Spark Sintering Process Research Articles

An in-situ three-dimensional study of the dynamic and mechanism during spark plasma sintering of aluminum alloys

An in-situ plasma spark sintering (SPS) apparatus, coupled with laboratory X-ray microscopy, was utilized to three-dimensionally investigate the dynamic evolution process of 7055 aluminum alloy during SPS process. The influences of sintering temperatures and particle morphology on the sintering kinetics were discussed in detail. It was observed that elevating the sintering temperatures enhanced both the rate of densification and the final compactness of the alloy. Furthermore, three-dimensional quantitative analysis of pore evolution indicated that greater discrepancies in powder size between neighboring particles facilitated pore elimination during sintering by increasing available interstitial spaces. Mechanistic analysis rationalized these observations by attributing the enhanced sintering kinetics to the greater particle size disparity, which resulted in higher necking curvature and accelerated densification. The present study therefore provides a comprehensive three-dimensional in-situ quantitative analysis on the dynamic SPS process, and is expected to advance the current comprehension of sintering mechanisms at the micron scale.

Influence of overstoichiometric boron and titanium addition on the properties of RF magnetron sputtered tungsten borides

In this work, (W,Ti)B2 films with different stoichiometric ratio Ti/W deposited on silicon and 304 stainless steel by radio frequency magnetron sputtering are presented. The coatings were deposited from plasma spark sintered targets obtained from the mixture of pure boron, tungsten and titanium powders. It is shown that during plasma spark sintering process using overstoichiometric boron and a low content of titanium change the WB2 to WB4 phase with almost no secondary phases. Subsequently, the impact of titanium content on the films properties is investigated systematically, including the chemical and phase composition, crystalline structure, surface and cross-section morphology. Simultaneously, nano-indentation test and ball-on-disk tribometery are performed to analyse the hardness and tribological properties of the films. It is shown that deposited films with titanium content of 3.6 and 5.5 at.% are formed in the zone T of the Thornton's Structural Zone Model. In opposite to α-WB2 magnetron sputtered coatings they are more flexible and hard nanocomposite coatings. The results show that the addition of titanium is apparently changing the film structure from nanocrystalline columnar to amorphous, very dense and compact structure with the addition of TiB2 phase. That films are simultaneously hard (H > 37.5 GPa), have high hardness to effective Young's modulus ratio values (H/E⁎ > 0.1) and elastic recovery (We > 60%) appropriate for tough and resistant to cracking materials. The presented (W,Ti)B2 films exhibit also tribological and corrosion properties better than unalloyed coatings.

Development of vapour-grown carbon nano-fibre-reinforced aluminium matrix composites by low-pressure infiltration process

This study was aimed for development of vapour-grown carbon nano-fibre(VGCNF)-reinforced aluminium matrix composites by the low-pressure infiltration process. First, VGCNF and Al powder (VGCNF + Alp) preforms for low-pressure infiltration were fabricated by spark sintering process at pressures of 5, 10, 20 and 40 MPa, respectively. Porosity of the preforms fabricated at pressures of 5 and 10 MPa was 44·89 and 40·87%, respectively. However, porosity of the preforms fabricated by spark sintering at pressures of 20 and 40 MPa was approximately 20%. Therefore, VGCNF + Alp/Al composites with the preform sintered at pressures of 5 and 10 MPa were fabricated by the low-pressure infiltration process under an applied pressure of 0·4 MPa, and the relative density was 81·4 and 76·0%, respectively. Moreover, the microstructure, porosity and electrical conductivity of the VGCNF + Alp/Al composites were estimated. Their electrical conductivities reduced with increasing porosity of VGCNF + Alp/Al composites.

