Key Engineering Materials Vol. 662

Abstract: Ongoing increase in demands on efficiency of power plants and other facilities leads to increased interest of new progressive materials and technologies. One of the modern methods which lead to enhancement of surface properties is application of coatings on surface of components composed of less quality materials. Commonly used methods protecting components are based on some form of heat treatment. The current pressure on increasing operating temperatures for enhanced performance of steam turbines caused elevation of operating temperature at limit of the applicability of commonly used protections. From this reasons the demand for using an alternative technologies which would provide such a desired protection rises rapidly. One of the key areas of protection in such environment is protection against hot temperature corrosion. Possible solution can be found in application of coatings based on alloys and cermets prepared by HVOF technology. This paper examines local mechanical and microstructural properties of NiCrBSi coating after exposition to extremely severe hot corrosion environment. Furthermore, the nanoindentation measurements of NiCrBSi coating were performed before and after the corrosion test. In this case the mixture of salts composed from 59% Na₂(SO)₄ with 34.5% KCl and 6.5% NaCl was used. Temperature of test was set on 525°C and 575°C. Duration of exposition to hot corrosion environment was 168 hours in autoclave.

Abstract: This paper deals with evaluation of mechanical properties of human trabeculae in the interconnection area. Local changes in the trabecular connections were evaluated using both quasi-static nanoindenation and modulus mapping technique. Connecting point of two trabeculae was revealed by precise grinding and polishing. A rectangular region in the interconnection was selected and inspected by modulus mapping procedure. Moreover several quasi-static indentation measurements using cube-corner indenter were performed along distinct lamellae. The obtained elastic properties were then compared with the values of the rod-like trabeculae. The comparison does not indicate significant differences in elastic properties between the trabecular rods and interconnections.

Abstract: The aim of this work is the description of microstructure and comparison of micromechanical properties of cylindrical shaped intraosseous parts of dental implants with plasma modified surface and with threaded modification. Differences in elastic parameters (such as reduced modulus (E_r) and hardness (H)) of investigated implants within the supporting part of the shaft and surface layer in two different directions (proximal and lateral) are compared using experimental method of nanoindentation. Machined implants of titanium alloys Ti6Al4V with plasma modified surface of sprayed titanium with hydroxyapatit (HA) Ca₁₀(PO₄)₆(OH)₂ from different batches of product were available for measurements. SEM element analysis revealed a heterogeneous structure and various concentrations of the essential chemical elements (C, O, P, Ca) on the surface of implants. Results of elastic moduli and hardness was monitored in different locations. On a large statistical set of measurements was indicated that average reduced modulus of implant shafts of titanium alloy is approximately 126 GPa. Differences of E_r in case of peripheral hydroxyapatite layer are in range of ~145 GPa – ~163 GPa according to the exact composition of surface modification in the individual batches of the product. The difference of measured values on individual samples in a proximal/lateral direction is approximately 10%.

Abstract: Bone implants in form of artificial scaffolds manufactured from poly-lactic acid (PLA) represent an attractive alternative to traditional surgical treatments of defective bones (i.e. autografts and allografts). In this work factors influencing biocompatibility and primary stability of implants manufactured from PLA using direct 3D printing were assessed using nanoindentation. For this reason bulk sample of the PLA material and a printed object were subjected to nanomechanical measurement. Quasi-static nanoindentation was employed to identify elastic modulus and hardness distribution on surface and within volume of the samples. Moreover mechanical properties along scanning direction and interlayer characteristics were also assessed. Gradients in mechanical properties have been identified within volume of the material, within the printing layers and at contact between individual layers.

Abstract: The study deals with the development of highly porous undegradable ceramics based on silicon nitride as potential replacement of trabecular bone. These materials were produced using replication method with polyurethane foams as pore-forming agents to achieve similar porous structure to trabecular bone. Prepared porous ceramics had a bimodal pore structure with macro-pores larger than 200 μm and micro-pores smaller than 1 μm in diameter, which are necessary for tissue ingrowths, cell adhesion, adsorption of biological metabolites and nutrition delivery in organism. The microstructure and local mechanical properties (Young’s modulus and Yield strength) were evaluated and compared with human trabecular bone. Results showed that studied porous materials have satisfactory porosity and pore sizes for trabecular bone replacement. Young’s modulus of bone was 12.6 ± 2.23 GPa and porous silicon nitride samples ranged from 10.9 ± 3.38 GPa to 12.9 ± 1.13 GPa. The values of Yield strength of trabecular bone was determined as 493 ± 30.7 MPa and the values of porous samples varied from 250 ± 19.3 MPa to 558 ± 36.5 MPa. Young’s modulus and Yield strength increase with increasing of the pre-sintering temperature and multiple infiltrations.

Abstract: 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

Abstract: The stress distribution in cortical bone and dental implant has been modeled by finite element method (FEM) using linear static analysis in the case of monocortical and bicortical fixation of a real dental implant for three cortical bone thicknesses: 2 mm, 2.5 mm, 4 mm. The analysis revealed that the highest stresses in the cortical bone and in the implant after three-axial loading are localized at the edge of the cortical bone near the implant neck where bending moment is the highest. An increase of the maximum stresses has been observed with the decrease of the intraosseal length of the implant and cortical bone thickness.

Abstract: Powders comprised of Fe particles and 25, 30, 35wt.% of Mn particles were mixed, compacted and sintered to investigate the effect of Mn on the properties of sintered Fe-Mn alloys. It was found that the sample’s swelling, microstructure and distribution of local hardness values were strongly affected by the Mn content. The particles in Fe-25Mn and Fe-30Mn samples exhibited a distinct onion-like structure causing a considerable variability in local properties, while the particles in Fe-35Mn samples were at a glance more homogeneous, with a large volume fraction occupied by a nearly uniform material with almost constant properties.

Abstract: This paper deals with the use of X-ray microtomography in evaluating the porosity of barrage lock concrete. The main parts of the lock were built in the years 1914-1917. Its high and low heads were founded on 2.70 m thick concrete slabs. Samples for laboratory tests were taken by core drilling at half of the slab thickness. The compressive strength of the concrete was determined and the porosity of the concrete was evaluated using X-ray microtomography. The compressive strength values ranged from 17.3 to 37.3 MPa. The porosity examination results are compared with the destructively determined concrete compressive strength values.

Abstract: The scratch resistance of the silicon nitride with the addition of 1 and 7 wt% of graphene multiplatelets prepared by hot press sintering has been studied. The scratch resistance behaviour of Si₃N₄-GNP composites were investigated using a Rockwell indenter for normal applied loads ranging from 1-150 N. Si₃N₄-7-wt%GNP composite behaved differently during the scratch test depending on the normal applied load. The coefficient of friction changed dramatically at higher load and extensive crack propagation resulting in the chipping is observed.