Spark Plasma Sintering Technology Research Articles

Investigation on friction and wear behaviors of Cu–Zn composition with doped MoS2 powder under electric field

Molybdenum disulfide (MoS2) as a two-dimensional material and solid lubricant shows good friction properties in many applications. The study used the copper (Cu) and zinc (Zn) powder with doped MoS2 powder to prepare the alloy material through the spark plasma sintering (SPS) technology. The coefficient of friction (COF) and wear of alloys with different doped ratios (0 wt%, 3 wt%, 6 wt%, 9 wt%) of MoS2 were studied by using universal mechanical tester (UMT-5), which was based the ball-on-disk method. The results show that the alloy with 3 wt% MoS2 has the lowest COF, about 0.093. The COF of composites containing 9% MoS2 are close to those of un-doped composites, 0.673 and 0.712, respectively. It is mainly owing to excessive corrosion of Cu by MoS2, resulting in increased COF and wear rate. In addition, the effect of the applied electric field on the COF of the alloy was also investigated. It was found that the electric field can increase the COF and the wear rate of the composites. As the voltage increases, oxidation of the Cu was promoted and FeSx was formed to reduce friction and wear. This work provides a new method for manufacturing and studying electrical contact friction materials.

Preparation and properties of the VC/Cr3C2/TaC doped ultrafine WC-Co tool material by spark plasma sintering

This work is focused on the preparation and properties of ultrafine WC-Co cemented carbides. Samples were prepared by spark plasma sintering technology using WC and Co nanopowders and different inhibitors such as VC, Cr3C2 and TaC. The influence of inhibitors on the microstructure and mechanical properties of cemented carbides was investigated by using separate addition of VC/Cr3C2/TaC (0, 0.4 and 0.8 wt%) and pairwise addition (VC-Cr3C2, VC-TaC and Cr3C2-TaC). The results showed that with the addition of VC/Cr3C2/TaC, the average WC grain size decreased and VC led to smaller grain size than Cr3C2 and TaC. WC grain morphologies of cemented carbides with VC were triangular prisms with multi-step structure, whereas tended to be round and blunt in cemented carbides with Cr3C2/TaC. Moreover, the addition of inhibitors caused hardness to increase and fracture toughness to decrease in various degrees. Transverse rupture strength (TRS) was affected by changes in grain size and WC/Co interfacial energy caused by inhibitors. The sample with 0.4 wt% VC-0.4 wt% Cr3C2 sintered at 1250 °C had comprehensive mechanical properties. Its relative density, average grain size, hardness, fracture toughness and TRS were 98.9%, 200 nm, 2110 kg/mm2, 10.4 MPa⋅m1/2 and 1990 MPa, respectively.

Radio-frequency negative permittivity of carbon nanotube/copper calcium titanate ceramic nanocomposites fabricated by spark plasma sintering

Ceramic nanocomposites have been developed to provide a feasible and effective strategy in realizing extraordinary electromagnetic properties, such as negative permittivity. Here, copper calcium titanate CaCu3Ti4O12 (CCTO) nanocomposites incorporated with multiwall carbon nanotube (MWCNT) were prepared by spark plasma sintering (SPS) technology. It was found that MWCNT clusters were randomly embedded in CCTO matrix, which destroyed the microstructures of internal barrier layer capacitors in CCTO. The composites with low MWCNT content presented a hopping conduction behavior, while a metal-like conduction behavior was observed in the ceramic with 18 wt% MWCNT content. Interestingly, weakly negative permittivity (~ -103) was obtained in the ceramic consisting of interconnected MWCNT networks, as a great number of free electrons in the MWCNTs formed significantly collective oscillation state over 10 MHz-1 GHz range. Macroscopically, leakage current among MWCNT clusters or networks caused strong conduction loss at low frequencies. Equivalent circuit analysis manifested the correlation between low-frequency plasmonic state and inductive character in the composite with negative permittivity. This work could extend the potential applications of ceramic nanocomposites to metamaterials.

