Spark Plasma Sintering Specimens Research Articles

Effect of grain size on the dielectric and magnetic properties of YFeO3 ceramics densified by microwave sintering and spark plasma sintering from powders synthesized via reverse chemical co-precipitation

YFeO3 (YFO) ceramics were synthesized by reverse co-precipitation at different pH values followed by microwave sintering (MS) and spark plasma sintering (SPS) techniques. Also, the effect of the grain size on the magnetic and dielectric properties of the sintered ceramics was examined using various characterization methods. Moreover, FESEM micrographs showed that the particle size of the calcined samples has declined by increasing the pH value. Furthermore, the magnetization curves exhibited weak ferromagnetic behavior in the pre-sintered powder samples. Besides, the Ms value was enhanced from 1.26emu/g to 2.3emu/g by an increase in pH from 8.5 to 10.5 owing to reducing the particle size and subsequently raising the amount of uncompensated surface spins. Furthermore, the powder samples showed an increase in the Hc and Mr values from 15Oe to 28Oe and 0.127emu/g to 0.296emu/g, respectively, with a reduction in particle size from 0.632 μm to 0.272 μm. Additionally, the specimens processed through the sintering techniques demonstrated a remarkable reduction in magnetic characteristics. Therefore, a decrease in magnetic saturation values from 2.3emu/g to 0.43emu/g for the MS sample and to 0.17emu/g for the SPS specimen was attributed to a marked reduction in the amount of free surfaces and subsequently uncompensated surface spins. At last, the observed dielectric characteristics of all the sintered pellets had a common dielectric behavior. This signifies that by increasing the frequency the ε′ and tanδ decline at lower frequencies and become frequency-independent at higher frequencies based upon the Maxwell-Wagner polarization theory. On the other hand, the ε′ value for the SPS sample produced at pH = 10.5 underwent a decline of 2.5 times at the low frequency of 200 Hz compared to the MS one due to the significant decrement of the grain boundaries on account of the coarsening of grains.

Structural and compositional gradients in alternating current sintered aluminum-doped zinc oxide

Flash sintering revitalizes the exploration of electric field and current effects on the microstructure with novel phenomena including rapid densification, low-temperature sintering, and unique microstructures. The aim of this study is to investigate the influence of electric current on the microstructural development of Al-doped ZnO (nAl=4at.%). We apply two sintering techniques, namely spark plasma sintering (SPS) and flash spark plasma sintering (FSPS), both conducted under identical conditions (AC, f=50Hz, |E→0|=25V/cm, p=180MPa) for three different temperatures 600∘C, 800∘C and 1000∘C. The distinguishing factor between the two techniques lies in the passage of electric current flow through the specimens in the case of FSPS. The resulting microstructures of the sintered pellets are examined by XRD, SEM, EDX, TEM and SAED to identify the process-related differences. While SPS specimens reveal a homogeneous microstructure, FSPS specimens exhibit a complex microstructure which consists of two distinct regions. The major volume of the FSPS pellets exhibits a structural gradient with coarse ZnO grains and ZnAl2O4 spinel precipitates in the center to fine ZnO grains at the periphery. This microstructure results from Joule heating and geometry-dependent heat dissipation, creating a symmetric temperature profile with a hot center. A minor volume of the FSPS specimens shows a gradient in microstructure and composition. Here, ZnAl2O4 spinel precipitates accumulate in the center and the periphery reveals Al-depleted, dense and very coarse grains. Electromigration of Al-cations and the thermodynamically favored formation of ZnAl2O4 in the hot center are proposed as underlying causes for the observed microstructure. The electric current in FSPS significantly alters the microstructure and composition of sintered specimen where dopant electromigration is most significant under high current densities above |J→|=29(5)A/cm2.

Carbon contamination of elemental beta-boron promoted a stable boron carbide by spark plasma sintering

