Ultrafine Eutectic Alloys Research Articles

Mechanical Properties, Microstructural Features, and Correlations with Solidification Rates of Al–Cu–Si Ultrafine Eutectic Alloys

Due to their optimized mechanical properties under rapid solidification, Al–Cu–Si ultrafine eutectic alloys have been highlighted. The literature does not, however, establish correlations between thermal solidification parameters, mechanical properties, and microstructures of these alloys. Knowledge of cooling rates and growth rates and their associations with mechanical properties of Al–Cu–Si ultrafine eutectic alloys can guide the search for controlled and optimized processing conditions. Considering these issues, the present study analyzes the correlations between microstructures and mechanical properties of Al–15 wt% Cu–7 wt% Si, Al–22 wt% Cu–7 wt% Si, and Al–26 wt% Cu–7 wt% Si alloys produced by centrifugal casting in a copper mold. For this, Al–Cu–Si alloys’ samples with a stepped solidified form are subjected to microstructural assessment and mechanical properties characterization methods. The results show the existence of phases such as Al‐rich, Si, and Al2Cu in different proportions for each cylindrical casting part. Eutectic bimodal structures have been observed. With the increase in either alloy Cu content or solidification cooling rate, increase in hardness is observed. However, the compressive strength is shown to be unaffected by the microstructural scale. These variations are discussed to guide the best balance of properties. Samples of the Al–26 wt% Cu–7 wt% Si alloy produced under eutectic growth rates between 0.8 and 1.2 mm s−1 are those with superior properties.

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.

Influence of Nb on microstructure and mechanical properties of Ti-Sn ultrafine eutectic alloy

In this study, A series of the high strength (T82Sn18)100-xNbx (x=0, 1, 3, 5, and 9 at%) ultrafine eutectic alloys with large plasticity are developed by suction casting method. The Ti82Sn18 binary eutectic alloy consists of a mixture of a hcp Ti3Sn and a α-Ti phases having the plate-like lamellar type duplex structure with micro scaled eutectic colony. From the (T82Sn18)97Nb3, the alloy display structural heterogeneous distribution of ultrafine-scaled phases composed of β-Ti(Nb) solid solution surrounded by alternating plate-like shaped Ti3Sn and α-Ti phases. With increasing Nb content, the volume fraction of β-Ti is continuously increased, which induced improving mechanical properties both strength and plasticity. Especially, (Ti82Sn18)91Nb9 alloy has the outstanding combination of the high strength (σ y ≈1.1 GPa) and large plasticity (e p ≈36%) at room temperature.

Micro-to-nano-scale deformation mechanisms of a bimodal ultrafine eutectic composite.

The outstading mechanical properties of bimodal ultrafine eutectic composites (BUECs) containing length scale hierarchy in eutectic structure were demonstrated by using AFM observation of surface topography with quantitative height measurements and were interpreted in light of the details of the deformation mechanisms by three different interface modes. It is possible to develop a novel strain accommodated eutectic structure for triggering three different interface-controlled deformation modes; (I) rotational boundary mode, (II) accumulated interface mode and (III) individual interface mode. A strain accommodated microstructure characterized by the surface topology gives a hint to design a novel ultrafine eutectic alloys with excellent mechanical properties.

Chemical heterogeneity-induced plasticity in Ti–Fe–Bi ultrafine eutectic alloys

Chemical heterogeneity in Ti–Fe ultrafine eutectic structure has been introduced by addition of Bi without structural heterogeneities such as length-scale, volume fraction and morphology of lamellar and colony structures. The detailed microstructural investigation clearly reveals that the Bi was highly saturated at the colony boundary of the ultrafine eutectic alloys. The chemical heterogeneity introduced by the additional Bi in the present investigation effectively dissipates the localization of the stress thus improving the plasticity up to 8.5% without compromising the strength of 2100MPa.

