scholarly journals Influence of Dwell Time and Pressure on SPS Process with Titanium Aluminides

Metals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 83
Author(s):  
Bernd-Arno Behrens ◽  
Kai Brunotte ◽  
Julius Peddinghaus ◽  
Adrian Heymann
Keyword(s):  
Titanium Aluminide ◽  
Dwell Time ◽  
Titanium Aluminides ◽  
Holding Time ◽  
Plasma Sintering ◽  
Process Route ◽  
Powder Metallurgy Process ◽  
Spark Plasma ◽  
Field Assisted Sintering ◽  
The Impact

Spark plasma sintering (SPS) or the field-assisted sintering technique (FAST) is commonly used to process powders that are difficult to consolidate, more efficiently than in the conventional powder metallurgy process route. During the process, holding time and applied holding pressure influence the product’s microstructure and subsequently its properties. In this study, in addition to the temperature impact, the influence of pressure and dwell time on the consolidation behaviour of titanium aluminide (TiAl) powders during the SPS process is investigated. Commercially available pre-alloyed TiAl48-2Cr-2Nb (GE48) and TiAl44-4Nb-0.7Mo-0.1B (TNM) powders were used, which have a high application potential in, for example, the aerospace industry. The results were evaluated based on microstructural analyses, hardness measurements and relative density calculations. It was shown that the investigated parameters significantly influence the sintering results, especially in the low temperature range. Depending on the temperature field in the sample, complete sintering is not achieved if the dwell time is too short in combination with too low a pressure. Above a certain temperature, the impact of holding pressure and holding time is significantly lower.

Exploitation of Field-Assisted Sintering Technology (FAST) to Produce Pre-Forged Billets from Metastable Beta Titanium Alloy Powder

2016 ◽  
Vol 716 ◽  
pp. 800-816 ◽  
Author(s):  
Emma Calvert ◽  
Bradley P. Wynne ◽  
Martin Jackson
Keyword(s):  
Grain Size ◽  
Dwell Time ◽  
Beta Titanium Alloy ◽  
Precise Control ◽  
Beta Titanium ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The University ◽  
Field Assisted Sintering ◽  
Metastable Beta

Powder produced by gas atomisation of metastable beta alloy Ti-5Al-5Mo-5V-3Cr has been consolidated using field-assisted sintering technology (FAST) to examine the suitability of the process to produce pre-forged billets as opposed to the conventional multi-step Kroll-VAR-forging route. FAST testing was performed using an FCT Systeme GmbH spark plasma sintering furnace type HP D 25 at The University of Sheffield. The dwell temperature was varied between 800 and 1200°C and the dwell time between 3 and 60 minutes. The process was found to allow very precise control over the beta grain size in Ti-5Al-5Mo-5V-3Cr by variation of the dwell time and dwell temperature, producing grain sizes between ~40 and ~350 μm. However, it was found that the grain size was increased more by increasing the dwell temperature than increasing the dwell time. The porosity was found to be between 99.5 and 100 % for all dwell temperatures at dwell times of 30 minutes or above. FAST has the ability to produce almost fully consolidated Ti-5Al-5Mo-5V-3Cr pre-forged material from powder with a controlled beta grain size, which is not possible by other methods.

scholarly journals Field-Assisted Sintering/Spark Plasma Sintering of Gadolinium-Doped Ceria with Controlled Re-Oxidation for Crack Prevention

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3184 ◽  
Author(s):  
Tarini Prasad Mishra ◽  
Alexander M. Laptev ◽  
Mirko Ziegner ◽  
Sree Koundinya Sistla ◽  
Anke Kaletsch ◽  
...  
Keyword(s):  
Spark Plasma Sintering ◽  
Dwell Time ◽  
Elevated Temperatures ◽  
Sintering Temperature ◽  
Doped Ceria ◽  
Reducing Atmosphere ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Field Assisted Sintering ◽  
Gadolinium Doped Ceria

