Spark Plasma Sintering Materials Research Articles

Comparative analysis of microstructure, mechanical, and corrosion properties of biodegradable Mg-3Y alloy prepared by selective laser melting and spark plasma sintering

This work explored possibilities of biodegradable magnesium alloy Mg-3Y preparation by two modern powder metallurgy techniques – spark plasma sintering (SPS) and selective laser melting (SLM). The powder material was consolidated by both methods utilising optimised parameters, which led to very low porosity (∼0.3%) in the SLM material and unmeasurably low porosity in the SPS material. The main aim of the study was the thorough microstructure characterisation and interrelation between the microstructure and the functional properties, such as mechanical strength, deformability, and corrosion resistance. Both materials showed comparable strength of ∼110 MPa in tension and compression and relatively good deformability of ∼9% and ∼21% for the SLM and SPS materials, respectively. The corrosion resistance of the SPS material in 0.1 M NaCl solution was superior to the SLM one and comparable to the conventional extruded material. The digital image correlation during loading and the cross-section analysis of the corrosion layers revealed that the residual porosity and large strained grains have the dominant negative effect on the functional properties of the SLM material. On the other hand, one of the primary outcomes of this study is that the SPS consolidation method is very effective in the preparation of the W3 biodegradable alloy, resulting in material with convenient mechanical and degradation properties that might find practical applications.

Fabrication of porous pure magnesium by MgH<sub>2</sub> produced by mechanical milling and spark plasma sintering (MM-SPS) process

Pure magnesium (Mg) powders with stearic acid added as process control agent (PCA) were mechanically milled (MMed) using a vibration ball mill. The MMed powders were consolidated into bulk materials by the spark plasma sintering (SPS). Changes in hardness, thickness and solid-state reactions of the SPS materials have been examined by hardness measurements, vernier caliper and an X-ray diffraction (XRD), respectively. The Vickers hardness of the SPS material decreased with increasing sintering temperature. Minimum value of Vickers hardness was 17 HV. The thickness of the SPS material increased with increasing sintering temperature. However, little effect of sintering time on the thickness was observed. In the SPS materials, the formation of MgH2 by solid phase reaction was observed during sintering. During sintering, MgH2 was decomposed to produce hydrogen gas; and it contributed to expand the SPS materials. Porous pure magnesium could be formed using only the MM-SPS process without the addition of a foaming aid.

Fabrication of Mg-Ti by MA-SPS process and its properties

Pure magnesium (Mg) powders together with pure titanium (Ti) powders were mechanically alloyed (MAed) using a vibration ball mill. Stearic acid was used as process control agent (PCA) for the mechanical alloying (MA) process. The MAed powders were consolidated into bulk materials by the spark plasma sintering (SPS). Changes in hardness and solid-state reactions of the MAed powders and the SPS materials have been examined by hardness measurements and an X-ray diffraction (XRD), respectively. The Vickers hardness of the MAed powders increased to 58 HV after MA 8 h. No solid-state reactions were observed in MAed powders. The Vickers hardness of the SPS materials fabricated from MA 8 h Mg-10 mass%Ti powders reached to 76 HV. Formation of TiH2 by solid-state reaction was observed for the SPS materials, but TiH2 did not act as a strengthening phase. The Vickers hardness of the SPS materials improved by increasing sintering temperature, but not improved by increasing the amount of titanium. Mg-Ti system of hardness can be improved by MA-SPS process.

Comparison of different sintering methods of Pb1−xCrxTe thermoelectric nanocomposites doped with iodine

N-type PbTe polycrystals were fabricated by the Bridgman method. Subsequently, the materials were pulverized in a planetary ball mill for 15h, pressed and sintered. In this paper we compare two sintering techniques: cold pressing followed by the sintering in a furnace (CPS) and the spark plasma sintering (SPS). The electrical and thermoelectric measurements were conducted for both materials (CPS and SPS) and the results are presented and discussed in the paper. Maximal ZT values of 0.2 and 0.45 were obtained for the CPS and SPS materials, respectively. Additionally, SEM and EDX analyses were performed. To determine the obtained crystallites size, the X-ray diffraction measurements were carried out. The obtained results show that the significant reduction in particle size may be obtained by the milling procedure - from a few milimeters in the polycrystalline material to a few tens of nanometers for the powdered one.

