Fachgebiet Metallische Werkstoffe
https://kobra.uni-kassel.de:443/handle/123456789/2007101819402
2024-03-28T21:22:50ZBend Straightening of a Carbonitrided Gear Shaft – Consequences on Residual Stresses and Retained Austenite near the Surface
https://kobra.uni-kassel.de:443/handle/123456789/15570
Carbonitriding of shafts in drive technology is strongly connected with distortion. Bend straightening is an important process step in order to eliminate distortion without removing the hardened surface layer. As shown in several investigations, even for simple part geometries, bending induced stresses and plastic deformations have a strong impact not only on the residual stress state but also on the microstructure after straightening. As gear shafts become increasingly filigree and complex in their geometry, the components state after straightening is only understood in rare cases. Due to indispensable, function based notches as well as changes in the cross section, these effects will occur especially in areas of small cross sections or notches in conjunction with high bending stresses. It is the objective of this work, to characterize these critical areas with respect to the distribution of residual stresses and retained austenite along the circumference as well as in the in-depth direction. Therefore, the measured distributions of residual stresses, integral width values and retained austenite near the surface will be presented and discussed. For this purpose a carbonitrided gear shaft taken out of a large production volume was investigated before and after a commonly used straightening operation.; In der Antriebstechnik stellt das Biegerichten nach der Einsatzhärtung von Wellen einen wichtigen Prozessschritt dar, um den oftmals unvermeidlichen Verzug zu beseitigen und gleichzeitig die harte Randschicht des Bauteils zu erhalten. Wie bereits in einigen Untersuchungen dargestellt wurde, beeinflussen die beim Richten vorliegenden Spannungen und die daraus resultierenden plastischen Deformationen sowohl den Eigenspannungszustand als auch die Mikrostruktur schon bei geometrisch simplen Bauteilen. Für die zunehmend filigranen und in ihrer Geometrie komplexen Wellen ist der Zustand nach dem Richten jedoch nur in seltenen Fällen bekannt und nachvollziehbar. Bei einer Welle, die konstruktiv notwendige Querschnittsänderungen oder auch Kerben aufweist, werden die genannten Effekte dort auftreten, wo Bereiche mit geringem Querschnitt und solche mit hohen Lastspannungen durch den Richtprozess zusammenfallen. Ziel dieser Arbeit ist es, diese kritischen Bereiche im Hinblick auf die Verteilung von Eigenspannungen und Restaustenit, sowohl entlang des Umfangs als auch in Tiefenrichtung, detailliert zu charakterisieren, um ein besseres Verständnis für den Zustand gerichteter Wellen zu gewinnen. Dazu werden die ermittelten randnahen Eigenspannungsverläufe und die Verteilungen der Integralbreiten sowie der Restaustenitgehalte am Beispiel einer in großer Stückzahl hergestellten Getriebewelle vor und nach einem praxisüblichen Richtprozess vorgestellt und diskutiert.
2017-06-20T00:00:00ZSchott, ChristopherZinn, WolfgangScholtes, BertholdNiendorf, ThomasCarbonitriding of shafts in drive technology is strongly connected with distortion. Bend straightening is an important process step in order to eliminate distortion without removing the hardened surface layer. As shown in several investigations, even for simple part geometries, bending induced stresses and plastic deformations have a strong impact not only on the residual stress state but also on the microstructure after straightening. As gear shafts become increasingly filigree and complex in their geometry, the components state after straightening is only understood in rare cases. Due to indispensable, function based notches as well as changes in the cross section, these effects will occur especially in areas of small cross sections or notches in conjunction with high bending stresses. It is the objective of this work, to characterize these critical areas with respect to the distribution of residual stresses and retained austenite along the circumference as well as in the in-depth direction. Therefore, the measured distributions of residual stresses, integral width values and retained austenite near the surface will be presented and discussed. For this purpose a carbonitrided gear shaft taken out of a large production volume was investigated before and after a commonly used straightening operation.
