Spark Plasma Sintering Route Research Articles

Improved functional response of spark plasma sintered hydroxyapatite based functionally graded materials: An impedance spectroscopy perspective

Owing to the inherent polarization regulated functionality of living bone, the present study aims to enhance the polarizability of hydroxyapatite (HA) without affecting its’ surface chemistry i.e., excellent biocompatibility. This concept has been materialized by the development of functionally graded materials (FGMs) using perovskites BaTiO3 and CaTiO3 as intermediary layers. These perovskites were sandwiched between HA layers via buffer interlayers to provide the structural integrity to the FGMs. FGMs were optimally processed using spark plasma sintering route at 1100°C for 10 min. Microstructural analyses of fractured surfaces revealed no sign of delamination between HA/BaTiO3 or HA/CaTiO3 layers, despite of differences in their coefficients of thermal expansions. Further, detailed impedance spectroscopic analysis was performed over a wide range of temperature (35–500°C) and frequency (1 Hz - 1 MHz). Almost two times increase in polarizability has been observed in both types of FGMs as compared to HA. Overall, the developed FGMs can be suggested as potential materials for polarized bone applications.

A novel spark plasma sintering route to process high-strength Ti–4Al–2Fe/TiB nano-composite

ABSTRACTTi–4Al–2Fe alloy and Ti–4Al–2Fe/TiB nano-composite were processed by a novel spark plasma sintering route. KBF4 was used as an alternative and inexpensive boron precursor to form TiB reinforcement in situ during sintering. Fe was used as an alternative to vanadium to make the (α + β) Ti matrix. The processed Ti–4Al–2Fe alloy exhibited excellent mechanical properties (CS = 1798 MPa). The TiB whiskers were distributed homogeneously and were fine (widths 130 nm and lengths from 100 nm to 3 µm). No residual TiB2 was found in the composite, in contrast with other methods. The TiB homogenised and refined the microstructure, while the hardness (710 HV), compressive strength (2414 MPa) and elastic modulus (140 GPa) all increased significantly when compared to the unreinforced alloy.

Spark plasma sintering of TiAl–Ti3AlC2 composite

A TiAl–15 wt% Ti3AlC2 composite was fabricated by spark plasma sintering (SPS) method, using as-purchased Ti and Al powders as well as as-synthesized Ti3AlC2 MAX phase. Ti3AlC2 was synthesized via mechanically-activated self-propagating high-temperature synthesis of Ti, Al, and C powders in a tubular furnace. The mixture of Ti, Al and Ti3AlC2 was ball-milled and spark plasma sintered at 1000 °C for a dwell time of 15 min under an external pressure of 40 MPa in vacuum atmosphere. The microstructure and phase evolution as well as the mechanical properties of the as-sintered composite were studied. A relative density of ~ 95%, Vickers hardness of ~ 4.5 GPa, fracture toughness of 11.9 MPa m1/2, and flexural strength of 336 MPa were obtained by such a low-temperature SPS route.

Cu-based composites as thermal barrier materials in DEMO divertor components

For DEMO fusion reactor an expected heat flux of about 10MW/m2 should be extracted by the divertor which will have, most likely, an armour part made of W and a following heat sink part made of Cu or ODS Cu alloy. Unfortunately, for these materials the optimum operating temperature windows do not overlap. Thermal barrier materials are interface materials included in such components, aiming to keep the temperatures of both armour and heat sink parts in the corresponding operating windows, and to mitigate the effects of their different thermomechanical properties. Here we propose a simple spark plasma sintering route to create Cu-based composites with a high content (10–40vol%) of various dispersed materials (Al or Y oxides, C, SiC), allowing a fine tuning of the content and a large pool of predefined shapes and dimensions. The resulting specimens can be further joined to armour and heatsink components via a similar electrical field assisted technology. Micro-structural and thermal properties are investigated for these materials allowing to select the most suited materials in view of their thermal conductivity and thermal expansion coefficients.

Spark plasma sintering route to synthesize aluminium doped zinc oxide

Spark plasma sintering increases conductivity in doped zinc oxide.

