Discontinuous Precipitation Research Articles

Differential effects of Fe, Ti and Fe + Ti addition on the discontinuous precipitation and properties of cu-Ni-Sn alloys

Controlling discontinuous precipitation is crucial for improving the microstructure and mechanical properties of Cu-Ni-Sn alloys. Through the utilization of various characterization techniques such as transmission electron microscopy, scanning electron microscopy, optical microscopy, and mechanical testing, we have successfully demonstrated that the introduction of either Ti or a combination of Fe and Ti elements effectively inhibits the formation of discontinuous precipitation. Notably, the combined addition of Fe and Ti elements showcases superior suppression of the discontinuous precipitation structure. Consequently, we have developed a novel alloy, namely Cu-15Ni-7.5Sn-0.5Fe-0.5Ti, which exhibits remarkable resistance to over-aging. Our analysis indicates that the mechanism of inhibiting discontinuous precipitation is multifaceted. The main effect is believed to be the reduction in nucleation sites and the pinning effect of the D024-Ni3Ti phase on grain boundaries, resulting in a significant decrease in the nucleation rate and growth of the DP reaction. The secondary impact may be due to the distribution of D024-Ni3Ti phase at grain boundaries, which leads to a decrease in grain boundary energy. Meanwhile, the formation of D019-Ni3Sn phase reduces the chemical driving force required for DP growth.

Synergistic grain boundary engineering for achieving strength-ductility balance in ultrafine-grained high-Cr-bearing multicomponent alloys

Precipitation strengthening is a crucial strategy for ensuring the overall performance of conventional and multicomponent alloys to meet industrial demands. However, the mechanical properties of high-Cr-bearing alloys are often compromised by brittle Cr-rich precipitates at grain boundaries (GBs), leading to severe embrittlement. In this work, a multi-step thermomechanical process is employed to regulate discontinuous dynamic recrystallization (DDRX) and static recrystallization, achieving an ultrafine-grained microstructure. This optimized approach simultaneously impedes the continuous precipitation of the ordered L12 nanocrystals within the matrix and actively encourages the synergistic discontinuous precipitations of submicron L12 and Cr-rich σ particles at GBs, thereby enhancing (yield) strength and high-temperature thermal stability. The ultrafine grains facilitate uniform plastic deformation, characterized by pronounced parallel dislocation slip and stacking faults (SFs) within face-centered cubic (fcc) grains, while second-direction slips, SFs, and Lomer-Cottrell (L-C) lock networks near GB precipitates greatly alleviate stress concentration. Critically, the submicron L12 particles enveloping σ precipitates at GBs also display plastic deformation via mechanical twinning and dislocations, effectively impeding rapid crack propagation along GBs. This research not only provides new insights into the ductility-strength balance in advanced alloys but also proposes a compelling route for optimizing biphasic precipitation, expanding the applicability of high-Cr multicomponent alloys.

High strength and excellent softening resistance Cu–15Ni–8Sn alloy by Ti addition

Cu–15Ni–8Sn alloy is commonly utilized in various applications because of its exceptional strength, elasticity, and softening resistance. Ti microalloying has been employed to enhance the mechanical properties of Cu–15Ni–8Sn alloy. By adding 0.5 wt% Ti, the peak-ageing tensile strength, microhardness, and elastic modulus of the Cu–15Ni–8Sn alloys reach 1401.3 MPa, 479.3 Hv, and 154.7 GPa, respectively, representing the greatest comprehensive performance reported in previous literature. Additionally, the Ti microalloying significantly enhances the softening resistance of Cu–15Ni–8Sn alloys. After ageing at 400 °C for 10 h, the tensile strength of the Cu–15Ni–8Sn-0.5Ti alloy decreases by only around 150 MPa, whereas the alloy without Ti addition experiences a decrease close to 350 MPa. Quantitative analysis reveals that the observed improvements can be attributed to the Ti microalloying inhibiting the dislocation annihilation and the formation of discontinuous precipitation during the ageing process, while simultaneously promoting the precipitation of Ni3Ti. This study provides a theoretical basis for preparing a high-performance Cu–15Ni–8Sn alloy by microalloying.