Evolution of microstructure, mechanical properties, electrochemical behaviour and thermal stability of Ti0.25-Al0.2-Mo0.2-Si0.25W0.1 high entropy alloy fabricated by spark plasma sintering technique

Near Equi-Atomic Ti0.25-Al0.2-Mo0.2-Si0.25W0.1 high entropy alloy (HEA) with enhanced mechanical properties and good corrosion resistance was synthesized by means of spark plasma sintering technology. The influence of spark plasma sintering temperature of developed Ti0.25-Al0.2-Mo0.2-Si0.25W0.1 HEA was investigated at 800 °C, 900 °C and 1000 °C. The analysis of the morphological and microstructural characteristics of the alloy revealed the presence of bcc phase structure along with intermetallic phases of TiSi2 and Mo2Si4. Microhardness, wear and oxidation resistance of the alloy were found to be dependent on sintering temperature. The performance of the samples increased with rise in sintering temperature. The electrochemical behaviour of the alloy was tested in 0.5 M H2SO4 solution and the results showed the alloy to possess good anti-corrosion properties. The subjection of the alloy to annealing conditions at 900 °C induced formation of stable phases that improved the microhardness of the samples.

Microstructural characteristics and thermophysical properties of spark plasma sintered Inconel 738LC

Nickel-based superalloys are used for turbine component parts in the power industry, aircraft engines, and in the marine sector. One such alloy that is available for these purposes is Inconel 738LC (IN738LC) nickel-based superalloy. Therefore, it is pertinent to have good structural and thermal stabilities for high-temperature applications, since these characteristics are important for its performance. In this study, spark plasma sintering technology was used to fabricate IN738LC nickel-based superalloy by using sintering temperature in the range of between 900 and 1200 °C. The fabricated products were characterized by using the scanning electron microscope and X-ray diffraction. There was the formation of the γ′(Ni3(Ti, Al)) intermetallic phase in the microstructure, which contributed to the material (Inconel 738LC) property. The solid solution elements present are chromium, cobalt, tungsten, and tantalum; these equally contribute to the structural stability of IN738LC. The density, hardness, and the predicted yield strength increased with increasing sintering temperature, while the porosity decreased with increasing sintering temperature. The thermal conductivity, which is an important thermophysical property of IN738LC, enables the evaluation of the usefulness and service life of IN738LC superalloy at high-temperature applications, was also examined. The thermal conductivity was measured by using a laser flash method in the temperature range of 100–600 °C. For the sintered alloy, the thermal conductivity was determined as a function of the thermal diffusivity, specific heat capacity, and density. Analysis showed inflection pattern with increase in temperature on the sample fabricated at 900, 1000, and 1100 °C, ; a monotonic increase with increase in temperature was observed on the sample fabricated at 1200°C, ; the inflections are associated with the γ′ precipitates dissolution and redistribution.

Synthesis of equi-atomic Ti-Al-Mo-Si-Ni high entropy alloy via spark plasma sintering technique: Evolution of microstructure, wear, corrosion and oxidation behaviour

Equi-atomic Ti-Al-Mo-Si-Ni high entropy alloys (HEAs) with outstanding wear and oxidation properties is fabricated by means of Spark plasma sintering (SPS) technology. The influence of sintering temperature on surface microstructure, phase evolution, densification, microhardness, corrosion, wear and oxidation properties of developed Ti-Al-Mo-Si-Ni HEAs was investigated at 800 °C, 900 °C and 1000 °C. The microstructural evolutions of the synthesized HEAs were evaluated by means of scanning electron microscope coupled with energy dispersive spectroscopy (SEM/EDS). The SEM images showed no significant major porosity; however for the HEA sintered at 800 °C, the densification results prove that 2.6% porosity is present in the HEAs. XRD showed the presence of BCC and FCC solid solution structures with intermetallic precipitates of TiSi2 and Ni2Si2. The Vickers microhardness and wear resistant properties was evaluated using diamond base micro hardness tester (EMCO) and tribometer (Rtec) respectively, with the sample sintered at 1000 °C showing maximum densification of 98.8% with microhardness of 612HV and coefficient of friction (CoF) of 0.23µ. The developed HEAs also showed good oxidation resistant behaviour after a test using thermal gravimetric analyzer (TGA).