Microstructures and Tensile Mechanical Properties of Consolidated Copper

Two consolidated copper samples were prepared by consolidation of a gas atomized powder using two different routes of spark plasma sintering (SPS), respectively. The first route was direct SPS of copper powder at 800 °C for 10 minutes, and the second route was compacting copper powder by die-pressing to produce a powder compact followed by SPS of the powder compact at 800 °C for 10 minutes. The microstructures and tensile mechanical properties and the fracture surfaces of specimens have been studied. It was found that the level of consolidation of the sample made using Route 1 was higher than that of the sample made using Route 2, as reflected by the relatively higher strength and better ductility of the first sample than those of the second sample. The lower consolidation level of the second sample was depicted by the higher volume fraction of cavities in the fracture surfaces of specimens which were formed by separation of the powder particles at the weakly bonded interparticle boundaries. The grain sizes of the first sample were larger than those of the second sample. The reasons for the differences in the levels of consolidation and grain sizes associated with two SPS routes are discussed.

Effects of passing a direct current on densification of SiC ceramics with 10 wt.% Al2O3 – Y2O3 as an additive

β – SiC powder mixed with 10 wt.% Al2O3 and Y2O3 powder in a molar ratio of 2: 3 was consolidated by spark plasma sintering (SPS) at 1700–1900 °C. Three SPS routes were designed to contrast the effects of passing a strong direct current (DC) on the densification behavior of the SiC materials. The wetting of the Y – Al – Si – O liquid to the SiC particles was increased by the DC, hence better densification. The resultant SiC ceramic had a finer uniform microstructure and high flexural strength.

Effect of processing route on phase stability in equiatomic multicomponent Ti20Fe20Ni20Co20Cu20 high entropy alloy

The evolution of microstructure and phase formation in equiatomic Ti20Fe20Ni20Co20Cu20 high entropy alloy synthesised by conventional arc melting followed with suction casting and ball milling with spark plasma sintering route is distinctly different. The cast microstructure exhibits one body centre cubic and two face centre cubic high entropy phases based on titanium, cobalt and copper respectively along with a eutectic containing Ti2Ni type Laves phase. On the contrary, spinodal decomposed microstructure consisting of cobalt and copper solid solution is obtained in the sintered sample. However, long term annealing of cast sample at 950°C reveals a eutectoid transformation with different phases than the cast sample. The aforementioned observations are discussed using CALPHAD thermodynamical approach and available literature.

Environmental assessment of solid state recycling routes for aluminium alloys: Can solid state processes significantly reduce the environmental impact of aluminium recycling?

Solid state recycling techniques allow the manufacture of high density aluminium alloy parts directly from production scrap. In this paper the environmental impacts associated with ‘meltless’ scrap processing routes based on three different techniques, namely hot extrusion, screw extrusion and spark plasma sintering (SPS), are compared with the corresponding remelting route as reference. Analysis of the obtained results allows clear conclusions on the perspectives offered by solid state recycling for systematic environmental impact reduction of aluminium recycling with material and energy savings as most important influencing factors. An overall impact reduction with a factor 2 for the SPS route and 3–4 for the extrusion routes is found to be realistic.

Preparation of nanostructured La0.7Ca0.3−xBaxMnO3 ceramics by a combined sol–gel and spark plasma sintering route and resulting magnetocaloric properties

This work proposes an original, easy to achieve and inexpensive route to synthesize manganite ceramics for magnetic refrigeration, combining sol–gel chemistry to Spark Plasma Sintering (SPS). The target La 0.7 Ca 0.3− x Ba x MnO 3 ( x =0, 0.1, 0.2) compounds are obtained as single phases which crystallize in the orthorhombic structure (Pnma space group). SPS allows a quick sintering at a relatively low temperature (700 °C in this work) compared to the conventional solid state method (≥1100 °C), leading to densified ultrafine grained pellets (85% of compactness). Magnetic studies show that Ba substitution does not affect significantly the relative cooling power (RCP) of these manganites, while it increases their Curie temperature ( T C ) by several tens of degrees. Typically, RCP values ranging between 267 and 270 J/kg (for a magnetic field change of 5 T) and T C between 205 and 245 K were measured when x was increased from 0 to 0.2, respectively. These results combined to the fact that the synthesis route is economically advantageous makes the obtained ceramics interesting as active refrigerants for magnetic refrigeration technology below room temperature. • Nanostructured La 0.7 Ca 0.3− x Ba x MnO 3 ceramics were obtained as single phase. • An original and low cost method was developed combining sol–gel chemistry and SPS. • The method can be extended to prepare most dense nanostructured oxides. • Our ceramics have higher RCP than those obtained by the solid state method. • The optimum temperature of the magnetocaloric effect is tunable with Ba content.

