Search

Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature. Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbides is highly desirable but still a big challenge. In this study, it is proposed that the high-temperature compression strength of ultra-coarse cemented carbides can be enhanced by modulating hard matrix grains by activated TaC nanoparticles, through solid solution strengthening of Ta atoms. Based on the designed experiments and microstructural characterizations combined with finite element simulations, the grain morphology, stress distribution and dislocation configuration were studied in detail for ultra-coarse grained cemented carbides. The mechanisms of Ta dissolving in WC crystal and strengthening ultra-coarse grains through interaction with dislocations were disclosed from the atomic scale. This study opens a new perspective to modulate hard phases of cemented carbides for improving their high-temperature performance, which will be applicable to a variety of cermet and ceramic-based composite materials.

Ti(C,N)-based cermets with different levels of Tantalum carbide (TaC) were fabricated through mechanical activation and subsequent in situ carbothermal reduction method, and microstructure and mechanical performance were studied. It was found the core-rim structure of the cermets became progressively pronounced as the TaC content increased, and when content of TaC reached at 6 wt %, a brighter inner rim phase could be observed in some hard phase particles. The grain size of the cermets decreased and then rose, reaching the finest grain size at 2 wt % TaC. As the TaC content increased, the overall comprehensive mechanical properties of the cermet, especially the TRS (Transverse Rupture Strength) value has been improved. Moreover, a new parallel orientation between the (1 1 1)R and (110)B planes formed at the solid solution phase/binder interface. Coherency was observed between the (200)R and ( 1 1 1 )B planes of the rim/binder interface in the hard particles with a core-rim structure. The cermet with 6 wt % TaC had the optimal comprehensive mechanical properties of 2399 ± 20 MPa for TRS, 87.9 ± 0.2 HRA for hardness and 19.1 ± 0.2 MPa m1/2 for fracture toughness. This was ascribed to the solid solution strengthening of the (Ti,Ta,Mo)(C,N) phase and improved interfaces between the binder and hard phase. The improved properties of the hard particles have also improved the thermal shock resistance of cermets, with a maximum critical thermal shock temperature of 470 °C.

Ti(C,N)-based cermets with a surface graded layer were obtained by nitrogen sintering under different nitrogen pressures at temperatures from 1300 to 1400 °C. The influence of nitrogen pressure in the range of 50–250 mbar on microstructure and mechanical performance of cermets were then systematically investigated and it was found that coarser solid solution grains formed at the surface of the cemets after sintering the Ti-rich and Ni-poor graded layer. Furthermore, tending with increasing nitrogen pressure, the overall grain sizes and surface region of the cermets became finer, and the surface graded layer thickness increased (the thickest graded layer was 194 μm). The formation of the graded layer and the increase in the thickness of the graded layer were all attributed to the high nitrogen activity on the surface during sintering. Moreover, nitrogen sintering allowed the Ti(C,N)-based cermets to increase the surface hardness of the cermets with a lesser reduction in strength. The maximum surface hardness and TRS (Transverse Rupture Strength) value of cermets after nitrogen sintering was about 14 GPa following a nitrogen pressure of 150 mbar, and 2267 MPa following nitrogen pressure of 100 mbar.

© 2021 The Society of Manufacturing EngineersThe current study examines the influence of various mono and proportional hybrid nanofluids prepared with multi-walled carbon nanotube (MWCNT), alumina (Al2O3) and molybdenum disulphide (MoS2) on the performance of cermet tools in turning of AISI 420 hardened steel. First, mono-nanofluids were prepared using each nanoparticle separately (i.e., Al2O3, MWCNT and MoS2). Afterward, hybrid nanofluids were prepared at three different nanoparticle mixture ratios i.e., particle A:particle B of 1:1 (50 vol% + 50 vol%), particle A:particle B of 1:2 (33.34 vol% + 66.66 vol%), particle A:particle B of 2:1 (66.66 vol% + 33.34 vol%) in a constant volume concentration of 0.6%. Prepared nanofluids (nine different hybrid nanofluids and three different mono nanofluids) were cooperated with the MQL system and their effects on the machinability characteristics such as surface roughness, surface topography, temperature, tool flank wear, and wear mechanisms were investigated. The results were compared with dry and base-fluid MQL assisted cutting results. The surface roughness was decreased by 41.54%, 37.38% and 30.62% through Al2O3:MoS2 (2:1), Al2O3:MoS2 (1:2) and Al2O3:MoS2 (1:1) hybrid nanofluids compared to base fluid, respectively. It was found that different ratios of one more than nanoparticles have a significant effect on the synergistic effect. Based on the all experimental results, it can be concluded that it is necessary to optimize the nanoparticle ratios used in the preparation of hybrid nanofluids.

The erosion behavior of three different cermet coatings namely, Al2O3, Al2O3 + 3% TiO2 and Al2O3 + 13% TiO2 was studied in order to perform erosion analysis. The coatings were sprayed using Plasma spray gun in a simulated coal-fired boiler conditions on SAE-347H steel. An optical profilometer was put to use in order to find weight loss, erosion profiles and erosion rate (mm3/g) in term of volume loss. All the Plasma gun sprayed cermet coatings were able to protect SAE-347H steel from erosive wear at incident angles of 30°, 60° and 90°. In case of uncoated SAE-347H steel specimens the solid particle erosion (SPE) rate was highest at an incident angle of 30°, nominal at incident angle of 60° and lowest at incident angle of 90°.

