Challenges and Opportunities for Spark Plasma Sintering: A Key Technology for a New Generation of Materials

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A comparative study of spark plasma sintering and hybrid spark plasma sintering of W-4.9ni-2.1Fe heavy alloy

Abstract: Mixed 93W-4.9Ni-2.1Fe powders were sintered via the spark plasma sintering (SPS) and hybrid spark plasma sintering (HSPS) techniques with 30 mm and 60 mm samples in both conditions. After SPS and HSPS, the 30 mm and 60 mm alloys (except 60mm-SPS) had a relative density (>99.2%) close to the theoretical density. Phase, microstructure and mechanical properties evolution of W-Ni-Fe alloy during SPS and HSPS were studied. The microstructural evolution of the 60 mm alloys varied from the edge of the sample to the core of the sample. Results show that the grain size and the hardness vary considerable from the edge to the core of sintered sample of 60 mm sintered using conventional SPS compared to hybrid SPS. Similarly, the hardness also increased from the edge to the core. The 60 mm-HSPS alloy exhibit improved bending strength than the 60 mm-SPS, 1115 MPa and 920 MPa respectively, former being similar to the 30 mm-SPS and HSPS alloys. The intergranular fracture along the W/W grain boundary is the main fracture modes of W-Ni-Fe, however in the 60 mm-SPS alloy peeling of the grains was also observed which diminished the properties. The mechanical properties of SPS and HSPS 93W-4.9Ni-2.1Fe heavy alloys are dependent on the microstructural parameters such as tungsten grain size and overall homogeneity

Revisión: Métodos de densificación de materiales cerámicos

Ceramics has played an important role in the technological and socio-economic development of humanity, so that they can be used to identify different historical periods of the humanity. Babylonians, Greek, Andalusian, among other cultures have used the ceramics and developed several methods to improve the products obtained by pottery. Generally, the ceramics can be divided into two big areas, traditional and structural ceramics. Ceramics manufactured with clay, Traditional Ceramics, currently they are being studied in the improvement of structural, abrasives, cement, refractory, among other materials. On the other hand, the ceramics developed as a result of new technologies and the exploitation of natural resources, Structural Ceramics, they are a great interest for the science of ceramic materials due to the development of ceramics with properties that incorporate attributes of various materials in only one material, in addition to the contributing to the phenomenological study at a scientific level. Advances in the processes of densification and doping of these materials have allowed to obtain ceramics with high mechanical resistance, high hardness, high resistance to attrition and corrosion, good chemical and thermal stability; features that have directly influenced the type of applications such as bulletproof vests, transparent shields, high temperature electrical insulators, superconducting devices, electronic materials among other applicationsLas cerámicas han tenido un papel muy importante en el desarrollo tecnológico y socioeconómico de la humanidad, a tal punto que pueden ser utilizadas para identificar diferentes periodos históricos de la humanidad. Babilonios, griegos, andaluces, entre otras culturas han utilizado la cerámica y desarrollado diversos métodos para mejorar los productos obtenidos a partir de la alfarería. En general, las cerámicas pueden ser divididas en dos grandes áreas, cerámicas tradicionales y cerámicas estructurales. Las cerámicas fabricadas con arcillas, Cerámicas Tradicionales, actualmente son estudiadas en el mejoramiento de materiales estructurales, abrasivos, cementos, refractarios, entre otros. Por otro lado, las cerámicas desarrolladas como consecuencia de las nuevas tecnologías y la explotación de recursos naturales, Cerámicas Estructurales, son de gran interés para la ciencia de los materiales cerámicos debido al desarrollo de cerámicas con propiedades que logran incorporar atributos de diversos materiales en un único material, además de contribuir con el estudio fenomenológico a nivel científico. Avances en los procesos de densificación y dopaje de estos materiales han permitido obtener cerámicas con alta resistencia mecánica, alta dureza, elevada resistencia al desgaste y a la corrosión, buena estabilidad química y térmica; características que han influido directamente en el tipo de aplicaciones como: chalecos antibalas, blindajes transparentes, aislantes eléctricos de alta temperatura, dispositivos superconductores, materiales electrónicos entre otras aplicaciones. Para que las propiedades sean óptimas se manipula la microestructura del material por medio de los parámetros de densificación los cuales caracterizan cada uno de los métodos, densificación convencional, densificación por impulsos de plasma y densificación por prensado en caliente. Este trabajo pretende establecer una relación entre los diferentes métodos y la influencia de estos en los materiales cerámicos, resaltando semejanzas, eficiencia, vigencia, sus posibles y futuras aplicaciones, ventajas y desventajas de cada métod

