Degradation von Werkstoffen
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Das DVS-Vorhaben 01.3211 „Herstellung beanspruchungsgerechter Oberflächen durch Kombination innovativer additiver und abtragender Fertigungsschritte an hochbelasteten Komponenten“ ist ein Kooperationsprojekt der Bundesanstalt für Materialforschung und -prüfung (BAM) und dem Institut für Schweißtechnik und Trennende Fertigungsverfahren (ISAF) der Technischen Universität Clausthal. Das Übergeordnete Projektziel ist das Erlangen von Erkenntnissen für eine sichere und wirtschaftliche, kombinierte additive und abtragende Fertigung aus kostenintensiven Werkstoffen hochbelasteter Komponenten insbesondere für KMU. Dabei stehe die beiden Werkstoffe CoCr26Ni9Mo5W (2.4681) und FeNi36 (1.3912) im Fokus. Mittels Modifikation der Schweißzusätze sind homogen und isotrop ausgeprägte Werkstoffeigenschaften und eine Erhöhung der Prozessstabilität und Fertigungsfreiheitsgrade bei der additiven Fertigung erzielbar. Darüber hinaus wird der Einfluss nachfolgender abtragender Bearbeitungsschritte des ultraschallunterstützen und des konventionellen Fräsprozesses untersucht. Im Laufe der Sitzung des projektbegleitenden Ausschusses (PbA) wurde der aktuelle Bearbeitungsstand sowie der Zeitplan vorgestellt. Darüber hinaus wurde mit dem PbA über die bereits erzielten Ergebnisse diskutiert. Abschließend wurde ein kurzer Ausblick über die zeitnah beginnenden Arbeiten beider Forschungseinrichtungen sowie ein Überblick über die vorhabenbezogenen Aufwendungen der Wirtschaft und des Ergebnistransfers in die Wirtschaft gegeben.
The sustainable and resource-efficient production of wind energy plants requires the use of modern high-strength fine-grain structural steels. This applies to both foundation and erection structures. During the assembly of steel structures, unacceptable defects can occasionally be found in the weld area. In most cases, the economical solution would be local thermal gouging of the affected areas and re-welding. Due to the high shrinkage restraint of the joint groove in the overall structure, the superposition of design and welding-induced residual stress can lead to crack formation and ultimately to component failure, particularly in interaction with the degradation of the microstructure and mechanical properties high-strength steels during the repair process.
In this context, component-related investigations (FOSTA-P1311/IGF-Nr. 20162 N) focusing on welding residual stress evolution during local thermal gouging and rewelding of S500MLO and S960QL are carried out using in-situ digital image correlation (DIC) and ex-situ X-ray diffraction methods (XRD). Therefore, self-restrained specimens were systematically gouged and rewelded with defined welding heat control (heat input, working temperature) and parameters. By means of structural mechanics calculations, geometries of self-restrained specimens were identified, that represent defined rigidity conditions of repair welds of real components. It could be shown that with increasing restraint intensity significantly higher residual stresses occur in the weld metal and heat affected zone. Furthermore, it revealed that the transverse stresses along the weld seam decrease at the weld seam ends leading to different stress state during gouging and welding. XRD analysis of the local residual stresses after cooling to RT longitudinal and transverse to the weld direction showed a good comparability with global DIC analyses.
Alloy Modification and ultrasonic assisted milling of wear resistant alloys with defined surfaces
(2023)
The targets for reducing CO2 emissions are closely linked to the development of highly efficient and economical steel components in plant, process and power plant technology, which require wear protection coatings tailored to the application and steel material for high combined corrosive, tribological, thermal and mechanical stresses. There is a growing demand in industry for defined functional surfaces of high quality for these coatings. Milling is a standard process for finish machining. The desired properties of wear resistant alloys imply significant challenges for the milling process due to high tool wear and surface defects. Besides the hardness of the coating materials, especially due to the precipitations, inhomogeneous, anisotropic weld structures of the claddings lead to further deteriorations of milling processes due to unstable milling conditions and process forces.
A joint project of BAM and ISAF of TU Clausthal (Fosta P1550/IGF 21959 N) investigates the optimization of these challenging machining conditions by means of alloy modifications of the welding powder for plasma transferred arc cladding, without reducing the wear protection potential and using ultrasonic assisted milling process.
In this paper, the influence of the microstructure and precipitation morphology adjusted by means of alloy modification on machining for a NiCrMoSiFeB alloy (trade name: Colmonoy 56 PTA) is investigated. Through metallurgical investigations and in-situ measurement of cutting forces and temperatures at the cutting edge during the milling process as well as the subsequent investigation of tool wear and surface integrity, a detailed analysis and correlation between microstructural properties and machinability is feasible. The findings allow recommendations for standards and processing guidelines, enabling safe and economical production of highly stressed steel components with non-critical, cost-reduced materials.
