Spark Plasma Sintering Technology Research Articles

Microstructure and mechanical properties of Nb25Mo25Ta25W25 and Ti8Nb23Mo23Ta23W23 high entropy alloys prepared by mechanical alloying and spark plasma sintering

In the present work, Nb25Mo25Ta25W25 and Ti8Nb23Mo23Ta23W23 refractory high entropy alloys (HEAs) were successfully prepared by mechanical alloying (MA) and spark plasma sintering (SPS) technologies. With the aid of ball milling, the stabilized single-phase BCC nano-crystalline structures can be obtained with the average crystallite size of about 10 nm. After the SPS process, the grain size of both alloys is less than 1 µm. The compressive yield strength, fracture strain and Vickers hardness of bulk Nb25Mo25Ta25W25 HEA are 2460 MPa, 16.8% and 7.78 GPa, respectively, which are remarkably superior to the same alloy prepared by the vacuum arc-melting (VAM) method. The addition of Ti can further promote the compressive properties in the Ti8Nb23Mo23Ta23W23 HEA, where the fracture strain and peak compressive stress surprisingly increased by 56.5% and 10.7%, respectively.

Research of Structure and Properties of NiCrSiB Sintered Materials Additionally Alloyed with Nb

Abstract Self-fluxing nickel-base alloys containing chromium, silicon, boron, and carbon (NiCrSiB) are widely used in industry because of their unique properties. In this study, various amounts of niobium (Nb) powder (2, 4, 6, and 8 wt. %) were added to the self-fluxing powder of an NiCrSiB system in order to obtain more wear-resistant and dense material by using the technology of spark plasma sintering (SPS). SPS of the powder blends was carried out by the SPS 10-4 apparatus (Advanced Technologies, Newport News, VA). The structure and phase composition of the sintered materials were investigated by optical microscopy, scanning electron microscopy, and X-ray diffractometry. This study gives details of porosity and microhardness measurements as well as tribological tests under the friction on the fixed abrasive particles’ conditions. This study demonstrates that phases (the central region of which is niobium carbide) are formed at the interfaces and in the junctions between the self-fluxing powder particles. The addition of Nb contributes to the decrease of porosity and the increase of wear resistance.

Synthesis, Characterization, Corrosion Resistance and In-Vitro Bioactivity Behavior of Biodegradable Mg⁻Zn⁻Mn⁻(Si⁻HA) Composite for Orthopaedic Applications.

Recently, magnesium (Mg) has gained attention as a potential material for orthopedics devices, owing to the combination of its biodegradability and similar mechanical characteristics to those of bones. However, the rapid decay rate of Mg alloy is one of the critical barriers amongst its widespread applications that have provided numerous research scopes to the scientists. In this present, porous Mg-based biodegradable structures have been fabricated through the hybridization of elemental alloying and spark plasma sintering technology. As key alloying elements, the suitable proportions of silicon (Si) and hydroxyapatite (HA) are used to enhance the mechanical, chemical, and geometrical features. It has been found that the addition of HA and Si element results in higher degree of structural porosity with low elastic modulus and hardness of the Mg–Zn–Mn matrix, respectively. Further, addition of both HA and Si elements has refined the grain structure and improved the hardness of the as-fabricated structures. Moreover, the characterization results validate the formation of various biocompatible phases, which enhances the corrosion performance and biomechanical integrity. Moreover, the fabricated composites show an excellent bioactivity and offer a channel/interface to MG-63 cells for attachment, proliferation and differentiation. The overall results of the present study advocate the usefulness of developed structures for orthopedics applications.

High Temperature Stability of an Al-Zr-Ti Alloy Prepared using Gas Atomization and Spark Plasma Sintering Technology

High Temperature Stability of an Al-Zr-Ti Alloy Prepared using Gas Atomization and Spark Plasma Sintering Technology

High-Temperature Plasma Sintering of the Mixture of Different Fractions of the Plasmadynamic Synthesis Product

The paper examines a technique for producing metal-cutting ceramics from the plasmadynamic synthesis product using the spark plasma sintering technology. It studies the dependence of physico-mechanical properties of ceramics on the mixture parameters. Increase in bulk density and effect produced by this increase are well observed when comparing the sintering process curves. Movable die displacement for non-activated powder is 3.5 mm, while powder activation allowed reaching the 1.75 mm displacement, other conditions being equal. Hardness of produced materials measured by Vickers method was 21 GPa for non-activated powder and 17 GPa for activated powder at relative densities of sintered ceramic workpieces in relation to osbornite monocrystal of 92% and 93.5% respectively. Significant increase in density of the sintered body is ensured mainly by elimination of the raw material agglomeration.