The effect of carbon contamination on the elemental beta boron (β-B) from the graphite components of spark plasma sintering (SPS) was investigated. The X-ray diffraction, analytical electron microscopy (AEM) and Raman spectroscopy witnessed boron carbide (B13+xC2-x where x=0.05–0.35), when SPS temperature was above 1750 °C. The degree of carbon contamination became severe with increasing SPS temperature to 1800 °C and 1850 °C and formed a single-phase rhombohedral boron carbide with about 12 wt% of carbon. Our observations indicate that the carbon gets kinetically trapped into β-B to form boron carbide with a primitive unit cell consisting mainly of icosahedral B11C and three-atom chain of CBB configurations. After 6 months of natural aging, it has been revealed that boron carbide formed at and below sintering temperatures of 1800 °C is not a thermodynamically stable phase, and transformed reversibly to β-B structure. X-ray photoelectron spectroscopy ascertained that there are no longer B-C bonds and the existence of more CC bonds in a 6 months aged specimen, suggesting carbon is no longer strongly bonded to boron, but precipitates as graphitic structure. Further examination using atom probe tomography and AEM confirmed the existence of carbon nanoclusters within grains and high concentration of carbon segregating onto grain boundaries. The phase transformation of boron carbide to mostly boron resulted in a significant loss of hardness and modulus in a bulk SPS specimen. This study underscores the importance of solid solution and local bonding environment in icosahedral boron-rich solids for phase stability and sustained properties.

Complex microstructure induced high thermoelectric performances of p-type Bi–Sb–Te alloys

In this research, we have fabricated the complex microstructure features along with the high density of twin boundaries using the combination of magnetic pulse compaction (MPC) and spark plasma sintering (SPS), which are exclusively improved the thermoelectric transport properties of p-type Bi0.5Sb1.5Te3 alloys via effective scattering of carriers and phonons at the grain boundary interfaces. The texture analysis confirmed the formation of bimodal (mixed grains) microstructural features in MPC + SPS specimens sintered at 350 °C, and 400 °C respectively due to the adhesion of fine grains (grain growth) and initiation of recrystallization at high temperatures. In addition to high density of twin structure, high-angle grain boundaries have also been identified. The power factor of 3.53 mW/m.K2 was obtained for the MPC + SPS at 400 °C due to increased Seebeck coefficient and larger electrical conductivity values. The maximum reduced thermal conductivity of 1.14W/mK was recorded due to a significant reduction in lattice thermal conductivity, which is mainly owing to strong scattering of phonons at the formation of mixed grain microstructures with high-density dislocations. As a result, maximum figure of merit, ZT = 1.17was achieved for MPC + SPS at 400 °C temperature.

Enhanced Abrasion Resistance of Spark Plasma Sintered and HVOF Sprayed Hadfield High Manganese Steel by Turning and Diamond Smoothing

Austenitic high-manganese steels (HMnS) offer very high wear resistance under dynamic loading due to their high work hardening capacity. However, resistance to static abrasive loading is limited. Various approaches to increasing abrasion resistance are known from traditionally manufactured metallurgical components. These confirm the high potential for surface protection applications. In this work, the powder of the Hadfield HMnS X120Mn12 is prepared and processed by high-velocity oxy-fuel (HVOF) spraying and spark-plasma sintering (SPS). A good correlation was observed between the results of the HVOF and SPS specimen. Different surface conditions of the coatings and the sintered specimens were prepared by machining. Compared to the polished state, turning and diamond smoothing can increase the surface hardness from 220 HV to over 700 HV significantly. Regardless of the surface finish condition, similar good wear resistance can be demonstrated due to strong work hardening under sliding and reciprocating wear loading. In contrast, the finish machining process clearly influences abrasion resistance in the scratch test with the best results for the diamond smoothed condition. Especially against the background of current trends toward alternative coating systems, the presented results offer a promising approach for the development of HMnS in the field of coating technology.

Dry sliding behavior of copper based composite materials prepared using conventional compaction and sintering technique and spark plasma sintering

The study aimed to investigate the dry sliding properties of as received copper based composite materials, with varying silica and copper content, and produced through two different techniques: conventional compaction and sintering and spark plasma sintering (SPS). The SPS process induced pronounced densification and hardness of the materials and a better distribution of constituents when compared to conventionally sintered specimens. The SPS specimens observed the presence of a C layer of varying thickness on their surfaces, transferred from the graphite die used for their production. The thickness and adhesion of the C layer was influenced by the silica content in the specimens. Specimens containing low silica content showed a significant C layer on the pin surface. This C layer was not removed during dry sliding pin on disc testing, thus resulting in very low COF (coefficient of friction) and pin wear. Specimens containing high silica content led to the formation of a sparse C layer on their surfaces due to the low chemical interactions of silica with other atoms or compounds, leading to easy removal during tests and elevated COF magnitude. However, high silica content also led to low adhesion between the friction layer and the worn surfaces, resulting in instability and higher pin wear. The specimens containing moderate silica content were identified as the best composition due to their ability to easily shed the C layer during testing, maintain smooth, compact, and continuous friction layer without any detachment/adherence issues, and demonstrate permissible COF and pin wear in the mild range.