Influence of high-energy ball milling on Mg-PSZ-reinforced TRIP steel-matrix composites synthesized by FAST / SPS

A composite with a high-alloy steel matrix was reinforced with varying amounts of Mg-PSZ and synthesized using Spark Plasma Sintering (SPS) technology. To prepare the powders for sintering, they were mixed in a planetary ball mill at two different rates of 100 rpm and 250 rpm. The influence of the rotation speed on the microstructures and compressive strengths of the sintered composites was investigated. Due to the high degree of deformation of the steel powder particles during milling at 250 rpm, the steel phase underwent grain refinement during SPS. Furthermore, the Mg-PSZ was more homogeneously distributed within the steel matrix and mechanically interlocked with the steel matrix. Thus, the compressive strength of the composite increased with increasing Mg-PSZ content and increasing rotation speed during milling of the powder due to grain refinement and the improved strength of the steel/ceramic interface. Furthermore, a larger amount of Mg-PSZ underwent stress-induced transformation under compressive loading.

Enhancement of Mechanical Properties and Corrosion Resistance of Ultra-Fine Grain Al0.4FeCrCo1.5NiTi0.3 High-Entropy Alloy by MA and SPS Technologies

Al0.4FeCrCo1.5NiTi0.3 high-entropy alloy (HEA) was prepared by mechanical alloying (MA) and spark plasma sintering (SPS), which were evaluated in this study by XRD and TEM. After SPS, the bulk alloy exhibited a structure with a dominant fcc phase, a minor volume fraction of bcc phase, and the formation of TiAl3 intermetallic compound. Deformation twinning was observed in the fcc phase in the bulk HEA. The latter had a compressive strength, strain and Vickers hardness of 2225 ± 15 MPa, 17.52 ± 0.50 % and 515 ± 16 HV, respectively. The corrosion resistance studies indicated that Al0.4FeCrCo1.5NiTi0.3 with ultra-fine grained micro-structure was easier to passivate and possessed excellent corrosion resistance. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.19452

Mechanical properties and the composition of Nd-rich phase in sintered Nd-Fe-B magnets prepared by spark plasma sintering

To study the relationship between the mechanical properties of sintered NdFeB magnets and composition of the Nd-rich phase, sintered NdFeB magnets with different mechanical properties and composition of Nd-rich phases were prepared by spark plasma sintering technology (SPS). Several correlations including the bending strength of the magnet to sintering temperature (σbb-t), the rare earth content in the Nd-rich phase to the sintering temperature (nRE-t), and the iron content in the Nd-rich phase to the sintering temperature (nFe-t) were investigated. Several empirical formulas for these relationships ware obtained by fitting these experimental curves. It is found that there is almost no change in the sum of Re and Fe content, revealing that the diffusion direction of RE and Fe atoms in the boundary phase between the main phases during sintering is opposite, and the relationship of σbb to nRE are approximately linear. Based on these, the mechanism of improving the mechanical properties of sintered NdFeB materials via changing the composition of Nd-rich phase was discussed.

Microstructure and its high temperature oxidation behavior of W-Cr alloys prepared by spark plasma sintering

W-10 wt.% Cr (W-10Cr) and W-20 wt.% Cr (W-20Cr) alloys were fabricated through mechanical alloying and spark plasma sintering technology. The microstructure of W-Cr alloys was characterized by XRD, SEM, TEM. The W-20Cr alloy significantly increased the microhardness from 333.5 HV of pure W to 961.3 HV. Oxidation experiments at 800 °C and 1000 °C confirmed that W-20Cr alloy shows better oxidation resistance. A suitable amount of Cr content is favorable for the formation of the oxide scale Cr2O3 and the quality assurance at the initial stage of oxidation, which is able to slow down the oxidation rate. The quality of the oxide scale CrWO4 is better than that of Cr2WO6, indicating that the formation of the oxide scale CrWO4 is beneficial to weaken the further oxidation of the W-20Cr alloy.

