Key Engineering Materials Vol. 527

Abstract: In this paper, a new technique to produce cast iron tubes used for liners of auto engines has been developed and examined. The tubes with an outer diameter of 90 mm and a wall thickness of 14 mm were produced massively by horizontally continuous casting. There are the values of casting parameters and constructions of crystallizers recommended for the continuous casting process of cast iron tubes in our paper. The metallographic microstructure, chemical composition and the mechanical properties of the tubes were investigated. The results of our investigations were successfully used for producing cast iron tubes suitable for liners of auto engines.

Abstract: In this study, the wettability and interaction of TiB₂ with melted iron and iron-molybdenum alloys have been investigated. The wetting contact angles were determined, the structure and phase composition of the drops have been investigated by the methods of energy dispersive X-ray microanalysis. The results showed that TiB₂–(Fe-13%Mo) system prove to be an optimum one for the new cermets production because of good wetting and minimal interaction between components. The TiB₂-(Fe-13wt.%Mo) cermets were produced by sintering in vacuum. The influence of initial TiB₂ particles size on the structure formation of the cermets above has been established.

Abstract: Flexural strength (MOR) and Young’s modulus (YM) of Sedlec kaolin were measured using the three point-bending method and modulated force thermomechanical analysis (mf-TMA). Thermal analyses DTA, thermogravimetry and thermodilatometry (TDA). An escape of the physically bound water (20 – 250 °C) strengthens the sample and YM and MOR increase their values significantly. MOR and YM lower their values as dehydroxylation starts at 400 °C. Both quantities, MOR and YM, pass through minimum in the dehydroxylation region (400 – 650 °C). Their next increase is probably caused by the van der Waals forces acting between metakaolinite crystals and by the starting of the solid-state sintering. YM steeply increases above 950 °C as a consequence of the solid-state sintering. A Weibull’s modulus passes through the sharp maximum at the interval 300 – 400 °C.

Abstract: Inherently, zirconium carbide (ZrC) suffers from low fracture toughness (~3 MPa*m1/2) and excessive porosity when sintered in vacuum. One way to improve ZrC’s sinterability and fracture toughness is the addition of binder metal or other carbides to increase densification. Using mechanical activated synthesis (MAS) to homogenously mix ZrC and titanium carbide (TiC) powders, followed by sintering at 1900 °C, produces a ZrC-TiC composite with hardness and fracture toughness at 20 GPa & ~7 MPa*m1/2, respectively. 80ZrC-20TiC (wt%) gave the highest fracture toughness value compared to other ratios. Varying TiC ratio from 20 - 50 wt% does little to affect mechanical hardness or densification of the composite. However, fracture toughness appears to increase marginally with decreasing TiC concentration down to ~20 wt%.

Abstract: The objective of this work is to synthesize pure and Mg-substituted hydroxyapatite (HAp) powders with different MgO content in synthesis media (in the wide range of 0.1-10.0 wt% in respect to Ca), and to study the influence of Mg²⁺ ions substitution on the physicochemical properties of HAp materials. In this work HAp and magnesium-substituted hydroxyapatite (Mg-HAp) were synthesized by modified wet chemical precipitation of homogenous suspension of Mg(OH)₂/Ca(OH)₂ and H₃PO₄ solution. Systematic investigation on as-synthesized and sintered Mg-HAp and HAp samples shows that the incorporation of MgO promotes decomposition of HAp to β-tricalcium phosphate (β-TCP) and significantly modified its microstructure. The effect and evidence of incorporation of Mg²⁺ ions into HAp structure is discussed.

Abstract: TiN and TiN/TiB_{Subscript text}2 nanoparticles with crystallite size of TiN in the range of 27–38 nm and TiB_{Subscript text}2 in the range of 55–90 nm have been prepared by thermal plasma technique. The prepared nanoparticles and mechanical mixture of TiN with amorphous boron have been densified using spark plasma sintering and the microstructure and density of the samples were compared. The relative density of the samples with content of TiB_{Subscript text}2 about 36 wt.% is in the range of 95.9–97.1% in dependence on the precursors. The higher relative density of the samples provided reactive sintering of TiN/B powder. The grain size of the composites in the range of 0.5–3 µm testified that spark plasma sintering intensified the grain growth in despite of the short sintering time.

Abstract: This paper studies influence of the process temperature and time on the properties of the compacts made of Ag-SiO2 powder by the pulsed electric current sintering (PECS). Silica particles doped with Ag nanoparticles were prepared by modified Stöber method, and calcinated at 573 K in air resulting in average silica particle size of ~1.1 µm and agglomerate size up to 32 µm. There was about 7 wt.% of silver in the structure and the diameter of the silver particles on the silica carriers was 30 ±7 nm on average. The composite powder was sintered into porous compacts by PECS at 873, 973, 1073, or 1173 K for 10, 20, or 30 min under pressure of 50 MPa. Samples were characterized by SEM, XRD, UV-vis-spectrometer, and laser diffraction. During PECS compaction grain growth of silver particles was observed and the measured average size of Ag in 873 K and in 1173 K samples were 65 nm and 170 nm, respectively. The porosity of the materials did not show remarkable change, as the relative density ranged from 76 to 79 %. Thus, it is possible to produce porous silica based materials with controlled Ag-nanoparticle size by PECS. These materials may be optimized for, e.g., different kinds of antibacterial filters.

Abstract: Structure as well as mechanical and thermal properties of the nanocomposites based on recycled polyethylene terephthalate (RPET) are investigated. 1, 2 and 5 wt. % of unmodified montmorillonite nanoclay (MMT) were introduced in the RPET matrix by melt compounding in a twin screw extruder. Results of the investigations testify that optimum content of MMT for modification of RPET is between 1 and 2 wt. %. Up to this nanofiller weight content, the most rapid increase of stiffness, strength and impact toughness is observed. Besides it, at this nanofiller weight content the investigated composite have somewhat improved thermal resistance. It is demonstrated that the improvement of these properties is due to better distribution of MMT in the polymer matrix. At higher nanofiller content, the undesirable effects of the nanofiller agglomeration becomes more important.

Abstract: Different process methods and parameters together with different amount of additives were used to fabricate WC-Ni-ZrO2 hardmetals with mechanical properties aiming at improved performance under erosive wear. XRD observation showed the presence of tetragonal zirconia in the cermet matrix after processing. The best erosion resistance with erosion rate of about 0.7 mm3/kg was demonstrated by the specimen produced either by vacuum sintering or SPS and added by 0.2 wt% of free carbon. This cermet has also demonstrated the highest hardness of 17.7 GPa.