Alloy Modification and ultrasonic assisted milling of wear resistant alloys with defined surfaces
(2023)
The targets for reducing CO2 emissions are closely linked to the development of highly efficient and economical steel components in plant, process and power plant technology, which require wear protection coatings tailored to the application and steel material for high combined corrosive, tribological, thermal and mechanical stresses. There is a growing demand in industry for defined functional surfaces of high quality for these coatings. Milling is a standard process for finish machining. The desired properties of wear resistant alloys imply significant challenges for the milling process due to high tool wear and surface defects. Besides the hardness of the coating materials, especially due to the precipitations, inhomogeneous, anisotropic weld structures of the claddings lead to further deteriorations of milling processes due to unstable milling conditions and process forces.
A joint project of BAM and ISAF of TU Clausthal (Fosta P1550/IGF 21959 N) investigates the optimization of these challenging machining conditions by means of alloy modifications of the welding powder for plasma transferred arc cladding, without reducing the wear protection potential and using ultrasonic assisted milling process.
In this paper, the influence of the microstructure and precipitation morphology adjusted by means of alloy modification on machining for a NiCrMoSiFeB alloy (trade name: Colmonoy 56 PTA) is investigated. Through metallurgical investigations and in-situ measurement of cutting forces and temperatures at the cutting edge during the milling process as well as the subsequent investigation of tool wear and surface integrity, a detailed analysis and correlation between microstructural properties and machinability is feasible. The findings allow recommendations for standards and processing guidelines, enabling safe and economical production of highly stressed steel components with non-critical, cost-reduced materials.
Alloy modification and ultrasonic assisted milling of wear resistant alloys with defined surfaces
(2023)
The targets for reducing CO2 emissions are closely linked to the development of highly efficient and economical steel components in plant, process and power plant technology, which require wear protection coatings tailored to the application and steel material for high combined corrosive, tribological, thermal and mechanical stresses. In addition to increasing demands to replace conventional cobalt alloys with nickel alloys as a result of price and supply risks, there is a growing demand in industry for defined functional surfaces of high quality for these coatings. Milling is a standard process for finish machining. The desired properties of wear resistant alloys imply significant challenges for the milling process due to high tool wear and surface defects. Besides the hardness of the coating materials, especially due to the precipitations, inhomogeneous, anisotropic weld structures of the claddings lead to further deteriorations of milling processes due to unstable milling conditions and process forces.
A joint project of BAM and ISAF of TU Clausthal (Fosta P1550/IGF 21959 N) investigates the optimization of these challenging machining conditions by means of alloy modifications of the welding powder for plasma transferred arc cladding, without reducing the wear protection potential and using ultrasonic assisted milling process.
In this paper, the influence of the microstructure and precipitation morphology adjusted by means of alloy modification on machining is investigated. The alloy used is a NiCrMoSiFeB alloy (trade name: Colmonoy 56 PTA). Through metallurgical investigations and in-situ measurement of cutting forces and temperatures at the cutting edge during the milling process as well as the subsequent investigation of tool wear and surface integrity, a detailed analysis and correlation between microstructural properties and machinability is feasible. The findings allow recommendations for standards and processing guidelines, enabling safe and economical production of highly stressed steel components with non-critical, cost-reduced materials.
Alloy Modification and ultrasonic assisted milling of wear resistant alloys with defined surfaces
(2023)
The targets for reducing CO2 emissions are closely linked to the development of highly efficient and economical steel components in plant, process and power plant technology, which require wear protection coatings tailored to the application and steel material for high combined corrosive, tribological, thermal and mechanical stresses. In addition to increasing demands to replace conventional cobalt alloys with nickel alloys as a result of price and supply risks, there is a growing demand in industry for defined functional surfaces of high quality for these coatings. Milling is a standard process for finish machining. The desired properties of wear resistant alloys imply significant challenges for the milling process due to high tool wear and surface defects. Besides the hardness of the coating materials, especially due to the precipitations, inhomogeneous, anisotropic weld structures of the claddings lead to further deteriorations of milling processes due to unstable milling conditions and process forces.
A joint project of BAM and ISAF of TU Clausthal (Fosta P1550/IGF 21959 N) investigates the optimization of these challenging machining conditions by means of alloy modifications of the welding powder for plasma transferred arc cladding, without reducing the wear protection potential and using ultrasonic assisted milling process.
In this paper, the influence of the microstructure and precipitation morphology adjusted by means of alloy modification on machining is investigated. The alloy used is a NiCrMoSiFeB alloy (trade name: Colmonoy 56 PTA). Through metallurgical investigations and in-situ measurement of cutting forces and temperatures at the cutting edge during the milling process as well as the subsequent investigation of tool wear and surface integrity, a detailed analysis and correlation between microstructural properties and machinability is feasible. The findings allow recommendations for standards and processing guidelines, enabling safe and economical production of highly stressed steel components with non-critical, cost-reduced materials.