Compaction of tool steels by pulsed electric current (PECS) sintering process

This study had two major purposes: the microstructural investigation of High Chromium White Iron (HCWI) sintered with Pulsed Electric Current Sintering (PECS) and the evaluation of the abrasion resistance of high chromium white iron mixed with different amounts of Hadfield Steel. The objective was to obtain dense high chromium white iron compacts with fine and uniform carbide and grain structure. The materials included in the study were gas atomized high chromium white iron (2.60 wt% C, 19.48 wt% Cr, 1.02 wt% Nb) and Hadfield steel (1.95 wt% C, 4.09 wt% Cr, 13.87 wt% Mn).The experimental procedure involved preparation and characterization of the starting powders, consolidation of the powders by pulsed electric current sintering process, and characterization of the resulting compacts. Microstructural studies were carried out to establish a relationship between processing conditions and the resulting microstructure. Abrasion testing was conducted (dry sand rubber wheel test) to investigate the effect of Hadfield additions to the wear performance of the material.The optimal sintering parameters for obtaining dense high chromium white iron included sintering the material at 1050 °C for 5 minutes, heating rate being 100 °C/min and compaction pressure 50 MPa. The resulting microstructure contained fine chromium carbides dispersed in a martensitic steel matrix. The modification of dwell time and the heating rate did not influence the microstructure to any significant degree. In the abrasion tests the high chromium white iron performed noticeably better (~20% lower weight loss) than the material mixed with Hadfield steel in the abrasion test. The performance of the Hadfield steel was only slightly worse (~7% higher wear loss) than that of the high chromium white iron

Understanding and utilization of thermal gradients in spark plasma sintering for graded microstructure and mechanical properties

2022 Summer.Includes bibliographical references.Spark plasma sintering (SPS), also commonly known as electric field assisted sintering, utilizes high density electric currents and pressure to achieve rapid heating and significantly shorter sintering times for consolidating metal and ceramic powders, which could otherwise be difficult, time consuming, and energy intensive. SPS has attracted extensive research interests since the early 1990's, with the promise of efficient manufacturing of refractory materials, ultrahigh temperature ceramics, nanostructured materials, functionally graded materials, and non-equilibrium materials. Thermal gradients occur in SPS tooling and the samples during sintering, which can be a drawback if homogeneous properties are desirable, as the temperature inhomogeneity can lead to large gradients in microstructure such as porosity, grain size, and phase distribution. Many researchers have looked to mitigate or control these gradients by design and use of specialized tooling. However, the effect of the starting powder is relatively less investigated or overlooked. Feedstock powders can come in various shapes, particle size distributions, and surface chemistry. Effects of these powder characteristics on the SPS process and the consequent microstructure of the sintered parts remain as a gap in the fundamental knowledge of SPS. To fill in this gap, my research investigated the role of thermal gradients during SPS, and how the thermal gradients subsequently affect the location-specific pore distribution, and the consequent mechanical properties of the materials. From a practical point of view, design and fabrication of a bulk sample with a fully dense surface and an engineered pore architecture in the sample interior via one-step SPS will enable mechanical properties unattainable via conventional processing of fully dense bulk materials, such as alike combination of lightweight, high surface hardness, and wear resistance, and high toughness. Therefore, the overarching goal of my research was to provide fundamental insights into the material processing - microstructure - properties correlation so that the field assisted sintering technology can be advanced to control location-specific microstructure. To fulfill this goal, two metallic materials were selected in my study, austenitic stainless steel and commercially pure titanium, representing inherently heavy but widely used alloys, and a pure metal that is inherently lightweight, these materials were used to investigate the effects of powder morphology on the sintering behavior. The pure Ti was selected specifically to gain fundamental insight into the effect of powder shape on sintering, while mitigating the concern of alloying/precipitation events and integrating FEM with my experimental work. This work identified a relationship between decreasing pore size and increasing yield strength in stainless steel, which was attributed to fine precipitate formation surrounding submicron pores inducing local stiffening. Whereas larger pores where precipitates were not found are concluded to not have the necessary driving force for the precipitation event to occur. Ball milled stainless steel powders with higher aspect ratios were also shown to have smaller porosity gradients in comparison to their spherical gas atomized counterparts. A thermal electric finite element model is also proposed which incorporates the master sintering curve to simulate densification as an alternative to the more computationally costly and difficult to parametrize fully coupled thermal-electric-mechanical finite element model. Results from the combined model indicate strong agreement with experimental results within 2% accuracy of measured densification. Additionally, the model predicts higher porosity gradients for gas atomized powders in comparison to ball milled powders which is experimentally verified