Effect of Hf addition on structural transformation and aging stability of Cu–15Ni–8Sn alloy

The Cu–15Ni–8Sn-xHf (wt.%, x = 0–0.6) alloys were prepared by vacuum melting, and the effect of Hf on the micro-structure of as-cast, as-solution-treated and as-aged alloys was systematically investigated, as well as the alloy aging stability. The Hf addition provided a significant role on refining the solidification structure and reducing the micro-segregation degree, and it also made γ-D03 phases more likely to form in needlelike-shape rather than lamellar-shape. With the presence of more Hf atoms, their existence form was accordingly changed from solid solute atoms to nano-scale precipitation phases and then to micron-scale segregation phase. A small content of Hf (0.1 wt%) could effectively improve the aging stability by inhibiting the growth of γ-D03. Once its content reached or exceeded 0.3 wt%, the harmful discontinuous precipitation was completely inhibited, and the common lamellar-shape γ-D03 locating around the grain boundary was no longer formed. Even the alloy failed at higher temperatures, it could only be carried out through the continuous precipitation method, namely the generation of needlelike-shape γ-D03 uniformly in the matrix. The appropriate Hf addition was capable of extending the alloy aging window, and the hardness of Cu–15Ni–8Sn-0.3Hf alloy could still exceed 360 HV even after 48 h aging.

Mechanical and electrical performances of ternary Cu-2.8%Ni-0.7%Si alloy modulated by ultrasonic solidification

One-dimensional (1D) and three-dimensional (3D) ultrasounds were introduced into the solidification process of ternary Cu-2.8wt%Ni-0.7wt%Si alloy together with the in-situ measurements of acoustic fields. In the case of 1D ultrasound, stable cavitation was the main form of acoustic energy transmission. The grain size of α-Cu dendrites was reduced because stable cavitation improved the wetting between impurities and alloy melt, which further promoted nucleation process. When 3D ultrasounds were applied, transient cavitation was the dominant mode of acoustic energy dissipation. This induced local high undercooling in alloy melt, causing a significant increase in bulk nucleation rates and the formation of numerous tiny α-Cu equiaxed grains. Meanwhile, as ultrasonic dimension increased, the strengthened acoustic streaming accelerated solute and thermal diffusion and weakened the preferred orientation of growing α-Cu grains. The proportion of low-angle grain boundaries (LAGBs) increased consequently, which suppressed the nucleation and growth of δ-Ni2Si discontinuous precipitates (DPs) during subsequent annealing treatment. The tensile strength and electrical conductivity of 3D ultrasonically solidified alloy after annealing reached 688.2 MPa and 2.7×107 S/m respectively, showing obvious advantages in synergetic mechanical and electrical performances.

Effect of Sc/Zr ratio on superplastic behavior of ultrafine-grained Al–6%Mg alloys

Al–6%Mg-Sc-Zr alloys with a combined Sc and Zr ratio of 0.32 wt% make up the focus of this research. The content of Sc and Zr varied with an increment of 0.02%. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10−3 and 3.3·10−1 s−1. The values of strain hardening factor (n), strain rate sensitivity factor (m), and superplastic deformation threshold stress (σp) were determined. The microstructure and failure patterns of the alloys post superplasticity tests were studied. The effect of the Sc/Zr ratio on the superplastic behavior, cavitation fracture and dynamic grain growth of UFG Al–6%Mg alloys was investigated. The satisfiability of Hart's criterion for calculating uniform deformation value under superplastic conditions was verified. Grain boundary sliding and intragranular deformation make comparable contributions to superplastic flow in the UFG aluminum alloys under study. Al–6%Mg-0.20%Sc-0.12%Zr (Sc/Zr = 3.3 at.%) and Al–6%Mg-0.18%Sc-0.14%Zr (Sc/Zr = 2.8 at.%) alloys exhibit the highest superplasticity. Shown that changes in the Sc/Zr ratio affect the precipitating mechanism, spatial distribution and composition of the precipitating particles Al3(ScxZr1-x). The optimal Sc/Zr ∼2.6–3.3 (at.%) ratio for the Al–6%Mg alloy corresponds to an Al3(Sc0.5Zr0.5) and Al3Sc precipitated particles. The large Al3Zr particles formed through the discontinuous precipitation mechanism was detected at Sc/Zr < 1 (at.%).