Microstructure Development, Nanomechanical, and Dynamic Compression Properties of Spark Plasma Sintered TiB2-Ti-Based Homogeneous and Bi-layered Composites

The growing threats due to increased use of small-caliber armor piercing projectiles demand the development of new light-weight body armor materials. In this context, TiB2 appears to be a promising ceramic material. However, poor sinterability and low fracture toughness remain two major issues for TiB2. In order to address these issues together, Ti as a sinter-aid is used to develop TiB2-(x wt pct Ti), (x = 10, 20) homogeneous composites and a bi-layered composite (BLC) with each layer having Ti content of 10 and 20 wt pct. The present study uniquely demonstrates the efficacy of two-stage spark plasma sintering route to develop dense TiB2-Ti composites with an excellent combination of nanoscale hardness (~36 GPa) and indentation fracture toughness (~12 MPa m 1/2 ). In case of BLC, these properties are not compromised w.r.t. homogeneous composites, suggesting the retention of baseline material properties even in the bilayer design due to optimal relief of residual stresses. The better indentation toughness of TiB2(10 wt pct Ti) and TiB2-(20 wt pct Ti) composites can be attributed to the observed crack deflection/arrest, indicating better damage tolerance. Transmission electron microscope investigation reveals the presence of dense dislocation networks and deformation twins in a-Ti at the grain boundaries and triple pockets, surrounded by TiB2 grains. The dynamic strength of around 4 GPa has been measured using Split Hopkinson Pressure Bar tests in a reproducible manner at strain rates of the order of 600 s � 1 . The damage progression under high strain rate has been investigated by acquiring real time images for the entire test duration using ultra-high speed imaging. An attempt has been made to establish microstructure-property correlation and a simple analysis based on Mohr–Coulomb theory is used to rationalize the measured strength properties.

A combined sol–gel and spark plasma sintering route to produce highly dense and fine-grained La0.65Ca0.20Na0.15MnO3 ceramics for magnetocaloric applications

Sol–gel chemistry and spark plasma sintering were coupled to produce fine-grained and dense La0.65Ca0.20Na0.15MnO3 ceramics and their magnetic properties were explored in order to evaluate their efficiency for domestic magnetocaloric applications. The obtained manganites crystallize in the rhombohedral symmetry (R-3c). They present grain size in the sub-micrometer range. Their density and their average grain size increase when the sintering temperature increases from 600 to 800 °C. This entails an increase of the Curie temperature (TC) and of the maximum of the magnetic entropy change, even if these values remain smaller than those measured on their bulk counterparts prepared by a conventional solid state route. However, the magnetic transition occurs on a broad temperature range, resulting in a relative cooling power reaching about 265 J Kg−1 for an applied magnetic field of 5 T. This value is very close to that previously measured on bulk La0.65Ca0.20Na0.15MnO3 ceramics and represents about 64% of that measured on the standard Gd. The ceramics produced here by a low-energy and time-consuming method can thus be considered as technically and economically valuable for the desired applications.

Dielectric and electrical conductivity properties of multi-stage spark plasma sintered HA–CaTiO3 composites and comparison with conventionally sintered materials

One of the different issues limiting the wider application of monolithic hydroxyapatite (HA) as an ideal bone replacement material is the lack of reasonably good electrical transport properties. The comprehensive electrical property characterization to evaluate the efficacy of processing parameters in achieving the desired combination of electroactive properties is considered as an important aspect in the development of HA-based bioactive material. In this perspective, the present work reports the temperature (RT-200 °C) and frequency (100 Hz–1 MHz) dependent dielectric properties and AC conductivity for a range of HA–CaTiO3 (HA–CT) composites, densified using both conventional pressureless sintering in air as well as spark plasma sintering in vacuum. Importantly, the AC conductivity of spark plasma sintered ceramics [∼upto 10−5 (Ω cm)−1] are found to be considerably higher than the corresponding pressureless sintered ceramics [∼upto 10−8 (Ω cm)−1]. Overall, the results indicate the processing route dependent functional properties of HA–CaTiO3 composites as well as related advantages of spark plasma sintering route.

