Sintering Process Parameters Research Articles

Densification characteristics, microstructure and wear behaviour of spark plasma sintering processed titanium-niobium pentoxide (Ti-Nb2O5) based composites

The present study investigated the densification behavior, microstructure and wear properties of Ti-Nb2O5 based composites processed by spark plasma sintering (SPS). The SPS process was performed using sintering temperature of 1000 °C, holding time 10 min, heating rate 100 °C/min and applied pressure 50 MPa, as sintering process parameters. Optical and Scanning electron microscopy, X-Ray diffractometry, Relative density and hardness measurement, coefficient of friction and wear rate evaluation were used to characterize the composites produced. The CpTi and Ti-Nb2O5 composites attained full densification (relative densities ranged from 99.57 to 99.94%), and the total sintering times and densification stages were independent of the Nb2O5 reinforcement. However,the sinterability of the composites improved with increase in Nb2O5 content. The punch displacement curve of the Nb2O5 reinforced CpTi composite grades were higher compared to the CpTi. Also, the hardness values increased progressively with increase in Nb2O5 content. The microstructures that the addition of Nb2O5 resulted in structural transformation from lamellar (α) in the Cp Ti to bimodal (α + β) structures in the Ti-Nb2O5 composites accompanied with decrease in average grain size with increase in Nb2O5 content. The steady-state friction coefficients for all the composite samples ranged from 0.3 to 0.6. However, there was largely progressive increase in friction coefficient with Nb2O5 content. Generally, the wear resistance increased with increase in Nb2O5 content with the wear mechanism of the composites from wear track assessment, established to be mixed mode of adhesive and abrasive wear.

Parametric Optimization of ZrB2–SiC Composites Sintered Through Microwave Sintering Using Grey Relational Taguchi

Zirconium Diboride (ZrB2) is known as an ultra-high temperature ceramic with applications in various industries like refractory and foundry industries. In conjunction with Silicon Carbide (SiC), ZrB2ceramic finds extensive applications in the nose caps and leading edges of atmospheric re-entry vehicles and rocket propulsion. The primary objective is to optimize the output responses viz., Vickers micro hardness, relative density, compressive strength of ZrB2-30 vol.% SiC composites developed through microwave sintering. The three control factors viz., sintering temperature, heating rate and holding time are chosen as input process parameters for microwave sintering. Taguchi’s L9orthogonal array is used to obtain experimental runs. The Grey Relational Taguchi provides the optimal process parameters by binding the multiple responses (relative density, vickers micro-hardness, and compressive strength) into single comprehensive response [i.e., Grey Relational Grade (GRG)]. The results confirm that the optimal parameters attained using Grey Relational Taguchi maximize the performance characteristics of the microwave sintering process.

Mechanical and Microstructural Analysis of an Ultra-Flexible Nano-Silver Paste Sintered Joint

Soldering using common lead-free solder alloys is still one of the main die attach technology, in particular for applications in power electronics where high temperatures have to be met. However, some newly developed attach technologies promise to offer more interesting features in terms of both mechanical and thermal properties. Among these new methods, sintering of nano-silver particles allows to obtain a high thermal conductivity needed in the assemblies of electronic or optical components, as well as a relatively low elastic modulus for better stress accommodation and enhanced thermo-mechanical reliability. The sintering processing parameters, mainly the bonding pressure, the sintering temperature profile, and the sintering atmosphere, are known to have a critical effect on the properties of the sintered layer, such as its mechanical strength and electrical/thermal performances.In this study, copper substrates are fabricated and assembled by sintering using a nano-silver paste. The objective is to obtain a bonding joint with high mechanical flexbility, capable of addressing the thermomechanical stresses for systems operating under high temperatures. The measured mechanical properties of the sintered material show on the one hand low elastic modulus of the joint which is appropriate for strong difference in thermal expansion between components, and on the other hand sufficient mechanical strength for the assembly. Microstructure analyses reveal a highly porous silver network structure of the joint, with submicrometric silver grains and large micrometric porosities homogeneously distributed.