Effects of cobalt content on the microstructural and mechanical/electrical properties of graphene reinforced copper matrix composites

The microstructures and the mechanical/electrical properties of graphene nanoplates-copper (GNPs-Cu; 0.4 wt%) composites and the composites doped by cobalt (GNPs: 0.4 wt%; Co: 2, 3, 4 wt%) have been researched, which have been prepared by mechanical alloying and spark plasma sintering (SPS) technology. It is found that GNPs disperse evenly in Cu matrix with the ball milling time of 6 h. The compressive strength and the hardness of GNPs-Cu are 601.88 MPa and 128 HV, respectively, which were increased by 3 times and 42.2% compared to pure Cu. And the IACS of the GNPs-Cu composites was 79%. The GNPs-Cu composites with 3 wt% Co (3 wt% Co-GNPs-Cu) also present excellent mechanical properties. The compressive strength and the hardness is 571.32 MPa and 145 HV, respectively, which is raised by 2.81 times and 61.1% compared to pure Cu. And the IACS of the 3 wt% Co-GNPs-Cu composites is 65%. In addition, based on the first principle calculation the mechanism of the effect of Co doping on the GNPs-Cu interface bonding has been studied. Our results provide experimental basis for the preparation of high strength and high conductivity Cu matrix composites, which can be widely used in many fields, such as high-strength magnetic field, heat exchange material, etc.

Sintering effect on microstructural evolution and mechanical properties of spark plasma sintered Ti matrix composites reinforced by reduced graphene oxides

Ti matrix composites reinforced with 0.6 wt% reduced graphene oxide (rGO) sheets were fabricated using spark plasma sintering (SPS) technology at different sintering temperatures from 800 °C to 1100 °C. Effects of SPS sintering temperature on microstructural evolution and mechanical properties of rGO/Ti composites were studied. Results showed that with an increase in the sintering temperature, the relative density and densification of the composites were improved. The Ti grains were apparently refined owing to the presence of rGO. The optimum sintering temperature was found to be 1000 °C with a duration of 5 min under a pressure of 45 MPa in vacuum, and the structure of rGO was retained. At the same time, the reaction between Ti matrix and rGO at such high sintering temperatures resulted in uniform distribution of micro/nano TiC particle inside the rGO/Ti composites. The sintered rGO/Ti composites exhibited the best mechanical properties at the sintering temperature of 1000 °C, obtaining the values of micro-hardness, ultimate tensile strength, 0.2% yield strength of 224 HV, 535 MPa and 446 MPa, respectively. These are much higher than the composites sintered at the temperature of 900 °C. The fracture mode of the composites was found to change from a predominate trans-granular mode at low sintering temperatures to a ductile fracture mode with quasi-cleavage at higher temperatures, which is consistent with the theoretical calculations.

Current-Assisted Diffusion Bonding of Extruded Ti-22Al-25Nb Alloy by Spark Plasma Sintering: Interfacial Microstructure and Mechanical Properties

Spark plasma sintering (SPS) technology was used to current-assisted bond extruded Ti-22Al-25Nb alloy. The effects of bonding temperature (920-980 °C) and bonding time (10-30 min) on the microstructure evolution and shear strength of this alloy were investigated systematically. The temperature distribution in the specimen during the current-assisted bonding process was also analyzed by numerical simulation. It is noted that the highest temperature was obtained at the bonding interface. As the bonding temperature and bonding time increased, the voids in the interface shrank increasingly until they vanished. A complete metallurgical bonding interface could be produced at 960 °C/20 min/10 MPa, exhibiting the highest shear strength of 269.3 MPa. In addition, the shear strength of the bonded specimen depended on its interfacial microstructure. With increased bonding temperature, the fracture mode transformed from the intergranular fracture at the bonding interface to the cleavage fracture in the substrate.

Synthesis and Thermoelectric Properties of Ni-Doped ZrCoSb Half-Heusler Compounds

The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo1−xNixSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo1−xNixSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo0.92Ni0.08Sb sample at 850 K.

Phase composition and magnetic properties in hot deformed magnets based on Misch-metal

In this paper, the Rare-earth Iron Boron (RE-Fe-B) magnets were fabricated successfully by using the double main phase method through mixing the Neodymium Iron Boron (Nd-Fe-B) powders and Misch-metal Iron Boron (MM-Fe-B) powders with different ratio. Aiming at the nanocrystalline RE2Fe14B magnets prepared by using spark plasma sintering technology, phase structure and magnetic properties were investigated. It is found that the Misch-metal (MM) alloys promote the domain nucleation during the the process of magnetization reversal and then damage the coercivity (Hcj) of isotropic RE2Fe14B magnets, while the Hcj could still remain more than 1114.08 kA/m when the mass proportion of MM (simplified as: “a”) is 30%. Curie temperature and phase structure were also researched. Two kinds of mixed-solid-solution (MSS) main phases with different Lanthanum (La) and Cerium (Ce) content were believed to be responsible for the two curie temperature of the RE2Fe14B magnets with “a” ≥20%. This is resulted from the inhomogeneous elemental distribution of RE2Fe14B phase.

