Technical Program

Status: 3 June, 2022
Friday, 3 June, 2022
08:50 - 09:50
Hard Materials - Simulation and material design
Location: Walter Schwarzkopf Hall
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08:50 HM 48
Critical aspects for an efficient assessment of novel materials designs
de Oro Calderon R.1, Steinlechner R.1, Lunzer M.2, Wodak I.1, Edtmaier C.1, Schubert W.-D.1
1TU Wien, Austria
2boehlerit GmbH & Co KG, Austria
Finding a replacement for WC-Co hardmetals has been investigated for several years. The design space is rather limited when considering WC as hardphase, because most transition metals form detrimental interconnected-carbides when added above their solubility limit, which is in most cases rather low. However, the peculiar characteristics of WC make worthwhile the effort, as no other hardphase provides such an outstanding combination properties: hardness/toughness ratio, electrical and thermal conductivity, etc.
This paper illustrates with some examples how the design space can be efficiently studied when some critical aspects are tackled during the design. For instance, features such as solubility limits in the binder, the size of the carbon window or the dramatic changes in the binder composition at different carbon activities can be tuned differently depending on the binder chemistry
Thermodynamic software packages provide a very powerful tool to speed up the design of novel alternatives, and their further development might be the key to facilitate the discovery of new material combinations to cover not only current needs but also future ones.
09:10 HM 49
Binder-reinforced tungsten boride
Humphry-Baker S.1, Davidson J.1, Lin Y.1, Aihemaiti O.1, Athanasakis-Kaklamanakis M.1, Del Rio E.2, Ivanov E.2, Astbury J.3, Windsor C.3
1Imperial College, United Kingdom
2Tosoh SMD, USA
3Tokamak Energy Ltd, United Kingdom
WBx compounds are attractive alternatives to WC-based hardmetals, particularly in nuclear applications where oxidation resistance and neutron attenuation are needed. However, processing binder-reinforced materials is challenging due to the increased reactivity of boron. We demonstrate two alternative composite toughening strategies: W2B-W and W2B5-Cu. We begin by comparing the neutron-attenuation performance of the candidate materials, showing an improvement with increasing boron content. Oxidation resistance is systematically studied using thermogravimetry.  Previous works have shown that the W2B5 compound (~70 at.% B) is able to form a protective B2O3-WO3 layer with corresponding parabolic oxidation kinetics. We show that such protective layers also form in the range 16-50 at.% B although their efficacy degrades with decreasing B content. Thermal-mechanical properties are reported up to 2000°C. For W2B-W they depend heavily on the contiguous phase. W-dominant and W2B-dominant composites show ductile-brittle transitions at ~1000 and ~1800°C, and peak strengths of 0.9 and 1.2 GPa, respectively. With increasing boron, there is a trade-off between increased oxidation resistance and neutron attenuation on one hand, and decreasing strength and toughness on the other.
09:30 HM 51
Experiment and simulation study on sintering and phase diagram calculation for WC-Co cemented carbide
Terasaka S.1, Matsubara H.1, Takada M.2
1Tohoku University, Japan
2Nippon Tokushu Goukin, Co. Ltd., Japan
WC-Co cemented carbides are fabricated by liquid phase sintering. When the WC-Co green compact is heated, the eutectic melt of WC-Co is formed in the range of 1250-1300 °C. The temperature at which the liquid phase appears and the range of solid-liquid coexistence depend on the composition, and the situation of liquid phase sintering is complicated. In this study, WC grain size, Co content, and carbon content in two phase region are changed, and the effects of these changes are investigated in detail by simulation and experiment. The microstructure development by liquid phase sintering and the grain growth of WC by dissolution-reprecipitation mechanism (Ostwald ripening) before and after sintering are analyzed by Monte Carlo simulation and phase diagram calculation. These simulation results are compared with experimental results. WC-Co cemented carbide are sintered even before the liquid phase appears. The sintering behavior is not due to solid phase diffusion, but due to liquid phase flow, and the existence of a pseudo-liquid phase sintering state is indicated.
09:50 - 10:10
Location: Walter Schwarzkopf Hall
10:10 - 11:10
Refractory Metals - Characterization and simulation
Location: Walter Schwarzkopf Hall
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RM 30
Periodic facetting of the Mo(112)-p(2×3)-O reconstruction covered with thin silica films cancelled
Zhao X.1, Wang Y.2, Ma T.1
1Shenyang Agricultural University, China
2Shenyang Ligong University, China
The Mo(112) surface or reconstructions are susceptible to facetting and become severely rough during their oxidation processes. The experiment was performed on the typical Mo(112)-p(2×3)-O reconstruction with STM, XPS and other surface methods. Via delicate protection with thin silica films, the facetting proces could be well controlled to achieve long range ordered strucutures. The facetting was found to be dependent much on the dynamic parameters of depositing silica films, which could provide a possible method of repairing surface defects formed in the Mo(112)-p(2×3)-O reconstruction. Finally, the silica films could be removed to leave a clean and periodic facetting surface. Our results would pave a way of understand the early stage oxidation of molybdenum surfaces at atomic scale in the near future.