Novel processing of Ag-WC electrical contact materials using spark plasma sintering

Ag-WC (60-40wt%) contact materials based on three WC particle size powders were doped with 0.1wt% Ni and processed by an appropriate powder pre-treatment followed by spark plasma sintering (SPS). The contacts produced were already bonded to a copper profile during SPS in order to eliminate additional processing steps. The SPS composites had a more homogeneous microstructure and were tougher and softer than the materials produced by conventional press-sinter-infiltration. The infiltrated contacts had a lower arc-erosion whereas the contacts produced by both processes had a similar contact resistance. The microstructure after switching confirmed that the SPS materials had a porous contact surface layer and were crack-free in contrast to their press-sinter-infiltrated equivalents.

Physicomechanical properties of spark plasma sintered carbon nanotube-containing ceramic matrix nanocomposites.

Recently, a wide variety of research works have focused on carbon nanotube (CNT)-ceramic matrix nanocomposites. In many cases, these novel materials are produced through conventional powder metallurgy methods including hot pressing, conventional sintering, and hot isostatic pressing. However, spark plasma sintering (SPS) as a novel and efficient consolidation technique is exploited for the full densification of high-temperature ceramic systems. In these binary nanocomposites, CNTs are added to ceramic matrices to noticeably modify their inferior properties and SPS is employed to produce fully dense compacts. In this review, a broad overview of these systems is provided and the potential influences of CNTs on their functional and structural properties are addressed. The technical challenges are then mentioned and the ongoing debates over overcoming these drawbacks are fully highlighted. The structural classification used is material-oriented. It helps the readers to easily find the material systems of interest. The SPSed CNT-containing ceramic matrix nanocomposites are generally categorized into four main classes: CNT-oxide systems; CNT-nitride systems, CNT-carbide systems, and CNT-boride systems. A large number of original curves and bubble maps are provided to fully summarize the experimental results reported in the literature. They pave the way for obviously selecting the ceramic systems required for each industrial application. The properties in consideration include the relative density, hardness, yield strength, fracture toughness, electrical and thermal conductivities, modulus, and flexural strength. These unique graphs facilitate the comparison between reported results and help the reader to easily distinguish the best method for producing the ceramic systems of interest and the optimal conditions under which the superior properties can be reached. The authors have concentrated on the microstructure evolution-physicomechanical property relationship and tried to relate each property to pertinent microstructural phenomena and address why the properties are degraded or enhanced with the variation of SPS conditions or material parameters.

Structural characterization of Cu2SnS3 and Cu2(Sn,Ge)S3 compounds

Cu2SnS3 (CTS) and Cu2Sn0.83Ge0.17S3 (CTGS) compounds were successfully prepared by a powder technology using a combination of mechanical alloying (MA) and spark plasma sintering (SPS). Structural, compositional and optical properties were studied. A true alloy with composition similar to the starting constituents was formed after 2 h of MA at 400 rpm. Subsequently, SPS was performed at 600 °C for 5 min under a pressure of 50 MPa. The Cu/(Sn + Ge) composition ratios of the MA and SPS materials, determined by wavelength dispersive X-ray spectroscopy, are in the range of 1.84–1.94. Rietveld refinements of the powder X-ray diffraction data show a good agreement with the monoclinic crystal structure already for the MA materials. No structural changes were observed after SPS. Raman measurements coincide with XRD results in the identification of the characteristic peaks from phonon vibrational modes of monoclinic CTS phase. Band gaps between 1.24 eV and 1.34 eV were determined by diffuse reflectance for the mechanically alloyed and sintered samples.

Preparation and characterisation of fine-grained barium lead titanate ceramics by spark plasma sintering technique

Barium lead titanate ferroelectric ceramic is a promising material for electronic devices at high frequency and high temperatures. These fine-grained ceramics were obtained at a low sintering temperature of 900°C within a short sintering time by means of a new sintering method – spark plasma sintering (SPS). The ceramics are highly densified to >99% of the theoretical X-ray density with homogeneous microstructures, signifying that the SPS process is effective for the densifying of compacts and the inhibition of exaggerated grain growth. Temperature dependence of dielectric constant of SPS pellets shows three times higher than the conventional sintering (CS) Ba0.8Pb0.2TiO3 (BPT) pellet. The variations in properties between SPS and CS materials are mainly because of the differences of the resultant microstructures, especially grain size, of the ceramics.