Polylactic acid/graphene nanocomposite consolidated by SPS technique

The consolidation of polylactic acid/graphene nanocomposite via a novel SPS powder metallurgy route was elaborated in this study. The nanocomposite powders were prepared using the three-dimensional (3-D) tubular mixer and consolidated under different parameters of spark plasma sintering (SPS). The densification, porosity, hardness, and crystalline properties of the consolidated specimen were investigated as a measure of its mechanical strength. These properties were observed to have an obvious dependence on the sintering process parameters. The fracture morphology of the sample reveals the ductile fractured at elevated sintering temperature of 160 °C while a fragile intergranular fracture type was revealed at a lower sintering temperature of 135 °C. SEM images revealed a well-distributed and dispersed GNP in the PLA matrix across the varied process parameters of temperature and pressure. The crystallinity of the nanocomposite peak was enhanced via the process engineering of SPS. This was observed with increased crystalline peaks on the XRD and percentage crystallinity reported on the DSC. Changes in the range of transmittance with respect to sintering parameters were observed on the FTIR. The thermal stability improves with respect to the sintering temperature and pressure within the range of the parameters reported. This reveals a better mass barrier effect of the nanocomposite due to better intermolecular diffusion and reduced pore spaces in the sintered samples. The thermal stability was observed to appreciate due to the better polymer nanoparticle interaction. Hence, this study further attests that aside from the use of nucleation agents such as GNP and plasticisation, process engineering of SPS could help in modifying desired properties of nanocomposite.

Real-time process control of powder bed fusion by monitoring dynamic temperature field

This study aims to optimize the uniformity of the temperature field during sintering to improve part performance. A temperature-field monitoring system is established based on an infrared thermal imager and the temperature field data obtained during the sintering of a part can be measured in real time. The relationship among the sintering temperature field, sintering process parameters, and part performance is established experimentally. Subsequently, a temperature field monitoring and analysis system is constructed, and various sintering temperature-field control strategies are established for various part sizes. Finally, a dynamic control strategy for controlling the temperature field during sintering is proposed, experimentally validated, and fully integrated into a developed powder bed fusion (PBF) equipment. For eight-shaped standard parts, the range of sintering temperature field is optimized from 44.1 °C to 19.7 °C, whereas the tensile strength of the parts increased by 15.4%. For large-size H parts, localized over burning is eliminated and the final quality of the part is optimized. This strategy is critical for the optimization of the PBF process for large-sized parts, in particular in the large-sized die manufacturing industry, which offers promise in the optimization of part performance.

Transfer learning aid the prediction of sintering densification

In powder metallurgy engineering, the master sintering curve (MSC) is crucial for estimating the mechanical properties of sintered products and optimizing sintering process parameters. A rapid evaluation method, that is, a domain-adversarial neural network, is established in the field of sintering to transfer learning from Al2O3 to SiC, concerning the effect of the heating rate on the sintering densification, in which one material (e.g. SiC) lacks an MSC and the material (e.g. Al2O3) has an overabundance of MSCs. In the unsupervised mode, we can roughly predict the densification evolution of SiC based on the MSC data of Al2O3. In the semi-supervised mode, prediction accuracy gradually increases with the increase of Al2O3 data and approaches a certain upper limit. Compared with the traditional sintering density prediction models, the proposed approach can provide an effective and rapid solution to the problem of data scarcity in the sintering field.

Multi-scale Analysis and Phase Segmentation of FIB and X-ray Tomographic Data of Electrolyzer Electrodes Using Machine Learning Algorithms

An efficient conversion of electrical energy into hydrogen could be one of the most important key issues for future green energy supply. In case of electrolyzer cells, this can be achieved by increasing the active surface of Ni-based electrodes. This is a crucial topic for the research of alkaline electrolyzer cells in terms of improving the cell performance. Typical coating processes are scalable and effective techniques that are well suited for this purpose. Variations of sintering process parameters (i.e. duration or temperature ramps) have a distinct impact on the homogeneity of the coating layer and its thickness as well as on possible media transport paths during cell operation. In this study, we analyzed the impact of the coating layers on the structure and morphology of the electrodes using laboratory X-ray computer tomography. We introduce a workflow that is based on machine learning algorithms which enable to distinguish between substrate and coating layers. More detailed information was obtained using FIB/SEM (focused ion beam/scanning electron microscopy). This multi-scale approach enhances the understanding of the sintering processes and serve as a basis for CFD simulations.

