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This study has investigated the causes of pores' formation during fabrication of the first few layers on the support structure and the process of product improvement in Selective Laser Melting. The notable pores are, fundamentally, formation of the void with uneven shape and the voids containing partially melted or stuck particles. The voids spread over a few consecutive layers from the starting one. The porosity occurred due to unsupported areas among supporting points, improper melt pool formation, melt pool's instability, inconsistency of heat transfer, crescent shape formation, uprooting of the lifted edge by the powder re-coater, and materials' spattering. These phenomena can be regulated by controlling the amount of energy input, melting time, amount of re-melting, delaying between melting and re-melting, and reheating and cooling timing using the combinations of laser powers, scanning speeds, and hatch spacings. Eventually, a sample having almost flawless starting layers was fabricated from Ti-6Al-4V powder.

Properties of a product fabricated using Selective Laser Melting (SLM) technology depend upon its building orientation as well as Energy Density (ED) used for its fabrication process. As ED is the key factor among all the process parameters in SLM technology, this study has focused on ED along with building orientation. Seven sets of EDs and four sets of building orientations for each set of ED were selected to investigate the dissimilarities among tensile properties as well as other properties of Ti-6Al-4V alloy specimens. The scanning speed was varied to set the different ED values as it influences the thermal characteristics of the molten pool more than the other processing parameters. Tensile strengths of the specimens have differed significantly with respect to building orientations as well as EDs. The tensile characteristics of the specimens have been explored by tensile testing and analyzed regarding metallurgical properties, which are density, porosity, defect, microstructure, and surface morphology. Specimens built in lengthwise vertical position and the energy density of 65 J/mm3 have shown the best tensile properties in this study.

A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuous casting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy started with the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent: FCC-γ+G-phase, which replaced the low-melting eutectic (FCC-γ+NiBe) in the Be-bearing alloys. AlNi6Si3 and γ′ formed during the terminal stages of solidification by investment casting, while the formation of AlNi6Si3 was suppressed by continuous casting. The Scheil solidification model agreed very well with the experimental results.

Improving the metallurgical properties of the products fabricated by the Selective laser melting (SLM) process is still a challenge focusing on processing parameters and Energy Density (ED). In this study, the density, porosity and microstructure of cuboid Ti-6Al-4V alloy samples fabricated by the SLM process were investigated, paying particular attention to the manufacturing key factor ED. Seven different EDs between 39 J/mm3 and 260 J/mm3 were achieved by varying the scanning speed from 1000 mm/s to 150 mm/s. The results show the ED, as well as cooling conditions, have a great influence on the above mentioned metallurgical properties. Significantly different densities have been observed, with different Eds where the difference between the sample with the highest relative density and the sample with the lowest relative density was almost 2.45%. The highest relative product density of almost 99.45% was obtained at the ED value of 65 J/mm3. The volume, shape and numbers of pores were different with different EDs. The resultant microstructure consisted of four typical hierarchical α′ martensites, namely, primary, secondary, tertiary and quartic α′ martensites within columnar prior β grains.

The surface morphology of a product plays a crucial role under mechanical loading and chemical environment. Surfaces of Selective Laser Melting (SLM) products often contain high roughness, which varies in different planes as well. The authors have explored the surface characteristics of the SLM samples that are influenced by different combinations of laser processing parameters. The considered processing parameters were Energy Density (ED) and its technological parameters namely laser power, scanning speed and hatch spacing. Additionally, a comparison study has been executed by rescanning effects considering melting with low ED and, thereafter, rescanning by the best possible laser processing parameters. The results evidently showed that the surface morphologies differ significantly due to different laser processing parameters. Eventually, the thermal and physical behavior of materials, such as the viscosity of the melt pool, thermal and physical stability of the melt pool, solidification time, cooling time, shrinkage, capillary effect, surface tension, balling effect, and the amount of melting of a powder particle, influenced the surface properties of the samples, along with unpredictability. The results showed an interesting correlation between the processing parameters and the occurrence of microcracks on the vertical walls of the specimens caused by the partially melted adhered powder particles.