Effects of cold deformation and aging on the phase transformation and mechanical properties of a Cu-15Ni-8Sn alloy

A Cu-15Ni-8Sn alloy ingot was prepared in a medium-frequency induction melting furnace. First, the hot extruded alloy was subjected to solution treatment at 840 °C for 60 min, after which cold drawing treatment was applied under different deformation conditions (0–70%). Finally, the cold-deformed alloy was subjected to aging at different temperatures (340–520 °C) and insulation times (0–480 min). The evolution of grain characteristics, micromorphology and mechanical properties during cold drawing deformation and aging were systematically studied. The results show that during cold drawing deformation, the grains in the solid solution Cu-15Ni-8Sn alloy gradually elongate along the drawing direction with increasing deformation, and the texture changes from a discrete distribution to a hard orientation. Cold drawing deformation promoted coarsening of the modulated structure and the transition of the D022 ordered phase. Dislocations and twins increased the occurrence of nucleation for the discontinuous precipitates and promoted the growth of the discontinuous precipitates, but cold deformation inhibited the transition of the D022 ordered phase to the L12 ordered phase. The hardness, tensile strength and elongation of the Cu-15Ni-8Sn alloy after 50% cold deformation were 109.2 HRB, 1258.3 MPa and 7.5%, respectively, after aging at 400 °C for 60 min. The main strengthening mechanisms of the peak-aged alloy were precipitation strengthening and dislocation strengthening.

Influence of aging treatment on corrosion behavior of extruded 2195 Al−Li alloy

The 2195 Al-Li alloy was processed by under-aging (UA), peak-aging (PA), double-aging (DA) and retrogression re-aging (RRA) treatments, and the microstructure, intergranular corrosion (IGC), exfoliation corrosion (EXCO) and stress corrosion cracking (SCC) behaviors were observed and discussed. The results show that the sequence of IGC and EXCO resistance is: RRA > UA > DA > PA. The low corrosion resistance of PA and UA is mainly caused by the continuous precipitation of T1 phases at grain boundaries to form continuous corrosion channels, while the interruption of corrosion channels caused by coarse and discontinuous T1 phases and wider precipitate free zone is the reason for the best corrosion resistance of RRA. The RRA alloy exhibits the best SCC resistance, and the order of SCC resistance is: RRA > DA > UA > PA. The discontinuous precipitation of intergranular T1 phases promotes the propagation of corrosion cracks across grain boundaries, thereby improving the SCC resistance.

Precipitation behaviors and property variations of directionally solidified Cu-15Ni-8Sn alloy

The phase transformation process and its impact on the properties of directionally solidified Cu-15Ni-8Sn alloy have been comprehensively investigated. The results show that the phase transformation products during the aging process include the modulation structure, D022 ordered phase, L12 ordered phase, and ultimately the γ-D03 phase. The formation of modulation structure and D022/L12 ordered phases plays a crucial role in improving the mechanical properties of the alloy. During the aging process, the mismatch between the D022/L12 ordered phases and the matrix increases, resulting in larger coherent strains and further enhancing the mechanical properties. However, the formation of discontinuous precipitates can severely deteriorate the mechanical properties. These precipitates grow by consuming Ni/Sn atoms from both the ɑ'-matrix and D022/L12 ordered phases, thereby disrupting the structure of the D022/L12 ordered phases. By combining the Johnson-Mehl-Avrami-Kolmogorov and the Arrhenius equation, the kinetics of discontinuous precipitate formation during the aging process of directionally solidified Cu-15Ni-8Sn alloy were analyzed. The activation energy of discontinuous precipitates in directionally solidified Cu-15Ni-8Sn alloy is determined to be 225 kJ/mol. Significantly suppressing the formation of discontinuous precipitation is achieved through improvements in the preparation process.

Leveraging a coarse yet strong matrix in L12-strengthened high-entropy alloy through simplified thermomechanical processing

High-entropy alloys (HEAs), characterized by their unique design concept without a distinct major element, offer a versatile alloy design window while ensuring outstanding properties. In this study, the FeCoCrNi–AlTi alloy system, which exploits L12 phase with slow ripening kinetics due to the coherent interface with the FCC phase, has been researched to increase strength via precipitation. This system has been widely studied to improve mechanical properties through microstructure optimization, especially in a direction that suppresses discontinuous precipitation while enhancing strength. Herein, we propose a novel processing method utilizing hot-rolling followed by direct aging for a newly designed (FeCoNi)79.5Cr10.5Al5Ti5 (at%) HEA. The coarse yet strong FCC matrix, generated via hot-rolling, proves advantageous in the subsequent direct aging, as revealed through careful microstructural characterization of both continuous and discontinuous precipitates. A high yield strength of 1065.5 ± 0.4 MPa, a uniform elongation of 14.2 ± 0.0%, and a total elongation of 27.5 ± 0.9% are simultaneously achieved, due to maintaining high dislocation density and promoting continuous precipitation, whereas discontinuous precipitation is suppressed and occupies little area fraction of ∼8%. Careful discussions are provided regarding the impact of the newly proposed processing on the precipitation mechanism, and how the resulting microstructure influences the strengthening mechanisms. This work demonstrates the effectiveness of a simplified thermomechanical process, providing valuable insights into microstructure control in HEAs.