In der Antriebstechnik stellt das Biegerichten nach der Einsatzhärtung von Wellen einen wichtigen Prozessschritt dar, um den oftmals unvermeidlichen Verzug zu beseitigen und gleichzeitig die harte Randschicht des Bauteils zu erhalten. Wie bereits in einigen Untersuchungen dargestellt wurde, beeinflussen die beim Richten vorliegenden Spannungen und die daraus resultierenden plastischen Deformationen sowohl den Eigenspannungszustand als auch die Mikrostruktur schon bei geometrisch simplen Bauteilen. Für die zunehmend filigranen und in ihrer Geometrie komplexen Wellen ist der Zustand nach dem Richten jedoch nur in seltenen Fällen bekannt und nachvollziehbar. Bei einer Welle, die konstruktiv notwendige Querschnittsänderungen oder auch Kerben aufweist, werden die genannten Effekte dort auftreten, wo Bereiche mit geringem Querschnitt und solche mit hohen Lastspannungen durch den Richtprozess zusammenfallen. Ziel dieser Arbeit ist es, diese kritischen Bereiche im Hinblick auf die Verteilung von Eigenspannungen und Restaustenit, sowohl entlang des Umfangs als auch in Tiefenrichtung, detailliert zu charakterisieren, um ein besseres Verständnis für den Zustand gerichteter Wellen zu gewinnen. Dazu werden die ermittelten randnahen Eigenspannungsverläufe und die Verteilungen der Integralbreiten sowie der Restaustenitgehalte am Beispiel einer in großer Stückzahl hergestellten Getriebewelle vor und nach einem praxisüblichen Richtprozess vorgestellt und diskutiert.Pathways toward the Use of Non-Destructive Micromagnetic Analysis for Porosity Assessment and Process Parameter Optimization in Additive Manufacturing of 42CrMo4 (AISI 4140)
https://kobra.uni-kassel.de:443/handle/123456789/15568
Laser-based powder bed fusion of metals (PBF-LB/M) is a widely applied additive manufacturing technique. Thus, PBF-LB/M represents a potential candidate for the processing of quenched and tempered (Q&T) steels such as 42CrMo4 (AISI 4140), as these steels are often considered as the material of choice for complex components, e.g., in the toolmaking industry. However, due to the presence of process-induced defects, achieving a high quality of the resulting parts remains challenging in PBF-LB/M. Therefore, an extensive quality inspection, e.g., using process monitoring systems or downstream by destructive or non-destructive testing (NDT) methods, is essential. Since conventionally used downstream methods, e.g., X-ray computed tomography, are time-consuming and cost-intensive, micromagnetic NDT measurements represent an alternative for ferromagnetic materials such as 42CrMo4. In this context, 42CrMo4 samples were manufactured by PBF-LB/M with different process parameters and analyzed using a widely established micromagnetic measurement system in order to investigate potential relations between micromagnetic properties and porosity. Using multiple regression modeling, relations between the PBF-LB/M process parameters and six selected micromagnetic variables and relations between the process parameters and the porosity were assessed. The results presented reveal first insights into the use of micromagnetic NDT measurements for porosity assessment and process parameter optimization in PBF-LB/M-processed components.
2024-02-20T00:00:00ZEngelhardt, AnnaWegener, ThomasNiendorf, ThomasLaser-based powder bed fusion of metals (PBF-LB/M) is a widely applied additive manufacturing technique. Thus, PBF-LB/M represents a potential candidate for the processing of quenched and tempered (Q&T) steels such as 42CrMo4 (AISI 4140), as these steels are often considered as the material of choice for complex components, e.g., in the toolmaking industry. However, due to the presence of process-induced defects, achieving a high quality of the resulting parts remains challenging in PBF-LB/M. Therefore, an extensive quality inspection, e.g., using process monitoring systems or downstream by destructive or non-destructive testing (NDT) methods, is essential. Since conventionally used downstream methods, e.g., X-ray computed tomography, are time-consuming and cost-intensive, micromagnetic NDT measurements represent an alternative for ferromagnetic materials such as 42CrMo4. In this context, 42CrMo4 samples were manufactured by PBF-LB/M with different process parameters and analyzed using a widely established micromagnetic measurement system in order to investigate potential relations between micromagnetic properties and porosity. Using multiple regression modeling, relations between the PBF-LB/M process parameters and six selected micromagnetic variables and relations between the process parameters and the porosity were assessed. The results presented reveal first insights into the use of micromagnetic NDT measurements for porosity assessment and process parameter optimization in PBF-LB/M-processed components.Energy Resolved Residual Stress Analysis with Laboratory X-Ray Sources
https://kobra.uni-kassel.de:443/handle/123456789/15472
It is well known that existing residual stress fields play an important role for strength and lifetime of components. Consequently there is a great interest in the availability of fast, reliable and possibly nondestructive methods for their determination. In this context, X-ray diffraction methods play an important role in technical practice as well as in scientific research. They are based on the determination of lattice strains from which residual stresses are determined applying Hooke's law with appropriate elastic constants. In this paper – after a short survey of the basic principles – characteristic features of energy resolved methods for laboratory applications compared with angle resolved methods are outlined. A corresponding measuring device is presented and characteristic examples are given to demonstrate the possibilities and limitations of the method.; Aufgrund der Bedeutung, die Eigenspannungen für die Zuverlässigkeit und Beanspruchbarkeit von Komponenten besitzen, besteht ein großes Interesse an der Verfügbarkeit schneller, zuverlässiger und möglichst zerstörungsfreier Messverfahren. In diesem Zusammenhang kommt heute röntgenographischen Verfahren eine besondere Bedeutung in der Praxis zu. Sie basieren auf der Messung von Gitterdeformationen, aus denen unter Verwendung elastischer Konstanten Spannungen berechnet werden. In der vorliegenden Arbeit wird – nach einer kurzen Einführung in die Grundlagen – gezeigt, welche Besonderheiten bei energieauflösenden Verfahren im Vergleich zu den etablierten winkelauflösenden Verfahren bei der Anwendung im Labor bzw. einem industriellen Umfeld existieren. Ein entsprechendes Gerät mit seinen Möglichkeiten wird vorgestellt und anhand kennzeichnender Beispiele werden die zurzeit bestehenden Möglichkeiten und Grenzen energieauflösender Eigenspannungsanalysen aufgezeigt.