Alloy 36 (1.3912), also known as “Invar”, is an alloy with 36% nickel. The alloy has a remarkably low thermal expansion coefficient in certain temperature ranges. Therefore, it is used in applications in which dimensional stability is critical, such as moulding tools for composite materials in aerospace and automotive applications. Moreover, increasingly complex structures and the optimisation of resource efficiency also require additive manufacturing steps for the production or repair of components. Additively manufactured components have a heterogeneous microstructure and anisotropic mechanical properties. In part I of this investigation, the initial alloy 36 is modified with the elements Ti, Zr and Hf up to a maximum of 0.33 wt.-%. The influence of the modification elements on the microstructure as well as on the hardness of the AM components is examined. Part II focusses on the effect of the alloy modifications on machinability as well as on the surface integrity of plasma-transferred-arc-welded (PTA) and finish milled invar components. The results show that PTA welding cause numerous finely distributed precipitates with high silicon content.
Alloy 36 is an iron-based alloy with 36% nickel. It is used in applications in which dimensional stability is critical, such as molding tools for composite materials in aerospace and automotive applications. Moreover, increasingly complex structures and the optimisation of resource efficiency also require additive manufacturing steps for the production or repair of components. Additively manufactured components have a heterogeneous microstructure and anisotropic mechanical properties. In addition, the manufactured components require subsequent machining surface finishing due to the high requirements. Nickel iron alloys are difficult to machine. Additionally, inhomogeneous microstructure may lead to unstable cutting forces and conditions. Alloy modifications are made to the alloy 36. For this purpose, titanium, zirconium and niobium are added up to 1 % by mass each. Plasma-Transferred-Arc is used for the welding tests. The hardness profile is determined on the transverse section. The initial structure as well as the modifications have an austenitic structure. The microstructure of the modifications of Alloy 36 with 1% Ti and 1% Zr is not refined, instead the grain size increases.
Alloy 36 (1.3912), also known as “Invar”, is an alloy with 36% nickel. It was developed in 1897 by Guillaume and stands out for its very low thermal expansion coefficient. It is classified as a difficult-to-cut material and is commonly used for the production of fiber-reinforced composites in the field of mold construction. Additive manufacturing (AM) offers many economic advantages regarding the repair, modification and manufacture of entire components. Subsequent machining of the AM components is necessary to account for complex structures, final contours or defined surfaces. This is usually done using a tool with a geometrically defined cutting edge, i.e., milling processes. Surface integrity is determined by metallurgical (e.g., microstructure of the subsurface), topological (e.g., surface defects, roughness) and mechanical (e.g., residual stresses) factors, which is crucial in terms of component safety and performance. Modern, hybrid cutting processes, such as ultrasonic-assisted milling (US), provide potentially improvement of the cutting situation of these components.
In part I of this investigation, the initial alloy 36 is modified with the elements Ti, Zr and Nb up to a maximum of 1 wt.-%. The influence of the modification elements on the microstructure as well as on the hardness of the AM components is examined. Part II focusses on the effect of the alloy modifications on machinability as well as on the surface integrity of plasma-transferred-arc-welded (PTA) and finish milled invar components.
The results show a significant positive influence of ultrasonic assistance on the resulting cutting force of both materials. The modification with 1% Ti shows a positive influence on the surface integrity, as the roughness of the conventional machining processes is lower compared to the initial alloy, which has to be confirmed in further experiments.
Alloy 36 (1.3912), also known as “Invar”, is an alloy with 36% nickel. It was developed in 1897 by Guillaume and stands out for its very low thermal expansion coefficient. It is classified as a difficult-to-cut material and is commonly used for the production of fiber-reinforced composites in the field of mold construction. Additive manufacturing (AM) offers many economic advantages regarding the repair, modification and manufacture of entire components. Subsequent machining of the AM components is necessary to account for complex structures, final contours or defined surfaces. In part I of this investigation, the initial alloy 36 is modified with the elements Ti, Zr and Hf up to a maximum of 0.33 wt.-%. The influence of the modification elements on the microstructure as well as on the hardness of the AM components is examined. Part II focusses on the effect of the alloy modifications on machinability as well as on the surface integrity of plasma-transferred-arc-welded (PTA) and finish milled invar components. Machining tests were carried out, to investigate the influence of ultrasonic assistance and the effects of modification elements Ti, Zr and Hf on the occurring cutting forces, temperatures and resulting surface integrity of the AM components made of alloy 36 and their modifications. The results show a significant positive influence of ultrasonic assistance on the resulting cutting force as well as on the roughness of all materials investigated.