Effect of Cr addition on the microstructure evolution, precipitation behavior and properties of Cu–Ag alloy

This investigation systematically explores the impact of minor Cr additions on the microstructural evolution, precipitation kinetics, mechanical properties, and electrical properties of Cu–Ag alloys, with a specific focus on Cu–6 %Ag-(0.4 %Cr). The alloys underwent casting through a vacuum induction furnace, followed by meticulous treatments involving solution heat and aging at varied temperatures and durations. Results indicate a significant improvement in the mechanical properties of Cu–Ag alloy upon Cr addition, with only a slight reduction in electrical conductivity. As per differential scanning calorimetry (DSC) measurements, the activation energy for continuous precipitation in the Cu–Ag–Cr ternary alloy is slightly higher than that in Cu–Ag. However, Cu–Ag–Cr lacks peaks corresponding to the discontinuous phase. Microstructural analysis unveils that Cr incorporation suppresses the discontinuous precipitation of Ag, fostering continuous precipitation during aging. Moreover, both micro-sized and nano-sized Cr particles were detected in the Cu–Ag–Cr alloy, contributing to the formation of finely spaced continuous Ag precipitates and fine Cr precipitates. This intricate microstructure imparts higher hardness and strength to the alloy compared to Cu–Ag. Specifically, following aging treatment at 450 °C for 2 h, the Cu–6 %Ag-0.4 %Cr alloy exhibited a remarkable increase of 76.1 % in hardness, 43.6 % in strength, and a moderate decrease of 15.8 % in conductivity.

Hot isostatic pressing induced precipitation strengthening at room and high temperature of Ni-Fe-Cr-Al-V high-entropy alloy manufactured by laser powder bed fusion

The highly adjustable properties of high-entropy alloys (HEAs) offer great potential for developing superior materials for critical structural applications in high-temperature conditions. In this study, Ni-Fe-Cr-Al-V HEA was manufactured by laser powder bed fusion, which has a unique microstructure composed of dislocation substructure and Face-centered cubic + L12 coherent structure and achieves the desired strength-ductility combination. Hot isostatic pressing post-treatment was applied on the laser powder bed fusion-processed HEA to further improve the relative density and optimize the mechanical properties. During the hot isostatic pressing process, the precipitation of L12 and B2 phases can be ascribed to the precipitation modes dominated by continuous precipitation and discontinuous precipitation, respectively. With the tensile deformation temperature increasing from 773-1,173 K, the softening degree of HEA increases continuously, and the dominant deformation mechanism evolves from intragranular dislocation slip to grain boundary sliding. At temperatures below 773 K, precipitation strengthening significantly improves tensile strength and ductility. At 1,173 K, the grain boundary strength decreases and grain boundary area increases, which promotes grain boundary sliding and contributes to plastic deformation, resulting in significant softening.

Microstructural changes and dry sliding wear behavior of Cu-15Ni-8Sn-0.5Co alloy during deformation and aging treatment

The microstructural evolution and dry friction wear performance of the Cu-15Ni-8Sn-0.5Co alloy during deformation and aging treatment were studied using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and three-dimensional surface profilometry. The results show that the peak hardness of the Cu-15Ni-8Sn-0.5Co alloy initially increases and then decreases with increasing cold deformation, reaching a maximum hardness of 440 HV at 70 % cold deformation. During the aging process at 400 ℃, the phase transformation sequence of the Cu-15Ni-8Sn-0.5Co alloy with 70 % cold deformation is as follows: modulated structure - D022 ordered phase - γ-D03 phase. The rapid formation of the D022 ordered phase, which is coherently dispersed within the matrix, is the main reason for the significant improvement in the mechanical properties of the alloy. However, the rapid nucleation and growth of the discontinuous precipitation structure are responsible for the reduced mechanical performance and limited resistance to over-aging in the alloy. Additionally, it also causes decreased friction and wear resistance in the alloy with 70 % cold deformation. At a load of 20 N, the primary wear mechanism of the peak-aged Cu-15Ni-8Sn-0.5Co alloy with 70 % cold deformation is abrasive wear. As the load increased to 120 N, the wear mechanism shifted to a combination of abrasive wear and fatigue spalling wear in the alloy.

