt and radius of the W0.9Mo0.1C solid. When the Zr-Cu melts contact the W0.9Mo0.1C solid, W, Mo and C all dissolve in the melt. The precipitation of W and W2Zr is based on Zr activity in the Zr-Cu melt after a quick formation of ZrCx. Both the dissolution rate and the amount of WC solid increase with decreasing radius of the WC particles, increasing Zr content in the Zr-Cu melts, and increasing reaction temperature. If the dissolution rate of WC is fast enough and the WC particles are in small sizes, the dissolution-precipitation is the main aspect. If a continuous ZrC layer quickly forms to separate the WC solid from Zr-Cu melts. The reaction is, therefore, controlled by the diffusion of carbon through the W and/or ZrC layers.