T. Maity

Is the energy density a reliable parameter for materials synthesis by selective laser melting

ABSTRACT The effective fabrication of materials using selective laser melting depends on the process parameters. Here, we analyse the suitability of the energy density to represent the energy transferred to the powder bed, which is effectively used to melt the particles and to produce the bulk specimens. By properly varying laser power and speed in order to process the powder at constant energy density, we show that the equation currently used to calculate the energy density gives only an approximate estimation and that hatch parameters and material properties should be considered to correctly evaluate the energy density. GRAPHICAL ABSTRACT IMPACT STATEMENT Al-12Si SLM samples were fabricated at constant energy density. The laser power and laser scan speed combination variation was used to demonstrate the significant changes needed with energy density equation.

Origin of plasticity in ultrafine lamellar Ti-Fe-(Sn) composites

Transmission electron microscopic studies of eutectic Ti68.38Fe28.61Sn3 upon 5% and 10% plastic deformation reveal slip transfer across the β-Ti/FeTi lamellae interface. Strohs analysis suggests that addition of Sn to Ti70.5Fe29.5 increases the cleavage stress and reduces the slip stress around a dislocation pile-up at β-Ti/FeTi interface. The presence of ultrafine lamellar FeTi contributes strengthening whereas, dislocation slip is the origin of plasticity in high strength Ti-Fe-(Sn) composites.

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.

Nanoeutectic Composites: Processing, Microstructure and Properties

Abstract Nanostructured alloys exhibit high strength and large elastic strain limit. Unfortunately, the plasticity of these alloys is disappointingly low at room temperature than that of the coarse grain counterparts. In this work, a series of nanoeutectic composites have been developed in Ti–Fe and Ni–Zr based alloys, which exhibit very high strength, like bulk metallic glasses and large plasticity at room temperature. Systematic investigations have been performed to reveal the effect of alloy addition on the alteration of the microstructure and the properties of nano-lamellar phases. Even though, in some cases, alloy addition stabilizes micrometer-sized proeutectic bcc/fcc solid solution phase(s) with dendritic morphology, but the residual melt solidifies into a binary nanoeutectic comprised of alternating soft bcc/fcc phase together with hard intermetallic phase. Furthermore, electron microscopic studies of differently deformed specimens and strain rate jump test have been performed to reveal the role of eutectic lamellae on the strain rate sensitivity and to explore the origin of plasticity in nanoeutectic composites.

Strengthening Effects in Nano-/Ultrafine-Grained Carbon Nanotube Reinforced-Titanium Composites Investigated by Finite Element Modeling

The strengthening effects in nano-/ultrafine-grained carbon nanotube reinforced-titanium (CNT/Ti) composites are investigated based on the dislocation punched zone (DPZ) model from two aspects: CNT reinforcement and matrix grain refinement. Considering the geometrically necessary dislocations constrained in DPZs, the CNT/Ti composites are treated as three-phase composites consisting of CNTs, the DPZs, and the pure matrix. By using the Clyne method, the overall true stress–true strain relations of the CNT/Ti composites are predicted by finite element modeling. The predictions agree well with the experimental results. Then, the influences of the diameter, the aspect ratio, and the volume fraction of CNTs, as well as the matrix grain size, on the strengthening mechanisms in CNT/Ti composites are investigated. The results show that the grain refinement of the matrix increases the overall strength and simultaneously decreases the thermal expansion mismatch strengthening induced by CNTs. It can be concluded that the strength of CNT/Ti composites can be enhanced by increasing the aspect ratio and the volume fraction of CNTs, as well as by decreasing the matrix grain size and the diameter of CNTs. This work presents a method to easily allow the use of readily available finite element software to obtain the overall mechanical response of composites and helps to design composites with excellent mechanical properties.

Influence of Nb on the Microstructure and Fracture Toughness of (Zr0.76Fe0.24)100−xNbx Nano-Eutectic Composites

The present study demonstrates the evolution of eutectic microstructure in arc-melted (Zr0.76Fe0.24)100−xNbx (0 ≤ x ≤ 10 atom %) composites containing α-Zr//FeZr2 nano-lamellae phases along with pro-eutectic Zr-rich intermetallic phase. The effects of Nb addition on the microstructural evolution and mechanical properties under compression, bulk hardness, elastic modulus, and indentation fracture toughness (IFT) were investigated. The Zr–Fe–(Nb) eutectic composites (ECs) exhibited excellent fracture strength up to ~1800 MPa. Microstructural characterization revealed that the addition of Nb promotes the formation of intermetallic Zr54Fe37Nb9. The IFT (KIC) increases from 3.0 ± 0.5 MPa√m (x = 0) to 4.7 ± 1.0 MPa√m (x = 2) at 49 N, which even further increases from 5.1 ± 0.5 MPa√m (x = 0) and up to 5.9 ± 1.0 MPa√m (x = 2) at higher loads. The results suggest that mutual interaction between nano-lamellar α-Zr//FeZr2 phases is responsible for enhanced fracture resistance and high fracture strength.