Influence of selective laser sintering process parameters on microstructure and physicochemical properties of poly(vinyl alcohol) for the production of scaffolds

Purpose This study aims to investigate the production of scaffolds by selective laser sintering (SLS) using poly(vinyl alcohol) (PVA) polymer, for in vitro studies, a relatively new and growing area in which scaffolds could be used in the design of three-dimensional models for in vitro disease model or tissue equivalent for safety and effectiveness tests. Design/methodology/approach The influence of the SLS process parameters laser power, 26 W and 32 W, and number of laser scans, 1, 2, 4 and 6, on the surface microstructure of the samples and on the degree of crystallinity and chemical stability of PVA material, was investigated using powder with particle size of 20-320 µm. Laser sintered PVA samples were subjected to cell culture tests using osteoblastic cells derived from human osteosarcoma (SaOs-2). Findings The laser power has no significant influence on the microstructure of the laser-sintered samples, however the number of scans has a considerable influence on the sintering degree; the SLS process causes a decrease in the degree of crystallinity and changes the chemical structure of the as-received PVA, especially when using higher laser power and more number of scans. Preliminary in vitro cell culture tests show that the laser-sintered PVA material is biocompatible with SaOs-2 cells. Originality/value SLS offers good potential for the fabrication of scaffolds and thus, may be applied as an alternative to conventional scaffold fabrication processes to overcome their limitations.

Effects of various processing parameters on the mechanical properties of sisal fiber/PES composites produced via selective laser sintering

A new type of sustainable material, i.e., a sisal fiber/poly-ether sulfone composite (SFPC), which is energy-efficient, environmentally friendly, and has a low cost, was developed for laser sintering additive manufacturing. This study was performed to explore the effects of the processing parameters on the SFPC composite parts produced via selective laser sintering (SLS). The effects of the laser sintering processing parameters, i.e., the preheating temperature, laser power, and scan speed, were studied. Bending and tensile testing of the SFPC specimens was successfully performed via SLS. The effect of the processing parameters on the SLS in terms of the mechanical strength of the laser-sintered parts was investigated. The results determined that the processing parameters had a significant effect on the mechanical strength of the sintered SFPC parts. When the preheating temperature and laser power were increased in the processing SLS system, the mechanical strength of the sintered SFPC parts was significantly increased. However, the scanning speed had an inverse proportional relationship to the mechanical strength of the SFPC SLS parts.

Low-temperature sintering of silver patterns on polyimide substrate printed with particle-free ink

In this study, a transparent particle-free reactive silver ink was used to fabricate conductive patterns on a flexible substrate. Thermal annealing and plasma irradiation at low temperature were utilized to improve the conductivity of the as-printed patterns. The effects of sintering process parameters on the microstructure and resistivity of the patterns were investigated. Under the optimized processing conditions, the resistivity of the pattern reached 1.2 × 10 −7 Ω · m by thermal sintering, while it was 8 × 10 −8 Ω · m after plasma sintering. Combined with these two sintering techniques, the resistivity was reduced to 6 × 10–8 Ω · m, close to that of bulk silver. This work provides an alternative solution for the fabrication of highly conductive feature patterns on common flexible substrates.

Quality Estimation for the Iron Ore Sinter Obtained via Separate Blend Preparation

This paper reveals that obtaining high-quality sinter, improved or stabilized by its size and strength, is a challenge to be solved by embracing both the formation of sinter with the strong structure and the optimal mineralogical composition of its bonds during the preparation of the sintering blend. The existing technological schemes of iron ore sintering do not allow producing the sinter where the amounts of fines with 0-0.5 mm of fraction would be less than the typical amounts of 8.1-20.4%. Therefore, the study to establish how the blend preparation with the preliminary made composites affects the parameters of iron ore sintering process and the quality of the resulting sinter has been carried out. It has determined that the use of separate pre-granulation has commonly positive effects on the process of blend preparation, namely it significantly decreases the amount of non-granulated fraction of 0-1 mm and increases the equivalent diameter of the granules, reduces the standard deviation and variation coefficient, indicating the more homogeneous granulometric composition of raw granules.