Present paper delineates a novel route adopted for successfully manufacturing single layer brazed patterned diamond wheels with enhanced attributes. A pneumatic pick-drop methodology is used for placing the grits in a uniform and patterned manner. Instead of commonly used Ni-Cr alloys, a novel formulation of μ-TiC inoculated composite Ag-Cu-Ti filler has been preferred, which helped in arresting crack formation at the root of grit brazement and simultaneously ensured high bond wear characteristics. Addition of μ-TiC particles substantially improved wear characteristics of basic Ag-Cu-Ti alloy but tend to impair its wetting ability on diamond surface with increase in its wt% in the composition. Therefore, its presence in the filler was restricted to only 2 wt% to keep such compromise within acceptable level. Wheels developed using active Ag-Cu fillers were further subjected to performance evaluation by grinding of WC-Co cermets. The operating parameters were changed in such a way that wheels experienced increasing order of grinding-aggressiveness. The degree of aggressiveness in the grit-work interaction has been defined by a unifying scalar quantity, termed as “aggressiveness number”. No trace of wheel loading was observed even in the most aggressive condition due to uniformly spaced grits. The failure counts of diamond grits are also related to this scalar. A detailed analysis is presented to address the suitability of μ-TiC reinforcement in the formulation of active Ag-Cu filler in the light of the grinding force and grit retention ability of the wheels.

TiC-Steel cermet is widely used in aerospace and mining machinery owing to its excellent performance. However, the high wear resistance and the heterogeneity make its machining a challenging task. To investigate the grinding performance of TiC-Steel cermet, vitrified bond cBN wheel was customized to conduct dry grinding experiments. Grinding force was measured using a Kistler dynamometer; surface topography and 3D surface roughness parameters were measured by laser microscopy and scanning electron microscopy. Results indicate that plastic removal of steel phase, brittle fracture of ceramic phase, ceramic phase wear, ceramic phase debonding and microcracks are main removal modes of TiC-Steel cermet. 3D surface roughness parameters Sa, Sq, and Sz consistently increase with increasing grinding depths from 25 μm to 125 μm and decrease with increasing spindle rotation speed. Effect of feed rate on the 3D surface roughness parameters is less than that of the grinding depth. The trend of the grinding force and surface topography is similar to that of 3D surface roughness parameters. Hence, the optimal processing parameters (vw = 1–2 m/min, ap = 25 μm, ns = 5130 rpm) were used to obtain the best surface quality and the lowest grinding force (the minimum FN and FT of 9.2 N and 3.5 N, respectively). This study is devoted to broaden the research on the machinability of carbide-based cermets and promote utilization rate of cermets in industry.

A new cermet material based on titanium carbide with a complex bond consisting of nichrome and nickel, additionally hardened with chromium carbide and a solid solution of chromium in titanium carbide, has been obtained. The influence of the technological parameters of the SHS-extrusion method (the delay time before the application of pressure, the pressing pressure, the speed of the press plunger movement) on the length of the extruded rod is studied, the optimal parameters are found. The microstructure and phase composition of the obtained material was investigated, the physical and mechanical characteristics were measured, and a comparison with analogs was given. It is shown that the microstructure, phase composition, and crystal lattice parameters of the phases do not change depending on the diameter of the extruded rod.

Pure niobium substrates were coated using laser cladding method. Pure molybdenum, Yttria Stabilized Zirkonia (YSZ) and corundum (Al2O3) powders were used as coating materials. Coatings were deposited on specimens as seperate paths with 3÷10mm width and 40mm of length. Two different laser power 3kW and 4kW were tested during deposition. In order to assess the quality of the Mo-YSZ and Mo-Al2O3 coatings, the light microscopy, Scanning Electron Microscopy (SEM), chemical analysis (EDS) and Vickers hardness test investigation were performed. The surface roughness and wear volume were also measured. As a result of YSZ-Mo powder cladding on the Nb substrate the composite layers were obtained without cracks and porosity not exceeding 1 μm. In addition, an increase in hardness of about 450 HV0.5 was revealed. As a result of Al2O3-Mo powder cladding on the Nb substrate the composite layers with many voids and cracks were obtained for each of the cladding variants.

The objective of the present work was to investigate the effect of different cermet coatings on tensile and high-cycle fatigue properties of AISI 1045 steel using High-Velocity Oxygen Fuel (HVOF) thermal spray process. In this study, the WC-12Co, WC-10Co-4Cr, and Cr3C2-25NiCr cermet powders were coated onto the surface of annealed AISI 1045 steel specimens via the HVOF thermal spray process. The corresponding HVOF thermal spraying results were compared with those obtained from hard chrome (Cr) electroplating process. The thermal spray coated specimens showed load drop tendency beyond the yield point with significant work hardening in the tensile results, but low fatigue life than the base material in high-cycle fatigue results due to defects and poor adhesion at the interface. However, those cermet coating materials showed higher fatigue strengths than the hard chrome plated material. Fractography tests showed that fatigue strength was not only dependent on residual stress, but also influenced by the modes of fatigue failure related to the coated layer's cohesion and adhesion strength. Overall, the Cr3C2-25NiCr cermet coating is preferable due to its less porosity, high fatigue property, and better adhesion than the other coated materials.

Core-shell particles are considered to be one of the primary strengthening and toughening methods of cermet. In this study, a (W,Ti,Ta)C based cermet was prepared by vacuum hot pressing sintering technology with the addition of c-BN@Al2O3 (Al2O3 coated c-BN). Localized high residual stress around the core-shell particles causes the strengthening and toughening mechanism at short distances behind the crack tip, such as crack deflection, secondary cracks, crack branching, and grain pull-out, even at a small volume fraction of 10 vol%. Compared with cermet without Al2O3 and c-BN, the flexural strength and fracture toughness of the cermet with 10 vol% c-BN@Al2O3 are increased by 35.62% and 28.45%, reaching 1462 ± 49 MPa and 13.68 ± 0.51 MPa m1/2, respectively.

3D printing is attractive for the fabrication of complex, three-dimensional parts from metallic powder based on a computer-aided design model. Here, we report an extrusion-based 3D gel printing (3DGP) for difficult to machine TiC-high manganese steel bonded carbide. The effect of rheological and crosslinking properties of steel bonded carbide slurries (inks) on their “printability” were explored, with strong emphasis on the optimization of ink formulation. 3DGP enables the control of printing parameters, and thus the resulting complex green bodies with accurate size and dense structure. A nearly full densification level and uniform microstructure of the 3DGP samples were achieved after sintering. Interestingly, a typical core–shell structure formed by TiC-Mo2C solid solution appeared and improved the reinforcement/matrix wettability. The 3DGP sample showed excellent high-stress abrasion resistance due to the work hardening ability of high manganese steel matrix and its excellent adhesion with TiC particles. 3DGP provides a reliable way to manufacture TiC-high manganese steel cermet and similar metal matrix composites, and has the potential to be used to design and develop multiphase composite material as well as gradient composite.

