Imre Kientzl

Mechanical Behaviour Al-Matrix Composite Wires in Double Composite Structures

The fibre reinforced metal matrix composites (FRMMC-s) are one of the main groups of the composite materials. The composite wires are continuous-fibre-reinforced aluminium matrix composites, which are made by a continuous process. Composite wires already have a few experimental applications for the reinforcement of high voltage electric cables. Other experimental application fields of these materials are the preferential reinforcement of the cast parts. In this way significant decrease in the weight could be achieved. The aim of this study is to show the excellent mechanical properties of the composite wires, and the contact relationship between the mechanical and other properties (i.e. thermoelectric power) and the possibility of their standardized production. The continuous production process of the composite wires and their test results were are shown as well. The difference between the composite wire reinforced double composite structures and direct fibre reinforced blocks were delineated as well. In this paper specimens were examined by tensile tests, bending tests, thermal aging tests and thermoelectric power measurement.

Production and Examination of Double Composites

Nowadays, metal matrix composites have many new areas of application owing to their excellent properties - for example their great tensile strength and high Young’s modulus with its relatively low weight. The aim of this work is to an examination of ceramic fibre-reinforced aluminium matrix composite wires made via continuous process. Furthermore, the research will outline the double composite products that are composite wire-reinforced metal matrix composites. Double composites are examined by tensile tests, bending tests and pressing tests. A lot of research has been done on the thermal aging of composite wires and on measuring the impact energy of thermal-aged specimens. The mechanical test shows us that structures reinforced with the composite wires have a notably higher load-carrying capacity than does a structure reinforced directly with fibres or a structure without any reinforcement.

Investigation of the mechanical and chemical characteristics of nanotubular and nano-pitted anodic films on grade 2 titanium dental implant materials

OBJECTIVE The objective of this study was to investigate the reproducibility, mechanical integrity, surface characteristics and corrosion behavior of nanotubular (NT) titanium oxide arrays in comparison with a novel nano-pitted (NP) anodic film. METHODS Surface treatment processes were developed to grow homogenous NT and NP anodic films on the surface of grade 2 titanium discs and dental implants. The effect of process parameters on the surface characteristics and reproducibility of the anodic films was investigated and optimized. The mechanical integrity of the NT and NP anodic films were investigated by scanning electron microscopy, surface roughness measurement, scratch resistance and screwing tests, while the chemical and physicochemical properties were investigated in corrosion tests, contact angle measurement and X-ray photoelectron spectroscopy (XPS). RESULTS AND DISCUSSION The growth of NT anodic films was highly affected by process parameters, especially by temperature, and they were apt to corrosion and exfoliation. In contrast, the anodic growth of NP film showed high reproducibility even on the surface of 3-dimensional screw dental implants and they did not show signs of corrosion and exfoliation. The underlying reason of the difference in the tendency for exfoliation of the NT and NP anodic films is unclear; however the XPS analysis revealed fluorine dopants in a magnitude larger concentration on NT anodic film than on NP surface, which was identified as a possible causative. Concerning other surface characteristics that are supposed to affect the biological behavior of titanium implants, surface roughness values were found to be similar, whereas considerable differences were revealed in the wettability of the NT and NP anodic films. CONCLUSION Our findings suggest that the applicability of NT anodic films on the surface of titanium bone implants may be limited because of mechanical considerations. In contrast, it is worth to consider the applicability of nano-pitted anodic films over nanotubular arrays for the enhancement of the biological properties of titanium implants.

Review: the potential impact of surface crystalline states of titanium for biomedical applications

Abstract In many biomedical applications, titanium forms an interface with tissues, which is crucial to ensure its long-term stability and safety. In order to exert control over this process, titanium implants have been treated with various methods that induce physicochemical changes at nano and microscales. In the past 20 years, most of the studies have been conducted to see the effect of topographical and physicochemical changes of titanium surface after surface treatments on cells behavior and bacteria adhesion. In this review, we will first briefly present some of these surface treatments either chemical or physical and we explain the biological responses to titanium with a specific focus on adverse immune reactions. More recently, a new trend has emerged in titanium surface science with a focus on the crystalline phase of titanium dioxide and the associated biological responses. In these recent studies, rutile and anatase are the major two polymorphs used for biomedical applications. In the second part of this review, we consider this emerging topic of the control of the crystalline phase of titanium and discuss its potential biological impacts. More in-depth analysis of treatment-related surface crystalline changes can significantly improve the control over titanium/host tissue interface and can result in considerable decreases in implant-related complications, which is currently a big burden on the healthcare system.

