TY - JOUR A1 - Vollert, F. A1 - Thomas, Maximilian A1 - Kromm, Arne A1 - Gibmeier, J. T1 - Solidification Cracking Assessment of LTT Filler Materials by Means of Varestraint Testing and μCT N2 - Investigations of the weldability of metals often deal with hot cracking, as one of the most dreaded imperfections during weld fabrication. The hot cracking investigations presented in this paper were carried out as part of a study on the development of low transformation temperature (LTT) weld filler materials. These alloys allow to mitigate tensile residual stresses that usually arise during welding using conventional weld filler materials. By this means, higher fatigue strength and higher lifetimes of the weld can be achieved. However, LTT weld filler materials are for example, high-alloyed Cr/Ni steels that are susceptible to the formation of hot cracks. To assess hot cracking, we applied the standardized modified varestraint transvarestraint hot cracking test (MVT), which is well appropriate to evaluate different base or filler materials with regard to their hot cracking susceptibility. In order to consider the complete material volume for the assessment of hot cracking, we additionally applied microfocus X-ray computer tomography (μCT). It is shown that by a suitable selection of welding and MVT parameter the analysis of the complete 3D hot crack network can provide additional information with regard to the hot cracking model following Prokhorov. It is now possible to determine easy accessible substitute values (e.g., maximum crack depth) for the extent of the Brittleness Temperature Range (BTR) and the minimum critical strain Pmin. KW - LTT weld filler materials KW - μCT-analysis KW - Hot cracking KW - Varestraint test PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-509126 DO - https://doi.org/10.3390/ma13122726 VL - 13 IS - 12 SP - 2726 PB - MDPI AN - OPUS4-50912 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fahrbach, M. A1 - Friedrich, Sebastian A1 - Cappella, Brunero A1 - Peiner, Erwin T1 - Calibrating a high-speed contact-resonance profilometer N2 - A European EMPIR project, which aims to use large-scale piezoresistive microprobes for contact resonance applications, a well-established measurement mode of atomic force microscopes (AFMs), is being funded. As the probes used in this project are much larger in size than typical AFM probes some of the simplifications and assumptions made for AFM probes are not applicable. This study presents a guide on how to systematically create a model that replicates the dynamic behavior of microprobes, including air damping, nonlinear sensitivities, and frequency dependencies. The model is then verified by analyzing a series of measurements. KW - Piezoresistive cantilever KW - AFM KW - contact resonance PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-509899 DO - https://doi.org/10.5194/jsss-9-179-2020 VL - 9 SP - 179 EP - 187 PB - Copernicus Publications AN - OPUS4-50989 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reichelt, Manuel A1 - Cappella, Brunero T1 - Influence of relative humidity on wear of self-mated 100 Cr6 steel N2 - The influence of relative humidity on friction and wear is subject of several studies in the last decades. A comprehensive understanding of physical and chemical phenomena affecting the tribology is hampered by the lack of reproducible experimental results, by the large number of variables, and by several difficulties in the detection of tribochemical processes and products. In the present work, we analyze the wear coefficient and the wear volumes of 686 unlubricated tests performed on different oscillating tribometers with 100Cr6 balls on 100Cr6 planes at different relative humidity. Aim of this work is to assess the repeatability and reproducibility of data, to determine the dependence of the wear coefficient on the relative humidity, to understand the underlying physicochemical phenomena and to build three dimensional maps of the wear coefficient as a function of both humidity and the product of normal force and sliding distance. KW - Wear KW - 100Cr6 KW - Relative humidity PY - 2020 DO - https://doi.org/10.1016/j.wear.2020.203239 VL - 450-451 SP - 203239 AN - OPUS4-50583 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vollert, F. A1 - Thomas, Maximilian A1 - Kromm, Arne A1 - Gibmeier, J. T1 - Hot crack assessment of LTT welds using μCT N2 - Investigations on weldability often deal with hot cracking, as one of the most popular failure during weld fabrication. The modified varestraint transvarestraint hot cracking test (MVT) is well known for the assessment of the hot cracking susceptibility of materials. The shortcoming of this approach is that the information is only from the very near surface region, which inhibits access to the characteristic of the hot crack network in the bulk. Here, we report about a new approach, illustrated in the example of low transformation temperature (LTT) weld filler materials, to monitor the entire 3D hot crack network after welding by means of microfocus X-ray computer tomography (μCT). T2 - 10th Conference on Industrial Computed Tomography (iCT 2020) CY - Wels, Austria DA - 04.02.2020 KW - Varestraint testing KW - LTT weld filler materials KW - Hot cracking KW - Welding KW - μCT-analysis PY - 2020 DO - https://doi.org/https://doi.org/10.58286/25121 SN - 1435-4934 VL - 25 IS - 2 SP - 1 EP - 7 PB - NDT.net CY - Kirchwald AN - OPUS4-50341 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reichelt, Manuel A1 - Cappella, Brunero T1 - Comparative analysis of error sources in the determination of wear volumes of oscillating ball-on-plane tests N2 - The accurate determination of wear volumes is a prerequisite for the study of numerous tribological phenomena. Wear volumes can be measured with different techniques or else be calculated starting from some quantities measured from the wear scar. Advantages and drawbacks of the measuring techniques are shown by means of wear scars and calottes resulting from ball-on-plane tests with 100Cr6 specimens. When measuring wear volumes, white light interferometry results to be one of the most suitable techniques. When wear volumes are calculated, errors result mainly from two sources: (1) the arbitrary choice of one or few line profiles for the determination of the width and of the planimetric wear, and (2) approximations in the calculation, which are even necessary when values of the wear volumes of the single tribological partners and not only the total volume are of interest. The effect of both error sources on the accuracy in the determination of wear volumes is characterized and elucidated by examples. It is found that errors due to approximations are negligible when compared to errors due to the arbitrary choice of one line profile. KW - Error sources analysis KW - White light interferometry KW - Statistical analysis KW - AFM KW - Wear KW - Oscillating ball-on-disc test PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-508407 DO - https://doi.org/10.3389/fmech.2020.00025 VL - 6 SP - Article 25 AN - OPUS4-50840 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe T1 - Application of fracture mechanics to welds with crack origin at the weld toe—a review. Part 2: welding residual stresses. Residual and total life assessment N2 - The two-part paper series provides an overview on the state-of-the-art in the application of engineering fracture mechanics to weldments limited to butt and fillet welds with crack initiation at weld toes. In the present second part, one focus is on welding residual stresses, their characteristics and stability under cyclic loading and their effect on structural integrity. Subsequently, features will be addressed which are essential for applying fracture mechanics to overall fatigue life and fatigue strength considerations of weldments. These comprise fatigue life relevant initial crack sizes and multiple crack initiation and Propagation due to various stress peaks along the weld toe. A concept is briefly introduced which covers all these aspects. KW - Fracture mechanics KW - Welding residual stresses KW - Multiple crack propagation KW - Fatigue strength PY - 2020 DO - https://doi.org/10.1007/s40194-019-00816-y VL - 64 IS - 1 SP - 151 EP - 169 PB - Springer AN - OPUS4-50263 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Spranger, Felix A1 - Schirdewahn, S. A1 - Kromm, Arne A1 - Merklein, M. A1 - Hilgenberg, Kai T1 - On the influence of TiB2, TiC, and TiN hard particles on the microstructure of localized laser dispersed AISI D2 tool steel surfaces N2 - The control of friction and wear is a major concern in many industrial applications. A promising method for tailored surface modification is the so-called laser implantation technique. This method combines surface texturing and material optimization in one processing step by a localized dispersing of hard ceramic particles using pulsed laser radiation. Wear resistant, protruding micrometric features (implants) with defined geometry can be created in a deterministic pattern where needed on highly stressed surfaces, i.e., on forming or cutting tools. However, in order to maintain the implants over the tool’s lifetime, a suitable selection of hard ceramic particles is a prerequisite. They must provide a defect-free metal matrix composite with a high share of homogeneously distributed particles and, especially, high implant hardness. In this study, TiN, TiC, and TiB2 hard particles were compared as implant materials for the first time. By a systematic variation of pulse power and pulse duration, their dispersing behavior and influence on the material properties of AISI D2 tool steel were investigated. Although all powder materials had grain sizes smaller than 10 μm, it was possible to disperse them by pulsed laser radiation and to obtain defect-free protruding implants. The highest share of dispersed particles (∼64%) was observed for TiB2. By scanning electron microscopy and energy dispersive x-ray spectroscopy, it was also shown that a significant share of the preplaced particles was dissolved by the laser beam and precipitated as nanometer sized particles within the matrix during solidification. These in situ formed particles have a decisive influence on the material properties. While the TiN and TiC implants have shown maximum hardness values of 750 and 850 HV1, the TiB2 implants have shown the highest hardness values with more than 1600 HV1. By x-ray diffraction, it was possible to ascribe the lower hardness values of TiC and