Sumanta Samal

Mechanical Behavior of Novel Suction Cast Ti-Cu-Fe-Co-Ni High Entropy Alloys

The present investigation reports mechanical properties of novel multicomponent TixCuyFe20Co20Ni20 high entropy alloys (HEAs) with different alloy chemistry (x/y = 1/3, 3/7, 3/5, 9/11, 1, 11/9 and 3/2). The alloy cylinders were prepared by vacuum arc melting-cum-suction casting route. The detailed electron microscopic observations reveal the presence of three different solid solution phases; FCC (a1) phase, FCC (a2) phase and BCC (b) phase for all the investigated alloys, whereas ultrafine eutectic between FCC (a1) phase, and Ti2 (Co, Ni) - type Laves phase has been observed for the HEAs with x/y = 9/11, 1, 11/9 and 3/2. Room temperature compression test of the suction cast cylinders with aspect ratio of 2/1 has been conducted to obtain mechanical properties of the HEAs. The optimum combination of strength (~ 1.88 GPa) and plasticity (~ 21 %) is obtained for x/y = 9/11; indicating simultaneous improvement of strength as well as plasticity of the novel HEAs. Fractographic analysis of the fractured surfaces reveals mixed mode of fracture for x/y = 1/3, 3/7 and 3/5, ductile mode for x/y = 9/11 and 1, whereas brittle mode of fracture for x/y = 11/9 and 3/2.

Development of ultrafine Ti-Fe-Sn in-situ composite with enhanced plasticity

The present investigation is aimed at developing ultrafine eutectic/dendrite Ti-Fe-Sn in-situ composite with balanced combination of strength and plasticity. It also studies the microstructure evolution in the series of hypereutectic Ti-Fe-Sn ternary alloys. Sn concentration of these alloys has been varied from 0 – 10 atom% in the binary alloy (Ti71Fe29) keeping the Ti concentration fixed. These alloys have been prepared by arc melting under an Ar atmosphere on a water-cooled Cu hearth, which are subsequently suction cast in a split Cu-mold under an Ar atmosphere. Detailed X-ray diffraction (XRD) study shows the presence of TiFe, β-Ti, and Ti3Sn phases. The SEM micrographs reveal that the microstructures consist of fine scale eutectic matrix (β-Ti and TiFe) with primary dendrite phases (TiFe and/or Ti3Sn) depending on concentration of Sn. α -Ti forms as a eutectoid reaction product of β-Ti. The room temperature uniaxial compressive test reveals simultaneous improvement in the strength (1942 MPa) and plasticity (13.1 %) for Ti71Fe26Sn3 ternary alloy. The fracture surface indicates a ductile mode of fracture for the alloy.

Microstructure Evolution and Mechanical Properties of Suction Cast Ti60Fe40-xCox (x = 0, 16, 18, 20, 22, 24) Alloys

The present work is aimed at understanding the microstructure evolution in a series of Ti60Fe40-xCox (x= 0, 16, 18, 20, 22, 24) alloys. The ternary alloys are synthesized by arc melting cum suction casting technique under high purity argon atmosphere to obtain alloy cylinders having 3 mm diameter and aspect ratio of 17:1. Detailed X-ray diffractometry and electron microscopic studies are carried out to identify the phases in the investigated alloys. It has been found that the alloys consist of fine scale eutectic matrix between bcc (b-Ti)ss and Ti(Fe,Co) phases along with the dendritic phase of Ti(Fe,Co), whereas the dendritic phase of Ti2(Fe,Co) has also been observed for x = 16 and 20. It is also found that ternary Ti60Fe20Co20 alloy shows good combination of compressive strength (~2507 MPa) and plasticity (~16.3 %) among the investigated alloys.

Phase Evolution and Mechanical Behaviour of Co–Fe–Mn–Ni–Ti Eutectic High Entropy Alloys

The current study is aimed to understand the microstructure evolution in Co20Fe20Mn20Ni20Ti20 and Co25Fe25Mn5Ni25Ti20 high entropy alloys (HEAs). The complete X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy analyses are carried out to recognize the phases in addition to understand the series of phase development in the presently studied HEAs. For Co–Fe–Mn–Ni–Ti HEAs, at first BCC (β) phase primary dendritic phase is created from the liquid, followed by peritectic reaction to form FCC (α) phase (i.e. BCC (β) + L → FCC (α)). Then the left over liquid undergoes eutectic reaction to form FCC (α) and Ti2(Ni, Co) phases (i.e. L → FCC (α) + Ti2(Ni, Co)). Furthermore, the pseudo quasi-peritectic reactions i.e. L + BCC (β) → FCC (α) +Ti2(Ni, Co) has been proposed based on the microstructure evolution study in case of Co–Fe–Mn–Ni–Ti HEAs. It is important to note that Co–Fe–Mn–Ni–Ti HEAs show eutectics between FCC (α) and Ti2(Ni, Co) phases. The multicomponent Co25Fe25Mn5Ni25Ti20 eutectic HEA shows the retention of high strength at elevated temperature.