Contact Multiphysics: A New SPS Paradigm to Enhance Material Fabrication by Design

Spark Plasma Sintering (SPS) is used extensively to fabricate a wide range of monolithic and advanced materials over a short time and at low temperatures which show inherent advantages over conventional hot-pressed materials. However, the presence of uncontrolled microstructure inhomogeneities, especially in relatively large SPS samples, greatly limits the successful transfer of this technology to an industrial process. The intricate complexity of the involved SPS phenomena, the nebulous role of contacts and the tight physical coupling between the powder and the device are the main concerns. This work has three aims: a) to introduce the concept of contact multiphysics in SPS: b) to illustrate that the current issues can be framed within the unifying concept of contact multiphysics: c) to point out that an in-depth understanding of contact multiphysics will contribute significantly to the shedding of the light on SPS phenomena, in order to solve the current limitations of SPS technology and to enable the desired SPS fabrication of materials by design.

Influence of pulsed current during high pressure sintering on crystallite size and phase composition of diamond with Ti[sbnd]B bonding phase

Diamond production by sintering and synthesis is known from the mid-fifties of the twentieth century. The sintering technology of PCD materials has not significantly changed even to this day. Nonetheless, there are publications providing a lot of success in the field of synthesis of diamond composite materials sintering using SPS technology, yet these studies are limited to pressures mainly up to 140MPa. In this work HP SPS (High Pressure Spark Plasma Sintering) device, was used to sinter diamond composite with titanium‑boron bonding phase. Thus obtained material was then compared with HP-HT (High Pressure High Temperature) sintered sample, to investigate the influence of the heating by means of direct pulsed current on the crystallite size and phase composition of diamond with 10wt% of Ti+2B bonding phase. Both HP SPS and HP-HT processes were carried out at 8.0±0.2GPa and at the temperature of 1650±50°C during 20s of holding time. The XRD analysis carried out showed that the different type of current used for heating has significant influence on kinetics of the sintering, which is visible in differences in phase composition and level of lattice strain, when comparing standard HP-HT with HP SPS methods.

Exploration of Viability of Spark Plasma Sintering for Commercial Fabrication of Nuclear Fuel Pellets

The viability of spark plasma sintering (SPS) for fabrication of industrial-grade nuclear fuel pellets is explored by utilizing die designs for single- and multiple-pellet manufacturing. Traditional UO2 pellets were also manufactured by systematically varying processing temperature and pressure as needed for single- and multiple-pellet fabrication. The pellets were then qualified against commercial fuel specifications for density, shape, microstructure, and surface flaws. Pellets produced one at a time met all commercial specifications except for grain size. Pellets produced in batches of two, four, and eight pellets showed suboptimal density indicating that further changes to sintering conditions are warranted. Additionally, commonly used graphite tooling for pellet fabrication was shown to be ineffective in producing large numbers of fuel pellets, as the die and punches were shown to undergo severe wear in each run thus decreasing the reliability of the tooling for production of pellets as per the specification. Finally, additional discussion is provided for identifying the avenues for scale-up of SPS to meet the current commercial demand of 400 million pellets/year. These studies are viewed as first step toward assessing the ability of SPS technology to meet the quality specifications and quantity demands of nuclear fuel pellets.

Synthesis and characterization of superalloy coatings by cathodic arc evaporation

Superalloy targets were produced from Ni-(Al-C-Co-Cr-Mo-Ta-Ti-W) powders by spark plasma sintering technology. The crystalline structure of the as-produced targets was investigated by XRD analysis and compared with the evolution of phases resulting from the operation of the cathodic arc at the target (cathode) surface. Coatings were synthesized at superalloy substrates utilizing these superalloy targets in non-reactive and reactive evaporation processes. Synthesized coatings and target surfaces were compared with respect to chemical composition and crystal structure. The interface between coating and superalloy substrates was investigated by TEM. As an example, a complete layer stack was synthesized by cathodic arc evaporation starting from the superalloy substrate - superalloy coating interface to a fully oxidized superalloy coating showing epitaxial growth in the interface to the superalloy substrate.