Comparison of Reactive and Non-Reactive Spark Plasma Sintering Routes for the Fabrication of Monolithic and Composite Ultra High Temperature Ceramics (UHTC) Materials.

A wider utilization of ultra high temperature ceramics (UHTC) materials strongly depends on the availability of efficient techniques for their fabrication as dense bodies. Based on recent results reported in the literature, it is possible to state that Spark Plasma Sintering (SPS) technology offers a useful contribution in this direction. Along these lines, the use of two different SPS-based processing routes for the preparation of massive UHTCs is examined in this work. One method, the so-called reactive SPS (R-SPS), consists of the synthesis and densification of the material in a single step. Alternatively, the ceramic powders are first synthesized by Self-propagating High-temperature Synthesis (SHS) and then sintered by SPS. The obtained results evidenced that R-SPS method is preferable for the preparation of dense monolithic products, while the sintering of SHS powders requires relatively milder conditions when considering binary composites. The different kinetic mechanisms involved during R-SPS of the monolithic and composite systems, i.e., combustion-like or gradual solid-diffusion, respectively, provides a possible explanation. An important role is also played by the SHS process, particularly for the preparation of composite powders, since stronger interfaces are established between the ceramic constituents formed in situ, thus favoring diffusion processes during the subsequent SPS step.

Effect of Air Annealing on the Structural and Magnetic Properties of LaMnO3 Perovskite Produced by Reactive Spark Plasma Sintering Route

Perovskite-type lanthanum manganite (LaMnO3) was synthesized from Mn2O3 and La2O3 precursor powders using the Spark Plasma Sintering technique (SPS). The in situ reaction proceeds in a few minutes at 1000 °C under 50 MPa with a very high heating rate of 100 °C/min. The Rietveld refinement of the X-ray powder diffraction shows that LaMnO3 sample crystallizes in a perovskite structure of O′-type orthorhombic symmetry with Pbnm space group. After annealing at 1000 °C in air for 10 hrs, the symmetry changes to rhombohedral with R-3c space group. For the as prepared sample, two critical temperature points in the temperature dependence of the ZFC and FC magnetization occurring at 125 K and 145 K are observed. They are suggested to be related to A-type antiferromagnetic Neel temperature and ferromagnetic short range order, respectively. The ferromagnetic component in the annealed sample increases indicating the expected variation in the concentration of Mn3+ and Mn4+ ions, which was attributed to the oxygen stoichiometry effects.

A novel route for processing Co-Cr-Mo orthopaedic alloys

Millions of people suffer from bone and joint inflammatory problems and usually result in extreme cases with total joint replacement. Most commonly affected joints are the hip and the knee. Over the past 20 years there has been a revival in interest of metal-on-metal hip replacements. Various alloys have been used in joint replacement, the most successful in the Cobalt-based alloys. As compared to others the cobalt based alloys have higher wear resistance and therefore less risk of failure. The most common Co-based alloy used in clinical application is the ASTM F75 alloy, which is extensively used in femoral and acetabular components. Conventional methods to fabricate the alloy are via cast or wrought techniques. Wrought alloys are better than their cast materials due to their superior mechanical properties as the forging process promotes plastic deformation. An alternative method of fabrication is via powder processing and has shown significant improvements to produce finer grained materials, which relate to enhancement in properties, such as strength, toughness, ductility. One of the key stages of powder processing is sintering of the powder to fuse the particles together. A superior but simple sintering processing is spark plasma sintering (SPS), which produces highly dense materials with minimum grain growth. This is achieved by a pulsed electrical current heating the material while applying a pressure to compact the powdered material. This process has the ability to densify nanopowders, in order to produce microstructures with finer grains and superior mechanical properties. Using SPS and nanopowders for the first time, we have been able to prepare the ASTM F75 cobalt–chromium–molybdenum (Co–Cr–Mo) orthopaedic alloy composition. In this work we have investigated, the effect of processing variables on the structural features of the alloy (phases present, grain size and microstructure). We have been able to produce specimens of >99% of the theoretical density. The structures were free of carbides, which a vital breakthrough. Detrimental carbide phases in the microstructure as found in the more conventional methods of fabrication have shown to cause problems in wear. The compacts are of higher hardness than cast or wrought products despite the absence of carbides in the microstructure. The gain in hardness is because of the presence of oxides in the microstructure and we hope to quantify the oxide content in the future. The mechanisms of oxide formation are explained by considering chemical thermodynamics and kinetics. The next step is to evaluate the tribological performance (wear, friction, lubrication regimes) of this SPS-processed material and compare its performance with conventional MoM products (cast and wrought). The SPS route offers significant advantages over the conventional cast and wrought routes used to prepare this alloy for orthopaedic applications.