Sintering and Reactive Sintering by Spark Plasma Sintering (SPS)

A wide variety of technological applications, especially in electronics, requires high‐density nanostructured solids, consolidated by sintering from nanoparticles. A new sintering technique known as spark plasma sintering (SPS) appears as the only method to reach high densities while preserving the final grain size within the nanometric range, with the added advantage of carrying out the process at significantly lower temperatures and shorter times as compared with the classical processes. Recent studies have revealed that in many cases, SPS can also accomplish the solid‐state reaction to achieve the desired compound, leading to reactive SPS (RSPS). In this chapter, a review of RSPS is presented, focusing particularly on magnetic oxide materials as functional solids

Al-doped ZnO ceramic sputtering targets based on nanocrystalline powders produced by emulsion detonation synthesis – deposition and application as a transparent conductive oxide material

Transparent conducting oxides (TCOs) have been largely used in the optoelectronic industry due to their singular combination of low electrical resistivity and high optical transmittance. They are usually deposited by magnetron sputtering systems being applied in several devices, specifically thin film solar cells (TFSCs). Sputtering targets are crucial components of the sputtering process, with many of the sputtered films properties dependent on the targets characteristics. The present thesis focuses on the development of high quality conductive Al-doped ZnO (AZO) ceramic sputtering targets based on nanostructured powders produced by emulsion detonation synthesis method (EDSM), and their application as a TCO. In this sense, the influence of several processing parameters was investigated from the targets raw-materials synthesis to the application of sputtered films in optoelectronic devices. The optimized manufactured AZO targets present a final density above 99 % with controlled grain size, an homogeneous microstructure with a well dispersed ZnAl2O4 spinel phase, and electrical resistivities of ~4 × 10-4 Ωcm independently on the Al-doping level among 0.5 and 2.0 wt. % Al2O3. Sintering conditions proved to have a great influence on the properties of the targets and their performance as a sputtering target. It was demonstrated that both deposition process and final properties of the films are related with the targets characteristics, which in turn depends on the initial powder properties. In parallel, the influence of several deposition parameters in the film´s properties sputtered from these targets was investigated. The sputtered AZO TCOs showed electrical properties at room temperature that are superior to simple oxides and comparable to a reference TCO – indium tin oxide (ITO), namely low electrical resistivity of 5.45 × 10-4 Ωcm, high carrier mobility (29.4 cm2V-1s-1), and high charge carrier concentration (3.97 × 1020 cm-3), and also average transmittance in the visible region > 80 %. These superior properties allowed their successful application in different optoelectronic devices

Electron microscopy observation of electric field-assisted sintering of stainless steel nanoparticles

The intrinsic role of electrical current on the electric field-assisted sintering (EFAS) process of stainless steel 316L nanoparticles has been revealed by both ex situ and in situ experiments. A novel device on the Si chip has been designed and fabricated to fit into the sample holder of a transmission electron microscope for these experiments. The evolution of nanoparticle morphology and microstructures during the EFAS process has been studied using scanning electron microscopy and transmission electron microscopy, which has been combined with the simultaneous measurement of the electric voltage and current changes. A preliminary four-stage mechanism for the EFAS process of stainless steel 316L nanoparticles has been proposed based on these experimental investigations