Spark Plasma Sintering of Mg-based Alloys:Microstructure,Mechanical Properties,Corrosion Behavior,and Tribological Performance

Within the past ten years,spark plasma sintering(SPS)has become an increasingly popular process for Mg manufacturing.In the SPS process,interparticle diffusion of compressed particles is rapidly achieved due to the concept of Joule heating.Compared to traditional and additive manufacturing(AM)techniques,SPS gives unique control of the structural and microstructural features of Mg components.By doing so,their mechanical,tribological,and corrosion properties can be tailored.Although great advancements in this field have been made,these pieces of knowledge are scattered and have not been contextualized into a single work.The motivation of this work is to address this scientific gap and to provide a groundwork for understanding the basics of SPS manufacturing for Mg.To do so,the existing body of SPS Mg literature was first surveyed,with a focus on their structural formation and degradation mechanisms.It was found that successful Mg SPS fabrication highly depended on the processing temperature,particle size,and particle crystallinity.The addition of metal and ceramic composites also affected their microstructural features due to the Zener pinning effect.In degradative environments,their performance depends on their structural features and whether they have secondary phased composites.In industrial applications,SPS'd Mg was found to have great potential in biomedical,hydrogen storage,battery,automotive,and recycling sectors.The prospects to advance the field include using Mg as a doping agent for crystallite size refinement and using bulk metallic Mg-based glass powders for amorphous SPS components.Despite these findings,the interactions of multi-composites on the processing-structure-property relationships of SPS Mg is not well understood.In total,this work will provide a useful direction in the SPS field and serve as a milestone for future Mg-based SPS manufacturing.

Fabrication of YAG:Ce^(3+) and YAG:Ce^(3+),Sc^(3+) Phosphors by Spark Plasma Sintering Technique

In this study,a single-doped phosphors yttrium aluminum garnet(Y_(3)Al_(5)O_(12),YAG):Ce^(3+),single-doped YAG:Sc^(3+),and double-doped phosphors YAG:Ce^(3+),Sc^(3+) were prepared by spark plasma sintering(SPS)(lower than 1 200℃).The characteristics of synthesized phosphors were determined using scanning electron microscopy(SEM),X-ray diffraction(XRD),and fluorescence spectroscopy.During SPS,the lattice structure of YAG was maintained by the added Ce^(3+) and Sc^(3+).The emission wavelength of YAG:Ce^(3+) prepared from SPS(425-700 nm) was wider compared to that of YAG:Ce^(3+) prepared from high-temperature solid-state reaction(HSSR)(500-700 nm).The incorporation of low-dose Sc^(3+) in YAG:Ce^(3+) moved the emission peak towards the short wavelength.

Spark plasma sintering of tungsten-based WTaVCr refractory high entropy alloys for nuclear fusion applications

W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a powder metallurgy process combining mechanical alloying and spark plasma sintering (SPS). The SPSed samples contained two phases, in which the matrix is RHEA with a body-centered cubic structure, while the oxide phase was most likely Ta2VO6through a combined analysis of X-ray diffraction (XRD),energy-dispersive spectroscopy (EDS), and selected area electron diffraction (SAED). The higher oxygen affinity of Ta and V may explain the preferential formation of their oxide phases based on thermodynamic calculations. Electron backscatter diffraction (EBSD) revealed an average grain size of 6.2μm. WTaVCr RHEA showed a peak compressive strength of 2997 MPa at room temperature and much higher micro-and nano-hardness than W and other W-based RHEAs in the literature. Their high Rockwell hardness can be retained to at least 1000°C.

Influences of oxide content and sintering temperature on microstructures and mechanical properties of intragranular-oxide strengthened iron alloys prepared by spark plasma sintering

How to increase strength without sacrificing ductility has been developed as a key goal in the manufacture of high-performance metals or alloys. Herein, the double-nanophase intragranular yttrium oxide dispersion strengthened iron alloy with high strength and appreciable ductility was fabricated by solution combustion route and subsequent spark plasma sintering, and the influences of yttrium oxide content and sintering temperature on microstructures and mechanical properties were investigated. The results show at the same sintering temperature,with the increase of yttrium oxide content, the relative density of the sintered alloy decreases and the strength increases. For Fe–2wt%Y_(2)O_(3)alloy, as the sintering temperature increases gradually, the compressive strength decreases, while the strain-to-failure increases. The Fe–2wt%Y_(2)O_(3)alloy with 15.5 nm Y_(2)O_(3)particles uniformly distributed into the 147.5 nm iron grain interior sintered at 650℃ presents a high ultimate compressive strength of 1.86 GPa and large strain-to-failure of 29%. The grain boundary strengthening and intragranular second-phase particle dispersion strengthening are the main dominant mechanisms to enhance the mechanical properties of the alloy.