The paper presents the methodology behind the statistical selection of input parameters using the example of spraying two cold-sprayed coatings. The Ti and Cr3C2-25(Ni20Cr)-Gr coatings were tested. Despite the large difference in the structure of these coatings, nanoindentation studies were carried out focusing on the nano hardness H and elastic modulus E. Based on the four input parameters and two output parameters, a 2-level factorial 2(k-p) experimental design was performed. The conducted analysis showed the significant influence of the spray distance on the H and E values in the case of the Ti coating. The input parameters of the spray distance and the type of carrier gas used turned out to be statistically significant in the case of the cermet coating. Taking into account the statistical analysis, the coatings were sprayed with modified values of the input parameters.

The powder metallurgy method including mechanical activation of powders in a planetary mill and spark plasma sintering at 1470 °C in an inert atmosphere was used to obtain NiAl–45vol.%Al2O3 cermet samples with the addition of nanoparticles of magnesium aluminum spinel in an amount of 0.05 vol.%. The features of their microstructure were investigated. Spinel nanoparticles are located at the boundaries between the grains of composite components. The results of X-ray phase analysis at t = 25 and 800 °C were obtained. The main components of the material at t = 20 °C are α-Al2O3 and NiAl. The dependence of internal friction on temperature in the range of 20–900 °C was studied, and the influence of magnesium aluminum spinel nanoparticles on the nature of its change was established. The internal friction curve shows that vibration damping occurs up to 600 °C. Dependences of the ultimate bending strength of cermets at t = 20÷750 °C were determined. The positive effect of introducing a small amount of magnesium aluminum spinel on the elastic properties of composites was established. The best mechanical properties were demonstrated for NiAl–42vol.%Al2O3–0.05vol.%MgAl2O4 samples. On average, the ultimate bending strength of this material was 8–15 % higher compared to samples without nanoparticles. The materials obtained in this research had an ultimate bending strength under normal conditions of 460–490 MPa. A summarizing analysis of NiAl–Al2O3 cermet researches was carried out to determine the nature of the ultimate bending strength dependence on the ratio of components. It was found that it has an extreme nature: the maximum is observed when using the ratio of aluminum oxide to aluminum nickel equal to 0.5.

Many machinery parts working in contact with a fast-flowing fluid flow (e.g. turbine blades of hydroelectric power plants, valves, pump impeller blades, ship propellers, cooling systems for various units, etc.) are subjected to such type of wear as cavitation erosion. An important objective is to eliminate or reduce cavitation erosion so as to achieve a considerable economic effect. This research uses a patented technique developed to evaluate the cavitation erosion resistance of cermet thermal spray coatings (WC–10Co4Cr and WC–20CrC–7Ni). These coatings were prepared using high velocity air fuel thermal spraying (HVAF). The aim of this study is to test a new technique for evaluating coating cavitation resistance, which differs from the standard one by specimen positioning relative to the testing liquid. In addition, scanning electron microscopy (SEM) was used to analyze the initial structure of the coatings prepared and study their behavior after cavitation exposure. The material volume loss criterion during the cavitation test was used to evaluate the coating resistance. The results of cavitation tests showed that the WC–20CrC–7Ni coating has a somewhat higher cavitation resistance than that of WC–10Co4Cr despite its slightly lower average hardness (850±90 HV0.5 versus 950±60 HV0.5). The study of coating surfaces and cross-sections showed that they feature by different erosion mechanisms. It can be concluded that the presence of defects (pores) in the coating structure is the main reason for reducing their cavitation erosion resistance. Therefore, the developed technique proved effective in obtaining experimental data to analyze cermet thermal spray coatings for cavitation wear.

The cermet fuel element was achieved by dispersing the UO2 particles with or without tungsten (W) coating layer uniformly in the W matrix. It is considered to be a robust and secure fuel for use in nuclear thermal propulsion in the near future. In this study, the effect of deposition temperature on the densification and grain refinement of the W coating layer was investigated. A high-density (19.24 g·cm−3) W layer with a uniform thickness (~ 10 μm) and fine grains (~ 297 nm) was prepared by spouted-bed chemical vapor deposition. The prepared high-density, fine-grained W layer has the following advantages. It can prevent direct contact between fuel particles, resulting in a more uniform fuel distribution. In addition, it can decrease the reaction probability between the fuel kernel and H2, and prevent the release of fission products from the fuel kernel by extending the diffusion path at grain boundaries more efficiently. Moreover, the high-density, fine-grained W layer showed outstanding thermal and mechanical performance. Its average hardness and Young’s modulus were approximately 7 and 200 GPa, respectively. The thermal conductivity of the W film was 101–124 W·m−1·K−1 at 298–773 K. This work furthers our understanding of the potential application of the high-density, fine-grained W layer in nuclear thermal propulsion.

The tribological behaviour of WC–Co Cermet coatings coated on Al6061 alloy was studied in this work. WC–Co Cermet coatings have been coated with different thicknesses by changing the amount of the cobalt using HVOF (High velocity oxy fuel technique). The coatings produced have been subjected to microhardness, friction and wear testing. A disc and pin type machine has been used for assessing friction and wears characteristics. The influence on tribological performance of coating thickness and cobalt levels was examined and compared with aluminium alloy. WC–Co coating enhanced hardness by 34% and 42% in 100 and 200 micron thicknesses respectively, compared to aluminium alloy. The wear rate and the coefficient of friction are decreased by 48 and 12%, respectively, compared to uncoated aluminium alloy. Both coatings and substrates increase their wear rate and friction coefficient (COF) with the increase in load and sliding speed. Scanning Electron and Confocal microscopy examinations of worn surfaces were carried out to evaluate coating wear processes.

