Abstracts:In this work, an Al–Mg–Sc–Zr alloy was manufactured using selective laser melting (SLM) at platform temperatures of both 35 °C and 200 °C. The effects of platform temperature and applied energy density (E) on porosity characteristics were studied by image analysis. The results show that 60–70 J/mm³ is the minimum applied energy density threshold to build high density parts ($\>$ 99.7%), and that the number density and size of pores follow similar trends for both platform temperatures even though the number density of pores is consistently lower at the 200 °C platform temperature. The optimum processing condition of E = 77 J/mm³ was selected for building thin plates to evaluate the tensile properties based on the lowest porosity and highest hardness results. Tensile results indicate that 35 °C fabricated specimens have a low anisotropy, while 200 °C fabricated specimens have higher as-fabricated strengths but inhomogeneous properties from bottom to top. After peak aging, all samples achieve very similar tensile properties with yield strengths of close to 460 MPa, though the elongation for the 200 °C fabricated specimens still presents a gradual decrease from top to bottom of the plate. The microstructure and property evolution was explained in terms of thermal history effects on the different types of grains and precipitates in this alloy.

Abstracts:A composite consisting of Ti-6Al-2Sn-4Zr-2Mo as matrix and Ti-42.3Al-3.8Nb-1Mo-0.1B (at%; known as γ-TiAl-TNM) as reinforcement was developed to increase the working temperature for titanium based alloys. The volume fraction (10 wt%, 15 wt%) and the particle size (< 20 µm, 20–45 µm) of the TiAl-TNM, and the sintering temperature (1100 °C, 1150 °C) were varied. It was shown, that the working temperature of Ti-6Al-2Sn-4Zr-2Mo can be increased to 650 °C by the addition of 10 wt% TiAl-TNM due to an elongation > 2% at room temperature and an increase in yield strength of 100 MPa in the temperature range of room temperature to 650 °C compared to Ti-6Al-2Sn-4Zr-2Mo. Furthermore, the dissolving of TiAl-TNM, which takes place already at 650 °C, does not lead to a decline in yield strength and tensile strength.

Abstracts:A novel extrusion process, namely, slope extrusion (SE), was proposed to produce Mg–3Al–1Zn alloy sheet, thereby tailoring the strong basal texture of conventional extruded (CE) sheet. The grain morphology and texture were examined, and the tensile tests were performed along 0°, 45°, and 90° with extrusion direction. Moreover, the finite element simulation was performed to have a better understanding on the extrusion processes. An elongated weak double-peak texture titled from extrusion direction to transverse direction about 48° was obtained for the SE sheet and meanwhile the two peaks titled away from normal direction by ~ 35°. Therefore, the SE sheet showed lower yield strength and higher ductility compared with CE sheet. Especially, in terms of the transverse direction specimen of the SE sheet, the ductility reached 27.3%, which was considered as an excellent value for the wrought AZ31 sheet.

Abstracts:Microcompressive tests were performed to investigate the intrinsic modulation effect and extrinsic diameter effect on strength and deformation behaviors of nanolaminated Cu/Cu-Zr crystalline/amorphous micropillars within a diameter D range from 300 to 1500 nm as well as a modulation ratio η range from 0.1 to 3.0. Experimental results revealed a transition of D-dependent deformation mode from homogeneous-like to shear localization at large η, while D-independent homogeneous extrusion of Cu at small η. Furthermore, the flow strength increased with raising D at small η, but decreased at large η, exhibiting a D-insensitive strength at a critical η* ~ 0.5. These unusual results were rationalized in terms of a coupling effect of dislocation actions and shear transformation zone mediated operations.

Abstracts:The effect of alloying elements on room temperature stretch formability and its deformation mechanism was investigated using pure magnesium and its binary alloys containing an element of Ag, Al, Ca, Li, Mn, Pb, Sn, Y and Zn, respectively. All of the alloys as well as pure magnesium were produced by extrusion and had a similar average grain size. The alloying elements clearly affected stretch formability as measured by Erichsen testing. The addition of manganese or yttrium element played a role in improving formability; on the other hand, most of the alloying elements did not improve formability, as exhibited by their limited dome height values, which were similar to or lower than that of pure magnesium. This resulted from their differences in deformation mode. An intragranular misorientation axis analysis using electron back-scatter diffraction results revealed that the Mg-Y alloy had a high fraction of grains amenable to non-basal dislocation slips, which is a helpful deformation mode for improving formability. In contrast, pure magnesium and the Mg-Mn alloy, which had a high limited dome height, did not have a high fraction of such grains. Grain boundary sliding compensated for the lack of < c >-component, such as activating non-basal dislocation slips.

Abstracts:The excellent mechanical properties of recently developed polysynthetic TiAl-Ti3Al intermetallic single crystals lead to a high motivation to explore the micro-mechanical properties of their constitutional phases. However, the mechanical properties of the individual phases at the nanoscale are hard to obtain since the measurement requires a high lateral resolution and superior mechanical sensitivity. Here, using a method of scanning nanoindenter together with nanoDMA, we report the critical data of modulus maps and the nanoindentation hardness of their individual phases at the nanoscale. Furthermore, the yield strength and plasticity of the individual phases were obtained using an in situ nanoindentation on the focused ion beam machined nanopillars. The value of elastic modulus is measured to be about 140 and 180 GPa, respectively for α 2 -Ti3Al and γ-TiAl intermetallic phases, for samples with 0° lamellar orientation, which is higher than the value of about 120 and 160 GPa for the same phases in samples with 45° lamellar orientation. The relationship between the microscale and macroscale modulus can be described using the Voigt-Reuss approximation. More importantly, AFM results show that the plastic deformation is more uniform for the single crystals with 0° lamellar orientation, since they have more homogeneous microstructure and smaller difference in the hardness between the two phases. Our findings are useful to promote the applications and design of new TiAl-based single crystals as structural materials, from the perspective of the microstructure and micro-mechanical properties.

Abstracts:Al/Mg/Al laminates were fabricated by hot rolling at 400 °C and annealed at temperature ranging from 200 °C to 400 °C for 1 h to 4 h. Microstructural examination revealed that brittle intermetallics identified as Mg17Al12 and Al3Mg2 appeared at Mg/Al interface when annealing temperature exceeded 300 °C. Al layers in laminates annealed at 200 °C exhibited typical copper-type texture, which totally transformed to recrystallized cube texture at 400 °C with a higher intensity. Mg layers in annealed laminates presented (0002) basal texture with c-axis titling from normal direction (ND) to rolling direction (RD), and bimodal basal texture was observed at 400 °C. Recrystallization extent of Mg layer increased with the increase in annealing temperature and/or annealing time, and nuclei preferred to occur in grains near Mg/Al interface. Grain size, texture type of matrix, and thickness of intermetallic layers all influence mechanical properties of Al/Mg/Al laminates. Laminates annealed at 200 °C for 1–4 h exhibited better ultimate tensile strength (UTS) ranging from 223 MPa to 240 MPa and elongation (EL) ranging from 21% to 26%. Despite more extensive recrystallization of laminate annealed at 400 °C, thicker intermetallics greatly decreased its strength and plasticity because crack initials and quickly propagates along Mg/Al interface or in the interior of intermetallics.