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Gears made by powder metallurgical manufacturing processes fail in testing mainly by tooth root fracture. If compared to gears made by conventional manufacturing processes, inferior tooth root bearing capacities against the adjacent bending loads are verified. Even with a nearly fully densified material in the tooth root surface, comparable bending strengths cannot be attained. On the contrary, the bearing capacities of the tooth flank are considered to be competitive. In conjunction with the missing dimensioning guidelines for powder metallurgical components, the inferior tooth root bearing capacities lead to the fact that powder metallurgical gears are not generally used in automotive gearboxes. This applies despite of the lower-priced and energy-saving powder metallurgical manufacturing process, when it comes to mass production parts like gears. To reveal potential for optimization, the tooth root bearing capacity of two different powder metallurgical gears was calculated based on the fatigue strength of laboratory specimens. The material used was a sintered steel with 0.85% molybdenum, which is well-suited for the manufacturing of gears. The influencing variables considered were the density, the geometry and the carbon content. They were systematically varied in the manufacturing of the specimens in appropriate ranges. As an additional result of the calculation of the bearing capacity, the fatigue strength of the material is established. With the equations and coefficients given in this work, it can be described or used for component dimensioning. In parallel, two experimental series of the two gears were manufactured. Subsequently, the tooth root bearing capacity of both gears was tested in a pulsatory test rig for comparison with the calculations. The relative error between calculated and tested bearing capacity was less than 5% for both variants. The calculations provide information on how deep the densification of the tooth root surface has to be for optimal results. Also, the percentages of the tooth root bearing capacity were investigated, which are related to the manufacturing processes densification, carburization and hardening. Thereby, the impact of the manufacturing processes was estimated independently from one another. Based on the applicable calculation it was estimated how much an optimization of the tooth root geometry can improve the tooth root bearing capacity.

In engine design, the requirements for higher specific power in combination with low-polluting, economic and lightweight power train concepts are increasing. Highly charged diesel engines achieve nowadays a specific performance of 60-65 kW/l and a specific torque of 200 Nm/l. These specific performance values are expected to experience will a considerable increase in the next diesel engine generations. Due to these requirements the material conventionally applied in the manufacture of internal combustion engines meet their limits regarding thermal and mechanical properties. Compacted Graphite Iron (CGI) can be presented as a reasonable solution in this case. Its mechanical properties outperformer the mechanical properties of ordinary grey iron. CGI offers also acceptable damping characteristics and satisfactory heat conductivity. The fatigue behavior of CGI has not enough been investigated yet. The optimal utilization of the material potential can only be realized if the material behavior under cyclical loading conditions is better known. In the present research project, the fatigue behavior of Compacted Graphite Iron was investigated under uniaxial and multiaxial conditions by example of the CGI grade EN-GJV-450 and was compared with a fatigue failure hypothesis. A method for the estimation of the fully reversed axial fatigue strength of cast iron materials was developed by using image analysis for the evaluation of the graphite morphology and is also presented in this work.

The economical usage of natural resources and the reduction of polluting gas emissions are the most important challenges facing the designers of the next generation power plants. For this purpose a substantial contribution can be made through an increase of the thermal efficiency. Currently in modern natural gas fired combined cycle power plants thermal overall efficiencies of 58% can be achieved with maximum inlet temperatures inside the steam turbine of 600°C. The goal of the Collaborative Research Center 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer-Systems for Combined Cycle Power Plants” was to establish the technical and scientific basis for a thermal overall efficiency of 65% in gas fired combined cycle power plants of the future. To this end the process parameters temperature and pressure have to be increased significantly. This means for the steam turbine that a main steam temperature of 690°C in combination with a pressure of 300 bar is required. Since typical power plant materials have presently reached their operation limit with higher steam temperature, the application of a new cooling system could reduce the material temperature to tolerable conditions. In the context of this dissertation a new sandwich structure was investigated comprising a woven wire mesh interlayer between two plane sheets. This cooling structure is planned to be applied to the steam turbine casing as a wall cladding to cool down the casing to sustainable temperatures. Due to constant overpressure of cooling steam in combination with high temperature loads during operation, the structures are primarily subjected to creep deformation. Furthermore steam temperature fluctuations as well as starts and shutdowns of the steam turbine cause a superimposed fatigue process. Overall the structures are stressed during operation by a combined creep-fatigue-interaction with loads perpendicular and parallel to the intermediate layer. The task of this thesis was to characterise and to simulate with the Finite Element Method (FEM) the mechanical high temperature behaviour of the cooling structures in the regime of creep-fatigue-interaction. For this purpose the flow, creep and fatigue behaviour of cooling structure specimen manufactured from the nickel base alloy Nicrofer 6025 HT was investigated. Additionally the influence of different wire mesh geometries on the mechanical behaviour was examined. To simulate the flow and creep behaviour of the cooling structures precisely quasistatic tensile tests and creep tests in dependency on the temperature were carried out on the constituents straight wire and cover sheet. Constitutive equations were derived from the test results and implemented in adequate user subroutines of the commercial FEM software Abaqus. To predict the service life of the cooling structures under quasistatic and creep loads new damage models were developed. This way the moments of failure of the cover sheet - wire mesh - joints could be well estimated.