Spark Plasma Sintering of Aluminosilicate Ceramic Matrices for Immobilization of Cesium Radionuclides

The possibility of using spark plasma sintering (SPS) for preparing high-density ceramic matrices suitable for firm long-term immobilization of Cs radionuclides was examined. The kinetic features of sintering and phase formation of natural zeolite from the Far Eastern deposit, loaded with the adsorbed Cs ions (surrogate of radiocesium), under nonequilibrium SPS conditions were analyzed. The optimum SPS conditions were determined, and high-quality glass-ceramic matrices based on zeolites from various deposits, characterized by high density (98.5–99.8% of theoretical density), high compression strength (470–490 MPa), Cs content of up to 20.8 wt%, and low Cs leach rates (<10−5–10−6 g cm−2 day−1), were prepared. The SPS technology shows promise for radioactive waste management (in particular, for solidification of spent radioactive sorbents) and radioisotope industry (in particular, for production of special-purpose radionuclide sources).

Synthesis of Ceramic and Glass Ceramic Matrices with Immobilized Cesium Radionuclides for Active Zones of Ionizing Radiation Sources

The present study was devoted to the development of alternative solutions related to replacement of highly dispersed powder of cesium chloride (137CsCl) used as a filler of active zones of g-radiation IRSs (ionizing radiation sources of the closed type) by safer and more efficient in operation highly compacted ceramic or glass ceramic material. An advanced method of fabrication of highly compacted (density of ~99.8 % of the theoretical one) aluminosilicate (artificial NaA zeolites) ceramic and glass ceramic matrices characterized with high construction strength (compression strength ~149 MPa) applicable for reliable immobilization of cesium radionuclides (leaching rate &lt;10-5–10-6g/cm2×day) has been suggested. Unique matrices properties are ensured by advanced features of the technology of Spark Plasma Sintering (SPS) based on high-rate electro-pulse consolidation of the radioactive charge (adsorbed cesium content ~22.16 mass %) into thermodynamically stable ceramics or glass ceramics. The earlier unstudied features of the SPS consolidation of natural zeolite powders sorption-saturated with a radioactive cesium simulant are presented, including the dynamics of their compaction and specifics of phase and structural transformations under effect of irreversible spark plasma conditions.

Effects of Cr addition on the microstructures and oxidation of Nb-Si-Al-Ti-W alloys

The effects of Cr addition on the microstructures and oxidation kinetics of the Nb-20Si-5Al-15Ti-5W alloys have been investigated in this study. The alloys were prepared by Spark Plasma Sintering (SPS) technology. The results show that the microstructure of the alloys consists of (Nb, Ti, W)ss, α-Nb5Si3, γ-Nb5Si3 and (Nb, Ti)5Si3 phase. The addition of 3at% Cr improves the oxidation resistance of the composite at 800°C and 1100°C dramatically. The AlNb11O29, Ti2Nb10O29, TiO2, Nb2O5, Cr2Ti6O15, and Nb4W3O47 are present in the scales formed at 800°C. The phases present in the oxide scales formed at 1100°C consisted of AlNb11O29, Ti2Nb10O29, TiO2, Cr2WO6, and Nb2O5. The oxidation resistance of the composite at 1100°C is better than at 800°C because the oxide scale is more compact structure.