Development and microstructural analysis of beta-SiAlONs produced by spark plasma sintering

The development of refractory material (β-SiAlON) with excellent properties, such as good mechanical integrity and wear resistance is vital in order to ensure that the product will perform satisfactorily in service. In this study, ceramic powders, namely: β-Si3N4, AlN, Al2O3 and Y2O3 were sintered by using the spark plasma sintering technique, for the production of β-SiAlON. The Scanning Electron Microscopy (SEM) analysis of the β-SiAlON produced was carried out in order to evaluate the densification of the samples developed. The physical experiments were conducted using feasible combinations of the process parameters for the production of the β-SiAlON namely; the temperature, holding time, heating rate and z-value. The results obtained indicated that the sintering process parameters are critical parameters which influences the production and morphology of the β-SiAlON, hence the need for adequate process control. The optimum values of the process conditions which produced the least porosity were found to be temperature (1600 °C), holding time (5 min), heating rate (75 °C/min) and z-value (1.5). The SEM results also show the evidence of increasing densified samples with increase in the temperature, heating rate and z-value up to the optimum with significant evidence of porosity below or above these values. This work will assist material developers using the SPS technique in their quest for process control and efficiency.

Microstructure-oxidation resistance relationship in Ti3AlC2 MAX phase

Spark Plasma Sintering and Hot Isostatic Pressing were used to synthesize coarse-grained and fine-grained Ti3AlC2 specimens. Moreover, Spark Plasma Sintering processing parameters were modified in order to vary the TiC, Al2O3 and TixAly impurity and the porosity contents in the fine-grained samples. The influence of the Ti3AlC2 microstructure on the oxidation resistance was assesed. It is demonstrated that the grain size can drastically modify the oxidation resistance. The higher density of grain boundaries, in fine-grained specimens, increases the number of Al diffusion paths and leads to the formation of a protective alumina scale. In coarse-grained sample, Al diffusion is the rate limiting step of the α−Al2O3 formation and TiO2 is formed simultaneously to alumina. TiC impurities and porosity are demonstrated to be detrimental to the oxidation resistance in the 800 °C–1000 °C temperature range by favouring TiO2 formation. Finally, it is also shown that, for fine-grained specimens, the oxide scale grows very slowly for oxidation times in the range 20–40 days.

Emerging trend in manufacturing of 3D biomedical components using selective laser sintering: A review

Additive manufacturing (also known as 3D printing) process is an emerging technique for the fabrication of biomedical components. Selective laser sintering or melting is one of the widely used additive printing technology for manufacturing of metallic and non-metallic components used in the industry. This review paper presents, a summary of the published research papers on the fabrication of biomedical components using selective laser sintering technique. Therefore, author meticulously attempted to investigate individual biocompatible material-wise review which includes Ti6Al4V, Ti-7.5 Mo alloy, β-Ti35Zr28Nb, PEEK, PA2200, and Polyamide/Hydroxyapatite. In addition, this article also explores the effects of the various laser sintering process parameters such as laser power, scanning speed, density of the material on the mechanical properties, tribological properties, porosity and surface roughness of the fabricated alloy. Moreover, the author also investigated challenges and future prospective of the laser processing of biomedical implants.

The Impact of Sintering Process Parameters on Density of Parts Produced by Metal Injection Moulding (MIM)

The Impact of Sintering Process Parameters on Density of Parts Produced by Metal Injection Moulding (MIM)

The preparation and mechanical properties of nano-magnesium alloy bulks

In this paper, nanocrystalline (nc) AZ91 magnesium alloy bulks, with average grain sizes of ∼15 nm, were processed via the combined processing of hydrogenation-disproportionation-desorption-recombination (HDDR), spark plasma sintering (SPS) and hot extrusion. The effects of different sintering temperatures and holding times on the sintering properties of magnesium alloy were analyzed and the optimum SPS sintering process parameters of nanocrystalline AZ91 powder were determined. The tensile strength of nc AZ91 magnesium alloy rods is up to 267 MPa at room temperature. Meanwhile, when the grain size is less than 20 nm the particular mechanical behavior of nc magnesium alloy emerged, which implies an inverse Hall-Petch relationship.

