Volume 55, Issue 11-12

The jewelry industry has been searching for sterling silver with high hardness values as it is believed by the industry to have direct effect on scratch resistance as well as improved mechanical properties such as “spring” property. Even though the direct relationship between hardness and how springy the jewelry articles are could not be linked. However it is a conventional wisdom of goldsmith to observe the usual trend for alloys with higher hardness to be more elastic. Moreover it is a common and cheap test to apply to a jewelry article. Therefore it is common find jewelry manufacturers to discuss and compare hardness values. The current commercial alloys could reach 140–170 HV after careful heat treatments and/or mechanical treatments. In our research, we focused on a systematic alloy development study of ultra-hard silver alloy systems. These systems could reach high hardness values in as-cast state without subsequent post-processing treatments. The complex system comprises of silver content in the range of 80.0–92.5 wt.- % with supersaturated matrix. Twenty-two alloying element candidates and fifteen supersaturated ternary and quaternary compositions were investigated. Vickers hardness tests were performed on prototyped alloy ingots. X-ray diffraction analysis was used to measure the lattice distortion as well as to identify second or third phases in the alloys, if they existed. Metallography and electron microscopes were used to identify the microstructures. Seven developed alloy systems were presented in this paper as the investigation led to the discovery of a quaternary ductile alloy system with the hardness value of 142 HV as cast. The microstructure of the quaternary alloy was mostly single phase and these preliminary results suggested the alloy could be a good candidate for jewelry application.

This research studied mechanical properties and oxidation resistance of Haynes 214 after pack aluminizing. The Haynes 214 samples were heat treated at various temperatures (973 K, 1073 K and 1173 K) for 1, 1.25, 4 and 6.25 hours, respectively. After aluminizing, there were two layers at the surface: the inner layer (Ni 2 Al 3 ) located adjacent to Haynes 214 substrate and the outer layer (Ni 2 Al 3 and NiAl 3 ) at the surface. After aluminizing, surface hardness significantly increases from about 250 HV of substrate to more than 570 HV. With increasing hardness, wear resistance of aluminized samples can also be improved as can be seen from decreasing the specific wear rate from 2.24 × 10 −6 g N −1 m −1 to 7.6 × 10 −7 g N −1 m −1 after aluminizing. Cyclic oxidation tests of Haynes 214 with and without aluminizing show that both of them have good oxidation resistance due to slow growth rate of oxide film.

Kurzfassung Es wird eine neuartige Methode zur Rissüberwachung in Bauteilen aus dünnwandigen plattenartigen Strukturen vorgestellt. Dazu wird ein Sensorfeld aus piezoelektrischer Polyvinylidenfluorid-Folie (PVDF-Folie) auf die Oberfläche des rissbehafteten Bauteils appliziert. Infolge der Verformungen in der Rissumgebung entstehen elektrische Signale an den PVDF-Elektroden. Ausgehend von den gemessenen Signalen werden infolge der Lösung einer inversen Aufgabe die charakteristischen Risskenngrößen berechnet, d. h. die Spannungsintensitätsfaktoren des Risses und dessen Lage. Dieses Sensorkonzept wurde in [1–4] bereits für Scheibenprobleme erfolgreich entwickelt. In dieser Arbeit erfolgt die Erweiterung des Sensorkonzeptes auf Plattenprobleme, wobei speziell die Kirchhoff'sche Plattentheorie gewählt wurde. Die Messmethode wird am Beispiel eines Risses der Länge 2a in einer unendlichen Platte unter allseitiger Biegung erprobt.

In this study, fracture analysis of a eutectoid steel used as material for a clamping head and which failed in service was carried out to investigate the effect of heat treatment and also the microstructural features on the failure. The fracture surface was initially examined by scanning electron microscopy to determine the fracture type and possible paths for crack propagation. In the next step, the cross section of the steel was prepared by metallographical techniques and the matrix phases were determined using light microscope in etched condition. The steel surface exhibited a mixed fracture consisting of typical intergranular and quasi-cleavage fracture. The matrix showed segregation regions as band structure and included retained austenite in addition to martensite. Furthermore, several internal cracks were observed in the matrix due to the quenching effect, and the martensitic regions were very effective on the formation of intergranular fracture. Retained austenite possibly plays an important role in forming quasi-cleavage fracture during service loading.

Aseptic loosening of the tibial component is a primary concern of total knee replacement (TKR), which may be caused by stress shielding in cancellous bone of tibia and may require subsequent revision surgery. There is no doubt that materials and design are important issues within general product development and even more in biomedical products. In this study, a 2D axisymmetric finite element model of the tibia and tibial prosthesis is designed to find the optimal functionally graded material (FGM) constituents as well as the optimal gradation direction. The results showed that the optimal design of a tibia tray material is represented by grading it vertically from hydroxyapatite at the end of stem tibia to collagen at the upper layers of the tibia plate. This new design is found to reduce stress shielding in cancellous epiphyseal and diaphyseal bone by 78 % and 68 %, respectively, compared to cementless titanium tibia tray. However, the interface shear stress in cancellous diapyseal bone is reduced by 24 % using FGM tibia tray, which will reduce the pain at the end of stem after the surgery. It is concluded that the new tibial design will increase the life of the knee prosthesis.

The surface structure of a X 12 CrNi 1810 Ti low-carbon steel after saturation with nitrogen and carbon as a consequence of electrolytic plasma nitriding and carbonitriding was studied in this work. It turned out that the X 12 CrNi 1810 Ti steel surface has a modified martensite structure and high hardness after electrolytic plasma processing. It was determined that carbide and nitride particles are formed in the surface layer during nitriding and carbonitriding followed by tempering. The X 12 CrNi 1810 Ti steel wear resistance after carbonitriding and nitriding was investigated and a decrease of the friction coefficient was observed.