Microstructure and Its High Temperature Oxidation Behavior of W-Cr Alloys Prepared by Spark Plasma Sintering

W-10 wt.% Cr (W-10Cr) and W-20 wt.% Cr (W-20Cr) alloys were fabricated through mechanical alloying and spark plasma sintering technology. The microstructure of W-Cr alloys was characterized by XRD, SEM, TEM. The Cr added into W-20Cr alloy remarkably improves its relative density and the microhardness from 333.5 HV to 960.7 HV. The semicoherent precipitated phase Cr-O in W-20Cr alloy enhances the boundary strength, which consequently changes the fracture mode from typical intergranular fracture to a thorough transgranular fracture. Oxidation experiments at 800 °C and 1000 °C confirmed that W-20Cr alloy shows better oxidation resistance. During the oxidation process, W-rich phase exerts adverse effect on the antioxidant property of W-Cr alloys, Cr2WO6 and CrWO4 in oxide layer help improve the oxidation resistance. During the irradiation process, the doping of Cr element reduces the irradiation damage of W matrix and protects from forming the fuzz structure.

Influence of sintering temperature on microstructural evolution of spark plasma sintered Inconel738LC

This work studied the effect of processing temperature on the microstructure of sintered Inconel 738LC nickel-based superalloy processed via spark plasma sintering technology. The processing parameters used were, 50Mpa pressure, 5minuts holding time and 100 ˚C/min heating rate, with the sintering temperature varied over three different temperatures at 1000, 1100 and 1200 °C. Inconel 738LC powder was mix at the same proportion for all the samples and under the same condition. Test samples were fabricated from the admixed powders and the influence of sintering temperature on the microstructure, porosity and fracture toughness was characterized. Scanning electron microscope (SEM-EDS) was used to investigate the bulk morphology of the sintered alloy, the phases present within the bulk volume of the fabricated samples was investigated, using energy dispersive X-ray diffraction spectroscopy (XRD). From the result analyzed, the increase in sintering temperature lead to a reduction in porosity, decrease in fracture toughness and increase in hardness value. Increase in sintering temperature had positive impact on the sintered alloy, by reducing the level of porosity present in the sintered samples. There is a reduction in the fracture toughness value of Inconel 738LC, this is expected due to the increase in hardness property.

Thermophysical Properties of Silicon-Carbide-Based Ceramic Composite Materials Obtained by Spark Plasma Sintering (SPS)

The factors influencing the thermal conductivity of SiC-based ceramic composite materials obtained by the spark plasma sintering technology with relative density 99% and B4C, AlN, Si3N4, Y2O3, Al2O3, and HfB2 as additives are examined. The thermophysical properties were determined in the temperature range 20 – 1300°C: specific heat, thermal diffusivity, and thermal conductivity of composites. The thermal diffusivity and specific heat were measured by the laser-spark method. The measurements of specific heat are supplemented by measurements performed with a DSC and adiabatic calorimeter. The thermal conductivity is calculated using data on the thermal diffusivity, specific heat, and density.

Spark plasma sintering of nickel and nickel based alloys: A Review

Abstract The use of spark plasma sintering technique has been identified as a means of enhancing materials properties, especially nickel-based alloys. Nickel and nickel-based alloys are essential materials that combine different properties which include; high-temperature strength, good mechanical properties, appreciable toughness, resistance to thermal shock, resistance to thermal fatigue, resistance to chemical attack, resistance to creep, resistance to corrosion/oxidation and good surface stability at the high-temperature environment. The above qualities have made alloys gain more patronage and acceptance in recent time. However, a higher percentage of the demand comes from the aerospace industry, gas/steam power plant, petrochemical plant, nuclear reactors and marine industry. Spark plasma sintering is one of the powder processing methods in metallurgy that has been used to fabricate nickel-based alloys with exceptional qualities. The process involves, mixing metallic powders to form the desired stoichiometry composition (in the case of forming an alloy), either by direct mixing or mechanical alloying. The already mixed powder is transfer to a graphite mould and then compacted in the heating chamber of the furnace. Heat is supply to sinter the compacted powder at a temperature below the alloy melting point, in order to ensure metallurgical bonding between the powder particles. The application of spark plasma sintering technology is a promising one, especially for processing nickel alloys. It promotes the formation of gamma (γ) matrix phase, gamma prime (γ’) intermetallic phases, secondary gamma prime (γ”) intermetallic phase and precipitation of solid solution strengthening elements. These are the phases that improve the mechanical properties of sintered alloys. Spark plasma sintering minimizes the problems associated with conventional fabricating routes such as; micro segregation, pores and pin holes.

