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The effects of the addition of different percentage compositions of graphene nanoplatelets (GNPs) to a nickel-based superalloy were investigated in this study. A spark plasma sintering (SPS) method was employed in the development of the nickel-based alloy/composites, and the developed bulk nickel-based alloy and its composites were from high-purity micron-size powder. Subsequently, the microstructure and mechanical properties (i.e., microhardness and tensile yield strength) were examined. The SPS-processed nickel-based alloy/composite samples exhibited high densification ranging from 97.64 to 98.87 pct. The addition of GNPs greatly influenced the microhardness results, which ranged from 384 to 459 Hv, and the tensile yield strength between 675 and 883 MPa. The results indicated that the addition of graphene nanoplatelets played a significant role in the microstructure and mechanical properties of spark plasma-sintered nickel-based composites. The addition of graphene nanoplatelets caused grain boundary strengthening, load transfer from the matrix to GNPs, and grain boundary strengthening by impeding dislocation movement. Coupled with the improvement caused by GNPs is the enhancement of the mechanical properties of the materials developed as a result of the high relative density values obtained.

This work investigated the dry sliding wear behaviour of spark plasma sintered (SPSed) Ti-Ni binary alloys produced at varying nickel content with alloy steel ball as the counterface material, at room temperature under varied applied normal loads. Finite element modeling was used to investigate the high-velocity impact response of the sintered alloys due to the dimensional constraint associated with SPSed samples. Microstructural analysis results revealed the presence of intermetallic phases of Ti-Ni with increasing nickel content. The best wear resistance ranging from 0.25 x 10-3 mm3/Nm to 0.22 x 10-3 mm3/Nm across all applied loads was obtained in Ti-6Ni alloy. This was attributed to the compaction of the protective triboxide and carbide layers on the surface of the sample. Oxidative and wear by adhesion were observed at low applied normal load while at high loads the prevalent wear mechanism was abrasive with reduced influence of oxidative and adhesive wear. Finite element analysis results also showed that Ti-6Ni alloy possessed the optimum combination of absorbed energy and ductility to reduce the possibility of brittle failure under impact loading. Keywords: Ti-Ni binary alloys; Spark plasma sintering; Dry sliding wear; High-velocity impact; Finite element analysis.

This review provides information on spark plasma sintering (SPS) as a novel approach for polymer and polymer composite manufacturing. Over the years, the potential of this technique has been widely researched and attested for fabricating different metallic and ceramic-based composite without much emphasis on polymers. However, in recent times, this process has been employed to solving numerous challenges encountered while engaging the conventional polymer processing technique such as compression, injection moulding and extrusion in processing high viscous polymers and others. The numerous merit of this process, its mode of operation and applications are thoroughly explained in this review. It also evaluated the outstanding performance and unique properties obtained from the spark plasma-sintered polymer specimen when compared to the conventional polymer processing techniques. It was hence discovered that the thermoelectric properties, thermal conductivity, thermal stability, crystallinity, microstructural, mechanical and tribological properties of the polymer can be greatly enhanced through this process compared to other conventional means. This review will help polymer scientist, industrialist and engineers to properly understand and explore this alternative route in solving many material development challenges.

This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

In this work, the synthesis, characterization and mechanical properties of sintered In situ Ni-based quaternary superalloy (Ni–9Fe–22Cr–10Co) were studied. All the Ni–9Fe–22Cr–10Co quaternary alloy specimens were consolidated via spark plasma sintering technique at temperature range and sintering pressure of 850–1100 °C and 50 MPa, respectively. The densification of sintered alloys was obtained through Archimedes technique while the micro-indentation hardness of the alloys was conducted using Vickers microhardness tester. The specimens were characterized using the optical microscope and scanning electron microscope equipped with energy-dispersive spectroscopy while the phase identification was carried using X-ray diffractometer. The microstructural characterization results revealed that the relative density, surface morphology as well as the micro-indentation hardness properties depend on the sintering temperature. In addition, it was observed that high sintering temperature aided grain refinement and bulk compaction of the material leading to high relative density. XRD analysis shows the formation of Ni–Fe and Co–Fe as the major phases. Generally, the densification and grain size of the alloys increased with increasing sintering temperature with optimum results obtained at a temperature of 1100 °C and sintered density of 98% while the maximum Vickers hardness value of 439.17 HV1 was recorded.

Graphene/Inconel 738LC composites were synthesized using spark plasma sintering technique and the microstructural features were investigated using Optical microscope, Scanning electron microscope and X-ray diffraction machine. The microhardness, porosity and fracture toughness of the graphene-reinforced Inconel 738LC matrix composites were obtained. The processing parameters used were sintering pressure of 40 MPa, heating rate of 100 °C/min, soaking time of 5 min and varied sintering temperatures between 1000 and 1100 °C. The results show that spark plasma sintering is a viable powder metallurgy technique to develop graphene-reinforced Inconel 738LC composite. The increase in sintering temperature shows that there was significant increase in the hardness property of the sintered composites while the porosity and fracture toughness significantly reduced. Intermetallic and solid solution phases were formed within the microstructure which enhanced the strength of the sintered composites. In this study, the highest microhardness value (469 Hv), lowest porosity (1.47%) and fracture toughness value (26) was obtained in the composite sintered at 1100 °C.