Gadolinium-Doped Ceria (GDC) is a prospective material for application in electrochemical devices. Free sintering in air of GDC powder usually requires temperatures in the range of 1400 to 1600 °C and dwell time of several hours. Recently, it was demonstrated that sintering temperature can be significantly decreased, when sintering was performed in reducing atmosphere. Following re-oxidation at elevated temperatures was found to be a helpful measure to avoid sample failure. Sintering temperature and dwell time can be also decreased by use of Spark Plasma Sintering, also known as Field-Assisted Sintering Technique (FAST/SPS). In the present work, we combined for the first time the advantages of FAST/SPS technology and re-oxidation for sintering of GDC parts. However, GDC samples sintered by FAST/SPS were highly sensitive to fragmentation. Therefore, we investigated the factors responsible for this effect. Based on understanding of these factors, a special tool was designed enabling pressureless FAST/SPS sintering in controlled atmosphere. For proof of concept, a commercial GDC powder was sintered in this tool in reducing atmosphere (Ar-2.9%H2), followed by re-oxidation. The fragmentation of GDC samples was avoided and the number of micro-cracks was reduced to a minimum. Prospects of GDC sintering by FAST/SPS were discussed.

scholarly journals Influence of CFRC Insulating Plates on Spark Plasma Sintering Process

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 393
Author(s):  
Alexander M. Laptev ◽  
Jürgen Hennicke ◽  
Robert Ihl
Keyword(s):  
Temperature Distribution ◽  
Spark Plasma Sintering ◽  
Energy Demand ◽  
Composite Powders ◽  
Fem Method ◽  
Plasma Sintering ◽  
Axial Temperature ◽  
Spark Plasma ◽  
Power And Energy ◽  
The Impact

Spark Plasma Sintering (SPS) is a technology used for fast consolidation of metallic, ceramic, and composite powders. The upscaling of this technology requires a reduction in energy consumption and homogenization of temperature in compacts. The application of Carbon Fiber-Reinforced Carbon (CFRC) insulating plates between the sintering setup and the electrodes is frequently considered as a measure to attain these goals. However, the efficiency of such a practice remains largely unexplored so far. In the present paper, the impact of CFRC plates on required power, total sintering energy, and temperature distribution was investigated by experiments and by Finite Element Modeling (FEM). The study was performed at a temperature of 1000 °C with a graphite dummy mimicking an SPS setup. A rather moderate influence of CFRC plates on power and energy demand was found. Furthermore, the cooling stage becomes considerably longer. However, the application of CFRC plates leads to a significant reduction in the axial temperature gradient. The comparative analysis of experimental and modeling results showed the good capability of the FEM method for prediction of temperature distribution and required electric current. However, a discrepancy between measured and calculated voltage and power was found. This issue must be further investigated, considering the influence of AC harmonics in the DC field.

scholarly journals A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 331-363
Author(s):  
Eugeniy Lantcev ◽  
Aleksey Nokhrin ◽  
Nataliya Malekhonova ◽  
Maksim Boldin ◽  
Vladimir Chuvil'deev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Phase ◽  
Continuous Heating ◽  
Diffusion Creep ◽  
Hard Alloys ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact ◽  
Kinetics Of

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

Effect of Spark Plasma Sintering on the Microstructure Evolution and Properties of M3:2 High-Speed Steel

2014 ◽  
Vol 788 ◽  
pp. 329-333
Author(s):  
Rui Zhou ◽  
Xiao Gang Diao ◽  
Jun Chen ◽  
Xiao Nan Du ◽  
Guo Ding Yuan ◽  
...  
Keyword(s):  
Powder Metallurgy ◽  
Spark Plasma Sintering ◽  
High Speed ◽  
Bending Strength ◽  
Sintering Temperature ◽  
High Speed Steel ◽  
Continuous Heating ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact

Effects of sintering temperatures on the microstructure and mechanical performance of SPS M3:2 high speed steel prepared by spark plasma sintering was studied. High speed steel sintering curve of continuous heating from ambient temperature to 1200°C was estimated to analyze the sintering processes and sintering temperature range. The sintering temperature within this range was divided into groups to investigate hardness, relative density and microstructure of M3:2 high-speed steel. Strip and quadrate carbides were observed inside the equiaxed grains. SPS sintering temperature at 900°C can lead to nearly full densification with grain size smaller than 20μm. The hardness and bending strength are higher than that of the conventionally powder metallurgy fabricated ones sintered at 1270°C. However, fracture toughness of the high speed steel is lower than that of the conventional powder metallurgy steels. This can be attributed to the shape and distribution of M6C carbides which reduce the impact toughness of high speed steels.