International audience; A method is proposed for the evaluation of surface fatigue damage of hot forming tools that undergo severe thermo mechanical loading. Fatigue crack propagation in a hot work tool steel X38CrMoV5-47HRC is investigated using single-edge cracked tension specimens (SET). The effect of thickness (ranging from 2,5mm to 0.10mm) and R values is investigated. Numerical simulation is performed by ABAQUS® Standard to evaluate J integral and stress intensity factor KI. The Paris curves are established. Short crack propagation in thin specimens is addressed. Effect of slip bands on crack propagation mechanism is investigated.

Within this work the relationship between the pore morphology and the fatigue properties of sintered pure iron and steel has been investigated. The mechanical properties of P/M are controlled by their microstructure and the porosity. Many parameters are influencing the microstructure and the porosity. A few of these parameters were considered in the investigation, which will have a significant influence on the performance characteristics of the materials. These parameters are the density, the kind of the powder, the sinter temperature and technique of alloying as well as the composition. The density acts as main parameter because it includes all other parameters. Therefore, the density has the maximum potential for optimizing the properties of the sintered components. The above mentioned parameters influence the morphology of the pores. Due to this, the characterizing of the pore characteristics is very important. The mechanical properties and the porosity have been investigated by varying the density, the sintering temperature and basic powder for sintered pure iron and alloyed steel. The investigated materials were Distaloy AE and SE, pure iron ABC 100.30 and MH 65.17. Basic powder was water atomized and pure broken sponge iron. The sintering conditions were 1120°C and 1280°C in an atmosphere of 70% N2 and 30% H2 in industrial equipment. If the relationship between the geometrical features of the pores and the influencing parameters is known, it is possible to optimize the morphology of the pores by the influencing factors. The base characteristics are pore area and perimeter, convex perimeter, maximum and minimum pore dimensions and the intercepts or distances between the pores. From the primary data a huge variety of secondary quantities can be derived which are used to describe the pore size, the pore shape, and pore interpore space. The pore morphology was quantified by image analysis. According to the results of the image analysis, the majority of all pores is small and rather round. Only a few large pores which are automatically also very irregular can act as potential fracture initiation sites. For this reason 98% of all pores were excluded from the further processing. Only 2% of the remaining larger and most irregular pores were evaluated. Pore irregularities are commonly characterized by a shape factor. The bending fatigue strength was investigated for a varying density by different sintering temperatures and basic powders. For each experimental condition 60 specimens were used in fully reversed flat bending tests at 6 stress levels of which 3 occurred in fracture. The endurance limits were determined for 50% probability at 107 cycles. Many properties of porous sintered materials are related to the pore microstructure. An attempt was made to correlate the fatigue behavior of industrially manufactured sintered iron and steels with quantitative pore characteristics. Crack initiation in fatigue tests was restricted to very few large irregular pores. All efforts to correlate average pore size or shape factors with fatigue strength values yield at best tendencies. Powder laws to describe the relationships between the strength, the density, and the shape factor the coefficients were calculated by regression analysis.