This study aims to investigate the microstructure, corrosion and tribological properties of spark plasma sintered graphene nanoplatelets (GNPs) reinforced Inconel 738 low carbon composites. The matrix and reinforcement were thoroughly milled in order to ensure homogeneity. Thereafter, the milled powders were consolidated by using spark plasma sintering. The microstructural evolution and the phases formed were examined by the using scanning electron microscopy and X-ray diffractometry techniques. The corrosion analysis was investigated in acidic and basic media, while the tribological test was conducted under dry sliding conditions at varying loads. The results show that the microhardness values were significantly influenced by varying the GNPs constituents in Inconel 738LC from 384 to 459 HV0.5, while the sintered density was influenced by the sintering parameters. The corrosion response of the sintered composites in both acidic and basic media are comparable, irrespective of the varying GNPs content in the matrix. The wear performance suggests that the addition of GNPs to IN738LC, greatly enhanced the wear resistance and reduced the friction coefficient of the sintered IN738LC-GNPs composites. The improvement is attributed to the influence of the graphene-based tribofilm that formed on the sliding contact interface, which reduced friction coefficient. Likewise, graphene has a slight potential of forming continuous tribofilms at the friction interface due to its lubricity. It is thought that the GNPs reinforcement reduced the pull-out tendency, during wear activities.

It has been established over the years that Nickel-based superalloys are very difficult to manufacture as a result of the combination of various elemental composition. In this study, elemental powders of Ni-9Fe-22Cr-10Co wt.% superalloys were synthesized via spark plasma sintering technique at sintering temperatures ranging from 850 to 1100 °C with holding time, heating rate and pressure of 5 min, 50 °C/min and 50 MPa. The microstructural analyses were performed using an optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy, while phase analyses were carried out using X-ray diffractometry. The potentiodynamic polarization tests were performed in 1M H2SO4 solution at ambient temperature. Results obtained show that the densification of the alloys increased with increasing sintering temperature with optimum results obtained at a sintered temperature of 1000 °C corresponding to sintered density of 98%. Furthermore, the morphologies of the sintered compacts reveal homogenous dispersion of elemental composition with less morphological defects obtained at 1000 °C. For corrosion analysis, all sintered samples display passivation region with few fluctuations. However, sample sintered at the 1000 °C yielded more stable passivity with corrosion rate of 0.0181 mm/year.

Materials made from alloys of titanium are of utmost importance for various engineering applications owing to their low density and remarkable mechanical properties. Nevertheless, there is a need to enhance their mechanical properties to improve their capacity for load-bearing applications. In this work, spark plasma sintering technique was employed to fabricate TiN nanoceramic reinforced Ti–7Al–1Mo composite. The influence of nano-TiN reinforcement additions on the densification, microstructural evolution, and mechanical properties of Ti–7Al–1Mo ternary alloy was investigated. Scanning electron microscope equipped with energy dispersive x-ray spectrometer was used to investigate the microstructural evolution. The phases present in the sintered composite were investigated using X-ray diffractometer. Unreinforced Ti–7Al–1Mo alloy showed a microstructure with distinct grain boundaries made up of Widmanstatten lath-like morphology with mainly alpha (α) phase and a small percentage of beta (β) phase. Nano-TiN reinforced Ti–7Al–1Mo composites’ morphology revealed a bimodal structure. Ti–7Al–1Mo/7TiN composite was found to possess the highest hardness value of 549 ± 22 HV1.0 and the highest compressive yield strength of 1295 ± 7 MPa, which depicts an increment of 74 HV and 323 MPa respectively when compared to unreinforced Ti–7Al–1Mo ternary alloy. The developed composites showed strong potentials for load-bearing applications.

Spark plasma sintering (SPS) is a type of electric discharge sintering technique used to consolidate metallic/ceramic powders. This technique could also be used to join dissimilar materials and build functionally graded materials. In this study, spark plasma sintering was used to fabricate two different stainless steel powders; 316 L austenitic (ASS) and 2205 duplex stainless steels (DSS). The parameters that influence the sintering process such as sintering temperature, heating time and pressure have been investigated. Results show that different sintering processes influenced the sintered relative density, hardness and microstructure of the sintered samples. Also, the structure of the sintered materials was well densified after the SPS process. The relative density increased with the increment of sintering temperature. Microhardness values at the interface were indifferent with no visible cracks or delamination at the interface.

Polylactic acid (PLA)/graphene GNP nanocomposites with 0, 3, 5, 7% wt.% GNP concentrations have been prepared using the novel Spark Plasma Sintering (SPS) technique. This was performed under a fixed operating temperature of 160 °C, pressure of 25 MPa, heating rate of 20 °C/min and holding time of 10 min. The appearance of peak around 26.5° for PLA/GNP nanocomposites in the X-ray diffraction (XRD) analysis is typical of the presence of GNP. The thermogravimetric-fourier transform infrared radiation (TG-FTIR) analysis and differential scanning calorimetry (DSC) were carried out to investigate the thermal behaviour of the sintered nanocomposite. The surface morphology of the nanocomposite was performed using the scanning electron microscopy (SEM). The result shows that the thermal degradation temperature of PLA has been enhanced by an approximate double-fold increase via the novel SPS technique. The crystallinity and melt temperature of the sintered nanocomposites only improves slightly as compared to sintered pure PLA. The thermal stability, residual content, and stiffness of the nanocomposites also increases with increasing GNP filler content in the PLA matrix. Furthermore, the dynamic mechanical analysis (DMA) confirmed a better enhancement in thermal stability of the nanocomposites through increase in glass transition temperature than the DSC report. This is own to the better sensitivity of DMA to local segmentation motion compared to DSC. However, the SPS processing technique can be said to have contributed greatly to the enhancement in thermal stability than the inclusion of GNP as-sintered pure PLA exhibited similar patterns and close thermal properties to the sintered PLA/GNP nanocomposites samples. Furthermore, this process route enables the development of highly densified, lightweight polymer nanocomposite material within a short processing time.