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Metakaolinite was obtained by thermal treatment of natural kaolinite. Both of them, kaolinite with structurally bonded water and metakaolinite without it, were, after sieving to acceptable size fraction, plasma sprayed. The coatings were rather lightweight and composed predominantly of amorphous material. Stainless steel was used for producing self standing deposits, whereas other materials like carbon steel or ceramic tiles formed a permanent substrate-coating system. Metakaolinite coating was less porous, harder and its thermal behavior was simpler compared to kaolinite. Crystallization and formation of secondary phases was monitored after annealing with and without dust particles known in the barrier coatings field as CMAS. Resumen: La metacaolinita se obtuvo por tratamiento térmico de caolinita natural. Ambos, caolinita con agua ligada estructuralmente y metacaolinita sin ella, después de tamizar a una fracción de tamaño aceptable, se proyectó mediante un plasma. Los revestimientos eran bastante porosos y estaban compuestos predominantemente de material amorfo. El acero inoxidable se usó para realizar depósitos independientes, mientras que otros materiales como el acero al carbono o las baldosas cerámicas formaron un sistema permanente de revestimiento de sustrato. El recubrimiento de metacaolinita fue menos poroso, más duro y su comportamiento térmico fue más simple en comparación con la caolinita. La cristalización y la formación de fases secundarias se controlaron después del recocido con y sin partículas de polvo conocidas en el campo de las barreras térmicas como CMAS.

Thanks to the low working temperature, less product size limitations and one order of magnitude higher deposition rates compared to the established additive manufacturing techniques, more attention has been brought to the potential of cold spraying for additive manufacturing . As a process dealing with deformation of solid particles possibly leaving non-bonded interfaces and causing work hardening, any optimization should (i) adjust spray parameters to obtain high performance as-sprayed parts and (ii) tune ductility and internal stresses by post-treatments. The present study first deals with strategies to optimize spray parameters for fabrication of high performance steel 316 L deposits. Next, the performances of deposits are further adjusted by various heat treatments. The structural strength of the freestanding samples before and after the heat treatments is evaluated under static and cyclic axial loading and supported by fatigue crack growth rate analysis. The results highlight the feasibility of obtaining high quality steel 316 L deposits using N2 as process gas, rather than the costly He that is commonly suggested. This study demonstrates the potential of cold spraying to be used for deposition of freeform structural components with a static strength comparable to that of bulk and laser-based additive manufactured materials and a fatigue strength similar to that of bulk cast material.

Alloying of Mg with rare-earth (RE) elements proved to be beneficial for their in-vitro and in-vivo performance. In this work, a novel WN43 (Mg-4 wt%Y-3 wt%Nd) alloy with a well-defined composition was prepared, where, unlike in the commercial WE43 alloy, the possibly harmful RE mischmetal was substituted by less toxic Nd. A modern spark plasma sintering (SPS) technique was used to effectively produce WN43 samples from atomized powders. Sintering temperatures of 400 °C – 550 °C and holding times of 3 or 10 min were used and well-compacted final materials were successfully prepared. It was shown that a superior combination of corrosion and mechanical properties was attained in the samples sintered at 500 °C and 550 °C, while the effect of sintering time was rather negligible. The performance of this material was exceptional within the group of Mg alloys prepared by powder metallurgy and comparable with conventionally prepared alloys. Moreover, it was shown that a great variety of mechanical and corrosion characteristics can be obtained by altering the SPS parameters so as to fulfill case-specific requirements typical of biomedical materials. Consequently, the novel WN43 alloy prepared by SPS seems to be a particularly suitable material for biomedical use.