Key Engineering Materials Vol. 865

Abstract: Selective laser melting (SLM), as the main representative of additive manufacturing technologies, has a high variability of process parameters setting, which provides wide possibilities in tuning porosity and mechanical properties of final parts. To ensure a high relative density of SLM parts, thorough process optimization is required. Efforts so far developed in this research area suggest that the optimization is desirable for each machine, material and suitably even for a specific product. As even the adjustment of a specific machine may affect the resulting part quality, we carried out an initial process optimization for a specific SLM machine applied to the processing of Ti6Al4V alloy. We studied a range of energy density values between 40-400 J/mm³ by changing scanning speed and hatching distance. The results of this initial optimization demonstrated how porosity and mechanical properties can be varied widely with different parameter settings, suggested a processing window for reaching the highest relative density and revealed that changing the energy density might be also associated with microstructural changes influencing the mechanical performance of a final part. Therefore, our follow-up study will focus on detail microstructural characterization.

Abstract: This study investigated the prospective application of the advantageous intensive plastic deformation method of rotary swaging for production of Al-Cu composite wires. Such materials are perspective to be used within a wide range of commercial and industrial branches, from transportation to electrotechnics. Cu-Al laminated wires with two unique different stacking sequences were rotary swaged down to 5 mm diameter at room temperature to minimize the development of brittle intermetallics at the interfaces. The analyses primarily focused on the mutual comparison of both the stacking sequences (Al sheath reinforced with Cu wires vs. Al sheath and Al core reinforced with Cu inter-layer) from the viewpoints of mechanical properties, sub-structure development, and occurrence of residual stress. While the individual Cu wires exhibited bimodal structure and the presence of residual stress within the growing grains, the Cu inter-layer featured recrystallized grains and homogeneous stress distribution. The mechanical properties for both the composites were enhanced by the swaging technology; the composite reinforced with Cu wires exhibited slightly higher ultimate tensile strength than the one with Cu inter-layer (258 MPa vs. 276 MPa). However, the latter featured significantly higher plasticity.

Abstract: Scandium aluminum nitride (ScxAl1-xN) is a promising material for sensor applications as it exhibits enhanced piezoelectric properties compared to pristine AlN while maintaining other advantageous properties like high thermal stability. Magnetoelectric sensors in particular are used to detect magnetic fields which leads to special requirements regarding the investigated ScAlN in order to achieve high sensor sensitivities. Co-sputtered ScAlN layers are investigated in this work using XRD, XPS, FTIR and Raman spectroscopy for scandium concentrations from 0 to 34 %. The impact of Sc incorporation regarding residual biaxial strain and bond softening is discussed on basis of the experimental results. The activity of the B1 and E2 modes found in the FTIR measurements is of special interest as the presumably oxygen related excitation is expected to influence the piezoelectric properties.

Abstract: Exposing smart materials to electron beam radiation can induce free radical reactions, such as chain branching or crosslinking, hence enhancing the characteristics of the polymers. Poly (N-vinylcaprolactam) (PNVCL) is a smart material which was synthesised by photopolymerisation. Subsequently, samples were exposed to electron beam technology, where electron beam irradiation was utilised in a novel approach. This led to the modification of the rheological and phase transition properties. Modifying PNVCL through electron beam irradiation opens new avenues and potential applications in the biomedical field. Physically cross-linked PNVCL polymers were prepared by photopolymerisation and samples were subsequently irradiated at different dose ranges (5kGy, 25kGy and 50 kGy). The rheological properties of the PNVCL based samples were established by rheological analysis. Similarly, the PNVCL based sample polymers were further characterised in solution to determine the phase transition of PNVCL.

Abstract: Soldering using common lead-free solder alloys is still one of the main die attach technology, in particular for applications in power electronics where high temperatures have to be met. However, some newly developed attach technologies promise to offer more interesting features in terms of both mechanical and thermal properties. Among these new methods, sintering of nano-silver particles allows to obtain a high thermal conductivity needed in the assemblies of electronic or optical components, as well as a relatively low elastic modulus for better stress accommodation and enhanced thermo-mechanical reliability. The sintering processing parameters, mainly the bonding pressure, the sintering temperature profile, and the sintering atmosphere, are known to have a critical effect on the properties of the sintered layer, such as its mechanical strength and electrical/thermal performances.In this study, copper substrates are fabricated and assembled by sintering using a nano-silver paste. The objective is to obtain a bonding joint with high mechanical flexbility, capable of addressing the thermomechanical stresses for systems operating under high temperatures. The measured mechanical properties of the sintered material show on the one hand low elastic modulus of the joint which is appropriate for strong difference in thermal expansion between components, and on the other hand sufficient mechanical strength for the assembly. Microstructure analyses reveal a highly porous silver network structure of the joint, with submicrometric silver grains and large micrometric porosities homogeneously distributed.