Cermets with enhanced electronic conductivity were synthesized by incorporating Ag nanoparticles into a mullite matrix. Silver nanoparticles, altogether with a ceramic optimized processing and a sintering temperature, contribute to the reduction of the surface porosity of the ceramic materials. The electrical properties of the mullite-Ag cermets were analyzed by means of the Electrochemical Impedance Spectroscopy technique between 400 and 700°C in a frequency interval of 10MHz–10 mHz. The associated electrical conduction mechanism of the cermets was accomplished with an equivalent circuit model. With 1% of silver nanoparticles incorporation in the mullite matrix, the resistivity was drastically reduced (conduction increases mainly through the grain border) likewise the activation energy. Moreover, the nanometric character of the silver particles was confirmed by SEM and their interaction on the surface of the grain boundaries of the mullite determined by XPS.

To improve the performance of Mo-based cermets, Mo-(Ni)-Al2O3 cermets were prepared with raw materials of nano-sized Al2O3 powder. The effects of Al2O3 and Ni additions on the densification behavior, microstructure, bending strength, and hardness of the Mo-(Ni)-Al2O3 cermets were experimentally analyzed. The results showed the content of Al2O3 had a great influence on the degree of densification of Mo-Al2O3 cermets at the sintering temperature of 1600°C. In addition, the Al2O3 particles were distributed evenly in the matrix of Mo-based cermets, which refined the grains of Mo and increased the hardness of cermets. Because of the weak interfacial bonding strength between Al2O3 ceramic phase and Mo metal phase, the bending strength decreased continuously with increasing Al2O3 content. However, Ni addition improved the wetting and adhesion of Al2O3 and Mo. With the addition of Ni, the relative density increased, and thus hardness and bending strength were improved.

This paper discusses the relationship between the elongation and compression behavior and microstructural changes under redox cycles of porous Ni(O)–YSZ cermets for solid oxide fuel cells (SOFC). Mechanical damage in SOFC and SOEC is one of the most important degradation factors governing the electrical performance of cells. Therefore, it is necessary to know the mechanical properties of each component material, such as elastic and deformation properties, in the operating environment. Particularly, of the Ni(O)–YSZ cermets which currently makes up 90% of the volume of the cell, with present mainstream anode supported SOFC and SOEC. Therefore, understanding the properties of the Ni(O)–YSZ cermets plays an important role in ensuring the performance of the entire SOFC and SOEC. In this study, the microstructural changes of Ni(O)–YSZ cermet by reduction, re-oxidation and re-reduction were observed in detail using microstructural observations and systematically compared with the dimensional change behavior. For the dimensional change behavior, a simple model considering the initial porosity and Ni content is proposed, which successfully predicts the dimensional change due to re-oxidation. Furthermore, Ni(O)–YSZ cermets with high Ni content show large initial dimensional changes, but the dimensional reversibility improves with increase of the number of redox cycles.

Despite advances in NiCr + Cr3C2–NiCr coating improving the erosion wear resistance at low impact angles, the deterioration at medium and high impact angles has not been solved for the impeller subjecting to multi–impact angle. Herein the conflict is circumvented by combining the erosion performance of the NiCr and Cr3C2–NiCr under different impact angles and proposing a novel coating structure. First, the NiCr + Cr3C2–NiCr coating specimens with different NiCr content were prepared using the plasma spraying system. Second, the erosion rate of NiCr + Cr3C2–NiCr coatings in relation to the impact angle and the concentration of NiCr was measured by an air jet erosion test system, the microhardness was measured on the polished cross-section, and the erosion morphology was observed by SEM and analysed. Erosion behavior analysis showed that the NiCr + Cr3C2–NiCr coatings exhibited the coupling erosion wear mechanism of high toughness and high hardness, where the dominant characteristic was depending on the concentration of NiCr. Then, a tangential functional gradient coating structure was proposed by combining the excellent erosion wear resistance of ductile and brittle materials at varying impact angles, and a semi-theoretical erosion rate model considering the influence of the NiCr concentration was established based on the deformation wear theory. The erosion rate model was validated by experiments which showed the error was within 9.15%. Consequently, the erosion rate can be regulated on demand along the entire eroded surface, which significantly improves the erosion resistance of cermet at medium and high impact angles, thus prolonging the residual life of remanufactured impeller.

(Ti, V, W, Mo)C-based cermets were synthesized by varying the amount of WC and Mo. Scanning electron microscopy, x-ray diffraction detection, Vickers hardness, and transverse rupture strength tests were used to examine the microstructure and mechanical properties. The results demonstrate that comprehensive mechanical properties were improved with dispersed white particles in the binder, and the crack propagated with deflection and bridging. In the fracture morphology, more dimples were formed. However, when the WC and Mo content was increased to 20 wt.%, the in-situ precipitated white particles agglomerated, and was difficult for the binder to release stress via deformation, resulting in a decrease in the toughness.

Ti(C,N)-WC-Mo2C-TaC-Co-Ni cermets with various content of La2O3 were prepared by gas-pressure sintering at 1450 °C. The effects of ultrafine La2O3 additions (0, 0.05, 0.1 and 0.2 wt%) on the microstructure, mechanical properties, wear resistance and cutting performance of cermets were explored. In the microstructure of cermets, the La2O3 particles and dissolved La element in binder phases were observed, which could inhibit the dissolution-precipitation process of ceramics phases during liquid-sintering. Furthermore, the La2O3 could absorb and react with the impurity Al element with low melting point from raw powders, avoiding the appearance of liquid phase at the low temperature and partial overheating during sintering process. These mechanisms could inhibit the abnormal growth of Ti(C,N) core-(Ti,W,Mo,Ta)(C,N) rim structures effectively, leading to the thinning of brittle rim phases and coarsening of wear-proof Ti(C,N) particles. The decrease of proportion of brittle rim phase and ultrafine Ti(C,N) particles promoted the fracture toughness. The increase of proportion and grain size of Ti(C,N) improved the hardness, wear resistance and cutting performance significantly. However, the excessive addition of La2O3 would result in the agglomeration of La2O3, causing the sharp decline of mechanical properties and cutting performance. The cermet with 0.1 wt% La2O3 addition possessed the optimal mechanical properties with Vickers hardness, transverse rupture strength and fracture toughness of 1710 (HV30) Kgf/mm2, 2480 MPa and 11.7 MPa m1/2, respectively.