RM 34
Improving the Intermediate Temperature Oxidation and Corrosion Resistance of Refractory Metals and Mo-based Systems cancelled
Beck K.1, Ulrich A.S.1, König T.1, Hinrichs F.2, Heilmaier M.2, Galetz M.C.1
1DECHEMA Research Institute, Germany
2Karlsruhe Institut of Technology, Germany
Refractory metals and their alloys are characterized by a very high melting point but are prone to two different attack mechanisms at intermediate temperatures: pesting, which leads to the total disintegration of metal into powder, and hot corrosion, which is the accelerated corrosion of metals exposed to sulfur and alkali metal salt containing atmospheres. To counteract these mechanisms, the formation of protective oxide scales (e.g. Al2O3) is necessary. Two different approaches have been developed: i) smart alloying with Si and Ti and ii) coating application (e.g., Al-based).
Via pack cementation Al-coatings (up to 120 μm) were successfully applied on four refractory metals (Mo, Nb, Ta, W) and two Mo-Si-Ti alloys (Mo-20.0Si-52.8Ti, Mo-21.0-34.0Ti). Using thermogravimetric analysis (700 °C and 900 °C) the oxide formation was investigated and the improvement of the oxidation behavior correlated to Al2O3 scale formation was confirmed. The effect of the coating on hot corrosion was demonstrated in type II hot corrosion environment at 700 °C. XRD, EPMA, and SEM measurements were used to investigate the applied coatings and the formed oxide scales.
10:10 RM 31
Effect of boron doping on grain boundary cohesion in technically pure molybdenum investigated via three-point-bending tests
Jakob S.1, Weissenböck T.1, Hohenwarter A.1, Lorich A.2, Knabl W.2, Pippan R.3, Clemens H.1, Maier-Kiener V.1
1Montanuniversität Leoben, Austria
2Plansee SE, Austria
3Erich-Schmid-Institute of Materials Science, Austria
Molybdenum has highly advantageous functional and high-temperature properties. However, plastic deformation as well as structural applications are limited due to a propensity for brittle, intercrystalline failure, especially at low temperatures. It is well known that oxygen segregations have a detrimental effect, whereas carbon and/or boron show a beneficial effect on grain boundary cohesion. An advanced approach for the improvement of these interfaces is segregation engineering, e.g. the addition of cohesion enhancing elements segregating to the grain boundaries. To investigate early stages of crack formation, three-point bending tests on recrystallized commercially pure and boron micro-doped molybdenum were conducted between -28°C and room temperature. The tensile-loaded top surface of the specimens was examined post-mortem close to the final fracture area via scanning electron microscopy. The occurring, mainly intergranular, separations of grains are investigated for distinct features such as crystallography and length of open grain boundaries. The chemical composition of the interface is complementary measured by atom probe tomography. Necessary requirements for a direct comparison between the material variants and the effect of boron doping are discussed.
10:30 RM 32
Characterization of refractory metal powders based on block-like motion evaluation for DEM simulations
Kronlachner T.1, Pirker S.2, Leitz K.-H.3, Lichtenegger T.2
1K1-MET Metallurgical Competence Center, Austria
2Johannes Kepler University Linz, Austria
3Plansee SE, Austria
Industrially used refractory metal powders consist of small, irregular-shaped particles, which makes them highly cohesive. Apart from particle size and morphology, their flow behavior is influenced by various factors, like preconditioning, aging, and environmental conditions. These properties make it challenging to understand and predict the flow characteristics. A powerful tool to model the behavior of refractory metal powders is the Discrete Element Method (DEM). However, these simulations require reliable material parameters that generally cannot be found in the literature.  
In this contribution, we report a methodology for estimating the required parameters for the interaction models used in the DEM simulation based on the developed block-movement characterization technique for rotating drum devices. By numerical optimization, parameters for different materials and powder states were determined based on a comparison of experimental and simulation data. The developed method makes it possible to describe the dynamic flow behavior of cohesive refractory metal powders and simulate their behavior during production processes, like die filling for example.
10:50 RM 33
Multi-physical modelling of the fast cooling system in high temperature furnaces with respect to a reduced energy consumption
Leitz K.-H.1, Valentini B.1
1Plansee SE, Austria
High temperature furnaces for heat treatment processes equipped with a fast cooling system generally suffer from a high energy consumption as the openings necessary for the gas cooling are a major source of energy losses. In this contribution thermo-electric and thermo-fluid dynamic finite element models of a high temperature furnace with a refractory metal hot zone and a fast cooling system will be applied for a detailed analysis of the cooling process and the gas system with respect to cooling efficiency and energy consumption. The presented simulation models are able to predict cooling rates in good correspondence to experimental data. The results show that achievable cooling rates significantly depend on the arrangement of the loading inside the furnace and that a reduction of the number of nozzles does not necessarily lead to lower cooling rates. Therefore, a gas system optimized by thermo-fluid dynamic simulations allows significant energy savings in high temperature furnaces without a loss of cooling efficiency.
11:10 - 11:45
Farewell Address
Location: Walter Schwarzkopf Hall