Abstract: The vibration of perforated plates is central to certain engineering applications, such asdroplet-on-demand, inject printing and aerosol generation. To the author’s knowledge, there is limitedpublished literature outlining the effect of perforations on the natural frequency of a flat circular plate.This paper aims to further the understanding in this field research, by determining analytically theeffect of perforations on the natural frequency of boundary clamped flat circular plate. The methodology of this paper outlines the development of a dynamic finite element (FE) model which accurately embodies the effect of perforations on the natural frequency of a boundary clamped flat circular plate using modal analysis. This dynamic FE model aids in optimising the vibrational mechanics of perforated plates for specific engineering applications. The finding from this analysis demonstrates that the published literature is less conservative when compared to the FE method in predicting the effect of perforations on the natural frequency of a boundary clamped flat circular plate. Published literature uses a numerical analysis which underestimates the effect of perforations on the natural frequency of a boundary clamped flat circular plate when compared to the FE analysis reported in this study.

Abstract: The aim of the paper is to define the limits of substitution and phase stability for solidsolutions of orthovanadates with zircon structure Sc1–xLnxVO4, where Ln is a rare-earth element(REE), Ln = Ce – Lu. The mixing energies (interaction parameters) and critical decompositiontemperatures of Sc1–xLnxVO4 solid solutions with the zircon structure were calculated using thecrystal-energy theory of isomorphous miscibility. Diagram of thermodynamic stability visualizingthe substitution limits (x) by the decomposition temperature or the decomposition temperature bythe substitution limits, the dependencies of the decomposition temperatures on the REE atomicnumbers is presented. This diagram also allows assessing areas of stability, instability, andmetastability for Sc1–xLnxVO4 solid solutions. Results of calculations were compared with literaturedata on thermodynamic stability of solid solutions and on substitution limits. The results of thisstudy can be used in the development of new luminescent materials based on ScVO4 modified withREE, in the selection of REE for matrix and activator, in defining optimal proportions of REE inSc1–xLnxVO4 matrices.

Abstract: Tissue scaffolds can be designed to mimic the native extracellular matrix (ECM), making them attractive for the development for a range of regenerative medicine applications. The macromolecules present in the ECM are critical for the provision of structural support to surrounding cells and signalling cues for the modulation of diverse processes including cell migration, proliferation and healing activation. Here, conformational and transitional behaviour of the ubiquitous ECM protein, fibronectin (Fn), in the presence of bone tissue regeneration scaffolds and living C2C12 myoblast cells is reported. Spectral monitoring of Fn functionalised high plasmonic resonance responsive gold-edge-coated triangular silver nanoplates (AuTSNP) is used to distinguish between compact and extended fibronectin conformations. Large spectral red shifts of ~20 to ~59 nm indicate Fn unfolding and fibril formation on incubation with C2C12 cells. The label-free nature, excellent sensitivity and straightforward application of the AuTSNP within cellular environments presents them as a powerful new tool to signature protein conformational activity in living cells and monitor essential protein activity for the assisted development of improved tissue scaffolds promoting enhanced tissue repair.

Abstract: The purpose of the work is influence investigation of modifying Nd₅Mo₃O_16+δ oxygen-conducting fluorite-related compound by lead at the crystal structure and conductivity. The substitution of lead for neodymium was studied by XRD (with structure refinement), scanning electron microscopy, FTIR-spectroscopy and conductivity measurements. The compositions Nd_5-xPb_xMo₃O_16+δ (x = 0 – 1.6) were obtained by a solid state reaction from the oxides. It was determined that single-phase solid solution Nd_5-xPb_xMo₃O_16+δ is formed up to x ≈ 0.82. The Rietveld structure refinement shows that lead is statistically located in the Ln1 and Ln2 positions. The introduction of lead does not significantly affect the nature and values of conductivity.