Preparation of porous silicon nitride ceramics by microwave sintering and its performance evaluation

In this paper, the preparation methods of porous silicon nitride materials with controllable dielectric constant and pore structure were systematically studied. By using microwave sintering technology, porous silicon nitride materials with high closed pore ratio were prepared by adjusting the content of sintering additives and sintering process parameters, and controlling the grain boundary phase and pore structure and size. The effects of sintering conditions on the total porosity, closed porosity, pore structure and dielectric properties of materials were systematically studied.

Optimization of spark plasma sintering parameters of inconel 738LC alloy using response surface methodology (RSM)

The quality and properties of a material can be improved by the choice of processing technique adopted. This study investigates the influence of process parameters of spark plasma sintering (SPS) method on the densification and microhardness properties of IN738LC superalloy. In order to reduce the numbers of experiments and eliminate trial by error approach, design of experiment (DOE) approach was adopted. This involved the use of response surface methodology and central composite design (CCD) with temperature and pressure as the SPS experimental variables. Analysis of the variance (ANOVA) was studied to validate the developed model, coupled with understanding the influence of individual variable and their combined interaction on the output (responses). In this case, the responses were the density and the hardness properties. The data obtained from the numerically predicted values and the physical experiment was statistically examined to obtain a predictive model which harmonizes the density and the hardness as a function of the independent operation parameters. Empirical models were developed for the responses and fifteen solution runs was processed to establish whose response desirability is closest to 1. It was observed that SPS processing temperature (variable) have a major effect on the responses and the most desired temperature is 1200 °C at 50 MPa pressure. Under this condition, the hardness is 362.028 HV and the corresponding percentage relative density id 98.457% (7.772 g/cm3). The theoretical density is given as 7.894 g/cm3.

Experimental evaluation of the usage of residues for sintermaking

The shifts in quality of global reserves of iron ore, as well as the progressive advances in environmental legislations, are tendencies that have motivated researches on the usage of iron and carbon-bearing residues in the production of sinter for blast furnace ironmaking. These residues, however, are commonly limited in use due to their physical (particle size distribution) and chemical (heavy metals, alkali and zinc contents) properties as compared to sinter feed. In that sense, it is necessary to verify the impact of these materials on sinter quality and on sintering process parameters. In order to assess the recycling potential of residues via sintermaking, mixtures with increasing proportions (4.5–50%) of iron and steelmaking residues were prepared and tested in controlled laboratory conditions representing those of the sintering machine. The effect of residues on sinter mineral phases and chemical quality was evaluated and showed few differences in sinter quality for a mixture resulting from recycling 100% of a plant’s residue generation (4.5% of the mix). The greatest impact was an increased presence of wustite in the produced sinter, beyond 25% of residues in the mixture. The results indicated that there are opportunities, in the industry, for increasing the recycling of residues via sintermaking.

The microstructures and mechanical properties of graphene-reinforced titanium matrix composites

This study uses spark plasma sintering (SPS) to prepare graphene nanoplatelet (GNP)-reinforced titanium matrix composite materials. Heat treatment is used during rolling and annealing (R&A) to enhance the interfacial bonding strength between the graphene and titanium crystal grains, uniformly disperse the graphene and refine the grains. Studies have shown that the relative density (RD) of composites increased from 84% to 98% as the processing temperature increased from 600 °C to 1100 °C. Under the optimized plasma sintering process parameters, the best solid-phase reaction temperature is 850 °C, and the tensile strength at room temperature after R&A can reach 1206 MPa for 0.3 wt% GNP titanium matrix composites; this result represents an increase of 46% compared with pure titanium (PTi) under the same conditions. The reduction of area (ψ) of the 0.3 wt% GNP titanium matrix composite can reach 48%. The strengthening mechanisms include composite, grain and second-phase strengthening, wherein composite strengthening is the controlling factor. Additionally, the strength of composites at 1100 °C also increases, but ψ remains a lower level. The formation of nanocarbide particle layers causes a significant reduction in ψ.