Al-50 wt%Si Alloy by Spark Plasma Sintering(SPS)for Electronic Packaging Materials

A hypereutectic Al-50 wt%Si alloy for electronic packaging was prepared by spark plasma sintering(SPS)technology using gas-atomized Al-50 wt%Si powder.The effect of sintering parameters on alloy phase composition,microstructure,thermal performance and the tensile strength at different temperatures was investigated.The experimental results show that the alloy can obey the diffraction peaks of silicon and aluminum without other peaks appearing.The primary silicon in the prepared alloy can be evenly distributed in the aluminum matrix.The coefficient of thermal expansion(CTE)and thermal conductivity(TC)of the alloy will improve with the increase of sintering temperature,but they will decrease after sintering for a long time,which is caused by the large difference of coefficient of thermal expansion between silicon and aluminum.The tensile properties of the alloy at room temperature will increase with the increase of sintering temperature,but higher test temperatures will inhibit the tensile properties except the elongation.The morphology and fracture mode of the tensile fracture are also analyzed to determine the good bonding strength of the alloy.

Synthesis of Ti_3SiC_2 by spark plasma sintering(SPS) of elemental powders

Ti 3SiC 2 materials have been fabricated by spark plasma sintering of the elemental powders with the addition of Al. At the heating rate of 80 ℃/min and under the pressure of 30 MPa, the ideal synthesis temperature of Ti 3SiC 2 is in the range of 1 1501 250 ℃. The addition of Al is in favor of the formation of Ti 3SiC 2. The synthesized compound has the molecular of Ti 3Si 0.8Al 0.2C 2 and lattice parameters of a=0.306 9 nm, c=1.767 0 nm. Its grain is plane-shape with a size of about 50 μm in the elongated dimension. The prepared material has Vickers hardness of 3.55.5 GPa(at 1 N and 15 s) and is as readily machinable as graphite’s.

Synthesis and Sintering of Mg_2Si Thermoelectric Generator by Spark Plasma Sintering

Raw Mg,Si powder were used to fabricate Mg2Si bulk thermoelectric generator by spark plasma sintering （SPS）.The optimum parameters to synthesize pure Mg2Si powder were found to be 823 K,0 MPa,10 min with excessive content of 10wt% Mg from the stoichiometric Mg2Si.Mg2Si bulk was synthesized and densified simultaneously at low temperature （823 K） and high pressure （higher than 100 MPa） from the raw powder,but Mg,Si could not react completely,and the sample was not very dense with some microcracks on the surface.Then,Mg,Si powder reacted at 823 K,0 MPa,10 min in SPS chamber to form Mg2Si green compact,again sintered by SPS at 1023 K,20 MPa,5 min.The fabricated sample only contained Mg2Si phase with fully relative density.

Effect of Annealing Process on Microstructure and Mechanical Properties of Ultrafine Copper Prepared by Spark Plasma Sintering

The spark plasma sintering （SPS） method is used to prepare the ultrafine copper with the average grain size less than 10 μm and the tensile strength greater than 280 MPa.The ultrafine copper is annealed at different temperatures for 60 min,and the annealing microstructure is observed and the hardness and the deformation behavior of the bulk copper are tested.The results indicate that the grains grow very slowly when the annealing temperature is less than 450 ℃.However,the grain growth becomes remarkable when the annealing temperature exceeds 450 ℃.And the plasticity of the bulk copper is the best when the annealing temperature of 450 ℃ is adopted.After stamping and spin forming,the deformed copper is recrystallized completely and the grain is refined when the copper is annealed at 500 ℃ for 30 min.