Electrical Conductivity of Spark Plasma Sintered W-Cu and Mo-Cu Composites for Electrical Contact Applications

Tungsten copper and molybdenum copper composites, with weight percent copper in the range of 20% - 40%, have been produced using the spark plasma sintering (SPS) technique. Other specimens having similar compositions were also developed using the conventional techniques of Liquid Phase Sintering (LPS) and Infiltration. Electrical conductivity measurements showed that the specimens produced by the SPS process had substantially higher levels of electrical conductivity than those produced by the other methods. Relative density measurements showed that the SPS specimens achieved very high densification, with relative densities in the range of 99.1% - 100%. On the other hand, the specimens produced by LPS and infiltration had relative densities in the range of 88% - 92% and 96% - 98% respectively. The superior conductivity of the SPS specimens has been attributed to the virtually full densification achieved by the process. The effect of porosity on electrical conductivity has been discussed and three standard models were assessed using results from porous sintered skeletons of pure tungsten and pure molybdenum.

An investigation of the corrosion behavior of 316L stainless steel fabricated by SLM and SPS techniques

The microstructure and corrosion characteristics of 316L stainless steel specimens fabricated by spark plasma sintering (SPS) and selective laser melting (SLM) techniques were investigated. SPS specimens have a relatively low density compared with SLM specimens. Microstructural analysis showed that SPS specimens consisted of fully and partially sintered regions and contained initial pores, which are located at the powder boundaries (PBs). SPS specimens have relatively low density and high kernel average misorientation (KAM) values near the interface of the pores and the matrix. In the case of SLM specimens, the scanning strategy did not affect the spatial distribution of the KAM, while it affected the extent of surface defects. Electrochemical analysis revealed that the corrosion behavior of SPS specimens was similar to localized corrosion, and weak levels of passive protection were observed in the anodic response curves due to the initial surface pores. SLM specimens with well-connected scan tracks showed passivation behavior similar to that of as-rolled specimens. Moreover, due to a homogeneous microstructure distribution and lower porosity, in NaCl solutions the SLM specimens showed corrosion performance that was significantly enhanced compared with that of SPS specimens. Cross-sectional analysis of corroded SPS specimens revealed that the configuration and connectivity of pores (or small cavity) affected the morphology of open spaces under the corroded surface.

Dynamic Strength of Heavy 90W—7Ni—3Fe Alloy Produced by Spark Plasma Sintering

The dynamic strength of heavy 90W—7Ni—3Fe alloy (wt %) was studied on two types of specimens: formed from submicron powder by spark plasma sintering (SPS) and from coarse-grained powder with a particle size of ≈20 µm by standard liquid phase sintering (LPS). Mhe study shows that the dynamic strength of the LPS and SPS specimens ranges up to 2750 and 3150 MPa, respectively, and that the SPS projectiles at an impact velocity of 1200 m/s penetrate 60% deeper into a steel target than the LPS projectiles. The difference in the penetration depth results from different penetration mechanisms: piercing for the coarse-grained material and cratering for the fine-grained one.

Dual Substitution and Spark Plasma Sintering to Improve Ionic Conductivity of Garnet Li7La3Zr2O12.

Garnet Li7La3Zr2O12 is one of the most promising solid electrolytes used for solid-state lithium batteries. However, low ionic conductivity impedes its application. Herein, we report Ta-doping garnets with compositions of Li7-xLa3Zr2-xTaxO12 (0.1 ≤ x ≤ 0.75) obtained by solid-state reaction and free sintering, which was facilitated by graphene oxide (GO). Furthermore, to optimize Li6.6La3Zr1.6Ta0.4O12, Mg2+ was select as a second dopant. The dual substitution of Ta5+ for Zr4+ and Mg2+ for Li+ with a composition of Li6.5Mg0.05La3Zr1.6Ta0.4O12 showed an enhanced total ionic conductivity of 6.1 × 10−4 S cm−1 at room temperature. Additionally, spark plasma sintering (SPS) was applied to further densify the garnets and enhance their ionic conductivities. Both SPS specimens present higher conductivities than those produced by the conventional free sintering. At room temperature, the highest ionic conductivity of Li6.5Mg0.05La3Zr1.6Ta0.4O12 sintered at 1000 °C is 8.8 × 10−4 S cm−1, and that of Li6.6La3Zr1.6Ta0.4O12 sintered at 1050 °C is 1.18 × 10−3 S cm−1.

