Composite wires obtained from aluminium shell, micron sized aluminium powder and nano - sized TiN, SiC and Al2O3 powders were fabricated by a two stage process. The stages included ultrasonic treatment and hot extrusion. TEM and SEM observations were performed to investigate the wires’ microstructure. Individual nano powder particles as well as particle agglomerations were observed by two microscopic methods, as well as nanoparticles distribution and localization in the matrix. It was found that the observed nanoparticles and clusters were in the volume of micron-sized Al particles and along the grain boundaries of the matrix. The provided EDX analysis confirms the presence of nanoparticles in the aluminium matrix. From the obtained results, it can be concluded that the two stage fabrication process of nanocomposite wires leads to better wetting of the nano powders from the aluminium melt. Nanocomposites obtained by mixing and extruding TiN, SiC and Al2O3 nano powders and Al micro powders can be used as modifiers of aluminium alloys, as the nanoparticles will contribute to grain refinement and will participate as additional crystallization centers.

This study focuses on the microstructure's evolution upon different aging conditions of a high-strength low-density steel with a composition of Fe–28Mn–9Al–1C. The steel is hot rolled, subsequently quenched without any solution treatment, and then aged under different conditions. The microstructure of the samples was studied by means of Scanning Electron Microscopy, Electron Backscatter Diffraction, and Transmission Electron Microscopy. The aging treatment leads to the formation of an ordered face-centered cubic L1₂ phase named κ-carbide. This study aims to characterize the formation and growth of these κ-carbides qualitatively and quantitatively under different aging conditions. Then, an effort is made to relate the fraction and size of this phase with the tensile properties of the steel to determine the optimal aging conditions that will lead to a good combination of strength and ductility. It has been found that the κ-carbides start to form intragranularly through concentration fluctuations of aluminum and manganese inside the austenite grain. Then, with the process of spinodal decomposition, they grow in size coherently with the matrix. During this process, the strength and hardness of the steel increase while maintaining a relatively high elongation. The best combination of high strength and ductility was achieved at the aging condition of 8 h at 550 °C with an ultimate tensile strength up to 1157 MPa and total elongation of 51%. Increasing the aging temperature and time, κ-carbides start to form intergranularly, lose their coherency with the matrix and severely compromise the hardness and strength. The shearing of the carbides during deformation is also studied.

Laser powder bed fusion (L-PBF), categorized as additive manufacturing technique, has a capability to fabricate NiTi (Nitinol) shape memory alloys with tailorable functional properties and complex geometries. An important processing parameter, hatch distance (h), is often related to macroscale structural defects; however, its role on controlling the microstructure and functional properties is usually underestimated in L-PBF of NiTi. In this work, equiatomic NiTi (50.0 at% Ni) parts were fabricated with various hatch distances to tailor the microstructure and their shape memory characteristics. Contrary to what is observed in Ni-rich NiTi alloys, in this work, we demonstrate that phase transformation temperatures of L-PBF equiatomic NiTi do not decrease proportionally with hatch distance but rather relate to a critical hatch distance value. This critical value (120 μm) is derived from the synergistic effect of thermal stress and in situ reheating. Below this value, epitaxial grain growth and in situ recrystallization are enhanced, while above, irregular grains are formed and dislocations induced by thermal stresses decrease. However, the critical value found herein is characterized by high dislocation density and fine grain size, resulting in a superior thermal cyclic stability. The proposed finite element model is proven to be an effective tool to understand and predict the effect of hatch distance on grain morphology and dislocation density evolutions in L-PBF NiTi SMAs. In the present study, we provide a comprehensive understanding for in situ controlling L-PBF NiTi microstructure and functional characteristics, which contributes to designing 4-dimensional shape memory alloys.

Pulsed laser beam welding was used successfully to join the oxide dispersion-strengthened (ODS) Eurofer steel. The joining was conducted with a laser power of 2500 W and a pulsed duration of 4 ms. With the filler material being used, a minor material loss and microvoids were observed in the joint. The microstructure of the fusion zone consists of dual phase elongated structures. The heat-affected zone has a width of around 0.06 mm with finer grains. The transmission electron microscopy observation reveals that nanoprecipitates are finely distributed in the fusion zone. The tensile strength, yield strength and elongation of the joint are slightly inferior to the base material. The fractography results reveal a typical ductile fracture. The experimental results indicate a reasonable joint from the perspective of both the microstructure and mechanical behaviour.

The multiphase microstructure of carbide-free bainitic steels comprises bainitic ferrite laths, retained austenite with different morphologies, a minor fraction of carbides and so-called martensite-austenite areas, which partially transform during the last cooling step. While the other constituent received much attention, little is known about the structure of the martensite-austenite constituent in carbide-free bainitic steels. Thus, in this study, it was structurally and chemically investigated by high-resolution techniques such as transmission electron microscopy and atom probe tomography after preceded unambiguous identification by electron backscatter diffraction in conventional as well as transmission mode. The results, ranging from carbon segregation to cementite precipitation in the martensitic part, indicate strong auto-tempering during final cooling which is followed by aging. Also, some kind of structural modulation in the austenite belonging to the martensite-austenite areas was observed. Atom probe tomography revealed a heterogeneous carbon distribution, further supporting the findings by transmission electron microscopy.

In this work a carbide-free bainitic steel was examined by a novel correlative microscopy approach using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The individual microstructural constituents could be identified by TKD based on their different crystal structure for bainitic ferrite and retained austenite and by image quality for the martensite-austenite (M-A) constituent. Subsequently, the same area was investigated in the TEM and a good match of these two techniques regarding the identification of the area position and crystal orientation could be proven. Additionally, the M-A constituent was examined in the TEM for the first time after preceded unambiguous identification using a correlative microscopy approach. The selected area diffraction pattern showed satellites around the main reflexes which might indicate a structural modulation.