Röntgenographische Untersuchung von Spannungszuständen in Werkstoffen. Teil III. Fortsetzung von Matwiss. und Werkstofftechn. Heft 3/1995, S. 148–160 und Heft 4/1995, S. 199–216

X-Ray Investigation of Stress States in materials X-ray stress analyses on crystalline or partially crystalline materials are based on the determination of elastic lattice strains which are converted to stresses by means of theory of elasticity. The development of the sin²Ψ-method of X-ray stress analysis and of diffractometers substituting film chambers during the 1960s initiated an enormcus progress in X-ray stress analysis during the following three decades both in respect of the knowledge of the underlying principles and in respect of the practical application This report sketches the historical development of X-ray stress analyses and describes the actual state of the art of this important tool for materials science and engineering. Besides some important elements of X-ray physics and theory of elasticity, experimental aspects of practical applications are outlined. Standard measuring procedures and special measuring problems are described and hints for practical solutions are given. In particular, examples of destructive and non-destructive depth profiling of residual stresses, of residual stress analyses in thin coatings, in multilayer structures of thin coatings and in chemically graded coatings, of residual stress analyses in presence of textures, of residual and loading stress analyses in heterogeneous materials, in coarse grained, and in single crystalline materials are presented. The methods established up to now are explained and possible future developments are pointed out.     

Röntgenographische Untersuchung von Spannungszuständen in Werkstoffen. Teil II. Fortsetzung von Matwiss. und Werktoffechn. Heft 3/1995, S. 148–160

X-ray Investigation of Stress States in Materials X-ray stress analyses on crystalline or partially crystalline materials are based on the determination of elastic lattice strains which are converted to stresses by means of theory of elasticity. The development of the sin² ψ-method of X-ray stress analysis and of diffractometers substituting film chambers during the 1960s initiated an enormous progress in X-ray stress analysis during the following three decades both in respect of the knowledge of the underlying principles and in respect of the practical application. This report sketches the historical development of X-ray stress analyses and describes the actual state of the art of this important tool for materials science and engineering. Besides some important elements of X-ray physics and theory of elasticity, experimental aspects of practical applications are outlined. Standard measuring procedures and special measuring problems are described, and hints for practical solutions are given. In particular, examples of destructive and non-destructive depth profiling of residual stresses, of residual stress analyses in thin coatings, in multilayer structures of thin coatings and in chemically graded coatings, of residual stress analyses in presence of textures, of residual and loading stress analyses in heterogeneous materials, in coarse grained, and in single crystalline materials are presented. The methods established up to now are explained and possible future developments are pointed out.     

Röntgenographische Untersuchung von Spannungszuständen in Werkstoffen

X-Ray Investigation of Stress States in Materials X-ray stress analyses on crystalline or partially crystalline materials are based on the determination of elastic lattice strains which are converted to stresses by means of theory of elasticity. The development of the sin² ψ-method of X-ray stress analysis and of diffractometers substituting film chambers during the 1960s initiated an enormous progress in X-ray stress analysis during the following three decades both in respect of the knowledge of the underlying principles and in respect of the practical application. This report sketches the historical development of X-ray stress analyses and describes the actual state of the art of this important tool for materials science and engineering. Besides some important elements of X-ray physics and theory of elasticity, experimental aspects of practical applications are outlined. Standard measuring procedures and special measuring problems are described, and hints for practical solutions are given. In particular, examples of destructive and non-destructive depth profiling of residual stresses, of residual stress analysis in thin coatings, in multilayer structures of thin coatings and in chemically graded coatings, of residual stress analyses in presence of textures, of residual and loading stress analyses in heterogeneous materials, in coarse grained, and in single crystalline materials are presented. The methods established up to now are explained and possible future developments are pointed out.     