Field Assisted Sintering Technology (FAST) Model for Prediction of Final Properties

2010 ◽  
Author(s):  
Rajiv Paul ◽  
Anil K. Kulkarni ◽  
Jogender Singh
Keyword(s):  
Electrical Breakdown ◽  
Extensive Literature ◽  
Heating Rates ◽  
Predictive Tool ◽  
Simultaneous Application ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Data Points ◽  
Field Assisted Sintering ◽  
The Relationship

Sintering is the process of making materials from powder form by heating the powder below its melting point until the particles fuse to each other. Field assisted sintering technology (FAST), also sometimes known as spark plasma sintering (SPS), uses a pulsed and/or continuous electric current along with the simultaneous application of compressive pressure which leads to extremely high heating rates and short processing durations. A high relative density and small grain size promote superior properties such as greater hardness and electrical breakdown. Hence, selection of the proper sintering parameters is of paramount importance and a predictive model would be extremely useful in narrowing the range of experimental parameters. This will drastically reduce the number of extra attempts at obtaining certain properties in a material and save experimentation time, effort and material to name a few. Four of the most important FAST parameters: target temperature, holding time, heating rate and initial particle size, have been reviewed to assess their effect on the densification, hardening and grain growth of Alumina, Copper, Silicon Carbide, Tungsten and Tungsten Carbide through extensive literature survey. The relationship between each has been incorporated in a Microsoft Excel program which acts as a predictive tool to determine an estimate of the final properties based on the initial parameters chosen. This is done by curve fitting a polynomial onto the existing data points as closely as possible and using the polynomial to obtain final properties as a function of the initial parameters. The model was verified against an existing paper which sought to obtain the optimum sintering parameters for Copper. While the actual experimentation range was 400°C to 800°C, the program would have suggested a much narrower range from 650°C to 800°C and hence saved unnecessary additional efforts.

Formation of Metal-Intermetallic Laminate Composites by Spark Plasma Sintering of Metal Plates and Powder Work Pieces

2014 ◽  
Vol 698 ◽  
pp. 277-282 ◽  
Author(s):  
Daria V. Lazurenko ◽  
Vyacheslav I. Mali ◽  
Alexander Thoemmes
Keyword(s):  
Spark Plasma Sintering ◽  
Titanium Aluminide ◽  
Elevated Temperatures ◽  
Intermetallic Layer ◽  
Functional Materials ◽  
X Ray Diffraction ◽  
Laminate Composites ◽  
Plasma Sintering ◽  
Metal Plates ◽  
Spark Plasma

Laminate composites with an intermetallic component are some of the most prospective constructional and functional materials. The basic formation method of such materials consists in heating a stack composed of metallic plates reacting at elevated temperatures to form intermetallic phases. The temperature of the process is usually approximately equal to a melting point of a more easily fusible component. In this study, an alternative technology of producing a titanium – titanium aluminide composite with a laminate structure is suggested. It consists in combining metallic (titanium and aluminum) powder mixtures pre-sintered at 400 оС with titanium plates, alternate stacking of these components and subsequent spark plasma sintering (SPS) of the fabricated workpieces. Applying this technology allowed for the fabrication of metal-intermetallic laminate (MIL) materials with an inhomogeneous structure of intermetallic interlayers. The phases revealed in the composite by X-Ray diffraction (XRD) were α-Ti, Al, Al3Ti and Al2Ti. Moreover, the results of the energy-dispersive analysis gave the evidence of the formation of Ti-enriched phases in powder layers after SPS. A small number of voids were observed between the structural components of the intermetallic layers. Voids were also detected at “metal-intermetallic” interfaces; however, the quality of connection between different layers in the composite was very high. The microhardness of an intermetallic layer formed in the composite was comparable to the microhardness of the Al3Ti compound. The microhardness of titanium was equal to 1600 MPa.