The results of a study of the effect of temperature on the thermophysical characteristics of cermet coatings formed by carbo-vibro-arc hardening (CVAH) are presented. It was found that with an increase in temperature from 25 to 970°C, the coefficient of thermal conductivity λ of the coatings varies in the range from 18.1 to 24.0 W/(m·K), the specific heat from the coatings varies in the range from 560 to 895 J/(kg·K), and the thermal diffusivity coefficient a practically does not change, its average value is 5.1 × 10–6 m2/sec. The results of the research can be used to simulate the formation of high-quality metal-ceramic coatings by the CVAH method.

The results of studies to determine thermophysical characteristics of multicomponent pastes used for formation of hardening cermet coatings by the method of carbovibro-arc hardening (CVAH) are presented. The coefficients of thermal conductivity and thermal diffusivity, as well as the specific heat of multicomponent pastes for CVAH at different temperatures, have been determined. It is shown that the results of the research and the obtained values of thermophysical characteristics of multicomponent pastes can be used to develop a thermal model of the CVAH process, on the basis of which it is possible to determine appropriate process regimes for hardening machine parts with different geometric dimensions

Herein, Mo2FeB2-based cermets, with nominal composition of Mo2FeB2-2.06Fe-2.9Ni-2.5Cr-xWC-0.04C (x = 0, 2.5, 5, 10 wt %), are fabricated by multi-step sintering to investigate influence of tungsten carbide (WC) content on microstructure and mechanical properties. Results reveal that the microstructure of WC-free cermets resembles that of traditional cermets. However, microstructure of WC-containing cermets (x = 2.5 wt %) is composed of fine black core/grey rim Mo2FeB2 grains and coarse white-colored coreless Fe3(W,Mo)3C grains. Furthermore, at x ≥ 5 wt %, most of white coreless Fe3(W,Mo)3C grains are transformed into a white core/black rim structure. From these observations, it can be concluded that growth of nearly round-shaped Mo2FeB2 grains is through diffusion-control, leading to normal grain growth (NGG), whereas the growth of polyhedral Fe3(W,Mo)3C grains is dictated by the interfacial reactions, resulting in 2D nucleation and partially abnormal grain growth (AGG). In addition, grain size distribution of WC-containing cermets exhibits distinct bimodal characteristics, where average grain size is smaller than that of WC-free cermets. More importantly, presence of WC significantly improves the mechanical properties, resulting in superior fracture toughness of 25.1 ± 0.5 MPa m1/2 and hardness of 90.3 ± 0.1 HRA, at x = 5 wt %, without compromising much of transverse rupture strength.

Friction stir welding (FSW) is employed primarily for metals characterized by poor weldability at fusion welding: aluminium, magnesium, titanium and copper alloys as well as stainless steels. The focus of the study was on the feasibility of application of WC-based hardmetal 85WC-Co and TiC-based cermet 80TiC-NiMo as potential tool materials for FSW of copper. The single-pass welding trials of Cu sheets were performed using a vertical milling machine. For better understanding of interactions between the tool and workpiece at welding temperature EDS line scans across the interfaces tool-workpiece after welding as well as after diffusion tests were performed. It was concluded that both tested ceramic-metal composites did not failure during multiple plunges and during the total transverse welding distance of 10 m. Also, significant tool wear was not observed after such a welding distance. The possibility of producing visually defect-free welds using tools from WC- and TiC- based ceramic-metal composites was proved and also mutual diffusion of elements across the interface tool-workpiece was discussed.

The present work investigated the microstructure and mechanical properties of TiCx-Cu cermets before and after thermal shock tests. Thermal shock temperature was from 800 °C to 1200 °C and number of cycles was from 1 to 20. The results indicated that TiCx-Cu cermets with co-continuous structure exhibited a stable and excellent thermal shock resistance. When quenched at 1000 °C for 1 cycle, the residual flexural strength of the cermet increased to 882 MPa, which was 10.1% higher than that without thermal shock. After 20 cycles of thermal shock, the residual flexural strength still maintain 760 MPa. When quenched at 800 °C and 1200 °C, the strengths of cermet decreased correspondingly, which were caused by the thermal mismatch between metal and ceramics and effusion of Cu or collapses of oxide layer, respectively. Herein, the recrystallization and refinement of metal phase grains caused during the thermal shock process, resulting in the superior thermal shock performance of cermet.

High-entropy alloys (HEAs) have attracted increasing attention because of their unique properties, including high strength, hardness, chemical stability, and good wear resistance. Powder metallurgy is one of the most important methods used to fabricate HEA materials. This paper introduces the methods used to synthesize HEA powders and consolidate HEA bulk. The phase transformation, microstructural evolution, and mechanical properties of HEAs obtained by powder metallurgy are summarized. We also address HEA-related materials such as ceramic-HEA cermets and HEA-based composites fabricated by powder metallurgy.

