Materials Science Forum Vols. 473-474

Abstract: 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.

Abstract: Bandsaw blades are one of the most commonly used tools of the wood cutting industry. Their base materials are mostly unalloyed or poorly Cr-alloyed tool steels. After the review of the bandsaw blade’s cyclic load characteristics, we present the typical failures, which can be, originate in it’s cracking. With the use of these information an overall systematization has been set up by the bandsaw blade cracking types and its root causes. The main place of the failure is the weld and the heat-affected zone’s area where the welding can failure or the lack of toughness can produce cracking. An other zone, where cracking may appear is the bandsaw blade’s tooth gullet because it raises the stress intensity factor. Special material testing methods have been made to investigate the tooth gullet’s notch sensitivity from the test results that a comparison of several bandsaw blade base material, are reviewed. With the use of the results a notch sensitivity rating system has been worked out, which can be used to rate different bandsaw blade base material’s notch sensitivity.

Abstract: The silicone elastomers offer in our days new perspective for the construction in the precision engineering and in the medicine because of their special mechanical, electrical, optical and chemical properties. Since the essential material parameters like storage modulus and loss modulus depend on temperature and frequency explicit it is important for simulations to know these characteristics. This report is about determining of relaxation behaviour of silicone rubbers and about finding the mathematical relation to describe time-temperature equivalence of silicone elastomers. As conclusion we can declare that the common used Williams–Landel-Ferry equation to describe temperature and time dependent behaviour of polymers is not applicable for silicone rubbers.

Abstract: In the recent years several new high strength steel grades have been developed, which exhibit improved cold formability and thus are especially suitable for the car body. These multi-phase steels have to be processed via continuous annealing lines. The best combination of strength and uniform elongation is obtained with ferrite-bainite-retained austenite multiphase steel, which rely on transformation induced plasticity (TRIP effect) during the cold forming operation. The production route for TRIP steel, which relies on two isothermal heat treatments, is explained as well as the role of the major alloying elements. In order to optimize the property combinations, microalloying with niobium is a successful means. Niobium increases the strength of the steel with 15 MPa per 0.01 %Nb and simultaneously provides also a higher amount of stable austenite, thus guaranteeing both, increased strength and formability. The metallurgical background for providing these results is explained. Even though the amount of high strength steel in automobiles is continuously increasing, the application of TRIP steel is still limited. However, the good experience in trials and first successful applications make an increased usage of this steel type also realistic, despite its relatively high production costs and reduced weldability.

Abstract: Fe40Ni40B16Si4 alloy was prepared by the melt spinning method with 50µm thickness. The crystallization of the amorphous alloy was analysed using a differential scanning calorimeter, X-ray diffraction method and a transmission electron microscope.

Abstract: Composite materials combine the advantages of their components. Carbon fibre reinforced composites are used in construction where reduced weight is critical. To produce carbon fibre reinforced composites, aluminium alloys can be the matrix. Advantageous properties of aluminium matrix composites – good toughness, low weight – are applied in aerospace and automotive industry. Because aluminium alloys are not reactive to carbon, therefore the coating of the fibres can solve the problem. Nickel coated and chemically treated carbon fibres were used to producing of aluminium matrix composites. The investigated composite materials were prepared by pressure infiltration. The influence of treating of carbon fibres was examined on the fracture mechanical properties of aluminium matrix composites. Three types of matrix materials, three types of carbon fibres and four types of surface treatment were studied. Fatigue crack growth tests were performed under mode I loading condition and the failure mechanisms of the composite materials were investigated. Test results belonging to different coated fibres were compared, and our results were compared with the results from the literature, too.

Abstract: Structure and magnetic properties of ferrimagnetic bioceramics in the system {0.45(CaO, P2O5) ySiO2 xFe2O3 0.03Na2O}, x=0.05, 0.10, 0.15, 0.20, were studied by x-ray powder diffraction and magnetic measurements. Magnetite and calcium phosphate, crystallizing in the hexagonal and monoclinic crystal systems, are the major phases in the compounds. Phase development, crystal structure, and magnetic properties of the composites are determined by the specific starting composition of oxides and the heat-treatment temperature.

Abstract: Diamond layers have a potential application as the highest band-gap semiconductor for electronic devices. One of the major problems is to form electric contact on the diamond surface useful for an electronic device. This paper shows the properties of the contacts formed by the very promising ion implantation technique. The diamond layers were deposited with Microwave Assisted Chemical Vapor Deposition (MW-CVD) equipped with special extra features like High Voltage Bias and Heated Substrate Holder [1]. Phosphoruos ion implantation and gold deposition were used for the contact formation. This technique resulted graphitization the top of the diamond film and intermixing of gold with the graphite or diamond surface. The properties of the contacts were tested with surface conduction characterization methods, and the properties of the contact to diamond interface was investigated with SIMS (Secondary Ion Mass Spectroscopy ) and XPS (X-ray Photoelectron Spectroscopy).

Abstract: The interest in bulk nanostructured materials (NSM), processed by methods of severe plastic deformation (SPD), is justified by their unique physical and mechanical properties. Equalchannel angular pressing (ECAP) is one of the methods of severe plastic deformation (SPD) that produces ultra fine-grained material. Due to the cyclic nature of the process, it is difficult to produce specimens with a high length to diameter ratio. Ratios of 6-7 have been reported in the literature to date. Longer specimens, however, are useful since the homogenous part is larger and the relative size of end effects is smaller. A new method was developed to obtain length to diameter ratios as high as 8-10. This new technique was developed using the multi-pass finite element simulation. The as-received alloy used in this study was the 6082 commercial Al-Mg-Si alloy. High strength and high ductility phenomenon that was found recently in materials after SPD were reached with the route C. The induced anisotropy of specimens after ECAP was monitored.

Abstract: Tribological performance of technical ceramics is influenced by various factors. Among the others the material properties, loading conditions, residual stresses as well as chemical reactions and interaction between contacting parts effect the damage process. The current paper focuses on the material features, investigating the possibility of modifying the wearing characteristics of a Si3N4 based technical ceramics by post-heat treatment. The microstructure, the mechanical properties and the wearing characteristics were studied on HIP-sintered SiAlON samples, post heattreated in oxidizing atmosphere at different temperatures. Wearing performance was characterized by pin-on disc tests. The wear rate varied with the temperature of heat treatment. From tribological point of view especially treatment at 1200°C proved to be advantageous Microstructural investigations by TEM and X-ray diffraction studies revealed some explanations of these changes. The above studies were completed by mechanical tests. Microhardness, E-modulus, four point bending strength and indentation fracture toughness have been determined in order to study the correlation between the tribological and mechanical properties. Based on our results, the post heat treatment may be useful to improve the wearing performance of SiAlON ceramics.