高導電性・高耐摩耗性亜共晶Cu-Zr合金SPS材の開発

This study aimed to develop hypoeutectic Cu-Zr bulk alloy materials with high electrical conductivity and wear resistance, and low processing cost, by spark plasma sintering (SPS). Starting raw materials for SPS were prepared with two different types of powders: high-pressure gas-atomized powder (HGA powder) and powder prepared by ball-milled method from commercial Cu powder and Cu-50 mass% Zr master alloy powder (BM powder). All of Cu-1, Cu-3, and Cu-5 at.% Zr alloy SPS materials prepared from these raw materials were of good consolidation. The structure, electrical conductivity, and wear resistance of the obtained SPS materials were examined.The SPS materials had a two-phase structure consisting of α-Cu and intermetallic Cu5Zr phases. In the HGA-SPS material, fine Cu5Zr grains were uniformly distributed in α-Cu. On the other hand, in the BM-SPS materials, coarse Cu5Zr grains were heterogeneously distributed in α-Cu. Electrical conductivities of the SPS materials of the same composition prepared from different raw materials were comparable. The wear resistance followed the order of oxygen-free copper (OFC) < HGA-SPS < BM-SPS. SPS material prepared from the BM powder was found to have high electrical conductivity and wear resistance with low processing cost.

10 to 25-fold increase in the transport superconducting critical current density of spark-plasma sintered Bi-2223 superconductors

Pre-reacted powders of (Bi-Pb)2Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at two different temperatures TD: 750 and 830 °C. The results indicate the occurrence of grains with core-shell morphology, where the shell is oxygen deficient. A post-annealing heat treatment (PAHT), performed in air, at 750 °C, and for a brief time interval, is responsible for a 10 to 25-fold increase in the transport superconducting current density at 77 K. The role of the oxygen-deficient shell, before and after the PAHT, was investigated by means of magnetic and transport measurements. We argue that the PAHT is two folds: (i) it is responsible for the decrease of the width of the oxygen-deficient shell, then increasing the oxygen content along the grain boundaries; (ii) it promotes the formation of conduction current paths along the grain boundaries of the SPS material.

Recent Progress in Scalable Nanomanufacturing

As the size of materials becomes close to 10 nm, materials exhibit a unique electronic band structure that is not observed in traditional bulk materials. The modified band structure offers new opportunities for future technological innovation because it exhibits unprecedented electrical, optical and magnetic properties that are absent in their bulk counterparts. Fabrication and manufacturing of such novel nanomaterials have been significantly improved in the past few years. The section sponsored by the Nanomaterials Committee in the January issue of JOM has a unique combination of short review papers and research papers on the scale-up and integration of nanomaterials into functional architectures and bulk systems for engineering applications. A paper written by Graeve et al. shows recent progress and current status of spark plasma sintering (SPS) which is beneficial in manufacturing of bulk materials comprised of nanosize grains. Manufacturing of nanostructured bulk material has been a daunting challenge, since the dramatic growth of nanocrystals is accompanied by the densification during the sintering. SPS addresses this trade-off between densification and grain growth. In this paper, principles of SPS sintering and materials prepared by SPS are summarized, showing that various materials (metal, ceramics and polymers) can be sintered without substantial growth of nanosize particles in SPS. In addition, SPS has an economic benefit over other sintering techniques such as hot press, reducing equipment cost and electricity consumption, and increasing a throughput rate. Technical and economical strengths of SPS indicate that SPS may pave a way toward commercialization of bulk nanostructured materials. Therefore, interest in SPS continues to grow in academic and industrial communities. Currently remaining tasks for the commercialization of SPS are near-net and net-shape forming, scalability, and high-throughput systems, and several groups are working to solve these problems. Two-dimensional (2-D) dimensional materials are very attractive, since electrons confined in 2-D planes produce intriguing responses to external optical, electrical, magnetic, and thermal stimuli. Graphene is a well-known 2-D material which exhibits extremely