Structural Analysis of PM Biocomposites Based on Hydroxyapatite Nanopowders Elaborated by Spark Plasma Sintering Route

The objective of this research is the development of a detailed structural analysis of biocomposites with ceramic matrix of hydroxyapatite (Hap) reinforced by titanium (Ti), elaborated by powder metallurgy technology. Nanometric Hap powders (<200nm) 75% wt and micrometric Ti powders (<150μm) are homogenized in a high energy ball mill Pulverisette 6. Spark plasma sintering (SPS) is the sintering route able to lead to nanostructured sintered samples when nanopowders are used as raw material. The SPS parameters are: the sintering temperature, T=(1000-1100)°C and the maintaining time, t=(10-20) minutes in vacuum. The influence of the sintering parameters on the composites structures is monitored using the optical microscopy (OM), electronic microscopy (SEM) and the X-Ray diffraction (XRD).

Synthesis and characterization of copper–alumina metal matrix composite by conventional and spark plasma sintering

The evolution of microstructure, density and hardness of Cu–Al 2O 3 metal matrix composites with different techniques of sintering have been demonstrated here. The effect of sintering atmosphere on the interfacial compatibility of matrix and reinforcement has also been discussed. Synthesis of microcomposites was carried out by reinforcing 5, 10 and 15 vol.% of alumina powder particles (average size ∼5.71 μm) in copper matrix via conventional sintering using N 2, H 2 and Ar atmospheres. Nanocomposites of 1, 5, 7 vol.% alumina (average size <50 nm) reinforced in copper matrix were fabricated by powder metallurgy route using spark plasma sintering technique. These micro- and nano-composites have been characterized by X-ray diffraction and scanning electron microscopy followed by density and hardness measurements. Cu–Al 2O 3 metal matrix micro- and nanocomposites fabricated by conventional and spark plasma sintering routes were studied and compared. Maximum Vickers hardness of 60, 75 and 80 was obtained when the Cu–15 vol.% Al 2O 3 was conventionally sintered in N 2, Ar and H 2 atmosphere respectively. However, maximum hardness value of 125 has been achieved for the Cu–5 vol.% Al 2O 3 nanocomposite prepared by spark plasma sintering. It has been observed that Cu–Al 2O 3 metal matrix composite (MMC) shows poor mechanical properties when it is conventionally sintered in N 2 or Ar atmosphere compared to that in H 2 atmosphere.

Production of Nitinol Wire from Elemental Nickel and Titanium Powders Through Spark Plasma Sintering and Extrusion

This study demonstrates the production of highly dense binary NiTi by spark plasma sintering (SPS) of elemental Ni and Ti powders. The sintered billets were extruded to 0.7 mm wire for tensile testing. Excellent mechanical properties and very dense microstructures were obtained in the wires produced in this way. The material demonstrated 4% recoverable strain, 14% elongation at fracture and 630 MPa ultimate tensile stress. Furthermore, a close control of the level of impurities was also possible. This highlights the efficacy of the SPS route in production-capacity manufacture of NiTi products.

Crystal structure and magnetic transition of MnFePGe compound prepared by spark plasma sintering

The crystal structure and magnetic transition were studied for the bulk Mn1.1Fe0.9P0.8Ge0.2 compound prepared by a simple blending and subsequent spark plasma sintering route. X-ray diffraction analysis and refinement show that the compound crystallizes in the hexagonal Fe2P-type structure, in which the Mn atoms occupy all the 3g sites and some 3f sites, the Fe atoms occupy the rest of the 3f sites, and P and the Ge atoms randomly occupy the 2c and 1b sites. Magnetic measurement indicates that the Curie temperature TC is at 253K and the thermal hysteresis of M-T curves at TC upon heating and cooling, a signature of a first-order magnetic phase transition, is about 15K. The maximum magnetic entropy change of the compound reaches as high as 49.2J∕kgK in a field change from 0to5T at 253K, while the adiabatic temperature change of the compound reaches only 1.2K in a field change from 0to1.5T at the same temperature.