TiN implants to high amounts of retained austenite in the metal matrix. By implanting TiB2, the formation of retained austenite was successfully suppressed due to the in situ formation of TiC particles, which was proven by electron backscatter diffraction. In conclusion, all the implant materials are basically suitable for laser implantation on AISI D2 tool steel. However, TiB2 has shown the most promising results. T2 - ICALEO 2019 CY - Orlando, FL, USA DA - 07.10.2019 KW - Laser implantation KW - Surface texturing KW - AISI D2 KW - TiB2 KW - TiN KW - TiC KW - Retained Austenite KW - Localized laser dispersing PY - 2020 DO - https://doi.org/10.2351/7.0000059 VL - 32 IS - 2 SP - 022028 EP - 022028-9 PB - AIP Publishing AN - OPUS4-50712 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schirdewahn, S. A1 - Spranger, Felix A1 - Hilgenberg, Kai A1 - Merklein, M. T1 - Localized Laser Dispersing of Titanium-Based Particles for Improving the Tribological Performance of Hot Stamping Tools N2 - Within the scope of this work, a new surface engineering technology named laser implantation has been investigated, in order to improve the tribological performance of hot stamping tools. This technique is based on manufacturing highly wear-resistant, separated, and elevated microfeatures by embedding hard ceramic particles into the tool surface via pulsed laser radiation. Hence, the topography and material properties of the tool are modified, which influences the thermal and tribological interactions at the blank-die interface. To verify these assumptions and to clarify the cause–effect relations, different titanium-based particles (TiB2, TiC, TiN) were laser-implanted and subsequently analyzed regarding to their geometrical shape and mechanical properties. Afterwards, quenching tests as well as tribological experiments were carried out by using titanium-diboride as the most promising implantation material for reducing the tribological load due to high hardness value of the generated implants. Compared to conventional tooling systems, the modified tool surfaces revealed a significantly higher wear resistance as well as reduced friction forces while offering the possibility to adjust the thermal interactions at the blank-die interface. Based on these results, a tailored tool surface modification can be pursued in future research work, in order to enhance the effectiveness of the hot stamping technology. KW - Hot stamping KW - Tribology KW - Surface modification KW - Localized laser dispersing PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-510981 DO - https://doi.org/10.3390/jmmp4030068 VL - 4 IS - 3 SP - 68 PB - MDPI AN - OPUS4-51098 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Friedrich, Sebastian A1 - Cappella, Brunero T1 - Application of contact-resonance AFM methods to polymer samples N2 - Contact-resonance AFM (CR-AFM) has been used in recent years for the measurement of mechanical properties. Compared with other techniques, CR-AFM has a much shorter acquisition time, compensating the incomplete theoretical understanding of the underlying physical phenomena. In the present paper, we propose a procedure, which allows to determine the elastic modulus of the sample as a parameter of the fit of the CR frequency as a function of the load. It is concluded that CR measurements are not appropriate for polymer samples. Major drawbacks are the bad resolution for moduli lower than ca. 10 GPa and the lack of a comprehensive physical model. KW - Atomic force microscopy KW - Contact resonance KW - Mechanical properties KW - Polymers KW - Wear PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-515621 DO - https://doi.org/10.3762/bjnano.11.154 VL - 11 SP - 1714 EP - 1727 AN - OPUS4-51562 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Genga, R. M. A1 - Rokebrand, P. A1 - Cornish, L. A. A1 - Nelwalani, N. A1 - Brandt, Guido A1 - Kelling, Norbert A1 - Woydt, Mathias A1 - Janse van Vuuren, A. A1 - Polese, C. T1 - High-temperature sliding wear, elastic modulus and transverse rupture strength of Ni bonded NbC and WC cermets N2 - The effects of rapid pulse electric current sintering (PECS), substitution of WC by NbC and Co by Ni, and carbide additives (TiC and Mo2C) on the microstructure, elastic modulus, B3B transverse rupture strength (TRS) and high temperature sliding wear on WC-Co, WC-Ni, NbC-Co and NbC-Ni cermets were studied. High temperature sliding wear tests were carried out using a ball-on-disk tribometer, with a 10 N force, at a sliding speed of 1.34 m/s for 0.8 km (10 min) and 2.4 km (30 min), using 100Cr6 (AISI 52100) steel balls at 400 °C and 0% humidity. Additions of TiC and Mo2C to NbC-12Ni improved the sliding wear resistance, with TiC having the greater effect, reducing the sample wear rate by over 30% from 15.1×10−6mm3/N·m to 9.4×10−6mm3/N·m after sliding distance of 2.4 km. Generally, the LPS samples had lower wear volumes than the corresponding SPS samples, due to higher K1c and TRS. KW - Pulse electric current sintering KW - Niobium carbide KW - Nickel KW - Molybdenum carbide KW - Titanium carbide PY - 2020 DO - https://doi.org/10.1016/j.ijrmhm.2019.105143 SN - 0263-4368 VL - 87 SP - 105143 PB - Elsevier Ltd. AN - OPUS4-51473 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -