Sebastian Herbst

Leibniz Universität Hannover · Institute of Materials Science

The detection of ductile damage by image-based methods is time-consuming and typically probes only small areas. It is therefore of great interest for various cold forming processes, such as sheet-bulk metal forming, to develop new methods that can be used during the forming process and that enable an efficient detection of ductile damage. In the pr...

In the present study, a novel approach is presented to achieve oxygen partial pressures corresponding to extremely high vacuum (XHV) to foster cold roll bonding. Cold roll bonding of Al/Al and Cu/Cu as well as the heterogeneous combination Al/Cu were investigated with a focus on the minimum degree of deformation required to form a solid bond. By ap...

The manganese-boron alloy 22MnB5 is particularly used for structural and safety-relevant parts in the automotive industry. Parts made from this alloy are usually produced using the hot forming process. Here, the sheet is heated to over 950 °C using an industrial roller hearth furnace. The heated sheet is then simultaneously formed and quenched in a...

Herein, the mechanisms of the electroplastic effect (EPE) in different hexagonal close‐packed (hcp) metals under varying loading conditions and current densities through the analysis of flow curves and microstructural changes are investigated. The investigations show a significant change in the forming behavior of the hcp materials as a result of s...

As oxygen negatively affects most production processes in the metalworking industry, a truly oxygen‐free production environment appears attractive in terms of the resulting material and component properties. This overview summarizes research conducted within the Collaborative Research Centre (CRC) 1368. The objectives of this CRC are twofold. First...

Pure iron is very attractive as a biodegradable implant material due to its high biocompatibility. In combination with additive manufacturing, which facilitates great flexibility of the implant design, it is possible to selectively adjust the microstructure of the material in the process, thereby control the corrosion and fatigue behavior. In the p...

To combine the advantages of two materials, hybrid bulk metal workpieces are attractive for subsequent processes such as metal forming. However, hybrid materials rely on the initial bond strength for the effective transfer of applied loads. Thus, a non-destructive evaluation of the bonding along the production process chain is of high interest. To...

Additive manufacturing with multi-material design offers great possibilities for lightweight and function-integrated components. A process chain was developed in which hybrid steel–steel-components with high fatigue strength were produced. For this, a material combination of stainless powder material Rockit® (0.52 wt.% C, 0.9% Si, 14% Cr, 0.4% Mo,...

The necessity of increasing the efficiency of the engines brings to the creation of new materials with improved properties to guarantee their stable use at high temperatures. Niobium-based composites represent promising alloys, whose production faces though technical limitations related to the melting process in conventional crucibles: feasibility...

One possibility to increase the interface strength of cold roll bonded materials is the application of a thin intermediate layer. In the present study, a tin coating was employed to strengthen the interface formed between cold roll bonded steel sheets, and the impact of subsequent heat treatment on the resulting bonding strength was investigated. T...

Deep cryogenic treatment of tool steels, incorporated in conventional hardening and tempering, has been a topic of intensive research in recent years. Yet, the governing microstructural mechanisms involved in the deep cryogenic treatment of high‐alloyed tool steels are still controversial. Thus, an in situ X‐ray diffraction study is conducted on th...

Metal forming of shape memory alloys (SMA) can be challenging since these are very often brittle due to their intermetallic character. However, formability is often needed not only for realising the desired geometry but also for tailoring the microstructure and the functional properties. To investigate whether the encapsulation in a steel shell can...

Magnesium alloys are important engineering materials due to their good combination of strength and very low densities. However, the low ductility imposed by the hcp-lattice has thus far limited the application of magnesium alloys as sheet material. The use of the electroplastic effect offers a route to increase formability of magnesium alloys while...

The influence of pre-strain on the very-low-cycle loading behavior as occurring, for example during roller leveling of sheet metals, is not yet fully understood. A key factor in this context is the stiffness of the material and its changes upon processing. To study the general mechanical property changes during low-cycle loading with small amplitud...