Abstract This study emphasis on a novel fabrication technique to fabricate hybrid cermets using Al 6061 alloy with nano sized SiC, Al2O3 and TiO2 as reinforcements. During the fabrication process, the melted pool was ultrasonicated to disperse nanoparticles at 20 kHz for 5 min and pressure of 50 MPa was applied to eliminate voids. The influence of nanoparticles on physical, thermal and mechanical properties were evaluated by tensile, wear and thermal studies. Cermets with Al2O3 reinforcements showed higher mechanical performance compared to Al alloy. This enhancement could be related to the uniform distribution of Al2O3 with refinement in grain size of Al alloy which was observed via surface analysis. The morphological studies provided justifiable evidence of homogeneous distribution, nominal cluster along with agglomeration and cavities shrinking on the cermets. The agglomeration of nanoparticles along with SiC protected the cermet in corrosion and abrasive wear by ~ 97% and ~ 71%. The study evidenced the novel fabrication method using ultrasonic rheo-squeeze casting led to improvement in mechanical and thermal properties of the hybrid cermets. Graphical abstract

To explore the effect of laser scanning speed on the microstructure and performance of Cr3C2-NiCr cermet layers fabricated by in-situ laser cladding, Cr3C2-NiCr cermet layers were laser cladded from Ni/Cr/Graphite (25:65:10 wt.%) elemental powder mixtures. The microstructures of the laser cladded cermet layers and the formation mechanism were investigated. In addition, the effect of laser scanning speed on the microstructure, friction and corrosion performance of the Cr3C2-NiCr cermet layers was studied. The results indicated that the in-situ laser cladded Cr3C2-NiCr cermet layers were composed of NiCr binder and Cr3C2. The laser scanning speed had a significant influence on the carbide content, composition and size. Furthermore, it affected the in-situ laser cladded cermet layer’s hardness and wear resistance. The corrosion resistance of the in-situ laser cladded cermet layer was superior to that of laser cladded nickel-based alloy and was improved with decreasing laser scanning speed.

Herein, Ti(C,N)-based cermets prepared via mechanical activation and subsequent in situ carbothermal reduction was studied. The correlation between microstructural and mechanical performance of these cermets was investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Results indicated that with the increase in tungsten carbide (WC) content, hard particles of ceramic gradually evolved from complete solid solution to partial solid solution with a little quantity of core–rim structure. Mean particle size of the cermet first increased, and then, slightly decreased. In addition, grain shape gradually changed from relatively faceted to nearly round. Initially, with the increase in WC content, the increase in transverse rupture strength (TRS) and slight increase in hardness were related to the strengthening of both solid solution and fine grains. However, with further addition of WC, the decrease in hardness was primarily because of lower hardness of (Ti,W,Mo) (C,N) phase with higher W content. Extremely high toughness of cermets with WC content of 0 and 3 wt% was mainly due to the decrease in interface area compared to traditional cermets, which resulted in significant reduction in interfacial strain between the rim and core. Moreover, toughness improvement of cermets containing 6 to 12 wt% of WC was due to comprehensive effect of superb coherent relationship of black core/grey rim particles, semi-coherent relationship with high-density dislocations of solid-solution particles, and solid-solution strengthening of white core-grey rim particles.

WC-Co cermets containing Ti and V metallic powders were prepared by ultra-fast microwave heating process. The mixing of WC-5wt%Co containing 5 wt% concentrations of Ti and V was performed by a high-energy mixer mill in ethanol media for 10 min. A fast microwave sintering process was carried out at temperatures of 1400, 1500 and 1600 °C with an average heating rate of 40 °C/min in a graphite bed without any soaking time. The XRD patterns showed WC, TiC and VC crystalline phases as reaction products. The FESEM images demonstrated uniform distribution of formed carbides in the microstructure of WC based cermet. By increasing the sintering temperature to 1600 °C, almost fully dense samples were obtained in both series of composites containing Ti and V. The maximum bending strength (981 ± 10 MPa), hardness (24.7 ± 0.1 GPa) and fracture toughness (8.6 ± 0.1) were measured for WC-Co-Ti hard metal at sintering temperature of 1600 °C.

The development of novel cermet composites based on porous ceramics with high porosity, interconnected pore structure and good mechanical property has attracted considerable attention in engineering application. In this work, water-based freeze casting process was employed to fabricate ZrB2-SiC porous ceramic with aligned lamellar-channels structure using PAA-NH4 as the dispersant. The results revealed that the well-dispersed suspension with best rheological behavior was obtained using 1.0 wt% PAA-NH4 at pH 9. The crack-free porous ceramic exhibited small volume shrinkage ranging from 2.59 % to 1.87 %. By varying the solid loading, the fabricated samples displayed a tailored porosity ranging from 76.12% to 59.37% and an excellent compressive strength of 7 MPa to 78 MPa. After oxidation, the samples displayed a decreased porosity and an increased compressive strength. The ZrB2­SiC porous ceramic fabricated in this work will be a promising candidate for the framework of cermet composite.

A series of novel steel-Ti(C,N) composites was fabricated by spark plasma sintering (SPS) and subsequent heat treatment. The hardness, indentation fracture resistance, and wear behaviour of the steel-Ti(C,N) composites were compared with those of the unreinforced samples, and their potentials were assessed by comparison with traditional cermet/hardmetal systems. The results showed that with the addition of 20wt% Ti(C,N), the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals. The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment enhanced the wear resistance. Although the presence of excessive in situ carbides improved the hardness, the low indentation fracture resistance (IFR) value resulted in brittle fracture, which in turn resulted in poor wear property. Moreover, the operative wear mechanisms were investigated. This study provides a practical and cost-effective approach to prepare steel-Ti(C,N) composites as potential wear-resistant materials.

A high-temperature air-stable solar selective absorber (SSA) based on TiW-SiO2 cermet is prepared by the co-sputtering method. The obtained SSA shows remarkable stability in spectrum, structure, and chemistry after air-annealing at 700 °C, demonstrating its resistance against air erosion at high temperature. Comparing with W-SiO2-based SSA, the addition of the Ti element is proved to be effective in enhancing the thermal stability of SSA. Nevertheless, as the temperature increases to 750 °C, perfectly round cavities appear and induce the deterioration of the coating. A phase transformation from α-W to β-W is found at the interface of TiW/HMVF (high metal volume fraction layer) during deposition. Consequently, the inverse phase transformation from β-W to α-W at above 750 °C results in small vacancies at the interface, being the incentive of cavity generation. Afterward, the violent morphological changes of oxidized TiW accelerate the cavities expansion. To enhance its tolerance ability of service temperature, a Cr barrier layer is introduced to prevent the diffusion of oxygen into the TiW layer. Therefore, the optimal SSA performs stably at 800 °C and the failure temperature is elevated to 850 °C, revealing that the air-stable TiW-SiO2-based SSA has outstanding potential in high-temperature photothermal conversion.

