Abstract Sinter-brazing of a powder-metallurgy porous copper-based composite to a wrought steel substrate was investigated. Two commercial Cu-based filler metals (Hi-Temp 548 disk and CDA 521) and different heating profiles were evaluated to identify a process window that maximizes joint performance while limiting wicking of the molten filler into the open porosity. Peak temperature (1010–1020 ◦C) and holding time (5–10 min) were varied under N2. Shear testing and metallography show that increasing peak temperature or holding time reduces joint shear strength due to excessive infiltration of the filler and associated microstructural coarsening. The maximum joint shear strength (8.76 ± 0.5 MPa) was obtained using Hi-Temp 548 at 1015 ◦C with a 5 min hold. A three-dimensional CFD model based on the volume-of-fluid method and the continuum surface-force formulation was developed to predict filler infiltration into the porous compact. The predicted infiltration depth (415 μm) agreed with experiments (389 μm) within 7%. Parametric simulations indicate that infiltration increases with decreasing filler density and viscosity and with increasing holding time, with holding time being the dominant factor.
an internationally known, highly qualified expert in fracture mechanics and in the field of development and complex characterization of advanced ceramic materials at the macro-/micro-and nano-levels both at room and high temperatures.
Abstract High entropy ceramic coatings, including multicomponent transition metal nitrides called also high entropy nitrides (HEN), are usually deposited using reactive arc and/or DC magnetron (co)sputtering. High Target Utilization Sputtering (HiTUS) was not applied in HEN systems up to now. Subsequently, the mechanical properties of HEN coatings prepared by HiTUS are also not known. The transition metals from the 4th and 5th group of the periodic table (Ti, Zr, Hf, Nb, V, and Ta) are strong nitride formers which would be the most suitable for HEN coating systems and therefore, investigation of their properties would be of significant interest. However, the nanoindentation measurements on thin coatings always produce „composite“ values involving the contribution from the substrate. The separation of the coating properties from composite values requires upgraded analytical approaches different from standard Oliver & Pharr analysis. Thus, the aim work is to investigate the structure, hardness, and elastic modulus of TiZrHfNbVTa–xN coatings with different nitrogen stoichiometry deposited by reactive HiTUS using both CSM for bulk and CSM for thin films methods and to compare the results obtained on 4 different substrates (Si wafer, sapphire, 100Cr6 steel, and Ti6Al4V alloy). The subsequent results showed systematic differences in the calculated mechanical properties depending on the substrate properties both in CSM and CSMTF modes. Stiffer substrates always resulted in the overestimations of the calculated hardness and indentation modulus compared to softer substrates with lower Young’s modulus and the differences were in the range of around 10 %. Obviously, better theoretical models for the calculations of true coating properties are required.
AbstractThe main shape deviations of a Berkovich indenter are the indenter bluntness and indenter tilt. The influence of the Berkovich indenter tilt on the results of the FEM modelling of steel nanoindentation is evaluated in this paper. The indenter tilt has an impact on the indentation curves and contact area. The X5CrNiCuNb 16-4 steel nanoindentation was modelled by FEM and the indentation curves were obtained. The Berkovich indenter was blunted and the tilt of the indenter was changed to determine its influence on the indentation curves. The results showed that growing tilt shifts the indentation curves to higher values of indentation forces and makes unloading curves steeper which is in agreement with a larger contact area. The calculated indentation curves were compared with the experimental indentation curves and the impact of the indenter tilt to the indentation curves was determined.
Abstract Welding of the austenitic stainless steel AISI 304 and Ti6Al4V is complicated by hard and brittle intermetallic compound formation. In this contribution, we study a laser welding method that partially overcomes this problem using interlayer. Bronze foil (CuSn6) of thickness 100 µm and 200 µm was inserted between steel and titanium sheets and lap welds were realized on pulsed Nd:YAG laser. Representative samples were investigated by nanohardness measurement, SEM/EDS, and XRD analysis to detect the localization of the intermetallic phases. The macrostructure of the weld cross sections was displayed by optical and digital microscopy. The nano-hardness test revealed the presence of very hard intermetallic mainly around the interface between the fusion zone and bottom metal sheet. EDS mapping displayed the main elements Fe, Cr, Cu and Ti distribution in the fusion zone, EDS line scanning detected elements‘ signals in the diagonal and horizontal directions. XRD analysis revealed expected intermetallic compounds FeTi and CuTi2 and solid solution Cu0.8Fe0.2.
