AlCuLi based alloys are attractive for the aerospace and automotive industries for their relatively high strength and low density. Sheet applications suffer from anisotropy of mechanical properties necessitated by a high number of rolling steps during production from large scale DC cast ingots. Formability and properties of these alloys could be improved by employment of alternative casting methods such as twin-roll casting (TRC), which produces thin sheets in the as-cast state combining casting and forming in a single step. The high cooling rates achieved during TRC cause a formation of a finer grain and cell structures with finer constituent particles. In this study, two dilute AlCuLi alloys based on the AA2195 alloy composition, one with an addition of Sc, were investigated. A novel processing scheme is proposed, combining homogenization and solution treatment into a single step. Dissolution of a large fraction of present constituent particles was achieved through this treatment due to shorter times of dissolution and transformation of small constituent particles and shorter diffusion lengths for solute redistribution in the TRC material. Heat treated materials were then aged for up to 100 h in oil. Mechanical properties and microstructure of the materials at different stages of processing were studied using a combination of microscopic observations, hardness measurements and deformation testing.
Ti-Nb-Zr-O based biomedical alloys were prepared from metallic elemental powders and titanium dioxide by Field Assisted Sintering Technique (FAST). Four heterogeneous samples with different oxygen content, each consisting of 6 layers, covering together 24 chemical compositions were prepared. Slow diffusion of Nb allows preparation of samples differing in the Nb content. Elastic constants for each layer were determined using resonant ultrasound spectroscopy and complemented by detailed SEM and XRD analysis. In the considered compositional space, elastic constants exhibit a dependence on the volume fraction of beta stabilizing Nb and interstitial oxygen. Particular composition stronlgy affects formation of martensitic phases and omega phase. Minimum elastic modulus was achieved for the compositions close to the stability limit between parent beta matrix and alpha double-prime martensitic phase.
Third-generation Al-Li-based alloys are widely used in aerospace, aviation, and military applications. They exhibit high strength, low density, good corrosion resistance and fracture toughness.
Coarse primary particles formed during conventional ingot or direct-chill casting should be dissolved or transformed during long-term homogenization treatment, usually occurring at high temperatures (typically above 500 °C). This treatment contributes to the unwanted depletion of the material from Li atoms. Twin-roll casting (TRC) of strips prepared from this type of alloy might be an effective method for replacing the traditional casting process. High cooling rates reached during TRC could refine a dendritic structure containing fine intermetallic particles composed of phases bearing impurity atoms and some of the main alloying elements in highly alloyed Mg- and Cu-containing alloys. Compared with conventionally cast Al-Li-based alloys, lower annealing temperatures and shorter periods could be used for homogenization. Electrical resistivity measurements were used to monitor phase transformations occurring in conventionally mold and TRC cast Al-Li-Cu-Mg alloys. Results were compared with in-situ heating STEM/SEM observations.
Additive manufacturing is a modern technology allowing fast and cheap fabrication of complex-shaped parts. Eequal channel angular pressing (ECAP), which belongs to severe plastic deformation (SPD) methods, introduces large amounts of strain and dislocations to the material, which results in its densification and strengthening. In this contribution, the unique combination of directed energy deposition (DED) and four-pass ECAP processing was investigated. The experimental material is DED-processed titanium alloy Ti-6Al-4V in as-deposited and ECAP-ed states. The material in both states was subjected to microstructure investigation using light (LM) and scanning electron microscopy (SEM), porosity and hardness measurement and mechanical testing (miniaturized tensile test). The fracture surfaces of the specimens after testing were observed using SEM. The ECAP processing led to significant deformation of original grains and refinement of microstructure. In the case of ECAP-ed specimens, a significant improvement of strength and elongation was observed.
The Cu-Cr-Zr alloys were cryogenically processed by ECAP from 1 to 4 and rolled with a rolling reduction of 98%, and then vacuum aging treatment (AT) was involved. The microstructure contains ultrafine-grains(UFG), nano-twins(NT), nano-precipitates(NP)as well as grain boundaries(GB) with high density of dislocations. The prepared Cu-Cr-Zr alloy has good comprehensive properties with a highest tensile strength of 731 MPa, the ductility of 8.5%, and the electrical conductivity of 80%IACS after 4P+CR+AT, which provides a significant breakthrough of the strength limit of Cu-Cr-Zr alloy and avoided the pronounced loss of electrical conductivity. It is a new way for Cu-Cr-Zr alloy foils to meet industry requirements for high strength and good conductivity.