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This paper aims to comprehensively evaluate the shear strength of various junctions between diamond chips and double copper bonded ceramic substrates. The study involves several stages, beginning with the deposition of Ti/Ni/Ag metallization system on diamond chips using a chemical vapor deposition (CVD) process. These metallization systems are selected to determine their suitability as ohmic contacts on diamond. In parallel, Ni/Au and Ni/Ag layers are electroplated onto the thick copper metallization of the ceramic substrate. Following these depositions, junctions are created for both Cu/Cu and C/Cu assemblies using different techniques: reflow process for AuGe solder joints, reflow-diffusion process for Ag-In joints, and a thermomechanical process for Ag nanoparticle joints. To assess the effectiveness of these techniques, the shear strength of the junctions is measured using a micro-shear test, which is analogous to a classical micro-scratching test. Additionally, the mechanical behaviors of the layers adjacent to the assemblies are analyzed through nano-indentation tests. Finally, the fracture surfaces are examined using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectrometry to identify the microstructure and damage modes. The work described in the paper exhibits several innovative aspects. It introduces the novel combination of Ti/Ni/Ag metallization system on diamond chips, evaluated for its suitability as ohmic contacts, potentially leading to improved electrical and thermal performance in diamond substrate applications. The study employs diverse junction creation techniques, such as reflow for AuGe solder joints, reflow-diffusion for Ag-In joints, and a thermomechanical process for Ag nanoparticle joints, allowing for a thorough comparison and identification of the most effective method for different scenarios. We have also introduced an integrated testing methodology, which combines micro-shear tests and nano-indentation tests and provides a robust framework for assessing both the shear strength and mechanical properties of the junctions and adjacent layers, enhancing the reliability and depth of the evaluation. The specific focus on metallization system and junctions suitable for diamond, known for its exceptional thermal and electrical properties, positions this work as highly relevant for advanced electronic and thermal management applications.

Three micro mechanical testing geometries including micro-pillars, micro-cantilevers and micro-shear specimen, were employed to measure the twinning stress of the Cantor high entropy alloy. This study presents a comparative analysis of the challenges in specimen preparation, effectiveness in activating deformation twinning and complexity of post mortem analyses associated with each geometry. Our findings demonstrate that micro-shear testing represents the optimal approach for twinning studies, offering direct activation of the twinning system with the superior reproducibility compared to other geometries. Micro-pillar compression is also suitable for twinning investigations, providing statistical analysis of mechanical data with relatively faster sample preparation. However, micro-cantilever testing presents challenges with a lower success rate in twinning activation and the stress gradients, which complicates quantitative interpretation, resulting in the least favorable geometry for twinning studies. [Display omitted] • The usability of 3 micromechanical geometries to quantify twinning was evaluated. • Micro-shear tests can directly activate a twinning system with reproducible data. • Dislocation slip and twinning can be better discriminated in a micro-shear test. • Micro-pillars are suitable to quantify and investigate twinning mechanisms. • Using bending cantilevers is not recommended due to stress gradients. [ABSTRACT FROM AUTHOR]

The Polish left ventricular assist device (LVAD – RELIGA_EXT) will be made of thermoplastic polycarbonate-urethane (Bionate II) with deposited athrombogenic nano-coatings: gold (Au) and titanium nitride (TiN). Referring to the physical model, the two-scale model of LVAD developed in the previous works in the authors’ finite element code is composed of a macro-model of blood chamber and a micro-model of wall: TiN, Au and Bionate II. The numerical analysis of stress and strain states confirmed the possibility of fracture based on localization of zones of the biggest values of triaxiality factor. The introduction of Au interlayer between TiN and polymer improved the toughness of the connection, and increased the compressive residual stress in the coating what resulted in reduction of stress and strain close to the boundary between substrate and coating.