This contribution deals with the numerical investigations to develop a novel process chain for hybrid solid components using Tailored Forming. For manufacturing a hybrid bearing bushing, co-extrusion is the first step to produce hybrid semi-finished workpieces followed by a die forging process, machining processes and hardening. Combining aluminium...

The production of multi-metal bulk components requires suitable manufacturing technologies. On the example of hybrid bevel gears featuring two different steels at the outer surface and on the inside, the applicability of the novel manufacturing technology of Tailored Forming was investigated. In a first processing step, a semi-finished compound was...

In this work, the influence of a cryogenic treatment on the microstructure, mechanical properties and wear resistance of the high-alloyed tool steels X38CrMoV5-3, X153CrMoV12 and ~X190CrVMo20-4 were investigated. Based on tempering curves of the steels, the heat treatment parameters were determined for the mechanical and wear specimens so that the...

In this work, the influence of a cryogenic treatment on the microstructure, mechanical properties and wear resistance of the high-alloyed tool steels X38CrMoV5-3, X153CrMoV12 and ~X190CrVMo20-4 were investigated. Based on tempering curves of the steels, the heat treatment parameters were determined for the mechanical and wear specimens so that the...

The microstructure and the fracture behavior of TiZrHfCoNiCu high entropy shape memory alloys with two different compositions were investigated. An unusual microstructure featuring pattern-forming nanoprecipitates was observed in dendritic and the interdendritic regions of both alloys. The unique higher-level order of these precipitates does not fo...

In the current study, the potential of dry machining of the titanium alloy Ti-6Al-4V with uncoated tungsten carbide solid endmills was explored. It is demonstrated that tribo-oxidation is the dominant wear mechanism, which can be suppressed by milling in an extreme high vacuum adequate (XHV) environment. The latter was realized by using a silane-do...

To manufacture semi-finished hybrid workpieces with tailored properties, a finite element simulation assisted process chain design was investigated. This includes the process steps of cross wedge rolling, hot geometry inspection, induction hardening, and fatigue testing. The process chain allows the utilisation of material combinations such as high...

The introduction of high-entropy alloys (HEA) into the field of shape memory alloys offers enormous potential for improving their functional properties. It is shown how a successive increase in chemical complexity results in strictly monotonically enlarged and increasingly distorted lattices. With increasing the number of elements added to the allo...

Application of products with properties locally adapted for specific loads and requirements has become widespread in recent decades. In the present study, an innovative approach to manufacture tubes with tailored properties in the longitudinal direction from a boron-alloyed steel 22MnB5 was developed. Due to advanced heating and cooling strategies,...

For specimen characterization, X-ray microscopy offers a variety of advantages like non-destructive investigations and reduced preparation effort for the samples. Orientation measurements are possible using diffraction contrast tomography (DCT). However, lateral resolution is lower as compared to scanning electron microscopy combined with electron...

For the determination of heat transfer coefficients in air-water spray cooling, two methods are presented that are capable of characterizing multi-nozzle cooling set-ups. The methods are based on the quenching of thin-walled tubes or massive cylinders on which cooling curves are recorded at given positions with thermocouples. The temperature depend...

For studies of the interface zone of metallic composites with significantly differing mechanical properties across the interface, high-quality sample preparation is paramount. In particular, the analysis of the composition or geometric characteristics of intermetallic phases close to the interface requires a preparation specifically adapted to the...

“In recent years, multi-material designs of technical components have been gaining in importance. When combining different materials in a single component, it is possible to achieve high performance and extended functionality while simultaneously saving cost-intensive or rare materials. One promising approach to manufacture hybrid parts such as bi-...

The manufacturing of complex drivetrain components made of steel requires multi-stage manufacturing processes, resulting in long processing times and high costs. Forged parts get their final geometry after multi-stage forming operations. One approach to shorten such process chains is close contour casting of steel preforms and a single subsequent f...