With the aid of Chalmers specimens according to DIN ISO 4368, part 2, the bonding strength between Babbit sliding bearing materials and steel support members was investigated. The experimental results proved that the bonding strength of the newly developed alloy Sn-12Sb-6Cu-1.8Bi remained insufficient, when the supporting shell of steel grade C 10 was dipped in a pure Sn bath, even with variations of Sn bath temperature or casting and cooling modifications. With Bi containing melts an oxide layer forms between steel and bearing metal when the alloy is poured into the tin coated cups requested for Chalmers specimens. This oxide layer prevents a proper Fe/Sn bonding. The reason for the formation of the oxide layer when using Bi containing melts is not understood. A possible solution to the bonding problem is the in situ formation of a new bond coating directly from a modified tin bath. To this end, the bath of pure tin is alloyed with an element which has a higher affinity to iron than tin does. One possible alloying element is Zn, which can form intermetallic Fe-Zn layers on the steel shell enabling higher bonding strengths than layers formed in pure tin baths. By modifying the tinning of steel support shells this way, the originally low bonding strength of the newly developed bearing alloy could be increased to the level of conventional tin based sliding bearing alloys. In addition, the bonding strength of conventional Babbit metals on tin base could be considerably increased. The modified Sn Zn bath yields high bonding strengths with the investigated new alloys Sn-12Sb-6Cu-1.8Bi, Sn-12Sb-6Cu-1.8B+Te5, Sn-12Sb-6Cu-1.8B+Ni5, Sn-12Sb-6Cu-1.8Bi+Zn50 as well as with the conventional Babbit alloys TEGO V738, TEGOSTAR and TEGOTENAX. With the lead based alloy LM-THERMIT an improvement is not achieved, yet, the bonding strength surpasses under all testing conditions a value of 50 N/mm2. This proves that the new bath is universally applicable. To test the alloy dependence of the bonding strength the Zn content was varied from 9 over 24, 50 and 60 to 70 weight - %. Depending on ZN content the bath temperature was raised from 280 to 380°C. On an average, the Zn content of 50% gave the most favorable strength values. As a bath temperature, 360°C turned out to deliver the best results.

A general problem with the structural durability calculation is the lack of clarity regarding the mathematical description of the Ultra High Cycle Fatigue (UHCF) region in the S-N diagram. Even taking into account that the fatigue strength still decreases beyond the standardized cycle limit, linear evaluation models lead to physically non-existing discontinuities. In the end, a non-linear and steady S-N curve has to be the basis for a suitable evaluation model containing the S-N field in its entity. In this work, a flexible algorithm based on the Modified Goniometric Model (MGM) is generated, tested and proven capable for practice. Not only the S-N curve itself but also the scatter is plausibly described. The distribution according to Müller and the tangent distribution developed here extend the spectrum of distribution functions. With a large sample size and an observable systematic error of the distribution, a transformation of the characteristic value via the tangent provides reliable extrapolations for quantiles with very high or low failure probability. The purely empirical MGM comprises steadily the continuous decrease of the S-N curve up to the UHCF region. In addition, a comprehensive transition from the LCF (Low Cycle Fatigue) to the HCF (High Cycle Fatigue) region is given. Therefore parts of the load spectrum beneath the so-called “endurance limit” and within the elastic-plastic region can be considered for the nominal stress concept. Extensive UHCF fatigue test data generated in this study on steel bolts of two material grades are successfully evaluated by means of the MGM. Furthermore it is shown that, independent of the material, the MGM permits plausible extrapolations of the fatigue strength beyond the standardized fatigue limit.

