A novel co-extrusion process for the production of coaxially reinforced hollow profiles has been developed. Using this process, hybrid hollow profiles made of the aluminum alloy EN AW-6082 and the case-hardening steel 20MnCr5 (AISI 5120) were produced, which can be forged into hybrid bearing bushings by subsequent die forging. For the purpose of co-extrusion, a modular tooling concept was developed where steel tubes made of 20MnCr5 are fed laterally into the tool. This LACE (lateral angular co-extrusion) process allows for a variation of the volume fraction of the reinforcement by using steel tubes with different wall thicknesses, which enabled the production of compound profiles having reinforcement contents of either 14 vol.% or 34 vol.%. The shear strength of the bonding area of these samples was determined in push-out tests. Additionally, mechanical testing of segments of the hybrid profiles using shear compression tests was employed to provide information about the influence of different bonding mechanisms on the strength of the composite zone.

Multi-material bulk metal components allow for a resource efficient and functionally structured component design, with a load adaptation achieved in certain functional areas by using similar and dissimilar material combinations. One possibility for the production of hybrid bulk metal components is Tailored Forming, in which pre-joined semi-finished products are hot-formed using novel process chains. By means of Tailored Forming, the properties of the joining zone are geometrically and thermomechanically influenced during the forming process. Based on this motivation, forming processes (die forging, impact extrusion) coupled with adapted inductive heating strategies were designed using numerical simulations and successfully realised in the following work in order to produce demonstrator components with serial or coaxial material arrangements. The quality of the joining zone was investigated through metallographic and SEM imaging, tensile tests and life cycle tests. By selecting suitable materials, it was possible to achieve weight savings of 22% for a pinion shaft and up to 40% for a bearing bush in the material combination of steel and aluminium with sufficient strength for the respective application. It was shown that the intermetallic phases formed after friction welding barely grow during the forming process. By adjusting the heat treatment of the aluminium, the growth of the IMP can also be reduced in this process step. Furthermore, for steel-steel components alloy savings of up to 51% with regard to chromium could be achieved when using low-alloy steel as a substitute for high-alloy steel parts in less loaded sections. The welded microstructure of a cladded bearing washer could be transformed into a homogeneous fine-grained microstructure by forming. The lifetime of tailored formed washers nearly reached those of high-alloyed mono-material components.

Spark plasma sintering (SPS) or the field-assisted sintering technique (FAST) is commonly used to process powders that are difficult to consolidate, more efficiently than in the conventional powder metallurgy process route. During the process, holding time and applied holding pressure influence the product’s microstructure and subsequently its properties. In this study, in addition to the temperature impact, the influence of pressure and dwell time on the consolidation behaviour of titanium aluminide (TiAl) powders during the SPS process is investigated. Commercially available pre-alloyed TiAl48-2Cr-2Nb (GE48) and TiAl44-4Nb-0.7Mo-0.1B (TNM) powders were used, which have a high application potential in, for example, the aerospace industry. The results were evaluated based on microstructural analyses, hardness measurements and relative density calculations. It was shown that the investigated parameters significantly influence the sintering results, especially in the low temperature range. Depending on the temperature field in the sample, complete sintering is not achieved if the dwell time is too short in combination with too low a pressure. Above a certain temperature, the impact of holding pressure and holding time is significantly lower.

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, 1.8% Ni, 1.2% V, bal. Fe) cladded onto ASTM A572 mild steel by plasma arc powder deposition welding was investigated. Extensive material characterization has shown that defect-free claddings can be produced by carefully adjusting the welding process. With a tailored heat treatment strategy and machining of the semi-finished products, bearing washers for a thrust cylindrical roller bearing were produced. These washers showed a longer fatigue life than previously produced bearing washers with AISI 52100 bearing steel as cladding. It was also remarkable that the service life with the Rockit^® cladding material was longer than that of conventional monolithic AISI 52100 washers. This was reached through a favourable microstructure with finely distributed vanadium and chromium carbides in a martensitic matrix as well as the presence of compressive residual stresses, which are largely retained even after testing. The potential for further enhancement of the cladding performance through Tailored Forming was investigated in compression and forging tests and was found to be limited due to low forming capacity of the material.

Internal die cooling during forging can reduce thermal loads, counteracting surface softening, plastic deformation and abrasive die wear. Additive manufacturing has great potential for producing complex geometries of the internal cooling channels. In this study, hybrid forging dies were developed combining conventional manufacturing processes and laser powder bed fusion (L-PBF) achieving conformal cooling channels. A characterisation of the used hot-work tool steel’s AISI H10 powder material was carried out in order to determine suitable parameters for L-PBF processing and heat treatment parameters. Additionally, the mechanical properties of L-PBF-processed AISI H10 specimens were investigated. Furthermore, the influence of different internal cooling channels regarding a possible structural weakening of the die were analysed by means of a finite element method (FEM) applied to a hot-forging process. The numerical results indicated that the developed forging dies withstood the mechanical loads during a forging process. However, during the investigation a large dependency between the resulting stresses and the chosen parameters were observed. By choosing the best combination of parameters, a reduction of the equivalent stress by 1000 MPa can be achieved. Finally, a prototype of the hybrid-forging dies featuring the most promising cooling channel geometry was manufactured.

Due to the high specific surface area of titanium aluminide powders, significant and unavoidable surface oxidation takes place during processing. The resulting oxides disrupt the conventional powder metallurgical process route (pressing and sintering) by reducing the green strength and sintered properties. Oxide-free particle surfaces offer the potential to significantly increase particle bond strength and enable the processing of difficult-to-press material powders. In this work, the effect of milling titanium aluminide powder in a silane-doped atmosphere on the component properties after pressing and the subsequent sintering was investigated. Ball milling was used to break up the oxide layers and create bare metal surfaces on the particles. With the help of silane-doped inert gas, the oxygen partial pressure was greatly reduced during processing. It was investigated whether oxide-free surfaces could be produced and maintained by milling in silane-doped atmospheres. Furthermore, the resulting material properties after pressing and sintering were analysed using density measurements, hardness tests, EDX measurements, and micrographs. It was concluded that ball milling in a silane-doped atmosphere produces and maintains oxide-free particle surfaces. These oxide-free surfaces and smaller particle sizes improve the component properties after pressing and sintering.