In this work, the high-temperature reduction of nickel oxide and reoxidation of metallic nickel in the YSZ–NiO anode material have been studied. As-sintered material (of mode 1) manufactured by tape casting underwent two treatment modes: one-time reduction (mode 2) in pure hydrogen for 4 h at 600 °C under a pressure of 0.15 MPa; reduction/oxidation (redox) for five cycles in hydrogen/air atmospheres at 600 °C (mode 3). The material of mode 1 exhibited a bending strength of about 209 MPa. This level is high enough for anode materials. Significant changes have been detected in the microstructure of the material reduced in hydrogen (mode 2). Agglomerates of particles (average size about 5 µm) with a predominance of the zirconium phase as well as regions of small particles (1 µm) with uniformly distributed both the nickel and zirconium phases were revealed. The intergranular fracture micromechanism prevailed in the specimens tested. The material strength (40 MPa) did not satisfy the requirements for anode materials. Despite too “rigid” redox treatment mode in pure hydrogen and air at 600 °C (mode 3), the cermet is not inferior in strength (85 MPa) to those fabricated using other techniques. On the specimen fracture surface, a porous core and dense outer layers have been revealed. An increased amount of nickel in the surface layer is probably a consequence of the microstructural transformation due to the diffusion of nickel from the subsurface region towards the surface. The redox treatment caused the specimen core degradation due to forming large pores, their coalescence into cracks, and loss of material integrity. In contrast to the mixed fracture micromechanism noted in the specimen surface layer, the intergranular one in the core was revealed. The reached level of electrical conductivity and a positive effect of the treatment on the material strength indicate the potential of the tape cast material, especially, in the case of reduction in Ar–5 vol% H2 gas mixture instead of pure hydrogen.

The technology for synthesizing fluoromagnesium apatite powder and the plasma-spraying technology for forming a coating based on it are presented. The recommended conditions for forming a coating based on fluoromagnesium apatite powder with open porosity > 40%, adhesive strength 15 MPa, hardness 190 HB and wettability are: arc current 300 A, dispersity of titanium powder up to 150 μm, dispersity of fluoromagnesium apatite powder up to 90 μm, consumption of plasma gas 20 L/min, spraying distance of titanium powder up to 150 mm, and the spraying distance of fluoromagnesium apatite powder up to 50 mm.

The thermal shock resistance of alumina ceramics with a fine-crystalline structure (crystal size 5 – 40 μm) and with a layered-granular structure, as well as t-ZrO2–Cr(40 vol. %) cermet, was studied. Layered-granular ceramics consisted of randomly oriented layered granules, including alternating dense fine-crystalline layers and porous layers made of corundum microballoons. The cermet structure is represented by two interpenetrating continuous skeletons formed from chromium grains and t-ZrO2 grains. To assess the thermal shock resistance, in addition to the known criteria R0, R1 it is proposed to use new criteria R0*, R1* and the kinetic characteristic of fracture γF/γI. These criteria were compared with the thermal shock resistance determined by the number of thermal cycles to failure N of samples and by the method of local thermal shock, which determines the relative loss of crack resistance of the sample after a single thermal cycle RT. Layered-granular Al2O3-ceramics exhibit the best thermal shock resistance due to the discrete and high-energy destruction mechanism. The use of chromium in the composition of cermet made it possible to significantly increase its thermal shock resistance in comparison with the thermal shock resistance of the ceramic component due to the presence of a heat-conducting metal component. It is shown that the application of the new criteria R0* and R1* makes it possible to reliably predict the thermal shock resistance of the studied materials from the indicators N and RT.

The process of formation of a multilevel multilayer B4C – Ti-6Al-4V cermet coating by the method of SLM is studied. The coating is characterized by presence of heterogeneous zones differing in the mechanical properties. It is shown that the use of the B4C – Ti-6Al-4V powder mixture with ceramics concentration 20 wt.% is not expedient, because it causes deficit of the metallic matrix and formation of cracks. At 10 wt.% ceramics in the powder mixture with alloy Ti-6Al-4V the wear resistance of the coating increases by a factor of 4.2.

t—The effect of ultraviolet (UV) laser radiation on the structure and adhesion properties of materials such as chromated bronze, stainless refractory austenitic chromium-nickel steels, and copper, has been experimentally studied. It has been shown that the surface microstructuring of elements of a diffusion-bonded joint improves its mechanical properties as to its tensile strength and tensile strain. Some results are presented for the laser perforation of a copper interlayer and the laser surface microstructuring of ceramic blanks which provide improvement in the mechanical properties of a Si3N4/Cu/Si3N4 welded joint.

This work proposes the application of pulsed electromagnetic coupling field processing (EMCFP) to enhance the lifetime and cutting performance of WC-15TiC-6Co cermet tool for the first time. Firstly, the developed electromagnetic field coupling equipment is introduced, the treatment process is analyzed, and the magnetization characteristics of WC-15TiC-6Co cermet tool are evaluated. Secondly, the strengthening effect of the EMCFP treatment is demonstrated by mechanical properties testing and cutting experiments, which reveal that the optimally treated tools exhibit a fracture toughness increased by 18%, an average cutting temperature decreased by 10%, and a friction coefficient for the rank face decreased by 7.9%. Collectively, these enhancements result in a tool lifetime increased by a factor of 1.92 relative to the lifetime of untreated tools. In addition, the results of simulation demonstrate that the simultaneously pulsed magnetic and electric fields contribute toward greater magnetic flux density and current density on the surface of the WC-15TiC-6Co cermet tool than would be obtained from the magnetic and electric fields alone.