Residual stresses are mechanical stresses in components, which are free from outside forces, moments and temperature gradients. They can considerably influence failure limits since they overimpose with external stresses. Two categories of residual stresses are macro residual stresses and micro residual stresses varying on a microscopic scale. The latter encompasses stresses between different phases of a material and stresses between differently oriented crystallites. The aim of the thesis is the investigation of microstresses in technical metal alloys after rolling, plastic axial deformation and cyclic loading. A substantial focus is laid on the possibilities to determine the residual stress state in a material with orientation-dependent microstresses. So far different evaluation methods already exist. Each of these procedures is based on restrictive conditions concerning the crystallite coupling, the kind of the residual stress state or on idealized conditions of the investigated material. In recent years a new promising evaluation method has been presented which apart from the macrostress state enables the analysis of the microstress state as a function of the crystal orientation. This so called “harmonic method” displays the strain or stress components depending on the crystal orientations by a series of symmetric harmonics. The unknown coefficients are derived with regression analysis from the experimental strain measurements. The generated strain/stress orientation functions result in macroscopic values by averaging over all orientations. So far the procedure has been rarely used in practice. As part of this work it was applied to Cu basis alloys. As comparative evaluation methods an advanced crystallite group method and the relatively simple method of linearization of averaged D(sin²psi) distributions are selected. The methods are applied to experimental data and tested concerning their restrictive conditions. Apart from the direct comparison of the evaluation methods, the sensitivity of the procedures was examined in relation to the inputs, i.e. the size of the measuring expenditure and possible measuring errors. Apart from the macro residual stresses the harmonic method provides the orientation-dependent micro stresses. Thus, a tool is available with which the development of these orientation-dependent micro stresses can be analyzed under plastic deformation. As part of this thesis Cu basis alloys were selected as exemplary material for analysis and examination. Apart from the evaluation of residual stresses the assessment of their influence on the endurance limits of components under static and dynamic loading is of particular interest. The positive and negative effects of macro residual stresses during cyclic loading have already been thoroughly studied. However, only few investigations have been conducted on the behavior and the influence of microstresses during cyclic loading. The microstresses can deviate severely from the macro residual stresses and can reach high absolute values compared to the yield points of the material. With a relaxation during cyclic loading they have rather little impact on failure limits. On the other hand rising or stable high initial values are more likely to influence failure limits. Therefore an examination of the development of the micro residual stresses is necessary and was conducted on a ferrite/austenitic duplex stainless steel with approximately balanced portions of the phases. A pulsating bending load was selected to apply pure tension on one side of the specimen and pure compression on the opposite side. Both phases can be measured well, so that apart form the development of the orientation-dependent microstresses primarily the stresses between the phases could be analyzed. The influence of a high anisotropy was examined with comparative measurements of a brass alloy.

Last stage rotor blades of low pressure steam turbines are still being under consideration. In order to increase the effectiveness of the low pressure turbine a new open porosity powder metallurgical composite should be developed, so that the condensed water could be sucked off over the whole surface instead of locally via slots. To this end chromium steel powder for the carrier material and the porous surface layer is combined with place holder material for the suction ducts. The open porous layer is formed from mixtures of chromium steel powder and pure iron powder and different salts as place holder powder. After hot isostatic pressing the powder metallurgical composite, the dummy material, which is used to finally yield the porosity in the composite, is be leached out. In different experiments the manufacturing parameters are established.

The current lavatories in passenger aircrafts show substantial deficits concerning hygiene, environment compatibility and expenses. It is the aim of the project ITK (innovative toilet system – waterless lavatory) to improve the before-named deficits, starting from the first prototype of a waterless lavatory (developed by Airbus Germany and the EADS within the framework of LUFO II). The requirements for a new lavatory system are based on the current lavatory system, test results with the existing prototype and problem areas of the current toilet system in aircrafts. On this basis, three concepts were compiled for the innovative lavatory system. These concepts were estimated on the bases of the main demands: hygiene, inflammability and complexity. The first evaluation made clear that the concept C offers the slightest advantages. Afterwards, a profitability analysis was executed. Main emphasis here was the target cost planning. It turned out that both concepts A and B would be in line with the target budget. Because of the better technical assessment of concept A it was decided to specify and detail this concept. The next step after detailing concept A was to investigate the current disposal ways. This was necessary because the new toilet system shell use the existing disposal ways. Afterwards, the nationally and internationally disposal directives were treated concerning environmental law. The next step was to compare different existing foil materials with the information and requirements collected. It turned out that none of the existing materials fulfills the requirements in aviation or requirements of the disposal ways. Therefore, a new foil material must be developed on the bases of the given requirements. The conclusion of this study is that cost can be saved with the chosen concept, as well as the hygienic standard raised. Due to constantly fresh foil on the toilet seat a maximum on cleanliness is given. This will of even further importance in times of rising passengers´ numbers and increasing hygiene consciousness. Perfect hygiene with every use of the toilet can also contribute to the passengers´ satisfaction which can lead to increasing passenger numbers of the different airlines. This concept for lavatories is not only usable in aircrafts; it can also be installed in all other traffic means, as for example railway, ships and buses. Another potential of use would even be a public lavatory, for example in restaurants. For this kind of application some constructive changes must be carried, yet out without changing the basic idea of a lavatory out-fitted with a foil bag mechanism.

