Sharif Digital Repository

As of today, metals and alloys are widely utilized as structural, mechanical, electrical, and magnetic materials in every aspect of technology and industry. The complexity and diversity of metals applications emphasize the need for a new production method to quickly and easily manufacture metallic components. Spark plasma sintering as a new solid-state sintering method has been recently developed to respond to these needs. Up to now, numerous papers and researches have been published in the field of spark plasma sintering and its ability to manufacture metallic samples. Density is a significant property that has a great influence on the physical, mechanical, and functional properties of... 

The use of ZrO2 nanoparticles is common in the Cu matrix to manufacture Cu/ZrO2 nanocomposites. Many approaches and parameters produce Cu/ZrO2 nanocomposites with an appropriate wear rate and other properties. Hence, proposing an accurate and reliable model was imperative. The main goal of this paper is to find out the best models among the ant colony optimization (ACO), gene expression programming (GEP), artificial bee colony (ABC), and gray wolf optimization algorithm (GWOA) to predict the wear rate of/ZrO2 nanocomposites. To the best of our knowledge, this is the first research that predicts Cu/ZrO2 nanocomposites wear rate using group modeling. To develop models, 105 data were collected... 

In the present work, spark plasma sintering (SPS) process was employed to prepare a nanostructured yttria-stabilized zirconia (8YSZ) coating on a nickel-based superalloy (INCONEL 738) with functionally graded structure. A stack layer of INCONEL 738/NiCrAlY powder/Al foil/NiCrAlY+YSZ powder/YSZ powder was SPSed in a graphite die at an applied pressure of 40 MPa under an vacuum atmosphere (8 Pa). The sintering temperature was ∼1040 °C. For comparison purpose, the air plasma spray (APS) technique was employed to prepare the thermal barrier coating (TBC). Microstructural studies by scanning electron microscopy showed that the SPSed coating was sound and free of interfacial cracks and large... 

A near fully dense mullite-TiB2-CNTs hybrid composite was prepared successfully trough spark plasma sintering. 1 wt%CNT and 10 wt%TiB2 were mixed with nano-sized mullite powders using a high energy mixer mill. Spark plasma sintering was carried out at 1350 °C under the primary and final pressure of 10 MPa and 30 MPa, respectively. XRD results showed mullite and TiB2 as dominant crystalline phases accompanied by tiny peaks of alumina. The microstructure of prepared composites demonstrated uniform distribution of TiB2 reinforcements in mullite matrix without any pores and porosities as a result of near fully densified spark plasma sintered composite. The fracture surface of composite revealed... 

Copper matrix composites have received more attentions as possible candidate for thermal and electrical conductive materials to be used in electrical contact applications. In this study, five-layered Cu/YSZ (yttria-stabilized zirconia) functionally graded material (FGM) and copper matrix composite specimens containing 3 and 5 vol% YSZ particles plus pure Cu specimen were synthesized using powder metallurgy (PM) route and spark plasma sintering (SPS) consolidation process. The microstructural and some physical, mechanical features of all specimens were characterized. Microscopic examinations showed that ultrafine YSZ particles were distributed in the copper matrix almost homogeneously. An... 

In the present study, yttria stabilized zirconia (YSZ) reinforced Cu matrix composite specimens were produced by spark plasma sintering (SPS). For comparison, pure Cu specimen was also produced in the same conditions. The effect of particles content on microstructure, relative density, electrical conductivity, and Vickers hardness was evaluated. The pin-on-disk test was also performed to determine dry sliding wear behavior of specimens under different wear conditions. After sliding wear tests, the worn surfaces were examined by field emission scanning electron microscopy (FE-SEM). Microstructural study showed satisfactory distribution of reinforcement particles in copper matrix. The relative... 

In this research, for the first time, SnO2-based varistors were fabricated via spark plasma sintering technique (SPS) and the microstructure and electrical properties of these varistors were investigated. Furthermore, the effect of post-annealing temperature in oxygen atmosphere on electrical properties of the SPSed samples was studied. The SPS process was performed at the sintering temperatures of 600, 650, and 700 ᵒC for 15 min with a maximum pressure of 90 MPa under vacuum condition. The SPSed sample which was sintered at 650 ᵒC possessed maximum density of 98% and the ultra-fine-grained microstructure with the mean grain size of 380 nm. Surprisingly, all SPSed samples exhibited Ohmic... 

Finemet bulk soft magnetic alloy was fabricated by spark plasma sintering of the milled ribbons. The amorphous melt-spun ribbons were milled for 36min by high energy vibrational mill and then sieved to separate particles smaller than 125μm. The size distribution of particles was determined by a laser diffraction particle size analyzer. Spark plasma sintering was carried out at super-cooled liquid region for short times of 7 and 21min. The structure of bulk samples was characterized using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and transmission electron microscopy techniques. The magnetization and coercivity of samples were measured using SQUID... 

Iron-borosilicate soft magnetic composites are suitable magnetic materials for high temperature and high frequency applications. In this research two different techniques have been applied to fabricate these composites: uniaxial pressing following by sintering and spark plasma sintering. Different processing parameters including the content of borosilicate, the amount of compaction pressure and the size of iron particles have been evaluated through the study of microstructure and magnetic properties. The microstructural observations showed that the borosilicate is distributed on the iron grain boundaries enhancing the resistivity and causing the loss of eddy currents. Increasing the... 

Monitoring the oxygen in the fume and controlling its amount at high temperatures is an efficient way to regulate combustion efficiency. Zirconia can be an attractive candidate for use in oxygen sensors due to its good physical and chemical properties. The crystal structure of pure zirconia nanopowder due to the lack of cubic phase cannot be used for the fabrication of gas sensor electrodes. Moreover, the change of temperature during ceramic processing and application can promote structural and phase stresses. In this work, to achieve a pure cubic phase, yttria was successfully added to zirconia by a large-scale and effective method called Pechini. The yttria-stabilized zirconia nanopowders... 

Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000°C). Spark plasma sintering is a new route for consolidation of materials, specially ultra high temperature ceramics (UHTCs), which are difficult to be sintered at temperatures lower than 2000°C.The purpose of this study is to consolidate Ta0.8Hf0.2C by spark plasma sintering at low temperature using MoSi2 and TaSi2 as sintering aid. In this regard, effect of different amounts of sintering aids and carbides ratio on densification behavior and mechanical properties of Ta1-xHfxC were investigated.Fully consolidation of Ta0.8Hf0.2C was achieved in presence of 12vol.% sintering aid after sintering at 1650°C for 5min... 

To study the effect of the production method on physical and mechanical properties of Cu-rGO nanocomposites, nanocomposite powder samples with rGO content of 0.25–1 wt.% were prepared via combined routes of molecular-level mixing (MLM) and powder metallurgy (PM). Spark plasma sintering (SPS) was applied to consolidate nanocomposite powders with better control on the grain size. According to the specific electrical resistivity measurements, microhardness, and pin-on-disk wear tests, the sample with 0.5 wt.% rGO comprised the best overall properties. For assessment, samples containing 0.5 wt.% rGO were also produced via PM and MLM routes, separately. The physical and mechanical properties of...