The deformation and fracture behaviors of 316L stainless steels fabricated by spark plasma sintering technique under uniaxial tension

In this study, 316L stainless steel (SS) specimens with different relative densities were fabricated using the spark plasma sintering (SPS) technique. These SPS specimens were used to capture the effect of microstructure heterogeneity on deformation and fracture behaviors during uniaxial tension. Microstructure analysis indicated that the SPS specimens consisted of fully sintered and partially sintered regions and contained initial pores which are located at the grain boundaries. Mini-tension tests combined with the digital image correlation (DIC) technique were carried out at room temperature to measure the mechanical properties of the SPS specimens and the evolution of strain heterogeneity on tensile specimens during uniaxial tension. In order to reveal the fracture mechanisms of the SPS specimens, the surfaces of the fractured specimens were analyzed via field emission scanning electron microscope (FE-SEM). The fracture mechanism in the fully sintered region was identified as a ductile fracture by the formation of cup-like dimples, while the fracture mechanism in the partially sintered region was identified as a decohesion of the interface between the powder and the matrix.

Shape memory characteristics and mechanical properties of powder metallurgy processed Ti50Ni40Cu10 alloy.

Ti-Ni-Cu alloy powders were prepared by gas atomization and porous bulk specimens were fabricated by spark plasma sintering (SPS). The microstructure of as-solidified powders exhibited a cellular structure and they contained a high density of nano-sized porosities which were located in the intercellular regions. XRD analysis showed that one-step martensitic transformation of B2-B19 occurred in all alloy powders and SPS specimens. When the martensitic transformation start temperature (M(s)) and austenite transformation finish temperature (A(f)) were determined in order to analyze the dependence of powder size on transformation temperatures, the M(s) increased slightly from -17.5 degrees C to - 14.6 degrees C as increasing the powder size ranging from between 25 and 50 μm to ranging between 100 and 150 μm. However, the M(s) and A(f) of the as-atomized powders is much smaller than those of SPS specimens and the M(s) of porous specimen was about 10.9 degrees C. Loading-unloading compressive tests were carried out to investigate the mechanical properties of porous Ti-Ni-Cu specimen. The specimen was compressed to the strain of 6% at a temperature higher than A,. After unloading, the residual strain was 2.1%. After the compressed specimen was heated to 60 degrees C and held for 30 minutes and then cooled to room temperature, the changes in the length of the specimens were measured. Then it was found that the recovered strain ascribed to shape memory effect was 1.5%.

In-situ synthesis and sintering of mullite glass composites by SPS

The main subject of this work is an investigation of the effects of heating rate and current on the crystallisation of amorphous precursors in spark plasma sintering (SPS). For this, dry gel of Al2O3-SiO2 with a molar ratio of 1:1, was synthesized and sintered in-situ by SPS, and also by hot pressing (HP) for comparison. Phase analysis showed that the only crystalline product in both cases was mullite, whose Al2O3 content was lower in the SPS specimens. The microstructures showed a low volume fraction of large mullite fibers in the SPS specimens, whereas a high volume fraction of fine equiaxed grains was present in the HP specimen. The main difference in microstructure between HP and SPS specimens could be explained in terms of the higher heating rate of the SPS specimens. The size of the SPS die also affected the size and aspect ratio of the mullite fibers produced, which might have been due to either the different electrical current required or a difference in specimen temperature profile.

Microstructures and Mechanical and Electrical Properties of Hypoeutectic Cu-1, C-3 and Cu-5 at%Zr Alloy Wires Preprocessed by Spark Plasma Sintering

