Institute of Materials Science and Welding

Настоящая работа -продолжение серии исследований матричных реакций молекул с малыми кластерами никеля. В [1] изучались реакции Ni и Ni 2 с кислородом с образованием соответствующих оксидов. Работа [2] была посвящена реакциям Ni и Ni 2 с водородом, метанолом и водой. В наших работах изучались ИК-спектры матриц из аргона (при 15 К) и ксенона (при 45 К), содержащих кластеры никеля. Было показано, что при определенных условиях в матрицах из аргона образуется значительное количество Ni 3 , а в твердом ксеноне основным продуктом является Ni 4 . Показано также [4], что Ni 4 является нежесткой молекулой, в которой четвертый атом никеля почти свободно распределен относительно сравнительно жесткого фрагмента Ni 3 , и которая имеет, по меньшей мере, два незначительно различающихся по энергии минимума при сильно различающихся геометрических конфигурациях. Кроме того, в [5, 6] изучены спектры матриц из аргона и ксенона с добавлением 0,2-0,5% метана или воды. Приведены наблюдавшиеся спектры и расчеты для систем Ni 3 (CH 4 ) и Ni 3 (H 2 O), однако интерпретация результатов для матриц из ксенона была неполной, поскольку на тот момент был неизвестен состав и строение кластера никеля, участвующего в реакциях в матрицах из ксенона. Было показано, что для изученных систем Ni n + RH (R=CH 3 , OH) основным состояниям соответствуют структуры с мостиковыми атомами водорода, размещенными симметрично относительно двух атомов никеля HNi n R. В данной работе новые измерения обсуждаются совместно с данными [4-6] и результатами квантово-химических расчетов комплексов Ni n (n = 2-4) с молекулами метана, воды и пероксида водорода.

Complexes of nickel atoms and small clusters with acetylene molecules are studied within the density functional theory. A trend toward the predominant formation of structures with bridge hydrogen atoms is observed in reactions between Ni n and acetylene with rising n.

During aluminium extrusion, the die experience cyclic thermo-mechanical loads that can lead to materials degradation and failure. For a process optimization and a comparison of different hot work tool steels, the finite element method is an appropriate means. Local inelastic strains result from the interaction of the applied temperature and stress loading and can be computed by suitable inelastic constitutive equations. Stress amplitudes and dwell times during extrusion result in creep-fatigue damage. A lifetime consumption model sums increments of a damage variable over time and defines materials failure as the accumulation of the resulting damage variable to a critical value. The procedure for the identification of the material parameters for both the constitutive and the damage model is described in detail, including the material parameters for the description of time-effects, and applied to the hot work tool steel Bö hler W300 ISOBLOC (EN 1.2343). The lifetime consumption for two different hot work tool steels is compared on the basis of an example in aluminium extrusion.

Lightweight design is essential for an economic and environmentally friendly vehicle. Aluminium sheet metal is well known for its ability to improve the strength to weight ratio of lightweight structures. One disadvantage of aluminium is that it is less formable than steel. Therefore complex part geometries can only be realized by expensive multi-step production processes. One method for overcoming this

Recently, the high cost and low productivity of machining hard materials such as Ti-6Al-4V has drawn major attention to the development of a modular and scalable tool system with integrated laser as one piece of equipment. The present study focuses on a new concept of laser-assisted milling with spindle and tool integrated laser beam guiding. The laser beam is located at the cutting area and moving synchronously with the cutter. In order to optimize the process with respect to the force reduction, various machining conditions were investigated, both experimentally and with simulation. The numerical 3D FEM simulations were carried out with the commercial software DEFORM 3D. In the simulation, a Johnson-Cook type material model was applied and specifically modified for very high strain rates and system temperature. Results such as temperature distributions and maximum cutting forces could directly be compared to the experimental findings. The simulation results expressed a good agreement with the experimental results.

This work presents approaches for the description of the microstructure evolution in a C-Mn microalloyed steel using cellular automata (CA) during thermo-mechanical treatment. The developed probabilistic-based model integrates the effects of the individual metallurgical phenomena related to the hot rolling process, such as hot deformation, dynamic recrystallization (DRX) and precipitation state, where the retarding effect of precipitates is considered. The precipitation kinetics of (Nb,Ti)(C,N) is simulated by means of the software package MatCalc. The results are validated by experimental data obtained by transmission electron microscopy. The simulations are directly applicable to the optimization of both, microstructure and properties, in the production of the tested steels.

During machining of hard materials, one approach to reduce tool wear is using a laser beam to preheat the material in front of the cutting zone. In this study, a new concept of laser-assisted milling with spindle and tool integrated laser beam guiding has been tested. The laser beam is located at the cutting edge and moving synchronously with the cutter. In experiment, a reduction in the resulting process cutting forces and tool wear has been observed in comparison to milling without laser. A three-dimensional finite element model in DEFORM 3D was developed to predict the cutting forces in the milling process with and without an additional laser heat source, based on a Johnson-Cook-type material constitutive model adapted for high strains and strain rates. Both in experiment and simulation, the deformation behavior of a Ti-6Al-4V workpiece has been investigated. The comparison of the resulting cutting forces showed very good agreement. Thus the new model has great potential to furth...

The outstanding mechanical properties of the nickel based superalloy Allvac 718Plus T M are sensitive to the microstructure, in particular to the grain size, which depends on the processing history. The grain structure is mainly controlled by thermo-mechanical processes like recrystallization and grain growth. This paper deals with the simulation of the evolution of the grain structure in alloy Allvac 718Plus T M during disc forging using the Finite Element (FE) code Deform 2D T M. Additionally the material flow, pressing forces and temperatures are of interest. The hot deformation behaviour of Allvac 718Plus T M has been characterized in a temperature range of 900-1050 • C and at strain rates of 0.1-10 s −1 by use of cylindrical compression tests. Particular emphasis is put on the identification of the parameters of a semi-empirical model for dynamic recrystallization. Furthermore the simulated results are compared with an industrial trialforging. The results of the simulations shall be the basis for the development of an optimized forging process with respect to cost effectiveness, product quality and low energy consumption.

It is imperative to understand the most common failure modes of total ankle arthroplasty (TAA) to appropriately allocate the resources, healthcare costs, enhancing surgical treatment methods, and improve design and longevity of the implant. The objective of this study was to investigate the primary mode or modes of failure (Loose talar component, loose tibial component, dislocation, instability, misalignment, deep infection, Fracture (near implant), Pain, defect polyethylene (PE), other, and missing information) of TAA implants, so these failure mode/modes can be targeted for future improvement. The Norwegian Total Hip Arthroplasty Register 2008 was chosen as the primary source of data since the register have been in existence for 20 years and also gives more specific failure modes than other registries. Tukey-Kramer method was applied to Norwegian Arthroplasty Register. After the application of the Tukey-Kramer method, it is evident that there is no significant difference between a...

In a wide range of materials, precipitation hardening is the key for optimizing properties such as strength or creep performance. In order to model strengthening effects with physically based concepts, precipitate kinetic simulations have to be linked to micromechanical models. Part of this link is the precipitate distance distribution in the glide planes of dislocations. Recently, a new model for the calculation of distance distributions has been introduced, which is specially designed for arbitrary size distributions and, thus, capable of handling more realistic microstructures when compared to classical approaches. Up to now, this model has been restricted to spherical precipitates. In this work, the model is advanced to account for all kinds of spheroids, that is, ellipsoids with rotational symmetry. Any prolate, oblate or globular precipitate shape can be represented by a specific shape factor, or aspect ratio, and an effective radius. The result is represented in the form of a...