The decisive advantage of PM manufacturing is the cost saving potential of producing net shaped parts with tight tolerances. Nevertheless, secondary operations such as machining are a major part in the manufacturing process of an increasing number of PM parts, since e.g. undercuts or holes perpendicular to the pressing direction cannot be produced by uniaxial pressing. Supplementary machining, mainly turning, drilling, and tapping, leads to noticeably increasing production costs, since machining is more difficult with porous PM parts than with pore-free materials. Especially the machining of high strength PM steels with martensitic or partially martensitic microstructure is often extremely difficult and cost intensive. Consequently, up to now heavy duty PM parts are often produced by double pressing, double sintering technology. With this technique, machining is usually done after the first sintering. From the economical point of view, it would certainly be preferable to save the second pressing and sintering steps and to produce the parts by alternative production routes. One of these alternative routes is the warm compaction technology, which can be combined either with green machining or with machining after sintering as a secondary shaping operation. The investigations presented in this thesis were started to provide for the first time reliable data on both process alternatives. The first part describes the chances and the limitations of green machining for the most important machining processes, drilling, tapping, and turning in interrupted cutting. The criterion for successful green machining is the product quality. The aim of the investigations is the optimisation of the cutting processes by variation of the cutting parameters and the tools. The optimum product quality which can be achieved by green machining is described quantitatively for all machining processes investigated. Additionally, the wear behaviour of different tool materials is tested in a spot check for one of the processes, the green drilling, to get a first impression of the relevance of tool wear for green machining applications. In the second part of the investigations, the machining behaviour after sintering is investigated for the same machining processes and for the same materials. For a comparison of the machining properties, cost optimum cutting speeds and the minimum cutting costs are established by tool life tests according to the Taylor and to the exponential model. Together with the results of the green machining tests, these data facilitate to decide which of both processes is favourable for a given application.

Objective of the present work is the measurement of electrochemical potential data on real surfaces in their state under operating conditions. During such a potential measurement a constant distance between the probe and the surface is the main parameter. A literature overview shows that only the Scanning Vibrating Electrode Technique (SVET) is suited for 3D scanning procedures, all others are restricted to plane surface applications. Yet, if a specimen has to be prepared for a 2D measurement, the surface of interest is changed and the recorded potential data are affected. The development of the measurement technique SCAn (Scanning Corrosion Analysis) is described here which allows to establish the potential map at deformed surfaces with a constant measurement distance. The procedure is executed in two steps: First, the topography of the surface of interest is measured by means of an opto-electronic device. Subsequently the scanning probe detects the potential distribution controlled by the stored surface data to attain a con-stant working distance between the probe tip and the specimen. Because of the measurement procedure in two steps, a relocalisation of the topographical data and the potential distribution is required. This is the main restriction for the detection of very small surface irregularities. During pilot tests with plane copper samples the main parameters of galvanostatic potential measurements were figured out. The measurement distance, which depends on the geometry of the probe, mainly affects the surface potential, and also the influence of the polarisation current of the electrochemical cell on the potential profiles is demonstrated. The line scans were additionally disturbed by microgeometric changes of the surface which may occur e.g. at weld seams. 3D potential distributions were taken from weld joints of micro-alloyed steels preferentially used in the shipbuilding industry. A measuring bed was set up for 3D SCAn comprising a controler for electrochemical cell measurements with the related software, a three axis manipulator, an electrochemical cell, a laser device and a computer. The computer controls the scanning procedures and the data handling by an especially developed software package written in LABView. Its modular structure offers the opportunity to expand the measurement software and to apply new or modified scanning techniques with the measuring bed. The 3D potential distributions around weld seams permit to distinguish the effect of changes of microstructure in the heat affected zones and the effect of the chemical composition of the applied filler materials. The strong influence of the measurement distance on the potential values, which was already detected by 2D potential profiles with copper materials, has been confirmed with potential scanning studies of technical surfaces. For future investigations, an improved measurement equipment can lead to a higher stability of the electronic periphery and an accurate reproducibility of the 3D-manipulator. Additionally, a micromechanically manufactured probe is highly appreciated. These measurement components are well known from other mapping techniques and enable a better mechanical and electrochemical resolution at 3D surfaces. One advantage of the measurement principle and the present assembly is the procedure performance in two steps. The topographical data scanning runs completely independent of the electrochemical potential record. Therefore the installation of an established scanning procedure like the Scanning Kelvin Probe (SKP) or the Scanning Reference Electrode Technique (SRET) is feasible. The modular structure of the measurement software can easily be adapted to a modified scanning equipment; a 3D-SKP or 3D-SRET measurement can be performed.