Richard Sedlák

Local Mechanical Properties of SiC - TiNbC Composite and its Constituents

SiC based composite with 50 % of additives (Ti and NbC with ratio of 9:16) has been prepared. The microstructure, porosity, and chemical composition were studied using SEM equipped with EDS analyser. Local mechanical properties such a hardness and elastic modulus of individual components of the composite were investigated by nanoindentation using Berkovich indenter tip. Hardness and fracture toughness of studied material as a whole was evaluated by means of classic Vickers macroindentation. Indentation cracks were observed and their propagation was analyzed. It was shown that the present phases were distributed uniformly. Moreover, final density was satisfactory with porosity lower than 1 %. The individual constituents shown similar elasticity modulus (550 - 590 GPa). Hardness (HIT) exhibited very pronounced load-size effect. At 10 mN load, hardness was 42.33 GPa ± 1.1 GPa for SiC and 35.73 GPa ± 0.9 GPa for TiNbC, while at 500 mN the composite hardness was 27.61 GPa ± 0.505 GPa. It is in good agreement with macrohardness values, when 27.6 GPa and 25 GPa has been measured for 1 and 10 kg loads, respectively. Indentation fracture toughness was 3.3 MPa.m1/2 ± 0.22 MPa.m1/2. Electrical conductivity was measured by four point probes method and its value was 8.8×104 ± 0.3×104 Sm-1.

Comparative Study on the Microstructural and Mechanical Properties of WC-Co/AISI 1020 Steel Brazed Joint Obtained by TIG and Oxyacetylene Process

In this work, the microstructural evolution and the mechanical properties of WC-Co / AISI 1020 steel brazed joint obtained by oxyacetylene and Tungsten Inert Gas (TIG) brazing process are investigated. The maximum peak temperature induced by TIG process and the introduction of a shielding gas cause a remarkable diffusion of Co and rearrangement of WC particles along the interface with the filler alloy. The Energy Dispersive Spectroscopy (EDS) analysis reveals that the inter-diffusion activity of elements across the interfaces especially Co and Ni is more important using TIG process compared to oxyacetylene process The mechanical behavior is carried out through micro-hardness measurements and toughness tests using Vickers Indentation fracture method on the WC-Co along the parallel line of the interface with the filler alloy. The results show that the brazed joint issued from TIG process becomes increasingly hard and brittle when approaching the WC-Co/braze interface and loses its toughness (7 MPa/m1/2 compared to 15 MPA/m1/2 for oxyacetylene process) with increasing the brazing temperature.

Wear and Mechanical Properties of Various Bone Cements – Influence of Saline Environment

Several bone cements were prepared in two ways of mixing (manual and vacuum bowl). Wear behavior, friction coefficient were studied by ball on disc method. Nano-hardness and Young`s modulus was studied by instrumented indentation. Obtained results were summarized by taking into account their way preparation, antibiotics content and testing conditions. There was found no significant time dependence of saline acting on Young`s modulus and nano-hardness values. Friction coefficient in saline was less than half in compare to dry sliding conditions