Key Engineering Materials Vol. 586

Abstract: The investigations of the failure characteristics of Fe76Ni2Si9B13 bulk amorphous alloys prepared by shock wave consolidation of powders were performed. The strength decreased with the lowering temperature from 300 to 4.2 K. For this temperature interval, the brittle failure prevails. The failure propagates across particles as well as along particle boundaries. The riverlike pattern with fine dimples was observed on the fracture surface. The apparent surface energy and the fracture toughness values estimated by means of the fractography were similar to these for typical brittle materials.

Abstract: Globe valves have widespread application in various industrial sectors. Due to this variety, valve is subjected to different working loads (static, dynamic, thermal etc.) that can cause valve failures. In this paper, the analysis is performed on globe valve subjected to external axial loading caused by pipeline dilatations. Experimental analysis was focused on determining local mechanical properties of critical areas, i.e. on local areas of globe valve housing with high geometrical discontinuities. Experimental analysis and numerical model verification were performed using system Aramis based on Digital Image Correlation method. Using full-field experimental results, numerical model behavior was improved and enabled acquiring more accurate results in transition areas that cannot be found in currently available literature. Determining local mechanical properties of critical areas enables better understanding of complex structures such as valve housing and provides an opportunity for further development and improvement for practical industrial application.

Abstract: The polymer additional cross-linking influences the surface nano and micro layers in the way comparable to metals during the thermal and chemical-thermal treatments (e.g. surface hardening, cementation). Our research confirms the comparable properties of surface irradiated polyamide 6 (PA6) with high performance polymers. The surface layer of polymer material such as polyamide 6 is modified by β – radiation. Material properties of the surface layer created are measured by microhardness test using the DSI method (Depth Sensing Indentation). The influence of irradiation dose on mechanical properties (materials parameter) of PA6 is a subject of this research.

Abstract: The subject of the article is focused on the refining of the cast structure of gamma TiAl–2Nb alloy using cyclic heat treatment and on the analysis of the grain refining mechanism. Microstructure evolution after applied cycles of heat treatment was characterized using light, laser and electron microscopy and using microhardness tests. Application of five heat treatment cycles during which two phase transformations (eutectoid and alfa-recrystallization reactions) repeatedly took place resulted αin refining of the cast columnar structure. The mean grain-lamellar colony size 0.512 mm was transformed to fully lamellar structure containing gamma and alfa2 phases having the mean grain size 0.229 mm. Lamellae thickness of gamma was not changed while the thickness of alfa2 phase decreased to 78 nm. Refining of alfa2 phase resulted in the increase of the microhardness by 20 %. The recrystallized cast structure obtained by cyclic heat treatment and the knowledge on the mechanisms of the refining the structure were compared and discussed with the literature data.

Abstract: The specimens in the present study were prepared by air plasma spraying of NiCrAlY coatings onto the INCONEL 713LC nickel-based superalloy substrate surface. Subsequently an aluminium sheet was cladded onto the coating surface by means of uniaxial cold pressing. After that the specimens were annealed at temperatures of 650, 850 and 1000°C for two hours in argon-flow atmosphere. The remelted NiCrAlY coating specimens were annealed at a temperature of 800°C for fifty hours in ambient atmosphere. A scanning electron microscope was used to record the changes in the modified coating microstructure. Chemical composition was measured by means of energy dispersive microanalysis. Qualitative and quantitative x-ray diffraction analysis was used for the final determination of phases. The microhardness of remelted air-plasma-sprayed NiCrAlY coatings before and after short thermal exposure was also measured.

Abstract: The aim of presented study was to select a proper material for caterpillar application in mobile robots. The fluorocarbon rubbers were chosen for investigation. The samples hardness of 40 and 50 Sh⁰A either without or with polyamide reinforcement were prepared. The uniaxial tensile tests on mini-samples were carried out. The tests were performed on virgin samples as well as on previously exposed for one hour in aggressive liquids. The changes of the surface before and after the exposition were observed via SEM. The relation between the surface changes and the mechanical properties were described

Abstract: In this study we present the investigation of the influence of multiple sterilization processes on micromechanical properties carried out on a composite based on carbon fibers (CF) and polymer matrix composite polydimethylsiloxane (PDMS). The effect of widely-used steam sterilization process on fibers/matrix interphase region properties was studied by nanoindentation.

Abstract: Most of fracture analyses often require an accurate knowledge of the stress/displacement field over the investigated body. However, this can be sometimes problematic when only one (singular) term of the Williams expansion is considered. Therefore, also other terms should be taken into account. Such an approach, referred to as multi-parameter fracture mechanics is used and investigated in this paper. Its importance for short/long cracks and the influence of different boundary conditions are studied. It has been found out that higher-order terms of the Williams expansion can contribute to more precise description of the stress distribution near the crack tip especially for long cracks. Unfortunately, the dependences obtained from the analyses presented are not unambiguous and it cannot be strictly derived how many of the higher-order terms are sufficient.

Abstract: Local mechanical properties of high Cr-alloyed sintered and cast steels with the same chemical composition were investigated using instrumented indentation method. Standard loading/unloading mode was applied, the measurements were done in load range 1 – 500 mN. Load size effect was observed and its parameters were evaluated. Indentation hardness and elastic modulus were found slightly higher for the sintered material. Differences in indentation parameters were explained based on microstructure of materials.

Abstract: In this study, numerical and experimental results of deep drawing process were compared. Drawn part, used in automotive industry was drawn and measured using ARGUS measurement system, which works on a digital image correlation method (DIC). In order to optimize and verify accuracy of a numerical simulation results, this process was modeled in two codes which work on principle of the finite element method (FEM). Two types of FEM codes were used. Code which works on base of both, implicit and explicit time integration scheme, were used for calculation. Results were compared and discussed.