Pulsed electrodischarged pressure sintering and flash sintering, a review

Abstract Electric current activated/assisted sintering (ECAS) is a growing class of versatile techniques for sintering particulate materials. Nowadays, most of the scientific attention is focused on pulsed electric current sintering known as spark plasma sintering (SPS). SPS has been successfully applied to electrically conductive and low-electrical-conductivity ceramics although the measured temperature is not directly related to the sintering temperature. Here, we summarize the present status and problems of SPS technology, and introduce our approach to develop SPS. Then, as a future direction, we will demonstrate flash sintering using SPS furnace and conductive powders.

Effect of two-time spark plasma sintering on microstructure and mechanical properties of W–6Ni–4Mn alloy

Tungsten heavy alloys (WHAs) are extensively applied in kinetic energy penetrators, but they exhibit poor self-sharpening properties—connected with high thermal conductivity, large grain size, and low hardness—which limit their application. In this study, we fabricated W–6Ni–4Mn alloys with low thermal conductivity by using the two-time spark plasma sintering (TTSPS) technology. To be specific, raw powders underwent SPS for the first time at 1000 °C followed by the second run at 1000–1200 °C. In our studies, long-time solid-phase sintering at low temperature is used to increase the density of the alloy, while short-time liquid-phase sintering at high temperature inhibits the dissolution and re-precipitation process to suppress the W grain growth. As a result, W–6Ni–4Mn alloy with W grains as small as 3.35 µm, hardness as high as 76.6 HRA, and the bending strength of 785.30 MPa were successfully prepared at 1100 °C. The marked improvement in the hardness of W–6Ni–4Mn alloys in comparison with the previous studies may be mainly ascribed to the fine-grain strengthening effect. When the sintering temperature was increased, the matrix volume fraction improved initially and then decreased and reached a peak value at 1100 °C. However, the W–W contiguity had the opposite change trend. The gray Ni-rich binder phase existed in the microstructure of the TTSPS alloys at temperatures less than 1100 °C, but it gradually transformed into a black Mn-rich binder phase at temperatures above 1100 °C.

Microstructural evolution and sintering kinetics during spark plasma sintering of pure tantalum powder

Spark plasma sintering (SPS) technology can significantly inhibit grain coarsening due to its characteristics of rapid sintering and densification, and obtain a material with high density and uniform microstructure. We completed the SPS sintering of tantalum powder, and characterized the microstructure and mechanical properties of the samples at different sintering temperatures. The results show that during the pure tantalum sintering process, the rapid densification temperature range is 800 °C–1300 °C, and the maximum shrinkage rate of the sample is 1100 °C. A creep model was applied to determine the densification mechanisms involved in the densification stage, which can be elucidated by evaluating the stress exponent (n) and the apparent activation energy (Qd) from the densification rate law. It shows that a series of interfacial reactions and grain boundary diffusions govern the densification process at low effective compaction stresses (n = 1.6, Qd = 107.01 kJ/mol), while dislocation climbing operate at higher effective compaction stresses (n = 3.1 and n = 4.1), which is confirmed by TEM. When the sintering temperature of tantalum powder increased from 1500 °C to 1700 °C, the density and grain size of the sample increase gradually, the tensile strength and flexural strength also increase. The surface hardness of the sample increases gradually. Moreover, surface hardness is much higher than core hardness. The fracture mode of the specimen changes from brittle fracture to ductile fracture. This study has enabled the selection of high quality tantalum alloy sintering routes and optimization of the sintering process.