10110 MA-SPSプロセスによるアルミニウム基磁性材料の作製とその特性

Pure aluminum and permalloy (Fe-Ni) powders were mechanically alloyed (MAed) using a vibrational ball mill, and the MAed powders were consolidated into bulk materials by spark plasma sintering (SPS). Magnetic properties of the SPS materials were evaluated by vibrating sample magnetometer (VSM). The saturation magnetic flux density of the SPS materials increased with the amount of the permalloy content. The amount of the Al_5FeNi and Al_3Ni, which were solid-state reaction product, was increased with an increase in sintering temperature. As the formation of the intermetallic compounds, the saturation magnetic flux density of the SPS materials decreased with an increase in sintering temperature.

Properties of AZ91 alloy produced by spark plasma sintering and extrusion

Mg alloys are characterised by several promising properties, including a good biocompatibility. In this work, a commercial AZ91 powder was used to produce cylindrical specimens by spark plasma sintering (SPS), and the specimens were further consolidated by hot extrusion. The SPS materials were found to be quite brittle because of the low bonding between the original powders. After hot extrusion, however, they displayed a ductile behaviour as revealed by room temperature tensile tests and hot compression tests. The metallographic investigation showed that extrusion induced a dynamic recrystallisation with grain refinement, but also an increase in the β phase content, which reduced the corrosion resistance of the materials.

S041022 粉末冶金法で作製したアルミニウム基磁性材料の特性に及ぼすボールミル処理の影響([S041-02]粉末成形とその評価(2))

Three different powders were produced; pure aluminum together with iron powders were mechanically alloyed (MAed); each elemental powder was mechanical milled (MMed); only pure aluminum powder was MMed, and subsequently MMed powder was added to pure iron powder: The all powders were consolidated into bulk materials by spark plasma sintering (SPS). Effects of MA, MM+MM or MM processes on magnetic properties of the SPS materials were evaluated by vibrating sample magnetometer. The formation of Al_5Fe_2 was observed in MA and MM+MM SPS materials. On the other hand, the aluminide compound was not formed in the MM SPS material. Formation and amount of the aluminide compounds were controlled by changing the process from MA to MM processing. As a result of suppression of formed alminide compounds, magnetic properties were improved in the SPS materials fabricated from powder produced by MM for only pure aluminum.

Effect of densification mechanism on the Σ2 grain boundary plane distribution in WC–Co composites

The effect of the densification mechanism on the Σ2 grain boundary plane distribution was investigated in WC–Co composites. Specimens were prepared separately by sintering in hot isostatic press (sinter-HIP) and spark plasma sintering (SPS). It was found that the Σ2 twist boundary is the most common boundary in both cases, but that the SPS material had more than three times the relative area of these boundaries compared to the sinter-HIP material. Measurements of the WC/WC and WC/Co boundary lengths are compared to measured mechanical properties and found to be consistent with established stereological results, suggesting a path to link interface area measurements to the mechanical properties of WC–Co samples.

Fabrication and Properties of Aluminium Based Phosphorescence Composite Material

In order to fabricate the aluminium based composite materials exhibiting phosphorescence properties, aluminium powder and phosphorescence powder (LG) were mechanically alloyed (MAed) using a vibrational ball mill, and the MAed composite powders were consolidated into bulk materials by spark plasma sintering (SPS). Changes in hardness, constituent phases, powder particle sizes and luminance of both the MAed powders and SPS materials were examined by a hardness tester, X-ray diffraction, scanning electron microscopy and luminance meter, respectively. The Vickers microhardness of the MAed powders increased both an increase in MA time and the amount of LG powder addition. No solid-state reactions could be detected in the MAed powders. The mean particle size of the MAed powders for 60 min was smaller than that for 5 min. The Vickers hardness of the bulk SPS materials increased both an increase in MA time and the amount of LG powder addition. SPS materials showed luminance properties in a darkroom after they were irradiated under black light. The optimum process conditions for MA time was 5 min and for the sintering temperature was 873 K.