High-temperature mechanical properties and deformation behavior of high Nb containing TiAl alloys fabricated by spark plasma sintering

A high Nb containing TiA1 alloy was prepared from the pre-alloyed powder of Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y （at%） by spark plasma sintering （SPS）. Its high-temperature mechanical properties and compressive deformation behavior were investigated in a temperature range of 700 to 1050℃ and a strain rate range of 0.002 to 0.2 s 1. The results show that the high-temperature mechanical properties of the high Nb containing TiA1 alloy are sensitive to deformation temperature and strain rate, and the sensitivity to strain rate tends to rise with the deformation temperature increasing. The hot workability of the alloy is good at temperatures higher than 900℃, while fracture occurs at lower temperatures. The flow curves of the samples compressed at or above 900℃ exhibit obvious flow softening after the peak stress. Un- der the deformation condition of 900-1050℃ and 0.002-0.2 s 1, the interrelations of peak flow stress, strain rate, and deformation tempera- ture follow the Arrhenius＇ equation modified by a hyperbolic sine function with a stress exponent of 5.99 and an apparent activation energy of 441.2 kJ.mol-1.

Effect of sintering temperature on the microstructure and thermal conductivity of Al/diamond composites prepared by spark plasma sintering

Spark plasma sintering was used to fabricate Al/diamond composites.The effect of sintering temperature on the microstructure and thermal conductivity（TC） of the composites was investigated with the combination of experimental results and theoretical analysis.The composite sintered at 550℃shows high relative density and strong interfacial bonding,whereas the composites sintered at lower（520CC） and higher（580-600℃） temperatures indicate no interfacial bonding and poor interfacial bonding,respectively.High relative density and strong interfacial bonding can maximize the thermal conductivity of Al/diamond composites,and taking both effects of particle shape and inhomogeneous interfacial thermal conductance into consideration can give a fairly good prediction of composites＇ thermal conduction properties.

Sintering of WC-Co powder with nanocrystalline WC by spark plasma sintering

A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering （SPS） at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of the position of low punch shown shrinkage of the sintered body began above 800℃. The shrinkage slowly rose as the temperature rose from 800 to 1000℃ and then quickly rose at above 1000℃ and then gradually rose at above 1150℃. The densities of the samples increased with an increase in sintering temperature, rapidly below 1100℃, and then gradually above 1100℃. WC grains grow gradually with increasing sintering temperature. The powder was sintered to near full density at 1100℃ for 5 rain under 10 kN. The best result of the sample with 275 nm WC grains and no pores was obtained at 1150℃ under 10 kN for 5 rain. The research found the graphite die had a function of carburization, which could compensate the sintered body for the lack of carbon, and had the normal microstructure.

Spark plasma sintering on mechanically activated W-Cu powders

Mechanically activated W-Cu powders were sintered by a spark plasma sinteringsystem (SPS) in order to develop a new process and improve the properties of the alloy. Propertiessuch as density and hardness were measured. The microstructures of the sintered W-Cu alloy sampleswere observed by SEM (scanning electron microscope). The results show that spark plasma sinteringcan obviously lower the sintering temperature and increase the density of the alloy. This processcan also improve the hardness of the alloy. SPS is an effective method to obtain W-Cu powders withhigh density and superior physical properties.

Preparation of multi-walled carbon nanotube-reinforced TiNi matrix composites from elemental powders by spark plasma sintering

Carbon nanotube (CNT)-reinforced TiNi matrix composites were synthesized by spark plasma sintering (SPS) employing elemental powders.The phase structure,morphology and transformation behaviors were studied.It was found that thermoelastic martensitic transformation be-haviors could be observed from the samples sintered above 800 ℃ even with a short sintering time (5min),and the transformation tempera-tures gradually increased with increasing sintering temperature because of more Ti-rich TiNi phase formation.Although decreasing the sin-tering temperature and time to 700 ℃ and 5min could not protect defective MWCNTs from reacting with Ti,still-perfect MWCNTs re-mained in the specimens sintered at 900 ℃.This method is expected to supply a basis for preparing CNT-reinforced TiNi composites.