Mechanische Wechselwirkungen an Werkstoffübergängen von Verbundkörpern aus ungleichartigen Werkstoffen. Teil II: Grundlagen zur Berechung von Spannungs- und Verformungszusänden

Mechanical Interactions at Material Transitions in Composite Bodies out of Dissimilar Materials. Part II: Basic Principles for the Calculation of Stress and Strain States . The different types of interfaces are defined with the help of the concepts of geometry and the material transitions occuring in them. Among other things, a possibility for exact quantitative definitions of continuous and discontinuous material transitions at the interface of bonded materials is given. The well-known error function, as well as the static and kinematic interface conditions, are made use of. These enable the establishment of quantitative expressions for the stress and strain states in composite bodies. The difference between the continuous and discontinuous type of material transition give rise to highly differing equations. The cylindrical composite bodies are at first considered. The special treatment of the composite bodies out of sheet and plate materials are discussed in a separate chapter. The “sufficient” interface conditions for the discontinuous material transitions in cylindrical, sheet and plate-composite bodies are further derived.     

Über den Einfluß von Eigenspannungen,Nahtgeometrie und mehrachsigen Spannungszuständen auf die Betriebsfestigkeit geschweißter Konstruktionen aus Baustählen

About the Influence of Residual Stresses, Weld Geometry and Multiaxial Stress States on the Oprational Fatigue Strength of Welded Constructions from Structural Steels For a fatigue design of welded structures among other influences also the influence of residual stresses, weld geometries and multiaxial stresses must be taken into account. Knowledge about the influence of residual stresses in the high-cycle fatigue region cannot be transformed unconditionally to the behaviour in the finite-fatigue life region or to variable amplitude loading with exceedances of the endurance limit, because the fatigue behaviour depends also on the stress concentration in the weld toe and the related stress relief. Principally, the fatigue strength is improved by a better weld geometry, e.g. by TIG-dressing, by introduction of radii which are big enough. In order to transform data obtained on specimens to components of bigger size criteria like structural or local equivalent stress, first technically detectable crack and size effects must be considered. For a fatigue life calculation for structures under variable amplitude loading a damage sum of D = 0.5 is recommended. While for the evaluation of multiaxial stress states with constant principle stress directions the von Mises criterion can be applied satisfactorily using structural or local stresses in the weld toe. However, conventional hypotheses fail by an overestimation of fatigue life, when the principle stress directions change, e.g. due to a phase difference between normal and shear stresses. Presently, in such cases only an experimental proof of the fatigue behaviour can be performed.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil III: Schleifen von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part III: Grinding of Hard Alloys Straight surface plunge grinding tests were performed at a peripheral wheel velocity of v_c = 15 m/s on exemplary iron based alloys FeCr12C2.1, FeCr13Nb9MoTiC2.3 and FeCr14Mo5WVC4.2 both in soft annealed and hardened and slightly relieved microstructural condition. Vitrified bonded wheels of type SC 60 3/4 (SiC) and 2B252 M6 V240 (CBN) with a diameter of D_S = 300 mm were used as abrasive tools. When selecting the machining parameters due consideration was given to materials related aspects and an acceptable volumetric removal rate per unit width of Q_w′ = 4 mm³/mms was taken into account. Subsequent examinations focused on the analysis of the thermomechanical load imposed on the microstructure. The grinding of hard alloys by means of conventional abrasives is significantly influenced by the content and type of the hard phases present. Due to their excessive hardness primarily solidified M₇C₃ are highly resistant to the ingressing abrasive grains. Accordingly, maximum grinding normal forces are encountered with the FeCr14Mo5WVC4.2 alloy. However, the normal forces are also found to be higher in case of a hardened metal matrix, when SiC is used as abrasive or a wet grinding process is applied. As regards tangential forces they also show a tendency of being influenced by structure-specific hard phases. Process temperature and stress condition ahead of the grain cutting edges are of great significance for the behaviour of the hard phases during grinding. If the mechanical component is predominant, accumulations of near-surface eutectic carbides are destroyed. Individual stalk-like carbides often break in the phase center. However, in the event of thermal load an eutectic M₇C₃ may also be deformed plastically. Through the cleavage fracture of coarse primary M₇C₃ phases microcracks are initiated that in the end will grow into macrocracks. Carbide fragments broken off will impair the surface quality. In particular the metal matrix reacts strongly to the process heat generated. In case of dry grinding using SiC a rehardening zone has been detected near the surface. The alloy-specific austenizing temperature of approximated 1000 °C was exceeded. As the distance to the surface increased a tempered area with hardness figures below those of the basic structure was found. No rehardening will occur if CBN is used as abrasive. The residual surface stresses determined correlate with the extent of thermal and mechanical load imposed. Whereas an extensive crack network is evident after dry grinding when SiC has been used as abrasive, no surface cracks were detected when employing the CBN abrasive. Due to the excellent thermal conductivity characteristics of this grinding medium a thermal damage during dry grinding can be avoided. While the use of grinding fluid will improve the surface roughness, cracks may form due to the abrupt quenching effect, especially if hardened material is involved. Increasing the workpiece velocity will also contribute to reduce the risk of crack development, but, on the other hand, leads to a surface quality deterioration that cannot be accepted.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil I: Gefüge und Eigenschaften von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part I: Structure and Properties of Hard Alloys Hard alloys count among the materials that contain hard phases. This involves primary and/or eutectic hard phases embedded in a metallic matrix. The characteristics of the individual microstructural constituents may be combined to form a material featuring excellent wear resistance and a high resistance to fracture. For that reason, the material can be widely used in all applications where the wear resistance to abrasion is essential. In the event low operating temperatures are involved the component costs to service life ratio speaks for hard alloys on Fe basis. Above 600 °C heat resistant Ni and Co matrices are to be given preference. Carbides and borides of the transition metals are specially suited as hard phases. They attach well to the surrounding matrix. Nowadays, alloys of the FeCrC system are primarily employed for economic reasons. As nickel-based material the NiCrSiB alloying system is frequently employed. Hard alloys on cobalt basis usually belong to the CoCrWC (stellite) system. In many fields of application components of this material group require a largearea metal cutting technique (eg for barrel extruders, crushing rollers, valve seats). However, problems may be encountered during machining due to the high hardness and excellent wear resistance of this material. The structural difference between hard phases and metallic matrix causes different reactions to stresses exerted during the machining process. Process-related changes of the microgeometric surface characteristics and the physical condition of the surface zone of a material are paraphrased by the term “surface integrity”. To create a basis for assessing the machining influence on the multiphase component surface layer, the first part of the paper discusses manufacturing techniques, constitution of the microstructure and main properties of the individual structural components.     