A novel ceramic coating-like (CCL) structure was proposed for preparing a potential ceramic cutting tool material. The influence of critical factors, including the material composition, composition content and surface layer thickness, on the residual stress was analyzed by the finite element method (FEM). Under the condition of the optimized parameters, the compressive stress generated on the surface layer of the CCL tool material ranged from −163 MPa to −248 MPa. Based on the obtained results, a (Ti,W)C/Al2O3+SiC CCL tool material was prepared by vacuum hot-pressing sintering, indicating the residual compressive stress (−122.3 MPa) of the surface layer. Compared with the performance of homogeneous cermet materials, the surface hardness and flexural strength of the CCL tool materials were increased by 46.58% and 37.76%, respectively. Moreover, the SEM imaging results of the sample surface and fracture morphology and the energy dispersive spectroscopy (EDS) analysis results showed that the dense ceramic surface and phase interfacial transition layer were formed with a uniform gradient distribution and without defects.

In this study, Cr3C2-25NiCr cermet coatings were fabricated by atmospheric plasma spraying on 304 stainless steel substrate. Then, the coatings were sealed with a Polytetrafluoroethylene (PTFE) emulsion by using two methods: conventional impregnation and ultrasonic vibration. The phase composition, surface morphology, porosity, permeability of PTFE emulsion into the coating, wear and corrosion resistance of the coatings were investigated. The results showed that in the PTFE sealed coatings, besides carbide phases, a PTFE phase with an hexagonal crystal structure was formed. The PTFE covered the surface of the coating. The ultrasonic vibration method increased the permeability of the PTFE emulsion into the coating by more than 2 times that of the conventional impregnation method. The PTFE sealed coating by ultrasonic vibration method had a lower porosity, higher wear and corrosion resistances in 3.5 wt.% NaCl solution than the PTFE coating sealed by conventional impregnation method and PTFE unsealed coating.

The permanent importance of molds and dies in the industry motivates new studies to obtain optimized parameters and processes, which contribute to the reduction of their wear and increase of their life cycle. Regarding this, coated forming tools are often applied and this paper aims to investigate the influence of the surface preparation of hardened AISI D2 steel substrate on the adhesion characteristics of an AlCrN coating deposited by physical vapor deposition (PVD). For this, an end milling process with different cutting conditions was applied and the coating was tested by indentation and scratch tests. From the obtained results, it could be observed that cermet cutting inserts used in milling process led to higher compressive residual stresses and lower roughness values in the substrate in comparison to cemented tungsten carbide inserts, increasing the critical load required for coating failure. Although scratch tests demonstrated enough sensitivity to differentiate substrate surface properties, indentation tests had no success.

This study explored the effect of diamond content (0, 0.3, 0.6, and 0.9 wt%) onTi(C0.5,N0.5)-based cermets prepared via vacuum sintering with respect to their final mechanical properties and microstructures, characterized using X-ray diffractionand scanning electron microscopy. After liquid phase sintering, all cermets exhibited a ‘black core/grey rim'and partial ‘white core/grey rim'structure. The cermet with 0.6 wt% diamond exhibited optimal mechanical properties with a Vickers hardness of 1795 ± 32 H V, transverse rupture strength of 2026 ± 45 MPa, and plane strain fracture toughness of 12.95 ± 0.3 MPa m1/2. This is due to grain refinement and the uniformly distributed ‘white core/grey rim'grains. During the incipient liquid formation stage,a higher carbon activity arising due to diamond graphitization may shift the equilibrium towards the product, thereby yielding additional white cores due to the consumption of heavy elements in the binder. Excessive diamond introduction inhibited the dissolution of Ti(C0.5,N0.5) into the binder, resulting in fewer white cores.

The gas turbines are the components which are commonly affected by severe high-temperature erosion wear due to impingement of solid particles entrained in the stream of fluid. The present investigation focuses on the applicability of plasma sprayed coatings for turbines by improving the erosion resistance of the base material. The present work includes high-temperature solid particle erosion behaviour of [35%(WC-Co)/65%(Cr3C2NiCr), [70%NiCrAlY + 30%TiO2] & [70%NiCrAlY + 25%Cr2O3 + 5%YSZ] coatings deposited by atmospheric plasma spray (APS) process. All the coating materials are considered by weight (%). The effect of impact angle on erosion performance of uncoated and coated specimens were comparatively studied by using the air-jet erosion tester (ASTM G76-13). The eroded surface morphology was analysed by using a porosity tests, microhardness values, scanning electron microscopy & X-ray diffraction analysis. All Coatings exhibits the ductile erosive mechanism at the temperature of 700 °C with severe plastic deformation. The NiCrAlY + TiO2 coating is more protective than the other two coatings in high temperature and erosion environments due to its higher ductility, homogenous microstructure, and lesser porosity of the coatings. However, uncoated MDN 420 steel exhibits lesser wear loss when compared to the coated substrates. This may be due to the alumina particles' embedment onto the coated surface, which might present a shielding effect against further material loss to occur.

This study aims to investigate the correlation between flow velocity and cavitation erosion (CE) characteristics of high-velocity oxygen-fuel (HVOF) sprayed Cr3C2-NiCr (CN) and WC-Cr3C2-Ni (WCN) coatings in 3.5 wt% NaCl medium, except for the microstructures, mechanical properties and electrochemical behaviors. In comparison with the CN coating, the WCN coating shows higher values of elastic modulus (E), hardness (H), H/E and H3/E2 as well as lower porosity, resulting in lower volume loss rate (VLR) and enhanced CE resistance in NaCl medium at each value of flow velocity. The VLR values of both coatings increase as the flow velocity increases. The change of the CE progresses in NaCl medium of the CN coating is the formation of cavitation pinholes, pits, craters and oxidation films coupled with the exfoliation of chromium carbide particles when the flow velocity is 23.4 and 33.5 m s−1 as well as the brittle fracture structure with layers delamination accompanied by the oxidation films when the flow velocity is 41.9 m s−1. In a wide flow velocity range, the formation of cavitation pinholes, pits and micro-cracks along with the oxidation films are addressed as the dominant CE mechanism in NaCl medium of the WCN coating.