2017-04-17T00:00:00ZLiehr, AlexanderZinn, WolfgangDegener, SebastianScholtes, BertholdNiendorf, ThomasGenzel, ChristophIt is well known that existing residual stress fields play an important role for strength and lifetime of components. Consequently there is a great interest in the availability of fast, reliable and possibly nondestructive methods for their determination. In this context, X-ray diffraction methods play an important role in technical practice as well as in scientific research. They are based on the determination of lattice strains from which residual stresses are determined applying Hooke's law with appropriate elastic constants. In this paper – after a short survey of the basic principles – characteristic features of energy resolved methods for laboratory applications compared with angle resolved methods are outlined. A corresponding measuring device is presented and characteristic examples are given to demonstrate the possibilities and limitations of the method.
Aufgrund der Bedeutung, die Eigenspannungen für die Zuverlässigkeit und Beanspruchbarkeit von Komponenten besitzen, besteht ein großes Interesse an der Verfügbarkeit schneller, zuverlässiger und möglichst zerstörungsfreier Messverfahren. In diesem Zusammenhang kommt heute röntgenographischen Verfahren eine besondere Bedeutung in der Praxis zu. Sie basieren auf der Messung von Gitterdeformationen, aus denen unter Verwendung elastischer Konstanten Spannungen berechnet werden. In der vorliegenden Arbeit wird – nach einer kurzen Einführung in die Grundlagen – gezeigt, welche Besonderheiten bei energieauflösenden Verfahren im Vergleich zu den etablierten winkelauflösenden Verfahren bei der Anwendung im Labor bzw. einem industriellen Umfeld existieren. Ein entsprechendes Gerät mit seinen Möglichkeiten wird vorgestellt und anhand kennzeichnender Beispiele werden die zurzeit bestehenden Möglichkeiten und Grenzen energieauflösender Eigenspannungsanalysen aufgezeigt.On the Challenges toward Realization of Functionally Graded Structures by Electron Beam Melting—Fe-Base Shape Memory Alloy and Stainless Steel
https://kobra.uni-kassel.de:443/handle/123456789/15471
In the present study, an iron-manganese-aluminum-nickel (Fe-Mn-Al-Ni) shape memory alloy was processed on an austenitic steel (AISI 304) build platform by electron beam melting in order to study the feasibility of realizing functionally graded structures consisting of two different materials (i.e., a functional and a structural material). Compression specimens consisting of the processed shape memory alloy and the austenitic build platform in equal parts were investigated. The microstructure was analyzed in the as-built state and after different heat treatments, focusing on the interface between both materials. Scanning electron microscopy and electron backscatter diffraction measurements were conducted to reveal the relation between processing steps and the microstructural evolution. It is shown that the microstructure after the electron beam melting process is characterized by a preferred 〈001〉 orientation with respect to the build direction and that a suitable microstructure for good pseudoelastic performance can be realized by post-processing heat treatments. Finally, incremental strain tests up to 12% compressive strain were conducted to analyze the overall mechanical performance of the specimens.
2020-09-22T00:00:00ZTorrent, Christof Johannes JaimeBauer, AndréVollmer, MalteNiendorf, ThomasIn the present study, an iron-manganese-aluminum-nickel (Fe-Mn-Al-Ni) shape memory alloy was processed on an austenitic steel (AISI 304) build platform by electron beam melting in order to study the feasibility of realizing functionally graded structures consisting of two different materials (i.e., a functional and a structural material). Compression specimens consisting of the processed shape memory alloy and the austenitic build platform in equal parts were investigated. The microstructure was analyzed in the as-built state and after different heat treatments, focusing on the interface between both materials. Scanning electron microscopy and electron backscatter diffraction measurements were conducted to reveal the relation between processing steps and the microstructural evolution. It is shown that the microstructure after the electron beam melting process is characterized by a preferred 〈001〉 orientation with respect to the build direction and that a suitable microstructure for good pseudoelastic performance can be realized by post-processing heat treatments. Finally, incremental strain tests up to 12% compressive strain were conducted to analyze the overall mechanical performance of the specimens.