S041021 粉末冶金法で作製したAl-Fe系磁性材料の特性

Pure aluminum and iron powders were mechanically alloyed (MAed) using a vibrational ball mill, and the MAed powders were consolidated into bulk materials by spark plasma sintering (SPS). Magnetic properties of the SPS materials were evaluated by vibrating sample magnetometer (VSM). The saturation magnetic flux density of the SPS materials increased with the amount of the iron content. The amount of the Al_<13>Fe_4 and Al_5Fe_2 was increased with an increase in sintering temperature. As the formation of intermetallic compounds, the saturation magnetic flux density of the SPS materials decreased by an increase in sintering temperature.

Effect of the Mechanical Milling Process Condition on Hardness of Pure Titanium

Effect of mechanical milling conditions on hardness and constituent phase of pure titanium was investigated. The mechanical milling atmosphere and amounts of stearic acid, added as a process control agent (PCA), were varied. The hardness of mechanically milled (MMed) pure titanium powders in the air atmosphere was approximately 15 % higher than that in the argon atmosphere. The mean particle size of the MMed powders in the air atmosphere was smaller compared to that in the argon atmosphere. The MMed pure titanium powders produced by two different atmospheres had almost the same constituent phase. The MMed powders were consolidated into bulk materials by spark plasma sintering (SPS). The hardness of the SPS materials produced from the MMed powder in the air atmosphere was 13 % higher than that in the argon atmosphere. The oxygen content in the SPS materials significantly increased by the MM processing in the air atmosphere. Formation of β-Ti or ω-Ti was observed in the all SPSed materials. The products formed by phase transformation were not influenced by the heating rate and the hold time in SPS process. Vickers hardness of 881 HV was obtained for the SPSed material fabricated from 4 h of MM with 0.50 g of PCA in Ar atmosphere at 1073 K for 180 s with the heating rate of 2.33 K/s.

Effect of Mechanical Alloying Conditions on Mechanical Properties of Ti-HAp Composite Materials

Ti-x HAp (x=10, 20 and 30 mass%) composite powders were synthesised by mechanical alloying (MA) using a vibrational ball mill, and MAed composite powders were consolidated into bulk composite materials by spark plasma sintering (SPS). Effects of MA conditions on the hardness and constituent phase of the MAed powder and SPS materials were investigated by hardness measurements and X-ray diffraction (XRD), respectively. No decomposition of HAp in the Ti-HAp composite powders was observed, whereas formation of CaO was observed in all the SPSed materials. In addition, formation of TiC occurred in the Ti-10 and 20 HAp SPSed materials. On the other hand, both CaTiO3 and TiN was formed in the Ti-30 HAp SPSed materials. The hardness of the Ti-HAp SPSed materials fabricated from the 0.5, 1 and 2 h MAed powders were higher than that of the pure Ti SPSed materials fabricated from the none MAed powder. A maximum value of Vickers hardness was 1101 HV when the Ti-20 HAp SPSed material was fabricated from 1 h MAed powder.

MA-SPSプロセスで作製したチタン&amp;ndash;ハイドロキシアパタイト複合材料の特性

Ti-x HAp (x=0, 10, 20 and 30 mass%) composite powders were synthesised by mechanical alloying (MA) using a vibrational ball mill, and MAed composite powders were consolidated into bulk composite materials by spark plasma sintering (SPS). The hardness and constituent phase of the MAed powder and SPS materials were investigated by hardness measurements and X-ray diffraction (XRD) , respectively. Mean particle size of the MAed powders and microstructure of the SPSed materials were characterised by scanning electron microscopy (SEM) and optical microscopy, respectively. No decomposition of HAp in the MAed Ti-10 and 20 HAp composite powders occurred. However, decomposition of HAp in the MAed Ti-30 HAp composite powders occurred to form both CaO and CaTiO3. Formation of both TiC and CaO was observed in the all SPSed materials. In addition, formation of both CaO and CaTiO3 was also observed in the Ti-30 HAp SPSed materials. The hardness of the SPSed materials increased by both an increase in the amount of HAp and in the MA time. The results thus imply that the Ti-HAp composite materials exhibiting the high hardness can be obtained by a controlling of the amount of HAp powder and MA time.