This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

http://www.eng.usf.edu/~volinsky/VolinskyActaMatReview2002.pdf

Interfacial toughness measurements for thin films on substrates

The confluence of two US energy policy mandates, the 2012 Corporate Average Fuel Economy Standards and Renewable Fuels Standard #2, provide the opportunity to examine the possibility of high-value materials from lignin with increased depth. In this case, the desire to provide lighter, low-cost materials for automobiles to reduce fuel consumption, and to improve the economics of biorefineries for fuel production, have led to an increased interest in low-cost carbon fiber manufacture from lignin. For this review the authors provide the context of subject matter importance, a cost comparison of potential low-cost carbon fibers, a brief review of historical work, a review of more recent work, and a limited technical discussion followed by recommendations for future directions. As the available material for review is limited, the author includes many references to publicly available government documents and reviewed proceedings that are generally difficult to locate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 713-728, 2013

https://onlinelibrary.wiley.com/doi/pdf/10.1002/app.39273

Recent advances in low‐cost carbon fiber manufacture from lignin

Modeling and experimental analyses were carried out to investigate current and temperature distributions under typical spark plasma sintering (SPS) conditions. The simulation utilized two sample materials with widely differing electrical conductivities, alumina and copper. Current and heat generation gradients were evaluated in the radial and axial directions for both cases. Radial gradients result in significant differences in temperature between the surface of the graphite die and its center, in agreement with experimental measurements. Axial gradients are shown to influence the homogeneity of the product.

Fundamental investigations on the spark plasma sintering/synthesis process: II. Modeling of current and temperature distributions

In this investigation an attempt has been made to understand the mechanism of friction stir weld formation and the role of friction stir welding tool in it. This has been done by understanding the material flow pattern in the weld produced in a special experiment, where the interaction of the friction stir welding tool with the base material is continuously increased. The results show that there are two different modes of material flow regimes involved in the friction stir weld formation; namely “pin-driven flow” and “shoulder-driven flow”. These material flow regimes merge together to form a defect-free weld. The etching contrast in these regimes gives rise to onion ring pattern in friction stir welds. In addition to that based on the material flow characteristics a mechanism of weld formation is proposed.

The role of friction stir welding tool on material flow and weld formation

In friction stir welding (FSW), a rotating threaded weld tool is inserted into a weld seam and literally stirs the edges of the seam together. To determine optimal processing parameters for producing a defect free weld, a physical understanding of the resulting metal deformation flow path is required. Marker studies are the principal method of studying the metal deformation flow path around the FSW weld tool. In our study, we have used a lead wire embedded in the weld seam as a tracer. At the welding temperature of aluminum, the lead becomes molten and is continuously carried with the macro-flow of the weld metal. A through thickness flow of metal was revealed in the X-ray imaging of the lead tracer in addition to revealing a cyclic oscillation in the plasticized metal affected by the process.

Interfacial sticking and slipping in the friction stir welding process

Compression pre-cracking to generate near threshold fatigue-crack-growth rates in two aluminum alloys

The more-stringent requirements for densification of new out-of-equilibrium powders have created a growing demand for nonconventional rapid sintering processes. Among those, field-assisted sintering techniques (FASTs) have seen a recent renewed interest motivated by their ability to consolidate a large variety of powder materials into high densities in short times. Characterization of a range of FAST-consolidated materials displayed relevant associated surface effects, such as grain boundary cleaning with direct grain-to-grain contact and advanced densification without sintering aids. These effects may be attributed to phenomena ranging from dielectric breakdown to a possible nonconventional plasma generation. Such surface effects provided a better intergranular bonding of powder particles during subsequent sintering

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400057678

Surface effects in field-assisted sintering

During friction stir welding (FSW) the material being joined is subjected to a thermal-mechanical process in which the temperature, strain and strain rates are not completely understood To produce a defect free weld, process parameters for the weld and tool pin design must be chosen carefully The ability to select the weld parameters based on the thermal processing requirements of the material, would allow optimization of mechanical properties in the weld region In this study, an attempt is made to correlate the microstructure with the variation in thermal history the material experiences during the FSW process

https://ntrs.nasa.gov/api/citations/20040034044/downloads/20040034044.pdf

Judy Schneider

Papers

Interfacial sticking and slipping in the friction stir welding process

Compression pre-cracking to generate near threshold fatigue-crack-growth rates in two aluminum alloys

Surface effects in field-assisted sintering

Tem Study of the Fsw Nugget in Aa2195-T81

Optimizing weld quality of a friction stir welded aluminum alloy