Property-Control of Ti Compacts in Spark Sintering Process

Property-Control of Ti Compacts in Spark Sintering Process

511 放電焼結法で作製したVGCF/アルミ二ウム複合材料の作製と熱・電気伝導性の評価(金属/金属基複合材料)

511 放電焼結法で作製したVGCF/アルミ二ウム複合材料の作製と熱・電気伝導性の評価(金属/金属基複合材料)

Fabrication and Electrical Conductivity of Vapor Grown Carbon Fiber Reinforced Aluminum Composites

Vapor grown carbon fiber (VGCF) reinforced aluminum matrix composites were fabricated by spark sintering processes. VGCFs in composites became to be dispersed uniformly in the aluminum matrix by decreasing a diameter of aluminum powder. The electrical conductivity of composites was reduced remarkably compared with monolithic aluminum block. On the other hand, the electrical conductivity of the composites was slightly reduced with increasing a diameter of aluminum particle. Meanwhile, the experimental electrical conductivity of VGCF/Al composites was lower than the theoretical one calculated by Chang’s and Fan’s models, which is caused by the strain fields containing larger residual stress in aluminum matrix around VGCF.

放電焼結のプロセス解析・制御とマイクロ・マクロモデリング

The densification or sintering processes in spark sintering has systematically investigated from the standpoint of punch-powder compact-die system, unlike the conventional situation such as the simple convenient method for fabricating sintered body. The systematic investigation consists of the following serial subjects; (1) clarification of principle of process, (2) modeling of coupling between micro- and macro-phenomena, (3) generalization of process control, (4) fabrication of high performance and multi-functional materials by optimization of process factors. Especially, the micro-phenomena in and/or between powder particles were coupled with the macro-phenomena such as heat transfer in the punch-compact-die system through micro/macro-coupling model. The coupling analysis for electricity (voltage and current) and heat was carried out by using Ohm's and Fourier's laws on the basis of the thermal energy conservation law. The optimized system for spark sintering process was proposed by the computer simulation based on micro/macro-coupling modeling and enabled to attain full densification even for poor sinterable materials, which led to the successful development of many metallic and ceramic materials in the industrial fields.

Erratum to “Temperature distribution at steady state under constant current discharge in spark sintering process of Ti and Al

Erratum to “Temperature distribution at steady state under constant current discharge in spark sintering process of Ti and Al

Temperature distribution at steady state under constant current discharge in spark sintering process of Ti and Al2O3 powders

Obtaining the distribution of the voltage and temperature of the punch–die–compact systems in the spark sintering process is useful for generalization of its process control. The temperatures of these systems using two kinds of powders, titanium and alumina, of a conductor and an insulator, respectively, are measured by thermocouples in the constant current discharging process. The steady state showing the constant values of temperature and relative density is achieved in this process, and the measured temperature distribution in the systems is changed depending on the kind of compacts. The voltage and temperature of the systems at the steady state are also calculated on the basis of Ohm’s and Fourier’s laws. The calculated voltage distribution or current flow in the punch and die for the titanium compact system is similar to that for the alumina compact system, although there is the minor difference of the voltage distribution between titanium and alumina compacts because of the difference in the specific resistivity of compacts. The calculated temperature distribution is changed in these systems depending on the kind of compacts, because of the difference in the amount of Joule’s heat of compacts, which agrees with the temperature distribution measured by thermocouples. It is found from the result obtained in this study that distributions in voltage and temperature can be estimated by this calculation method, regardless of a kind and shape of the punches, dies and compacts.

放電焼結法による純銅粉末の型内単軸圧縮における焼結速度

放電焼結法による純銅粉末の型内単軸圧縮における焼結速度

Adhesion properties of CVD diamond film on binder-less sintered tungsten carbide prepared by the spark sintering process

Abstract This paper describes the adhesion property of chemical-vapor-deposited (CVD) diamond film on tungsten carbide (WC) bodies prepared by spark sintering without a binder. WC bodies ranging from 70 to 95% of density ratio have been sintered under different sintering conditions, and their mechanical properties, such as hardness and bending strength, have been measured. High-quality diamond films with a higher nucleation density compared to that on WC–Co have been deposited on this WC substrate using the microwave plasma CVD method. A comparison study using indentation tests shows that the adhesive strength of diamond films on this binder-less sintered WC is remarkably superior to that on WC–Co, which is believed to result from the increase in diamond nucleation density, the enhanced mechanical bonding between the substrate and the diamond film and the well-matching of thermal expansion coefficients caused by the absence of the fatal obstacle of cobalt. Moreover, an increase in adhesive strength has occurred on the binder-less sintered WC with lower density ratios.