Effect of the Infiltration Pressure on the Properties of Composite Wires

Nowadays the development of composite materials has increasing importance. In this study Nextel 440 type alumina fibre reinforced aluminium matrix composite wires were investi-gated. Composite wires produced using the continuous process are suitable to simplify the introduc-tion of fibre reinforcements into aluminium castings as well as the production of double composite, sandwich and preferentially reinforced structures. This paper focuses on the porosity of composite wires because minimizing porosity is the primary condition of good mechanical properties. Compo-site wires were produced with different infiltration pressures (0.83 MPa, 1.03 MPa, 1.24 MPa, 1.52 MPa, 1.65 MPa 1.86 MPa and 2.07 MPa) and different diameters (1 mm and 2 mm) to determine the correlation between infiltration pressure and the porosity of wires. 10 grinded cross-sectional samples were made from each type of composite wires. Based on the micrographs of these samples the volume fraction of aluminium was determined by image analysis, which also yielded informa-tion on the porosity of wires. The results show that there is direct linear correlation between the infiltration pressure and the change in porosity. These findings, however, are valid only for the in-vestigated range of pressure.

Production and Behaviour of Aluminium Matrix Double Composite Structures

In this study Nextel 440 type alumina fibre reinforced aluminium matrix composite wires were investigated. Composite wires produced using the continuous process are suitable to simplify the introduction of fibre reinforcements into aluminium castings as well as the production of double composite, sandwich and preferentially reinforced structures. This paper focuses on the porosity of composite wires because minimizing porosity is the primary condition of good mechanical properties. Composite wires were produced with different infiltration pressure (0.83 MPa, 1.03 MPa, 1.24 MPa, 1.52 MPa, and 1.65 MPa) to determine the correlation between infiltration pressure and the porosity of wires. 10 grinded cross-sectional samples were made from each type of composite wires. Based on the micrographs of these samples the volume fraction of aluminium was determined by image analysis, which also yielded information on the porosity of wires. The results show that there is direct (linear) correlation between the infiltration pressure and the decrease in porosity. These findings, however, are valid only for the investigated range of pressure. The measured values were in good agreement with the theoretical model used for comparison.

Surface treatment and examination of Grade 2 and Grade 5 titanium

Surface characteristics play an important role in the implant-bone integration that is required for the long-term reliability of dental and orthopedic implants. In this paper, we investigate the effect of acid etching on the mass reduction and roughness of grade 2 and grade 5 Ti under controlled experimental conditions. Three different etching compounds were investigated: 30% HCl, 85% H 3 PO 4 and the compound of 30% (COOH) 2 × 2H 2 O and 30% H 2 O 2 in various treatment intervals under controlled temperature. Stereo microscopy, scanning electron microscopy, roughness and weight measurements were carried out on the samples. We found that neither 85% H 3 PO 4 nor the compound of 30% (COOH) 2 × 2H 2 O and 30% H 2 O 2 were able to remove the machining marks from the surface of Ti discs in our experimental setting. On the other hand, etching in 30% HCl yielded even surfaces both on Ti grade 2 and 5 discs. We also found that etching at higher temperatures in 30% HCl resulted in significant mass loss.

Heat treatment and impact testing of composite wires

The reinforcement of high voltage electric power cables is a promising application field of the composite wires. The temperature of the power cables can reach 200-300 °C due to an over-loaded electrical grid. The composite wires have to stand these high temperatures for a long time in the power cables. Long term heat treatments have been done to examine the eligibility of the composite wires. After heat treatment impact test was applied to measure the changes of the mechanical properties of composite wires. With the instrumented impact tester the process of the failure was examined. In this paper the continuous production method of ceramic fibre reinforced metal matrix composite wires and their properties are shown.

Wear of the Tungsten Electrode at the TIG Arc-Spot Welding of Dissimilar Metals

Micro-TIG welding experiments have been used for the welding of the contacts of special lamps. Since the welded materials were different, the welded joint was a heterogeneous bound. For the joints a 0.6 mm Ni-Mn alloy or 0.4 mm Mo wire were inserted onto the hole of AISI 304 type austenitic stainless steel sheet, with a wall thickness of 0.35 mm. The micro-TIG welding was completed with a welding machine of which control characteristics corresponded to all the requirements necessary for TIG arc-spot welding. The goal of the experiments was to find the optimum regarding the quality of the lamps’ welded joints that correspond with the needed production quality level. The problems that occurred throughout the welding process were due to the very high melting point of the Mo. Also, using optical microscopy and scanning electron microscopy have performed a proper testing in parallel with the experiments. The details, revealed that the geometry of the joint and the resistance depend very much of the arc length, shielding gas velocity and especially of the tip geometry of the tungsten electrode and its wearing. Regarding to the electrode’s wearing, there have been determined the tip angle, the tapering and the effect of the electrode’s material composition. The latter parameter was investigated for unalloyed, thorium-oxide, cerium-oxide and lanthanum- oxide alloyed electrodes.