Kurzfassung Ultraschallmessverfahren werden seit Langem erfolgreich für Prüfaufgaben, wie zum Beispiel die Ermittlung von Bauteilgeometrien, im Bauwesen eingesetzt. Um die Schallbündelung der Prüfköpfe zu verbessern, werden oft mehrere Prüfköpfe in einem Array angeordnet. Für die Entwicklung der Prüfkopfarrays ist es zweckmäßig, mithilfe von Modellierungen den Einfluss der Arraygröße, der Anordnung der Einzelprüfköpfe im Array und der Prüffrequenz auf das Schallfeld zu untersuchen. Dazu werden in der Praxis erfolgreich Modellierungen auf der Basis der Elastodynamischen Finiten Integrationstechnik (EFIT) und der Punktquellensynthese angewendet. Beim Aufbau der Arrays kommen zurzeit immer häufiger Transversal-Punktkontaktprüfköpfe zur Anwendung. Daher wird bei der Beschreibung der Schallfeldberechnung insbesondere auf die der Transversalwellenprüfköpfe eingegangen und mithilfe von Modellierungen und Experimenten gezeigt, wie sich die Prüfkopfpositionierung auf die Richtcharakteristik auswirkt.

The effect of different microstructures on the fatigue behaviour of a medium carbon vanadium microalloyed steel has been studied. Specimens were subjected to a controlled closed die forging followed by cooling in sand, air or oil, respectively. The hardness and fatigue properties of the microalloyed steel are determined and compared with those of ferrite-pearlite and martensite microstructures obtained by cooling with different mediums after forging. Relatively fine ferrite and pearlite increase the fatigue strength of the steel, while the martensite structure reduces the fatigue strength. Characteristics of fatigue fracture surface morphology are summarized and related to fatigue crack initiation and propagation mechanisms in the forged medium carbon microalloyed steel. The cooling rate has a remarkable effect on the microstructure, hardness, and fatigue behaviour at room temperature.

In the present work, the effect of Ti addition on microstructure and properties of high speed steel (HSS) used for rolls was investigated utilizing optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy spectrum analysis. The results indicated that as-cast microstructure of the HSS roll is mainly composed of MC, M 2 C and M 7 C 3 eutectic carbides and metallic matrix consishing of a mixture of martensite, austenite, and pearlite. The carbides are connected or placed next to each other to form a network along grain boundaries. The addition of 0.5 wt.-% Ti leads to a great change in the morphology, size and distribution of carbides. The carbide network tends to break, and all carbides are refined and distributed homogeneously in the matrix. After normalizing treatment at 1050 °C, the carbides in the Ti containing HSS roll transform into granular or nodular distribution. The mechanical properties, thermal fatigue, and wear resistance of Ti containing HSS roll are more excellent than that of the HSS roll without titanium.

Recently, nano-materials have received more attention due to their potential application as practical structural and functional materials. The unique mechanical properties of CNTs, especially their high strength and stiffness, make them highly attractive for potential improvement of mechanical properties of structural materials. The aim of this research is to investigate experimentally the effect of coated nano-composite with different concentrations on fatigue life behaviour of carbon steel specimens with 0.3 μm surface finish. Nano-adhesives of epoxy resin are synthesized and evaluated. They are modified by multi walled carbon nanotubes (MWCNT) (0.3 wt.- %, 0.5 wt.- %, 0.7 wt.- %) as reinforcement. Fatigue tests are conducted on specimens using a rotating bending machine of the cantilever type to evaluate the fatigue strength and these are compared with them obtained for the neat material. By comparing the results of specimens coated with different concentrations of MWCNT-epoxy composition with the base materials, it is found that 0.5 wt.- % of MWCNT composition is the best selection for specimens having 0.3 μm roughness. As compared to the base materials, the fatigue life increased by 383 %, 785 %, 1239 %, and 800 % by coating with neat epoxy as well as with 0.3 wt.- %, 0.5 wt.- %, and 0.7 wt.- % MWCNT-epoxy, respectively.

The active part of the endless saw blades is made of high-speed steel, HS2-10-1-8, and the holder from X32CrMoV4-1 alloyed steel. Joining of the both parts is realized by electron beam welding which provides narrow seams, small heat affected zones (HAZ), good reproducibility of the results, and uniform microstructure in welded joint zones. The present paper analyzes the structural modifications as well as the chemical composition in the welded joint zones obtained by the electron beam welding of two dissimilar steels. The phenomena which cause the continuous developement of the chemical composition of the weld are examined by energy dispersion X-ray technique (EDX) and scanning electron microscopy.

The dynamic compaction method was used to analyze the consolidation of a railway foundation. Based on the physical characteristics of sands, the parameters of an extended model were proposed by the soil tests. Such model is powerful for investigations of mechanical behaviour of sands under the dynamic compactions. By comparing with experimental results, it is indicated that the dynamic compaction was an effective method for understanding the consolidation of railway foundations. So, the numerical model based on the infinite element analysis was very significant for the practical conditions without the boundary reflection under the dynamic compactions.

A flexible function layer between concrete base and pavement slab is constructed to avoid slab breakdowns caused by poor vibration damping and energy absorption of cement structures. Practical experiments as well as testing and analyzing systems are employed to collect the frequency signals from the pavement structure vibration for a small pavement slab structure subjected to a ball-drop impact. The results reveal that the vibration can be damped out and energy can be absorbed using such a flexible function layer. Based on the contrastive tests, the pavement slab vibration is a declining process under the impact load. The vibration damping effect is more significant with the increase in thickness of the function layer, but becomes slower if the layer reaches a certain thickness. The tests also show that the flexible function layer has a significant role in the vibration damping and energy absorption.