Spinodal decomposition, ordering, and precipitation transformation in CoCrFeNiAl HEAs under GPa pressure

Pressure is a critical component of preparation processes regardless of its magnitude, whether it is a few megapascals, such as in metal squeeze casting, or thousands of megapascals, such as in the experimental preparation of amorphous materials, quasicrystals and nanocrystals. Spinodal decomposition and ordering are two common forms of unstable phase transformation in solid solutions. Reasonable regulation of these two transformations can effectively control microstructures and improve properties. Therefore, the study of solid solution instability under the effect of ultrahigh pressure is of great significance for regulating the properties of high-entropy alloys (HEAs). From this perspective, CoCrFeNiAl HEAs were prepared under pressures of ambient pressure, 4 GPa and 7 GPa. Both solid spinodal decomposition and ordering of the BCC structure were detected when CoCrFeNiAl HEAs are solidified at ambient pressure. Nevertheless, after high-pressure solidification, liquid‒liquid phase spinodal decomposition occurred. One phase was rich in (Fe, Cr), and the other phase was rich in (Ni, Al). Both phases experienced solid spinodal decomposition during cooling. Discontinuous precipitates were generated in the (Ni, Al)-rich solid phase, each with a size of approximately 1.4 μm. Furthermore, a graphic thermodynamic model was established to reveal the solidification behavior. After solidification at 7 GPa, the corrosion rate of the alloy decreased by 98.3 %; that is, the high pressure greatly improved the corrosion resistance of the alloy. This improvement was attributed to the influences of high pressures on the dynamics of spinodal decomposition processes.

Enhanced plasticity in a Zr-rich refractory high-entropy alloy via electron irradiation

Refractory high-entropy alloys (RHEAs) possess remarkable high-temperature mechanical properties and have significant potential for use in nuclear fission reactors. However, the phase stabilities of RHEAs are relatively poor in the intermediate temperature range. The coarsening of the nanoprecipitates weakens the plasticity of RHEAs, which imposes substantial restrictions on their scope of application. In this study, electron irradiation was employed to address the challenges associated with nanoprecipitate coarsening and discontinuous precipitation in Zr35Ti30Nb20Al10Ta5 RHEAs after intermediate-temperature annealing. Electron irradiation caused the B2 nanoprecipitates to dissolve, re-precipitate, and induce the precipitation of omega nanoprecipitates. Compared with the unirradiated Zr35Ti30Nb20Al10Ta5 RHEAs with poor plasticity (fracture before yielding), the elongation of irradiated Zr35Ti30Nb20Al10Ta5 RHEAs reaches up to 10 %. This study provides a unique viewpoint and pioneering methodology to effectively tackle the challenge of inadequate plasticity in RHEAs.

The influence of microalloying and preparation process on phase transformation, mechanical properties, and friction/corrosion behavior of Cu–Ni–Sn alloys: A review

This review provides an overview of Cu–Ni–Sn alloys, which have great advantages as a potential substitute for beryllium bronze. The characteristics of spinodal decomposition in Cu–Ni–Sn alloys are thoroughly discussed by conducting a comprehensive analysis of thermodynamics and the phase diagram. The traditional casting process for Cu–Ni–Sn alloys is subject to several limitations, including segregation during solidification as a primary constraint. Another significant limitation is the occurrence of discontinuous precipitation during aging. Thus, the strategies to overcome these limitations are further elaborated. Commonly used methods include thermal-mechanical processing and composition design. Finally, the application of Cu–Ni–Sn alloys in friction and corrosion is discussed. The purpose of this review is to provide a comprehensive summary of the research progress and significant limitations encountered in Cu–Ni–Sn spinodal alloys. This includes a discussion of traditional casting methods as well as novel preparation techniques. The aim is to serve as a valuable reference for the development of new manufacturing methods and the future advancement of Cu–Ni–Sn spinodal alloys.

