X-ray Thermo-Diffraction Study of the Aluminum-Based Multicomponent Alloy Al58Zn28Si8Mg6.

Newly designed multicomponent light alloys are giving rise to non-conventional microstructures that need to be thoroughly studied before determining their potential applications. In this study, the novel Al58Zn28Si8Mg6 alloy, previously studied with CALPHAD methods, was cast and heat-treated under several conditions. An analysis of the phase evolution was carried out with in situ X-ray diffraction supported by differential scanning calorimetry and electron microscopy. A total of eight phases were identified in the alloy in the temperature range from 30 to 380 °C: α-Al, α'-Al, Zn, Si, Mg2Si, MgZn2, Mg2Zn11, and SrZn13. Several thermal transitions below 360 °C were determined, and the natural precipitation of the Zn phase was confirmed after nine months. The study showed that the thermal history can strongly affect the presence of the MgZn2 and Mg2Zn11 phases. The combination of X-ray thermo-diffraction with CALPHAD methods, differential scanning calorimetry, and electron microscopy offered us a satisfactory understanding of the alloy behavior at different temperatures.

Influence of Minor Alloying Element Additions on the Crack Susceptibility of a Nickel Based Superalloy Manufactured by LPBF.

Inconel 738LC (IN738LC) is a nickel-based superalloy specially used in the hot section components of turbine engines. One of its main drawbacks relies on the cracking susceptibility when it is manufactured by laser powder bed fusion (LPBF). This paper analyzes the influence of minor alloying element concentration on cracking tendency of IN738LC superalloy manufactured by LPBF. For that objective, samples were manufactured using two powders, which presented different minor alloying elements concentration (Si, Zr and B). It was shown that the samples crack tendency was very different depending on the powder used for their manufacturing. In fact, the measured crack density value was 2.73 mm/mm2 for the samples manufactured with the powder with higher minor alloying elements concentration, while 0.25 mm/mm2 for the others. Additionally, a special emphasis has been put on elemental composition characterization in cracked grain boundaries in order to quantify possible Si or Zr enrichment. It has been also studied the differences of solidification ranges and grain structures between both samples as a consequence of different minor alloying elements concentration in order to analyze their effect on crack susceptibility. In this sense, Scheil-Gulliver simulation results have shown that samples with higher Si and Zr contents presented higher solidification range temperature. This fact, as well as an increase of the presence of high angle grain boundaries (HAGB), leaded to an increment in the crack formation during solidification. Therefore, in this research work, an understanding of the factors affecting crack phenomenon in the LPBF manufactured IN738LC was accomplished.

Optimizing Laser Powder Bed Fusion Parameters for IN-738LC by Response Surface Method.

A method to find the optimum process parameters for manufacturing nickel-based superalloy Inconel 738LC by laser powder bed fusion (LPBF) technology is presented. This material is known to form cracks during its processing by LPBF technology; thus, process parameters have to be optimized to get a high quality product. In this work, the objective of the optimization was to obtain samples with fewer pores and cracks. A design of experiments (DoE) technique was implemented to define the reduced set of samples. Each sample was manufactured by LPBF with a specific combination of laser power, laser scan speed, hatch distance and scan strategy parameters. Using the porosity and crack density results obtained from the DoE samples, quadratic models were fitted, which allowed identifying the optimal working point by applying the response surface method (RSM). Finally, five samples with the predicted optimal processing parameters were fabricated. The examination of these samples showed that it was possible to manufacture IN738LC samples free of cracks and with a porosity percentage below 0.1%. Therefore, it was demonstrated that RSM is suitable for obtaining optimum process parameters for IN738LC alloy manufacturing by LPBF technology.

Effect of biomaterials hydrophobicity and roughness on biofilm development.

Most hospitalized patients are carriers of biomedical devices. Infections associated with these devices cause great morbidity and mortality, especially in patients in intensive care units. Numerous strategies have been designed to prevent biofilm development on biodevices. However, biofilm formation is a complex process not fully clarified. In the current study, roughness and hydrophobicity of different biomaterials was analyzed to assess their influences on the biofilm formation of four leading etiological causes of healthcare-associated infections, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis and Candida albicans, using a CDC biofilm reactor. Hydrophobic materials allowed the formation of more abundant and profuse biofilms. Roughness had effect on biofilm formation, but its influence was not significant when material hydrophobicity was considered.

Design, Microstructure and Mechanical Properties of Cast Medium Entropy Aluminium Alloys.

In this work, the design, microstructures and mechanical properties of five novel non-equiatomic lightweight medium entropy alloys were studied. The manufactured alloys were based on the Al65Cu5Mg5Si15Zn5X5 and Al70Cu5Mg5Si10Zn5X5 systems. The formation and presence of phases and microstructures were studied by introducing Fe, Ni, Cr, Mn and Zr. The feasibility of CALPHAD method for the design of new alloys was studied, demonstrating to be a good approach in the design of medium entropy alloys, due to accurate prediction of the phases, which were validated via X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. In addition, the alloys were manufactured using an industrial-scale die-casting process to make the alloys viable as engineering materials. In terms of mechanical properties, the alloys exhibited moderate plastic deformation and very high compressive strength up to 644 MPa. Finally, the reported microhardness value was in the range of 200 HV0.1 to 264 HV0.1, which was two to three times higher than those of commercial Al alloys.

A parameter for the assessment of the segmentation of TEM tomography reconstructed volumes based on mutual information.

A method is proposed and verified for selecting the optimum segmentation of a TEM reconstruction among the results of several segmentation algorithms. The selection criterion is the accuracy of the segmentation. To do this selection, a parameter for the comparison of the accuracies of the different segmentations has been defined. It consists of the mutual information value between the acquired TEM images of the sample and the Radon projections of the segmented volumes. In this work, it has been proved that this new mutual information parameter and the Jaccard coefficient between the segmented volume and the ideal one are correlated. In addition, the results of the new parameter are compared to the results obtained from another validated method to select the optimum segmentation.

A methodology for finding the optimal iteration number of the SIRT algorithm for quantitative Electron Tomography.

The SIRT (Simultaneous Iterative Reconstruction Technique) algorithm is commonly used in Electron Tomography to calculate the original volume of the sample from noisy images, but the results provided by this iterative procedure are strongly dependent on the specific implementation of the algorithm, as well as on the number of iterations employed for the reconstruction. In this work, a methodology for selecting the iteration number of the SIRT reconstruction that provides the most accurate segmentation is proposed. The methodology is based on the statistical analysis of the intensity profiles at the edge of the objects in the reconstructed volume. A phantom which resembles a a carbon black aggregate has been created to validate the methodology and the SIRT implementations of two free software packages (TOMOJ and TOMO3D) have been used.