Key Engineering Materials Vols. 592-593

Abstract: During the last decade the titanium alloys were extensively used in a variety of applications due to their good mechanical properties, high biocompatibility and corrosion resistance. β-type Ti alloys composed of Nb, Ta and Zr elements have received much attention, because they feature high specific strength, bio-corrosion resistance, no allergic problems and biocompatibility. A Ti-29Nb-9Ta-10Zr (wt.%) alloy was subjected to thermo-mechanical processing and testing. Two states were investigated: recrystallized and 80% cold-rolled. Data concerning phase structure and developed texture, expressed by Inverse Pole Figures (IPFs) and Orientation Distribution Functions (ODFs), was obtained and analyzed.

Abstract: In recent years a significant increase in new Ti-based biocompatible alloys (such as TiTaZr or TiTa-Nb-Zr) development was reported. Titanium and its alloys have been widely used in medicine since the 1960s because of their known biocompatibility, superior mechanical properties, low density and remarkable chemical stability. The present study investigates the microstructures and the mechanical properties of a Ti-29Nb-9Ta-10Zr (wt.%) alloys in order to investigate structural changes occurred during recrystallization treatment of 90% cold rolled Ti-29Nb-9Ta-10Zr (wt.%) alloy. The investigated alloy was fabricated by vacuum arc induction melting in levitation, using a FIVES CELES MP 25 furnace, starting from elemental components. Structural changes occurred during recrystallization treatment were investigated using X-ray diffraction, using a Philip PW 3710 diffractometer, in Bragg-Brentano θ-2θ geometry, with negligible instrumental broadening. Data concerning alloys component phases, average coherent crystallite size and internal average micro-strain was obtained.

Abstract: The purpose of this study is to insight more thoroughly into the structural properties of graphene oxide (GO) in particular of the type generated by Hummer's method in relation with graphite precursor originating from different sources. The systematic study using elemental analysis (EA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) was performed to reveal the changes of GO microstructure. The results revealed considerable influence of both the original graphite source and isolation procedure of GO by lyophilisation. Further, maintaining of GO in a form of aqueous colloidal dispersion is crucial for preservation of its unique properties. SEM results revealed the occurrence of associated GO blocks formed form identically oriented planes.

Abstract: The paper deals with a creation of computational model of a high porous ceramic material. This type of material has a large-scale industrial utilization. The computational model was created based on micro-CT data in the ANSYS 14.0 software using Finite Element Method. A creation of a porous ceramic struts model which respect a micro architecture is quite difficult (computer demanding and micro-CT data). The micro-CT slices are converted into a 3D model using image processing (used software STL Model Creator). The local first principle stress was analyzed because, ceramic is the brittle material. Furthermore, the influence of the thick layer around the individual struts was analyzed.

Abstract: Various bone cements with different compositions were prepared in several model configurations which differed in volume (i.e. setting temperature profile) and mode of mixing (manual and vacuum bowl). Local mechanical properties (nanohardness, elasticity modulus) of all experimental states were measured by nanoindentation technique and compared. Role of the preparation route as well as influence of composition, particularly of presence of antibiotics, on the measured properties was investigated.

Abstract: Effect of solute interaction on interfacial segregation and grain boundary cohesion is modeled on basis of combined Guttmann and Rice-Wang approaches in binary and ternary systems. It is shown that attractive II binary interaction strengthens interfacial segregation and enhances intergranular embrittlement while repulsion exhibits an opposite effects. In a ternary system the segregation is suppressed by the IJ attraction while increased by the repulsion. The effect of the binary interaction is generally stronger compared to the ternary one.

Abstract: Specimens of the common cast alloy Al-7Si-0.3Mg (A356) were solution heat treated at different temperatures and times to modify (i) the precipitation strengthening effect in the aluminum solid solution phase and (ii) to spheroidize the eutectic silicon. Just 15 minutes of solution heat treatment at a temperature of 540°C are sufficient to reach the desired effect. Cyclic loading experiments revealed an increase in fatigue life as compared to specimens heat treated at lower temperatures. In particular in the HCF regime, fatigue cracks that were originally initiated at pores follow crystallographic slip bands under shear control (mode II) as it was proven by automated EBSD (electron back scatter diffraction) measurements. The smoothly polished surface of the fatigue specimens was observed continuously by a long-distance microscope and discontinuously by SEM (scanning electron microscopy) to identify the fatigue crack propagation mechanisms. It was shown that da/dN decreases strongly when the crack tip interacts with the eutectic areas. Obviously, the blocking effect of the eutectic silicon particles makes the crack leaving the straight slip-band path.

Abstract: This study describes the principles of synthesis and technological features of composition ceramics formation on the basis of silicon carbide and aluminum nitride by hot-pressing. The structural properties and composition of the ceramics were investigated by scanning electron microscope and the formation of the solid solution is confirmed. The elements distribution on the surface of failure pattern is shown. The results of the study are useful for optimization of manufacturing process of structural and functional high-density ceramics.

Abstract: The fracture behaviour of long fibre reinforced composites is predetermined mainly by properties of fibre-matrix interface. The matrix prepared by pyrolysis of polysiloxane resin possesses ability to resist high temperatures without significant damage under oxidising atmosphere. The application is therefore limited by fibres and possible changes in the fibre matrix interface. The study of development of interface during high temperature exposition is the main aim of this contribution. Application of various techniques as FIB, GIS, TEM, XRD allowed to monitor microstructural changes in the interface of selected places without additional damage caused by preparation. Additionally, it was possible to obtain information about damage, the crack formation, caused by the heat treatment from the fracture mechanics point of view.

Abstract: The main aim of this contribution is the fracture behavior of layered ceramic composite with residual stresses. The influence of laminate composition on crack propagation (influence of material interfaces on crack shielding, effect of residual stresses, etc.) was investigated. The crack behavior was described by procedures based on linear elastic fracture mechanics (LEFM) and generalized LEFM. Computations were performed in 2D geometry under plain strain assumptions. For determination of the real crack front shape during the crack propagation the three dimensional FEM models were developed. Both (2D/3D) approaches were compared and differences were closely discussed. The influence of laminate composition with residual stresses on critical values for crack propagation through laminate interfaces was also determined. The results obtained can be used for a design of new layered composites with improved resistance against propagation of cracks.