Wires prepared by the solid-phase-compaction followed by heavy wire-drawing of atomized Cu­Zr alloy powders were studied. Microstructures and mechanical and electrical properties of wires drawn from hypoeutectic Cu-1, Cu-3 and Cu­5at%Zr alloys, preprocessed by spark plasma sintering (SPS), were investigated. The microstructures of specimens formed by SPS of the powders changed into fine dual-phased structures comprising phases of Cu and the intermetallic compound Cu5Zr, which was dispersed in the Cu matrix. The volume fraction of the intermetallic compound Cu5Zr in SPS specimens increased with an increase in the Zr content. The ultimate tensile strength (UTS) values of the specimens increased, while their electrical conductivity (EC) values decreased simultaneously. The alloy wires, preprocessed by SPS, contained dual-phased microstructures in which the intermetallic compound Cu5Zr was dispersed in the shape of small islands in the Cu matrix. Drawn Cu1, Cu-3 and Cu­5at%Zr alloy wires exhibited UTS values of 603, 698 and 789MPa, respectively, and EC values of 87, 70 and 52% IACS (International Annealed Copper Standard), respectively. The UTS values were about 40­56% lower and EC values about 28­60% higher than those previously reported for wires preprocessed by casting. The lamellar structures of the i-Cu and eutectic (Cu+ intermetallic compound Cu9Zr2) phases in the drawn wires preprocessed by casting improved the mechanical properties of the wires. The microstructures of the intermetallic compounds Cu5Zr, which was uniformly dispersed in the Cu matrix in the drawn wires preprocessed by SPS, helped increase the electrical conductivity of the wires. [doi:10.2320/matertrans.M2013011]

Microstructure and martensitic transformation characteristics of gas-atomized Ti–Ni–Cu powders

Abstract Three batches of Ti–Ni–Cu powders (Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 ) were prepared by gas atomization and porous specimens were fabricated by spark plasma sintering (SPS). The microstructure of as-solidified powders exhibited a cellular structure. XRD analysis showed that one-step martensitic transformation of B2–B19 occurred in all alloy powders and SPS specimens. DSC measurements of as-atomized powder, sintered bulk specimens and as-cast ingots were performed in order to study the effect of rapid solidification on martensitic transformation behaviors. The dependence of powder size on martensitic transformation temperature is very small in the rapidly solidified powders. However, the transformation temperatures were strongly dependent on the Cu-content. The martensitic transformation starting temperatures ( M s ) of Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 powders ranging between 25 and 150 μm are −4.9, −17.6 and 32.1 °C and the austenite transformation finishing temperatures ( A f ) of Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 powders were 15.6, −4.4 and 38.3 °C, respectively. The M s and A f of the as-atomized powders are much smaller than those of SPS specimens and as-cast ingots for all Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 alloy systems. The temperature hysteresis ( A f − M s ) of Ti 50 Ni 45 Cu 5 powders was 20 °C and continued to decrease with increasing Cu-content. The temperature hysteresis of Ti 50 Ni 30 Cu 20 powders was only 7 °C.

Dielectric properties of Bismuth Titanate densified by Spark Plasma Sintering and Pressureless Sintering

Bismuth Titanate powder Bi4Ti3O12 of 175nm mean particle size has been synthesized through chemical precipitation and calcination of chemical precursors at 700°C. Ceramic pellets were sintered by conventional Pressureless Sintering (PLS) and Spark Plasma Sintering (SPS) techniques. SPS is shown to be effective in inhibiting grain growth and allowing the formation of a homogeneous microstructure. The optimum SPS temperature is 800°C in less than 5min. PLS specimens seem to be more sensible to temperature rise and sintering time, undergoing grain grow and plates-like morphology. This fact leads formation of a given crystallographic texture. Dielectric properties of SPS specimens are found dependent of the electric signal frequency and less sensitive to sintering temperature than PLS counterparts.

Microstructure and Shape Memory Characteristics of Powder-Metallurgical-Processed Ti-Ni-Cu Alloys

Even though Ti-Ni-Cu alloys have attracted a lot of attention because of their high performance in shape memory effect and decrease in thermal and stress hysteresis compared with Ti-Ni binary alloys, their poor workability restrains the practical applications of Ti-Ni-Cu shape memory alloys. Consolidation of Ti-Ni-Cu alloy powders is useful for the fabrication of bulk near-net-shape shape memory alloy. Ti50Ni30Cu20 shape memory alloy powders were prepared by gas atomization, and the sieved powders with the specific size range of 25 to 150 μm were chosen for this study. The evaluation of powder microstructures was based on a scanning electron microscope (SEM) examination of the surface and the polished and etched powder cross sections. The typical images showed cellular/dendrite morphology and high population of small shrinkage cavities at intercellular regions. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis showed that a B2-B19 one-step martensitic transformation occurred in the as-atomized powders. The martensitic transformation start temperature (Ms) of powders ranging between 25 and 50 μm was 304.5 K (31.5 °C). The Ms increased with increasing powder size. However, the difference of Ms in the as-atomized powders ranging between 25 and 150 μm was only 274 K (1 °C). A dense cylindrical specimen of 10 mm diameter and 15 mm length were fabricated by spark plasma sintering (SPS) at 1073 K (800 °C) and 10 MPa for 20 minutes. Then, this bulk specimen was heat treated for 60 minutes at 1123 K (850 °C) and quenched in ice water. The Ms of the SPS specimen was 310.5 K (37.5 °C) whereas the Ms of conventionally cast ingot is found to be as high as 352.7 K (79.7 °C). It is considered that the depression of the Ms in rapidly solidified powders is ascribed to the density of dislocations and the stored energy produced by rapid solidification.