Löten von Diamant – Grenzflächenreaktionen. und Benetzung

Diamond Brazing – Interfacial Reactions and Wetting Diamond tools are increasingly gaining importance as cutting materials for various construction materials. The quality of synthetic diamonds, monocrystalline as well as polycrystalline or CVD‐diamonds has been significantly improved over the last years. Integrating these cutting materials requires adequate joining technologies that produce sound joints without exposing the temperature sensitive diamond to too elevated temperatures. The paper highlights current developments in the joining of synthetic diamonds to steel and cemented carbide. Owing to their covalent atomic bonding diamonds cannot easily be wetted and joined by employing conventional brazing alloys. Hence, active agents are needed to foster an interfacial reaction. Different active filler concepts are presented and discussed regarding their joint formation. The brazing temperatures influence not only possible diamond degradation but also the interfacial decomposition of the diamond due to the formation of corresponding reaction layers.Active brazing, monocrystalline     

Funktionalisierung der Oberfläche von Mikrostrukturen – Technologie und Anwendungen –. Functionalization of Microstructure Surfaces

Microtechnology enables the dimensioning and fabrication of cost‐effective novel platforms for bio diagnostics. By the employment of plasma technologies for specific adjustment of surface characteristics, custom‐designed platforms are feasible. For a fast and reliable adjustment of product properties, special test chips have been developed. The conclusions for this development and first products are presented in this article.     

