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A Comparative Study of the Feasibility of Cellular MAX Phase Preforms Formation by Microwave-Assisted SHS and SPS Techniques

Dmitruk A., Lagos M., Naplocha K., Egizabal P.

Archives of Metallurgy and Materials

2020

Vol. 65, iss. 2

575--582

Two methods were evaluated in terms of manufacturing of MAX phase preforms characterized with open porosity: microwave-assisted self-propagating high-temperature synthesis (SHS) and spark plasma sintering (SPS). The main purpose of fabrication of such open-porous preforms is that they can be successfully applied as a reinforcement in metal matrix composite (MMC) materials. In order to simulate the most similar conditions to microwave-assisted SHS, the sintering time of SPS was significantly reduced and the pressure was maintained at a minimum value. The chosen approach allows these two methods to be compared in terms of structure homogeneity, complete reactive charge conversion and energy effectivity. Study was performed in Ti-Al-C system, in which the samples were compacted from elemental powders of Ti, Al, C in molar ratio of 2:1:1. Manufactured materials after syntheses were subjected to SEM, XRD and STEM analyses in order to investigate their microstructures and chemical compositions. As was concluded, only microwave-assisted SHS synthesis allows the creation of MAX phases in the studied system. SPS technique led only to the formation of intermetallic secondary phases. The fabrication of MAX phases’ foams by microwave-assisted SHS presents some interesting advantages compared to conventional manufacturing methods. This work presents the characterization of foams obtained by microwave-assisted SHS comparing the results with materials produced by SPS. The analysis of SPS products for different sintering temperatures provided the better insight into the synthesis of MAX phases, supporting the established mechanism. Dissimilarities in the heating mechanisms that lead to the differing synthesis products were also discussed.

Microwave assisted self-propagating high-temperature synthesis of Ti3SiC2 MAX phase

Dmitruk A., Naplocha K., Lagos M., Egizabal P., Grzęda J.

Composites Theory and Practice

2018

R. 18, nr 4

241--244

A method was developed to manufacture Ti3SiC2 MAX phase preforms characterized by open porosity. Samples compacted from elemental powders of Ti, SiC and C with the molar ratio of 3:1.2:1 were heated and synthesized in a microwave field under atmospheric pressure. As this particular composition of elements exhibits rather low reactivity, it was necessary to apply the “coupled” mode of the SHS method. The initiated synthesis first proceeded with the formation of Si-Ti intermetallic and TiC precipitates, whose highly exothermic reactions resulted in a significant increase in temperature to ca. 1800°C. Next, these phases were almost completely transformed into a plate-like Ti3SiC2 MAX phase forming the porous structure of the samples. Although the majority of the synthesized material consisted of Ti3SiC2, some inclusions such as TiSi2, TiC and SiC were also found and identified in the material by the means of scanning electron microscopy and XRD analysis. The manufactured preforms can be used for components working in extreme conditions (heat exchangers, catalyst substrates, filters) or as a reinforcement for composite materials.

Opracowano metodę wytwarzania preform fazy Ti3SiC2 typu MAX o porowatości otwartej. Sprasowane z proszków elementarnych Ti, SiC i C w stosunku molowym 3:1.2:1 próbki ogrzewano i syntetyzowano w polu mikrofalowym pod ciśnieniem atmosferycznym. Ponieważ ta szczególna kompozycja pierwiastków wykazuje relatywnie niską reaktywność, konieczne było zastosowanie "sprzężonego" trybu metody SHS. Po inicjacji syntezy jako pierwsze wytworzone zostają fazy: Si-Ti i TiC, pomiędzy którymi zachodzą wysoce egzotermiczne reakcje powodujące gwałtowny wzrost temperatury do ok. 1800°C. Następnie fazy te są niemal całkowicie przekształcane w płytkowe wydzielenia fazy Ti3SiC2 typu MAX, formując jednocześnie porowatą strukturę kształtek. Pomimo faktu, iż w przeważającej część otrzymany materiał stanowiło Ti3SiC2, znaleziono w nim również niewielkie ilości wtrąceń, które za pomocą skaningowej mikroskopii elektronowej (SEM) oraz analizy składu chemicznego metodą dyfrakcji rentgenowskiej (XRD) zidentyfikowano jako TiSi2, TiC i SiC. Wytworzone preformy mogą znaleźć zastosowanie w budowie elementów pracujących w ekstremalnych warunkach (wymienniki ciepła, katalizatory, filtry) lub jako wzmocnienia materiałów kompozytowych.