Grain-scale in-situ study of discontinuous precipitation in Mg–Al

Competitive continuous and discontinuous precipitation (CP and DP) have been studied in-situ for the first time in magnesium alloys, using the Mg–Al system as an exemplar. CP forms first, and strongly affects the subsequent migration of the high angle grain boundary (reaction front, RF) behind which DP occurs. It has been demonstrated that in contrast with expectations from classical DP theory, the RF does not migrate with a steady-state velocity, but instead proceeds in an irregular stop–start fashion. Furthermore, the RF velocity is not constant but varies from grain to grain, by a factor of 4 for the conditions investigated. This growth behaviour can be explained by the interaction of the RF with CP. Whilst a mean-field model has been demonstrated to correctly predict the overall CP and DP kinetics, it is shown that the irregular motion of the RF is due to local effects. A simple model has been developed that demonstrates how the locally depleted solute field around a CP leads to arrest of a segment of the RF until sufficient diffusion occurs along it to reactivate RF motion. Zener pinning and boundary curvature also play an important, but secondary role. The results have implications for controlling DP, which is usually considered undesirable.

Tuning heterogeneous precipitation behavior in Ni35Al35Co5Cr20Cu5 HEAs under 7 GPa high pressure

Pressure, as a thermodynamic parameter, has a significant influence on the solidification process of alloys, including the precipitation behavior of alloys. Based on this, a Ni35Al35Co5Cr20Cu5 high-entropy alloy (HEA) with a precipitated phase was designed in this study. Through a comprehensive investigation of the microstructure and properties of Ni35Al35Co5Cr20Cu5 HEAs solidified under ambient pressure (AP) and 7 GPa, we confirmed the influence of pressure on the precipitation behavior of the precipitated phase. The results indicate that the solidification microstructure of the AP alloy displays a diverse distribution of Cr-rich precipitated phases with varying sizes, ranging from approximately 40 nm to approximately 10 μm. It is also worth noting that as the size of the Cr-rich phase increases, it becomes closer to the grain boundary. However, under 7 GPa, the Cr-rich precipitated phases near grain boundaries disappeared, and heterogeneous precipitation (continuous and discontinuous precipitation) emerged. Meanwhile, the nanophase size decreases significantly to approximately 10 nm and achieves a more uniform distribution throughout the alloy. Moreover, the grains undergo significant refinement. Consequently, substantial improvements in both strength and plasticity are achieved.

Simultaneously enhancing the strength and electrical conductivity of Cu-Ni-Sn alloy through plastic deformation of an intermetallic compound

The precipitation strengthening can significantly increase the strength but inevitably sacrifices the electrical conductivity of Cu-Ni-Sn alloys. In this study, a Cu-9Ni-6Sn alloy was aged at various temperatures for different durations and then subjected to severe plastic deformation. When the alloy was aged at 400 °C for 36 h, the uniformly distributed fine precipitates totally transitioned to discontinuous precipitates. And formed nanofibers of intermetallic compounds after plastic deformation. The tensile strength and electrical conductivity of the treated alloy were 1178 ± 3 MPa and 25.0 ± 0.1 % IACS, respectively, which were close to those of Cu-Be alloys. Compared to traditional alloys, the strength and conductivity were both improved. The main strengthening mechanisms were dislocation and fiber strengthening. Considering these mechanisms, the theoretical yield strength was determined to be 1091 MPa, which was close to the experimental value. This work provides a new approach for the preparation of copper alloys with excellent comprehensive performance.

The phase decomposition in non-equimolar (ZrHfVNbMoW)Cx complex concentrated carbides via carbon content regulation

(Zr0.196Hf0.02V0.196Nb0.196Mo0.196W0.196)Cx complex concentrated ceramics (CCC) with variable carbon non-stoichiometry are fabricated by hot-pressing sintering at 2100 °C for 1 h. The influence of carbon content on phase decomposition behavior and microstructural evolution is investigated. With the decreasing carbon content, the phase transformation of single-phase solid solution → discontinuous precipitation → spinodal decomposition → single-phase occurs, consistent to the binary phase diagram with miscibility gap. The single-phase solid solution decomposes into (ZrHfNb)C-rich and (VMoW)C-rich phases during the phase separation. For spinodal decomposition, the nodular microstructure is formed with coherent crystal orientation relationship of (ZrHfNb)C-rich phase {011} // (VMoW)C-rich phase {011}. The spinodal decomposition leads to in-situ hardening and toughening effects due to the interface hardening and fine microstructure. The spinodal decomposition into two high entropy phases could potentially be beneficial to tailor properties and demonstrated in a future work.