The influence of alternating bending loads as they occur during roller levelling on the mechanical properties of sheet metals is not yet fully understood. A detailed knowledge of the influence of the commonly used levelling process on the resulting properties of sheet material is needed in particular for the design of subsequent processes with narr...

By using electrically assisted forming the usually rather poor workability of magnesium can be improved. The processes taking place during these forming operations have a strong influence on the microstructure. However, the metallographic preparation of magnesium is challenging due to its low hardness and strong tendency to oxidize. Therefore, a re...

The cold pressure welding of metals is a joining by forming technique capable of joining both similar and dissimilar metals in their solid state. In this article collective research on the cold pressure welding of metals with the aim of increasing both the overall weld strength and the weld‐ability is presented. The application of innovative strate...

A cold roll bonding (CRB) process for the symmetrical bonding of two sheets of the steel DX-51 (1.0226) with a galvanized zinc coating is presented. The coating was applied to form an intermediate layer between the two steel substrates during the bonding. The study is divided in two sections describing the role of the heat treatment prior to the CR...

The influence of increased manganese and nickel contents to improve the wear resistance of a modified hot-working tool steel 1.2365mod was characterized with regard to continuous cooling transformation, microstructure evolution and mechanical properties. In contrast to literature, increased yield strength, tensile strength, elongation at fracture a...

Researchers of the Collaborative Research Centre CRC 1153 are investigating novel process chains to manufacture function- adapted and lightweight machine components. In each step of the process chain, numerical simulation tools are utilised in the process design to take into account locally specific material behaviour under particular processing co...

The production of massive steel-aluminium hybrid components by means of massive (hot) forming following a joining operation requires advanced heat treatment strategies for the adjustment of local material properties with maximum joint strengths. For the given process-step sequence, the challenge is that the heat treatment of the hybrid component ca...

Recent research efforts aim at transferring the concept of tailored properties (known from tailored blanks) to massive steel-aluminum hybrid components under the term “Tailored Forming”. The specific feature of the employed process chain is that the dissimilar metals are joined before the forming process to allow for a modification of the joining z...

In the present study, a semi-automated method for the measurement of intermetallic compound layer thicknesses is introduced. Based on backscattered electron contrast images of the bond zones that feature a sufficient contrast between the substrates and the intermetallic compound layer, every line of pixels perpendicular to the bond zone is analyzed...

In the present study, friction welded rods made of AW6082 aluminum alloy and 20MnCr5 steel were subjected to different T6 heat treatments of solution annealing and aging. The bond strength of the joints was determined using tensile tests and the intermetallic compound (IMC) layer thickness along the bond zone was measured by scanning electron micro...

Air-water spray cooling was employed during a heat treatment to enhance the mechanical properties of microalloyed medium carbon steel test cylinders (38MnVS6, 88 mm diameter). Using appropriate cooling times and intensities, the test cylinders’ surfaces could be quenched and subsequently self-tempered by the residual heat of the core. Simultaneousl...

Numerical simulation of quenching by air-water spray cooling requires an accurate knowledge of the spray heat transfer coefficients (HTCs). In this work, a novel method of heat transfer determination is presented that takes lacking aspects of prior determination methods into account. The temperature trends during cooling of a thin-walled tube are u...

The reduction of distortion during quenching by air-water spray cooling requires an accurate knowledge of the heat transfer coefficients (HTCs) of the spray for different settings, layouts and along the quenched surface within the spray. In this work a novel method of HTC determination is presented that takes inaccuracies of prior determination met...

Welding by electromagnetic forming is an interesting alternative for material combinations which are not suitable for conventional welding by melting. Even though the underlying bonding mechanisms and the right choice of process parameters are thoroughly discussed in the current literature, there is still a lack of target-oriented process dimension...

Modern light structures increasingly require different alloys or metals to be joined with one another in the form of composite materials [1]. As a result of their different melting temperatures or of the formation of brittle inter-metallic phases, many combinations of metals cannot be produced using thermal methods. One alternative, however, is the...