Enhancing Mechanical Properties of Various Sintered Pellets with Nano-Additives

2021 ◽  
Vol 410 ◽  
pp. 62-67
Author(s):  
Tien Hiep Nguyen ◽  
Yury V. Konyukhov ◽  
Van Minh Nguyen
Keyword(s):  
Mechanical Properties ◽  
Spark Plasma Sintering ◽  
Bending Strength ◽  
Size Range ◽  
Pressureless Sintering ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Nano Additives ◽  
Free Spaces ◽  
The Impact

The impact of Fe, Co, Ni nano-additives on the density, microhardness and bending strength was investigated for several sintered pellets. Fe, Co, Ni nanopowders (NP) were prepared in the size range 67-94 nm using chemical metallurgy techniques. These powders (0.5 wt. %) were dispersed into three sets of micron powders: Co (+0.5 wt. % Co NP); Fe (+0.5 wt. % Fe NP); Fe+0.5wt. % C (+0.5 wt. % Co and 0.5 wt. % Ni NP). Mixtures were further mixed and processed using a magnetic mill and a turbulent mixer. Sintering was carried out using spark plasma sintering (SPS) as well as pressureless sintering (PS). The densities of sintered pellets were found to increase by 2.5-3% (SPS) and 3-5% (PS) in the presence of nano-additives; corresponding increases in microhardness and bending strength were determined to be 7.9-11.1% and 17.9-38.7%, respectively. These results are discussed in terms enhanced packing due to interparticle sliding and the filling of free spaces with the nanodisperse phase.

scholarly journals Microstructure Evolution and Mechanical Properties of Spark Plasma Sintered Manganese Addition on Ti-48Al-2Cr-2Nb Alloys

Metals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1577
Author(s):  
A. Raja Annamalai ◽  
Muthe Srikanth ◽  
Raunak Varshney ◽  
Mehta Yash Ashokkumar ◽  
Swarup Kumar Patro ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Spark Plasma Sintering ◽  
Titanium Aluminide ◽  
Sem Analysis ◽  
Tensile Fracture ◽  
Nominal Composition ◽  
High Heating Rate ◽  
Main Task ◽  
Plasma Sintering ◽  
Spark Plasma

Titanium aluminide (TiAl) is one of the most promising materials for aerospace applications. It is a suitable replacement for nickel-based superalloys predominantly used in these applications. Titanium aluminide with superior processability is the main task in carrying out this work. A less brittle TiAl alloy was fabricated using spark plasma sintering by adding the nominal composition (2.5, 5, and 7.5 wt.%) of manganese (Mn) to Ti-48Al-2Cr-2Nb. The samples were sintered at 1150 °C using spark plasma sintering (SPS), which helped produce highly dense models with fine grain sizes at the high heating rate (here, 100 °C per minute). The effects produced by Mn additions on the densification, mechanical properties (yield strength, hardness, and % elongation), and microstructure of the Ti aluminide alloys are studied. Scanning electron microscopy (SEM) has been used to explore the sintered samples’ microstructures. The alloyed materials are entirely dissolved in the gamma matrix due to the manganese approaching its melting point. XRD and SEM analysis confirmed the new intermetallic related to Mn neither with titanium nor aluminum. The enhancement of % elongation at break is evident for the little improvement in the ductility of TiAl by the addition of Mn. The samples’ tensile fracture nature is also evidence for enhancement in the alloy’s % elongation.

Characteristic and Sinterability of Alumina-Zirconia-Yttria Nanoparticles Prepared by Different Chemical Methods

2014 ◽  
Vol 87 ◽  
pp. 30-35
Author(s):  
Janis Grabis ◽  
Dzidra Jankovica ◽  
Ints Steins ◽  
Krisjanis Smits ◽  
Inta Sipola
Keyword(s):  
Phase Transition ◽  
Spark Plasma Sintering ◽  
Molten Salts ◽  
Preparation Method ◽  
Bulk Materials ◽  
Chemical Methods ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact ◽  
Sintering Method

The characteristics and sinterability of the Al2O3-ZrO2(Y2O3) nanoparticles produced by simple and effective microwave and molten salts methods and processed by using spark plasma sintering were studied and compared. The crystalline powders with the specific surface area in the range of 72–108 m2/g and crystallite size of 5–13 nm were obtained by calcination of samples prepared by both methods at 800 °C. The content of t-ZrO2 phase depends on concentration of Al2O3, Y2O3 and on calcination temperature but the impact of the preparation method is insignificant. The phase transition of tetragonal ZrO2 to monoclinic for the samples without Y2O3 started at 1000 °C though it was incomplete in the case of high content of Al2O3. The bulk materials with relative density of 86.1–98.7% were fabricated by the spark plasma sintering method at 1500–1600 °C depending on the content of Al2O3 and Y2O3.

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