Effect of Direct Current Pulse Discharge on Electrical Resistivity of Copper and Iron Powder Compacts

The relationship between the number of pulses and the specific resistivity for the copper and iron powder compacts has been investigated to reveal the phenomena which are caused between powder particles in the early stage in the spark sintering process. The values of specific resistivity of the both powder compacts decrease with increasing the number of pulses, and the rates of decrease of specific resistivity increase with decreasing applied punch pressures. The limited variations of the relative densities of compacts are observed in the continuously pulse discharge process. Therefore, it is considered that the specific resistivity of compacts are decreased, not because their relative densities are changed but because the properties of the contact area between powder particles are changed by the pulse discharge. Where, this change of the properties is caused by the dielectric breakdown of the oxide film between the powder particle surfaces in the pulse discharge process. The metallic contact parts are created between the powder particles after this dielectric breakdown. It is suggested on the basis of the simple model of electric resistance of a compact that the fraction of the metallic contact area created by the dielectric breakdown of the oxide film is extremely small. Furthermore, it is assumed on the basis of the first order equation of the chemical reaction that the rate of the creation of the metallic contact area between powder particles per pulse discharge is proportional to the fraction of the contact area consisting of an oxide film between particles. The relationship between the number of pulses and the specific resistivity of compacts can be explained quantitatively by this assumption.

銅および鉄圧粉体の比抵抗に及ぼす直流パルス通電の効果

The relationship between the number of pulses and the specific resistivity for the copper and iron powder compacts has been investigated to reveal the phenomena which are caused between powder particles in the early stage of the spark sintering process. The results are summarized as follows: The values of specific resistivity of the both powder compacts decrease with increasing the number of pulses, and the rates of decrease of specific resistivity increase with decreasing the applied punch pressures. The limited changes of the relative densities of compacts are observed in this continuously pulse discharge process. Therefore, it is considered that the specific resistivity of compacts are decreased, not because their relative densities are changed but because the properties of the contact area between powder particles are changed by the pulse discharge. Where, this change of the properties is caused by the dielectric breakdown of the oxide film between the powder particle surfaces in the pulse discharge process. The metallic contact parts are created between powder particles after this dielectric breakdown. It is cosidered that the spark can not be caused in these metallic contact parts.It is suggested on the basis of the simple model of electric resistance of a compact that the fraction of the metallic contact area created by the dielectric breakdown of the oxide film is extremely small.It is assumed on the basis of the first order equation of the chemical reaction that the rate of decrease of the area fraction of the oxide film between powder particles per one pulse discharge is proportional to this retained area. The relationship between the number of pulses and the specific resistivity of compacts can be explained quantitatively by this assumption.

A microstructural study of the wear behaviour of SiC p/Al composites

Wear rates of SiC p/Al composites and pure Al under a self-mated reciprocating sliding condition were measured. The content and particle size of SiC particles were varied systematically to show the trend of wear resistance. All samples were fabricated using a method combining mechanical alloying and spark sintering processes. The experimental results showed that the SiC p-reinforced composites were more wear resistant than the unreinforced Al sample. For a fixed size of SiC particles, wear resistance increased with the SiC content. On the other hand, for a fixed content of SiC particles, samples containing coarser particles were more wear resistant. Microstructural examinations showed that neither pulling out nor brittle fracturing of SiC particles occurred to a significant degree in the wear tests. Instead, the main mechanism for the removal of SiC particles was that SiC particles were buried in layers of Al matrix and carried away while the latter detached from the sample surface. Agglomerations of fine wear debris resulted in large wear particles which caused significant abrasion in the subsequent wearing process.

放電焼結法に関する最近の研究

放電焼結法に関する最近の研究