Kavitationsuntersuchungen an Werkstoffen und Beschichtungen – Vergleich verschiedener Auswerte‐verfahren und Gegenüberstellung der Kavitationserosion von EN‐GJS‐600‐3, G‐CuAl8Mn8 und GX4CrNi13‐4 + QT

Material damages in fluid flow machines which are charged by cavitation cause costs due to service and downtime of the affected machines. Therefore the aim of engineering needs to be cutback of cavitation by the optimization of fluid flows and suitable selection of materials relating to cavitation. Cavitation has to be moved to temporally uncritical time ranges. This is why the cavitation resistance of materials and coatings that may be used to increase product durability need to be tested. In regard to extensive test series the adequacy of different evaluation methods like touch slice measurement, white light profilometry, weighing and optical comparison got tested in regard to suggest a suiting evaluation method for all possible applications. The results are showing that for evaluation of material tests the weighing method with a highly resolving scale suites best. In fact the use of white light profilometry is much better for accurate evaluation of coating tests. The optical comparison method supports quick comparisons of specimen in both cases. Broader research shows the impressive cavitation resistance of G‐CuAl8Mn8 compared to the probed steel specimen.     

Die spezifische Wärmekapazität von metallischen Werkstoffen. III. Teil: NiCr 15 Fe (INCONEL 600) und vier weitere Werkstoffe aus der Gruppe der NE-Metalle

Specific Heat Capacities of Metallic Materials Part III: Five Non-ferrous Metals, Including NiCr 15 Fe (INCONEL 600) The following investigation deals with the measurement of the temperature dependence of five metallic materials, belonging to the group of non-ferrous metals. The specific heat capacity of NiCr 15 Fe is similar to pure nickel after subtracting the contribution of ferromagnetic order. Above 600°C an additional contribution is found, caused by the formation of Ni₃Cr-clusters with short range order. The titanium material Ti99.5 shows a similar behaviour like pure titanium. There are only small differences in the range of the phase transition. The values of TiAl 5 Sn 2 are slightly raised in comparison to pure titanium. CuNi 10 Fe and CuNi 30 Fe, both having excellent corrosion resistance against seawater attach, show nearly the same specific heat capacity as copper. In CuNi 10 Fe an additional contribution, due to the precipitation of nickel-iron particles, is found. There is no discontinuity in the specific heat capacity curve of CuNi 30 Fe, being caused by nickel-iron precipitation.     

Spannungsrißkorrosion in hochreinem Wasser von 3–3 ½% NiCrMoV-Vergütungsstählen für Dampfturbinen-Scheiben und -Wellen. Teil I

SCC in High Parity Water In recent years intergranular stress corrosion cracking has occured world-wide in the shrink-fitted discs of low pressure turbine rotors made of low alloy steels. Only in a few cases steam impurities such as NaOH, Na₂CO₃, Na₂SO₄, H₂S or Nacl, which initiate SCC, could be found. To clarify the SCC-behaviour experiments on turbine disc steels with different chemical compositions an yield strength were performed in high purity water. The results show, that chemical composition has no effect on the crack initiation. Under high purity water conditions no crack initiation due to stress corrosion cracking is observed on the steel with a yield strength of 850 N/mm². On the steel with a yield strength of 1250 N/mm² which is not used in service, crack initiation occurs in pure water. But if sharp cracks already exist, crack propagation occurs in both cases. The investigations showed, that stress corrosion cracking of turbine discs can be prevented by a good water chemistry with a cation conductivity less than 0.2 μS/cm (μmho/cm).     

Entwicklung mit Hilfe des Warmpreßverfahrens hergestellter Sinterstähle mit optimaler Warmstreckgrenze,Dauerfestigkeit und Kerbschlagzähigkeit – Teil 1

Development of Hot-Forged Sintered Steels with Optimum Yield Point at Higher Temperature, Fatigue and Impact Strength . The material characteristic values of hot-forged sintered steels are reported. Besides the usual properties, (ultimate tensile strength, yield strength and elongation at room temperature). The behaviour of materials at higher temperature is of great importance. Further, fatigue strength and impact strength must be considered. The influence of heat treatment on these properties were investigated and brought to a correlation with the formation of microstructures. The hot forging P/M preform requires a special attention on alloying elements and alloying techniques. Optimum properties results when using completely alloyed powders or mixed powders by employing special master alloys. This and further problems involving alloying techniques and particularly the behaviour of carbon as an alloying element is reported in details. The correlation between mechanical properties and fracture behaviour is discussed.