Bálint Katona

Compressive Behavior and Microstructural Characteristics of Iron Hollow Sphere Filled Aluminum Matrix Syntactic Foams

Iron hollow sphere filled aluminum matrix syntactic foams (AMSFs) were produced by low pressure, inert gas assisted infiltration. The microstructure of the produced AMSFs was investigated by light and electron microscopy, extended by energy dispersive X-ray spectroscopy and electron back-scattered diffraction. The investigations revealed almost perfect infiltration and a slight gradient in the grain size of the matrix. A very thin interface layer that ensures good bonding between the hollow spheres and the matrix was also observed. Compression tests were performed on cylindrical specimens to explore the characteristic mechanical properties of the AMSFs. Compared to other (conventional) metallic foams, the investigated AMSFs proved to have outstanding mechanical properties (yield strength, plateau strength, etc.) and energy absorbing capability.

Fatigue properties of expanded perlite/aluminum syntactic foams:

The main purpose of this paper is to present the basic fatigue properties of metal matrix syntactic foams. The investigated syntactic foams consisting of expanded perlite and A356 aluminum matrix were produced using an inert gas pressure infiltration technique. The obtained foams were subjected to cyclic compressive loading in order to investigate their fatigue properties. The standard procedure for cyclic fatigue testing was slightly modified to account for the variation of porosity and strength which is typical for metallic foam samples. This approach allows the direct comparison of the fatigue test results between all investigated samples. Depending on the applied load level, two different failure mechanisms were identified that resulted in characteristic deformation – loading cycle curves. The failure mechanisms were further investigated on the microstructural scale: traces of fatigue beachmarks and extensive plastic deformation were found. Furthermore, Wöhler-like deformation – lifetime diagrams were created in order to predict the expected lifetime of the properties of metal matrix syntactic foams .

On the effective Young’s modulus of metal matrix syntactic foams

ABSTRACT The effective Young’s modulus of aluminium matrix syntactic foams was determined by modal analysis. Two different matrix materials (Al99.5 and AlSi12) were used, and they were reinforced by Globocer grade ceramic hollow spheres. In order to validate the results, a full-scale finite element model was also created. A new algorithm was developed to place the spheres in a proper, probabilistic spatial distribution. Finite element simulations were carried out in modal analysis and compression test senses. In addition, three different analytical methods were studied to estimate the effective Young’s modulus. The measured values were compared with the finite element and analytical results. The determined effective Young’s moduli showed good agreement. This paper is part of a thematic issue on Light Alloys.

Development of Nitinol Stents: Etching Experiments

The present study focus on the chemical etching of shape memory nickel-titanium (nitinol) alloy stents made by laser cutting. Application of nitinol stents widely spread in case of atherosclerosis of peripheral vessels. This type of stent has to have appropriate surface quality, flexibility and strength. The aim of chemical etching is removing the burr, which arises during the laser cutting. Etching is one step of the production of stents. The appropriate parameters allow the laser burned surface and most of protruding material removing without significant damage of stent shape. During these experiments etching time was changed. After etching the cross section area was determined by metallographic examinations. The results of the examinations show the relationship between the etching time and the cross-section area. The analysis of measurement data revealed the change of etching velocity. Before and after etching the samples was examined by scanning electron microscopy (SEM). The different surfaces also were compared and the findings were discussed.

Chemical Etching of Dental Implant Material

In this article we dealt with the development of a new method of chemical etching on dental implant materials, Grade 2 and Grade 5 titanium. Certain process creates reproducible homogenous and microrough surface, furthermore improves the reproducibility and productivity for industry appliance. During the research we modified the surface roughness of 2 mm thick samples in a single step of acid etching with a mixture of HF, HNO3 and distilled water varying the etching time (15-600 seconds). After the surface treatment we obtained the changes of mass and the surface roughness on both sides of every sample. The resulting surface was examined with stereo-and electron microscopy. Based on our results we can determine a parameter setting where the homogenous and microrough surface is reproducible.

Examination of the Surface Phosphorus Content of Anodized Medical Grade Titanium Samples

In case of titanium dental implants, the main goal is to create a surface where the bone cells can attach well, therefore osseointegration can occur. The chemical composition of the surface has an important role, because the surface has a direct contact with the living tissue and induces different reactions for example peri implantitis or osseointegration. In our work titanium sample made from the most commonly used dental implant material (Ti Grade 5) were investigated. The samples were treated by chemical etching in hydrogen-chloride and in phosphoric acid to remove the cut generated burr. After that the samples were anodized in phosphoric acid solution at 10 V, 20 V, 30 V or 40 V. As a result of these treatments, titanium-dioxide layers were created on the surfaces. Phosphorus (originating from the phosphoric acid bath) may also be found on the surfaces. This may promote osseointegration. The surface compositions were investigated with the aid of Secondary Ion Mass Spectrometry (SIMS). Based on these results we can conclude that anodization in phosphoric acid solution increases the phosphorus content of the surface. Approximately to the middle of the titanium-dioxide layer the phosphorus content is constant but lower with one order of magnitude than on the surface. In the deeper layers the phosphorus content continues to decrease until the base material where it significantly reduce.