Effect of Sn on microstructure and mechanical properties of Ti-Fe-(Sn) ultrafine eutectic composites

High strength (Ti0.705Fe0.295)100-xSnx(0 ≤x≤ 6) composites have been prepared through arc melting and cold crucible casting. The microstructure consists of two phase ultrafine eutectic comprised of FeTi and β-Ti phases. The effect of Sn addition to the Ti70.5Fe29.5eutectic is assessed in terms of microstructure variations such as eutectic spacing, morphology, cell size, lattice parameter of the phases, and the resulting mechanical properties in terms of strength and plasticity under compression. The mechanical properties (maximum strength 1939 MPa, fracture strain 13.5%) of the ternary Ti-Fe-Sn (2 ≤x≤ 6) are considerably improved compared to the Ti70.5Fe29.5binary alloy (1733 MPa, 3.4%). The change in the morphology of the eutectic, the microstructure refinement, structural fluctuations, and supersaturation in the β-Ti phase, and the elastic properties of nanophases are crucial factors for improving the plastic deformability of the ultrafine eutectic alloys without presence of any additional micrometer-size toughening phase.

Microstructural modulation of Ti–Fe–V ultrafine eutectic alloys with enhanced mechanical properties

Systematic microstructural investigation on a series of (Ti 70.5 Fe 29.5 ) 100− x V x alloys with x = 0, 1, 3, 5 and 7 reveals that addition of V content causes microstructural refinement and formation of ω-phase. By adding small amount of V (1–3 at.%) into the Ti 70.5 Fe 29.5 binary eutectic alloy, both the strength and the plasticity of the alloys are spontaneously improved up to 2000–2200 MPa and ∼3.5%, respectively. However, large amount of V (5–7 at.%) leading to the high volume fraction of the ω-phase results in degradation in both strength and plasticity. These results suggest that the mechanical properties of the Ti–Fe–V ultrafine eutectic alloys are strongly governed by volume fraction of the eutectic matrix and ω-phases.

MICROSTRUCTURAL EVOLUTION AND MECHANICAL PROERTIES OF Ti-(Ni, Fe)-Sn ULTRAFINE EUTECTIC ALLOYS

Ultrafine eutectic alloys have been developed in Ti - Ni , Ti - Fe and Ti -( Ni , Fe )- Sn alloys. The Ti 76 Ni 24 and ( Ti 74 Ni 26)97 Sn 3 ultrafine eutectic alloys consist of a mixture of α- Ti and Ti 2 Ni phases, and β- Ti ( Sn ) and Ti 2 Ni phases, respectively, whereas the Ti 70.5 Fe 29.5 and ( Ti 70.5 Fe 29.5)97 Sn 3 alloys are composed by a mixture of β- Ti ( Sn ) and FeTi phases with relatively spherical colony. The compression tests of Ti 76 Ni 24, ( Ti 74 Ni 26)97 Sn 3 and Ti 70.5 Fe 29.5 ultrafine eutectic alloys reveal a strength of 1400 ~ 1800 MPa with very limited plastic strain of 0.1 ~ 1%. On the contrary, a ( Ti 70.5 Fe 29.5)97 Sn 3 alloy exhibits high strength of 2270 MPa with enhanced plastic strain of 3.1%. Based on these results, it is feasible to suggest that the eutectic morphology and interfacial coherency between the Ti solid solution and intermetallic phases influence to control the macroscopic plasticity of the Ti - Ni and Ti - Fe ultrafine eutectic alloys.

Influence of heterogeneities with different length scale on the plasticity of Fe-base ultrafine eutectic alloys

The evolution of microstructure and its influence on the mechanical properties of high-strength ultrafine eutectic Fe–(Ti, Zr)–(B, Co) alloys has been studied. The addition of B or Co improves the room temperature compressive plasticity from 1% to ∼8.5% or ∼14%, respectively, due to the formation of a heterogeneous microstructure with distinctly different length scales, which can delay the propagation of shear bands and promotes the activation of multiple shear bands.

Bulk ultra-fine eutectic structure in Ti–Fe–base alloys

An ultra-fine eutectic structure has been obtained in the Ti 70.5Fe 29.5 binary alloy by slow cooling from the melt through arc melting and cold crucible rod casting. The addition of 3.85 at.% Sn to the binary Ti–Fe alloy induces a change of the morphology of the eutectic and increases the volume fraction of the FeTi ( Pm3 m) phase. A significant improvement of the plastic deformability of the ternary alloy has been observed under uniaxial compressive loading resulting in 16% strain to failure compared to 3.4% for binary Ti 70.5Fe 29.5. The morphology of the eutectic colonies, their refinement and supersaturation of the β-Ti phase are crucial factors for improving the ductility of the ultra-fine eutectic alloys.