Descriptors for High Throughput in Structural Materials Development

Short-Term Material Characterization by Electrohydraulic Incremental Extrusion through Micro Channels

Conventional testing procedures for characterizing the mechanical behavior of materials require intense preparation in geometry and in the handling of the samples to apply specific stress conditions. Furthermore, these procedures are time consuming. In a novel method for high-throughput development of new material, spherical and cylindrical micro samples should also be tested within a short time. For mechanical testing, the samples need to be exposed to specific types of stress. As most conventional testing procedures are not applicable, new testing procedures are demanded. The incremental electrohydraulic extrusion of micro samples through micro channels is a new testing procedure that was introduced for short-term material characterization. Loading energy is used to cause shock waves that incrementally push the samples through the forming die. The resulting deformation progress is measured between the forming steps. In this research, process simulations are used for channel design and material flow analysis. The designed channels that cause specific stress in samples are realized by stacking elements radially or axially. The stacking enables sample access for measurement and unloading and ensures good machinability of the forming channels. New testing cases for short-term characterization of cylindrical as well as spherical micro samples by electrohydraulic extrusion are presented according to monotone tensile, compression, and torsion testing. Furthermore, production-related testing and cyclic load testing are introduced by incremental electrohydraulic extrusion. By measuring the deformation due to the dependence on supplied energy, flow curve equivalents are determined that correspond to values from conventional material testing procedures.

Characterizing the Local Material Properties of Different Fe-C-Cr-steels by Using Deep Rolled Single Tracks

As part of a novel method for material development, deep rolling was used in this work to characterize the mechanical properties of macroscopic specimens of C45 (AISI 1045), S235 (AISI 1015), and 100Cr6 (AISI 52100) in various heat treatment states. Deep rolling is conventionally used to enhance surface and subsurface properties by reducing the surface roughness, introducing compressive residual stresses, and strain hardening. In the context of this work, it was utilized to determine material-specific variables via a mechanically applied load. For that purpose, the geometries of individual deep rolled tracks were measured. In dependence of the process parameters such as deep rolling pressure and tool size, the track geometry, i.e., the specific track depth, was for the first time compared for different materials. A functional relationship identified between the specific track depth and the material state dependent hardness forms the basis for a future characterization of the properties of alloy compositions belonging to the Fe–C–Cr system. Since deep rolling is performed in the same clamping as machining operations, hardness alterations could easily be determined at different points in the process chain using an optical in-process measurement of track geometries in the future.

Reproducibility of High-Throughput Sample Properties Produced by a High-Temperature Molten Metal Droplet Generator

A high-throughput method for the discovery of structural materials requires a large number of samples with highly reproducible properties. We propose using spherical micro-samples, which can be quickly produced by molten metal single droplet processes with high geometrical reproducibility. However, geometrical reproducibility does not automatically yield in the reproducibility of specific properties that are governed by the microstructure and thermal history of the samples. This work evaluates the reproducibility of two different steels (AISI D3 and 5140) in their as-synthesized state without additional heat treatment. By determining a set of well-established high-throughput descriptors by electrochemical analysis, particle-oriented peening, and micro machining, we show that high reproducibility can be achieved. Additionally, the determined properties correlate well with their austenitic (AISI D3) and martensitic (AISI5140) state. The AISI D3 shows an improved corrosion resistance, increased cutting forces during machining, and a higher deformation during particle-oriented peening. The reproducibility of the sample synthesis indicates that this type of sample is well suited for high-throughput methods to find new structural materials.

Multiscale Material Characterization Based on Single Particle Impact Utilizing Particle-Oriented Peening and Single-Impact Peening

If conventional methods are used, the development of new structural materials is experience-based, but still intensive in terms of materials, time and cost. As part of the development of a new method for material development and characterization, particle-oriented peening is used in this work. By means of samples of different sizes-but matching microstructures (100Cr6 (AISI 52100), five different material states)-it is examined whether the quantities determined on microscopic samples can be transferred to macroscopic samples. Therefore, peening processes with matching peening parameters but different deformation related aims are compared. While the particle-oriented peening is used to deform the microscopic samples (d = 0.8 mm), the new method of single-impact peening is used to deform the macroscopic samples. For the cross-scale comparison, values characterizing the plastic material deformation (∆l and r_f, r_c) are used as well as the particle velocities after the impact influenced by the elasto-plastic material properties. It could be shown that the highly dynamic (material) behavior is comparable in both dimensions. For the future examination of new (unknown) material states it is therefore conceivable to make predictions regarding their material behavior and later on regarding their material properties on the basis of particle-oriented peening of quickly generated microscopic samples e.g., from drop-on-demand processes.

Short-Term Characterization of Spherical 100Cr6 Steel Samples Using Micro Compression Test

For the establishment of a novel development process of new structural materials, short-term characterization methods capable of testing hundreds of spherical micro samples are needed. This paper introduces a compression test on spherical micro samples as a short-term characterization method to investigate the elastic-plastic deformation behavior. To demonstrate the potential of this newly developed method, the micro compression test is performed with a maximum loading of 300 N on 100Cr6 (AISI 52100 bearing steel) samples, with a diameter of 0.8 mm, in 15 different heat treatment conditions. The austenitizing temperature is varied between 800 and 1150 °C. Tempering of the samples is carried out in a differential scanning calorimetry process with temperatures of 180, 230 and 300 °C. Out of force-displacement curves and stress-strain relations, so-called descriptors (characteristic values) which are sensitive to the applied heat treatment can be extracted. The change of mechanical properties due to heat treatment and the resulting microstructure is presented by the trend of a stress descriptor in dependence of austenitizing and annealing temperature, which can be compared to the trend of the tensile strength as a material property obtained by conventional tensile tests. The trend of the descriptor determined in the compression test on spherical samples indicates the validity of this approach as a short-term characterization method.