Obtaining Intermetallic Compound Copper-Tin: Plasma Dynamic Synthesis and Spark Plasma Sintering

The intermetallic compound tin-copper (Cu-Sn) is widely used in the creation of high-quality bearings, electric conductive lubricants, 3D printers. However, when connecting two metals, the bond between atoms in the lattice becomes covalent or ionic. This leads to the fact that the material becomes more brittle. Additionally, the production of intermetallic compounds is cost-based in terms of both material resources and money. In this paper, the ceramics has been sintered based on the intermetallic copper-tin powders, obtained by plasma dynamic method. The raw powdered materials based on Cu-Sn were obtained using a coaxial magnetoplasma accelerator with copper electrodes by adding the crushed tin into the accelerator. Using X-ray diffractometry (XRD) and transmission electron microscopy (TEM) analyses, the presence of such phases as copper Cu and tin-copper Cu41Sn11 in the obtained material has been confirmed. Further, such-synthesized powdered products were used to obtain bulk samples using the spark plasma sintering technology at various sintering parameters. Images from scanning electron microscope showed a uniform sintering of the product at the sintering temperature of 440 °C under a pressure of 60 MPa. It was found that the sintered intermetallic ceramics has the Vickers hardness equal to 120 Hv. The obtained sample has the lower friction coefficient and the smaller wear area in comparison with the sample, made of pure copper.

The use of Spark Plasma Sintering method for high-rate diffusion welding of high-strength UFG titanium alloys

The article provides an example of applying the technology of spark plasma sintering (SPS) to ensure high-rate diffusion welding of high-strength ultra-fine-grained UFG titanium alloys. Weld seams produced from Ti-5Al-2V UFG titanium alloy and obtained through SPS are characterized by high density, hardness and corrosion resistance.

Spark plasma sintering of high-strength lightweight ceramics

This research paper provides an illustration of how to use the Spark Plasma Sintering technology (SPS) for powder materials in order to obtain lightweight ceramics Al2O3/ZrO2 with enhanced strength properties. Optimization of SPS modes helps to produce ceramics with grain size of less than 400 nm, microhardness Hv = 24 GPa, and crack resistance KIC = 4.2 MPa·m1/2.

Microstructure evolution and mechanical properties of spark plasma sintered W–Ni–Mn alloy

Tungsten heavy alloys (90W–6Ni–4Mn) were prepared through spark plasma sintering (SPS) using micron-sized W, Ni, and Mn powders without ball milling as raw materials. The effects of sintering temperature on the microstructure and mechanical properties of the 90W–6Ni–4Mn alloys were investigated. SPS technology was used to prepare 90W–6Ni–4Mn alloys with relatively high density and excellent comprehensive performance at 1150–1250 °C for 3 min. The 90W–6Ni–4Mn alloys consisted of the W phase and the γ-(Ni, Mn, and W) binding phase, and the aγerage grain size was less than 10 µm. The Rockwell hardness and bending strength of alloys first increased and then decreased with increasing sintering temperature. The best comprehensiγe performance was obtained at 1200 °C, its hardness and bending strength were HRA 68.7 and 1162.72 MPa, respectiγely.

Synthesis and Thermoelectric Properties of ZnO/Cu<sub>2</sub>SnSe<sub>3</sub> Composites

Addition of nanoparticles into bulk materials is an efficient way to enhance the performance of thermoelectric materials. The nanoZnO particles were introduced into the Cu2SnSe3 matrix by ball milling method, and the ZnO/Cu2SnSe3 composites were fabricated by spark plasma sintering (SPS) technology. The phase constitution and microstructure were characterized by XRD, FESEM. The effects of nanoZnO particles on the electrical and thermal transport were investigated and discussed. The diffraction spectra of all composites samples well corresponded to that of the matrix diffraction plane. The nanoZnO agglomerated into irregular clusters with the size lager than 200nm and distributed on the grain boundary or the surface of Cu2SnSe3 grain, which significantly reduce the lattice thermal conductivity by scattering middle-long wavelength phonons. The optimal ZT value was obtained from the composite sample of 2.4 vol. % ZnO, which is 1.3 times as large as that of the Cu2SnSe3 matrix.

Effect of Spark Plasma Sintering Temperature on the Consolidation of SiC Fiber Reinforced Titanium Alloy Matrix Composites

Continuous SiC fiber reinforced titanium alloy matrix composite (SiCf/Ti) is a potential material in aeronautical field for its excellent mechanical properties. In this work, continuous SiC fiber reinforced TC17 alloy composites (SiCf/TC17) were fabricated by spark plasma sintering (SPS) at different sintering temperatures from 800 to 1000 oC with interval of 50 oC. Consolidated samples were investigated by SEM, EDS and Matrix erosion method. The results showed that the densification degree and the thickness of the interfacial reaction layer increased as the sintering temperature elevated. In addition, the interface reaction layer with typical tooth shape microstructure mainly consisted of TiC and TixSiy, which was quite similar to t that of hot isostatic pressing (HIP) sample. Due to the aggravation of interfacial reaction, there were lots of voids around interfacial layer above 1000 oC, and the residual stress was hardly affected by the sintering temperature. The SiCf/Ti composites can be consolidated at a lower temperature using SPS technology compared with the HIP processing, which is beneficial to the control of the interface reaction together with the reducing of the cost.