Volume 19 (2019): Issue 1 (September 2019)

The tetracalcium phosphate/nanomonetite (TTCPMH) biocements with the addition of sodium alginate were prepared by mechanical homogenization of powder mixture with hardening liquid containing sodium alginate. The effect of various viscosity of different alginates on properties of TTCPMH cement mixture was investigated. The medium viscous (MED) alginate had a more negative effect on setting process and compressive strength than low viscous (LOW) alginate. An approx. 50% decrease in mechanical properties (compressive strengths, Young´s modulus, work of fracture (WOF)) was revealed after an addition of 0.25 wt % with rapid fall above 1 wt % of LOW alginate in biocement. A statistically significant difference in the WOF was found between of 0.25 and 0.5 LOW alginate biocements (p<0.035) whereas no statistical differences were revealed between WOF of 0.5 and 1 LOW alginate biocements (p˃0.357). In the microstructure of composite cements, the increased amounts of granular or finer needle-like nanohydroxyapatite particles arranged into the form of more separated spherical agglomerates were observed. A low cytotoxicity of cement extracts based on measurement of cell proliferation was revealed.

Sintering of Cr-prealloyed PM steels requires atmospheres with good quality – low oxygen potential – to achieve satisfactory sintering results. But during heating even the best atmospheres may be oxidizing, the system turns to reducing conditions only at high temperatures, which can be monitored by thermal analysis. During the dewaxing process, oxidizing conditions are favourable for effective dewaxing without sooting and blistering. However, this may result in some oxygen pickup during heating, and then the final properties of the produced parts may be strongly influenced by this intermediate oxidation. This study demonstrates the behaviour of artificially oxidized steels (Fe-C and Fe3Cr-0.5Mo-C) during the sintering process by stepwise sintering. Iron and steel powder were slightly oxidized and then pressed and sintered at different temperatures. In parallel, as a second approach, pressed samples were oxidized and then sintered. Density, hardness and impact energy were measured and dilatometry/MS was used for online monitoring of the sintering process. The starting oxygen content of 0.20 to 0.30 wt% is high enough to change the sintering behaviour of the materials, but still leads to rather good properties. Thermal analysis showed that most of the oxygen picked up was present as iron oxides on the surface which were reduced by hydrogen at rather low temperatures, confirming that these were iron oxides, which also holds for the Cr-prealloyed variant. The biggest influence on the final performance was exerted by the final carbon content and the microstructural development of the material.

The effect of binder content and WC grain size on the mechanical properties is widely investigated in literature. An increase in binder amount and WC grain size leads to a decrease in hardness and an increase in fracture toughness. Actually, these correlations are related to the influence of binder content and WC grain size through the contiguity and mean binder free path, which are the microstructural parameters that affect the mechanical properties. The aim of this study is to verify the dependence of the two microstructural parameters that govern the WCCo mechanical behaviour, namely the contiguity and mean binder free path, on the mechanical properties of an extended range of WC-Co samples, which differ in terms of Co content and tungsten carbide grain size.

Neodymium niobate NdNbO4 (NNO) and tantalate NdTaO4 (NTO) thin films (~100 nm) were prepared by sol-gel/spin-coating process on Pb(Zr0.52Ti0.48)O3/Al2O3 substrates with annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The XRD results of NNO and NTO films confirmed tetragonal T-NdNbO4 and T-NdTaO4 phases, respectively, with traces of monoclinic MNdNbO4 and M´-NdTaO4. The surface morphology and topography were investigated by SEM and AFM analysis. NTO was smoother with roughness 5.24 nm in comparison with NNO (6.95 nm). In the microstructure of NNO, small spherical (~ 20-50 nm) T-NdNbO4 and larger needle-like particles (~100 nm) of M-NdNbO4 phase were observed. The compact clusters composed of fine spherical T-NdTaO4 particles (~ 50 nm) and cuboidal M´-NdTaO4 particles (~ 100 nm) were found in NTO. The results of this work can contribute to formation of different polymorphs of films for the application in environmental electrolytic thin film devices.

The influence of die wall lubrication during warm die compaction on densification, microstructure and mechanical properties of three low alloy ferrous powders was investigated. Specimens were sintered at 1250°C. Die wall lubrication leads to higher green and sintered density and enhances the dimensional stability. It does not affect the microstructure of the matrix, while pores are smaller and more rounded than in bulk lubricated specimens. In TRS tests, both strength and deformation are higher in die wall lubricated specimens than bulk lubricated ones.