Effects of silver powder particle size on the microstructure and properties of Ag-Yb_2O_3 electrical contact materials prepared by spark plasma sintering

mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing （SPS）. The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope （OM）, and the fracture morphologies were observed by scanning electron microscopy （SEM）. The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder （5 ktm）, homogeneous and fme microstmcture was obtained by fine silver powder （_〈0.5-1am）. At the same time, the electrical conductivity, microhardness, and tensile strength of the sin- tered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples （both by free and coarse silver powders） is more than 95%. The fracture characteristics are ductile.

Effect of processing parameters on the microstructure and thermal conductivity of diamond/Ag composites fabricated by spark plasma sintering

Diamond/metal composites with 50 vol.% diamond have been produced by spark plasma sintering（SPS） using pure Ag as a matrix and diamond particles as reinforcement.Three kinds of powder mixing processes were used to prepare the mixture of diamond/Ag powders：dry mixing without milling medium,wet mixing and magnetic blending.Subsequently,they were all consolidated by SPS at various processing parameters to produce bulk diamond/Ag composites.Then samples were heat treated in order to obtain a higher thermal conductivity.The effect of processing parameters on the morphologies of the mixed powders,the microstructure and the thermal conductivity of the composites were investigated by comparing the experimental data.It reveals that particles were easy to agglomerate and the distribution of mixed powders was inhomogeneous by dry mixing method,and wet mixing method is too complex.The most favorable mixing process is magnetic blending by which the powders can be homogenously mixed and the composites prepared by optimized SPS processing parameters can obtain the highest relative density and the best thermal conductivity among the composites prepared by different processes.The magnetic blending diamond/Ag composites even have a 23% increase in thermal conductivity compared with pure silver sintered by SPS.

Comparative study of β-Si_3N_4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis （SHS） with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering （SPS）. The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa·m1/2.

Change in relative density of WC-Co cemented carbides in spark plasma sintering process

The relative density of WC-Co cemented carbides during spark plasma sintering（SPS） was analyzed.Based on the change in displacement of the ram in the SPS system,the relative densities in the sintering process can be achieved at different temperatures.The results indicated that densification of the samples started at near 900°C,the density rapidly reached its maximum at the increasing temperature stage,in which the temperature was lower than the sintering temperature of 1200°C,and most of the densification took place in the stage.Besides,the theoretical values were consistent with the experimental results.

Spark plasma and microwave sintering of Al6061 and Al2124 alloys

Despite the importance of aluminum alloys as candidate materials for applications in aerospace and automotive industries, very little work has been published on spark plasma and microwave processing of aluminum alloys. In the present work, the possibility was explored to process A12124 and A16061 alloys by spark plasma and microwave sintering techniques, and the microstructures and properties were compared. The alloys were sintered for 20 rain at 400, 450, and 500℃. It is found that compared to microwave sintering, spark plasma sintering is an effective way to obtain homogenous, dense, and hard alloys. Fully dense （100%） A16061 and A12124 alloys were obtained by spark plasma sintering for 20 rain at 450 and 500℃, respectively. Maximum relative densities were achieved for A16061 （92.52%） and A12124 （93.52%） alloys by microwave sintering at 500℃for 20 min. The Vickers microhardness of spark plasma sintered samples increases with the increase of sintering temperature from 400 to 500℃, and reaches the values of Hv 70.16 and Hv 117.10 for A16061 and A12124 alloys, respectively. For microwave siutered samples, the microhardness increases with the increase of sintering temperature from 400 to 450℃, and then decreases with the further increase of sintering temperature to 500~C.

Spark plasma sintering of high-toughness ZrO_2 materials doped with yttrium

Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.

Microstructure and magnetic properties of bulk magnets Nd_(14-x)Fe_(76+x)Co_3Zr_1B_6(x=0,0.5,1) prepared by spark plasma sintering

Melt-spun ribbons with nominal composition of Nd14–xFe76+xCo3Zr1B6(x=0,0.5,1) were consolidated into isotropic bulk magnets by spark plasma sintering method.It was found that the Nd content and sintering temperature had significant influence on the density and magnetic properties of the sintered magnets.Homogeneous microstructure and fine grain(50–100 nm) were obtained when sintering below 700 ℃,and the initial magnetization curve showed that the coercivity was controlled by the pinning mechanism.However,ab...