Lenka Kvetková

Austenitic stainless steel strengthened by the in situ formation of oxide nanoinclusions

An austenitic stainless steel was prepared by laser melting. High resolution transmission electron microscopy with energy dispersive spectrometry confirmed the in situ formation of oxide nanoinclusions with average size less than 50 nm. Scanning electron microscopy examination revealed the homogeneous dispersion of the oxide nanoinclusions in the steel matrix. The tensile and yield strengths of the prepared specimens were 703 and 456 MPa respectively with high ductility which is significantly improved compared to its conventionally casted counterpart.

Mechanical and Tribological Properties of HiPIMS and HiTUS W-C Based Coatings

Several series of W-C based coatings were deposited by HiPIMS and HiTUS deposition technologies with different deposition parameters (power, frequency and pulse length in HiPIMS and pressure, acetylene content and RF bias in HiTUS). To investigate their effect on the hardness and tribological properties. The hardness of HiTUS coatings was up to 36 GPa and CoFs of these coatings were around 0.5, whereas the HiPIMS coatings exhibited lower hardness (18 – 20 GPa) but also lower CoFs (0.18 - 0.2).

FRACTURE MECHANISM IN Si3N4 – GRAPHENE PLATELETS COMPOSITES

Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPLs) as a filler. Two different sintering routes were applied which resulted in different microstructure: hot isostatic pressing (1700°C/3h/20 MPa) and gas pressure sintering (1700°C/0h/2 MPa). The influence of the GPLs addition and of processing routes on the fracture toughness and fracture mechanism of Si 3 N 4 +GPLs was investigated. The main toughening mechanisms, which originated from the presence of the graphene platelets are crack deflection, crack branching and crack bridging . These mechanisms are responsible for the increase of fracture toughness which is higher than that of monolithic Si 3 N 4 . The highest value of fracture toughness was obtained in the case of the composite processed by hot isostatic pressing using the GPLs with lowest dimension.