Effects of Ir Substitution and Processing Conditions on Thermoelectric Performance of p-Type Zr0.5Hf0.5Co1−x Ir x Sb0.99Sn0.01 Half-Heusler Alloys

A series of samples with the composition Zr0.5Hf0.5Co1−x Ir x Sb0.99Sn0.01 (x = 0.0 to 0.7) were synthesized by high-temperature solid-state reaction at 1173 K. High-density pellets of the powders were obtained using hot press (HP) and spark plasma sintering (SPS) techniques. The thermoelectric properties of the pellets were measured from 300 K to 750 K. Independently of the pressing conditions, all Ir-containing samples (x > 0) showed p-type semiconducting behavior. At 300 K, the electrical conductivity and thermopower of Zr0.5Hf0.5Co1−x Ir x Sb0.99Sn0.01 materials surprisingly increased with increasing Ir concentration. The largest electrical conductivity and thermopower values of 150 S/cm and 140 μV/K, respectively, were observed at 300 K for x = 0.7. The thermal conductivity of the synthesized materials decreased with increasing Ir content, went through a minimum value (x = 0.3), and increased thereafter with further addition of Ir. Pellets fabricated by SPS showed smaller thermal conductivity than pellets of the same composition obtained from uniaxial hot pressing. A thermal conductivity value of ∼2.0 W/m K was observed at 300 K for an SPS pellet with the com- position Zr0.5Hf0.5Co0.5Ir0.5Sb0.99Sn0.01. The thermal conductivity of Zr0.5Hf0.5- Co1−x Ir x Sb0.99Sn0.01 decreased with rising temperature, and the smallest value of ∼1.5 W/m K was observed at 750 K for the SPS specimen with x = 0.5.

Thermal expansion behaviour of SiCp/Cu composites prepared by spark plasma sintering and pressureless infiltration

The coefficient of thermal expansion and thermal strain response behaviour of SiCp/Cu composites prepared by spark plasma sintering (SPS) and pressureless infiltration were studied. The CTEs decreased with increasing reinforcement content. For a fixed SiC content, pressurelessly infiltrated specimens exhibited lower CTE than the SPS specimens. The CTEs of SPS specimens agreed well with the ROM model while the CTE of pressurelessly infiltrated specimens was close to Kerner's predictions. The strain hysteresis loops were developed during thermal cycling. The residual stress increased with increasing reinforcement content. The SPS specimens experienced large dimensional change due to the weak interfacial bond while the pressurelessly infiltrated specimens showed negligible strain hysteresis. The interfacial condition has a pronounced effect on the strain hysteresis behaviour. The improved interfacial bond was beneficial to the decreasing of the CTE and improving the dimensional stability of the composite.

電気化学的手法によるＳＰＳ技術により作製したＳＵＳ３０４ステンレス鋼の腐食特性

The corrosion behavior of SUS304 specimen produced by spark plasma sintering (SPS) has been studied through electrochemical tests such as polarization curve measurement, electrochemical reactivation ratio measurement and electrochemical impedance spectroscopy (EIS), compared to those of specimens produced by the conventional ingot metallurgy process (I/M) and the powder metallurgy process (P/M).The corrosion current density (icorr) of the SPS specimen has a tendency increasing with a decrease in electrochemical corrosion potential (Ecorr). The corrosion resistant of the SPS specimen was inferior to that of the I/M specimen because of carbon diffusion from a graphite punch rod while it was improved by removing the surface file through polishing.The electrochemical reactivation ratio of the SPS specimen without polishing was 27.4%, which was significantly higher compared to 0.13% for the I/M specimen because of its poor passivation film.The Rct value of the SPS specimen without polishing was 0.09 times as large as that of the I/M specimen, while it became 0.63 times for the SPS specimen with polishing. This result well agrees with the icorr value obtained by the electrochemical polarization test.