The research focuses on the mechanical properties and fatigue behaviour of individual parts of Heat Affected Zones (HAZ) in a weld joint on 18CrNiMo7-6 steel. In real welds, the HAZ is heterogeneous and narrow. Therefore, specimens having a desired HAZ microstructure uniform over the whole specimens‘ volume were prepared artificially by water quenching: The Coarse Grain HAZ (CG HAZ), with average grain size of 200 µm, Fine Grain HAZ (FG HAZ) with average grain size of 10 µm, and CG-FG HAZ with average grain size of 25 µm. Comparison with a real weld revealed that microstructures of specimens corresponded very well to the microstructures in HAZ in a real weld joint. Fatigue crack growth and the threshold for long crack propagation ΔKthR were determined on HAZ microstructures. A weld toe and its stress concentration due to weld cap were simulated by a U shaped groove on the fatigued specimens. Real HAZ often contains small defects where a crack usually initiates. Therefore, a defect was simulated with a Vickers impress at the bottom of the groove in all three HAZ-microstructures. Investigation revealed that the threshold for long crack propagation ΔKthR of the FG HAZ was the lowest, not much higher was the threshold in CG HAZ, while the threshold ΔKthR in CG-FG HAZ was significantly higher. On the other hand, long crack propagation in CG HAZ is faster in comparison to the long crack propagation in FG HAZ. In all three cases, a Paris curve and its coefficients were determined for R ratios −1 and 0.1. Fatigue tests revealed that some cracks, which had been initiated below the fatigue limit in CG-FG HAZ, stopped propagating due to strong grain boundary barriers and high toughness, but, in the cases of CG HAZ and FG HAZ, the cracks propagated without stopping until the breakage of the specimen. The fatigue limits were also determined for all three HAZ-microstructures in the presence of the defect.

In respect to the cost of constituents, Cu–Al–Ni alloys can be regarded as low-cost shape memory alloys. However, the processing is quite costly due to the brittleness of the ingots. Therefore it would be advantageous to produce semi-finished products directly from the melt via highly productive technique. A laboratory device for vertical continuous casting directly from the vacuum induction melting furnace was experimentally employed for continuous casting of the Cu-13 wt.% Al-4 wt.% Ni shape memory alloy. A water-cooled copper crystalliser with a graphite insert was used to cast ϕ 16 mm strands. Diverse sets of casting parameters were tested, the average casting speeds being within the range from 250 mm min −1 to 625 mm min −1 . The castability of the alloy using this technique was good. Strands were examined in the as-cast condition, and no cracks or other defects were discovered. Medium casting speeds resulted in good surface quality, and a fully martensitic microstructure was obtained even at the lowest average casting speed. The paper presents and discusses the surface quality, microstructures and mechanical properties.

The microstructure of an Al–Mn–Be–Cu alloy was characterised after melt spinning and heat-treatment at different temperatures. The optimised melt-spinning parameters made it possible to obtain ribbons with thicknesses ranging from 30 to 200 μm, having a microstructure composed of a supersaturated Al-rich solid solution, finely dispersed icosahedral quasicrystalline (IQC) particles, and a small fraction of Al 2 Cu. The finest dispersion of the IQC-particles, and consequently the highest microhardness, was obtained on the wheel-side. The initial microstructure started to decompose at temperatures around 400 °C. The IQC-phase was replaced by the intermetallic compounds τ 1 -Al 29 Mn 6 Cu 4 and Be 4 Al(Mn,Cu). The maximum hardness of the ribbons, which was approximately 50% higher than in the as-cast state, was attained after heat treatment at 400 °C, and could be attributed to the fine dispersion of τ 1 -Al 29 Mn 6 Cu 4 and IQC-particles.

In this work we characterized the structure of continuously cast small cross-section rods (O10 mm) of the Ni-based superalloy GMR 235. In the microstructure prevailed dendritic columnar γ-grains with γ′-precipitates. In the interdendritic regions MC-carbide and M3B2-boride were identified. The inverse macrosegregation was very faint, except at the secondary witness marks and natural corrugations. It was found that the alternating drawing mode had much greater influence on microstructure than other casting parameters. Special attention was given to explanation of processes leading to formation of surface marks (primary and secondary witness marks and natural corrugations). Formation of hot tears and appearance of inverse segregation is also discussed.