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Analysis of mechanical and microstructural characteristics of plunger-assisted ECAP strengthened Ti-6Al-4V alloy sheets

Sahoo Partha Sarathi, Meher Arabinda, Mahapatra Manas Mohan, Vundavilli Pandu Ranga, Pandey Chandan

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e194, 2023

EN

Often known as the workhorse among titanium alloys, Ti-6Al-4 V has been useful in the aerospace and biomedical sectors. For further enhancement of the mechanical characteristics of Ti-6Al-4 V alloy, its sheets procured for the present study have been subjected to equal channel angular pressing (ECAP) using a die setup having a channel angle of 120° and corner angle of 10° at its forming temperature of 650 °C followed by appropriate annealing treatments. Microstructural analysis post the hot-ECAP process has demonstrated ultrafine grain (UFG) refinement because of this severe plastic deformation technique of ECAP. Phase analysis has further substantiated the reduction of β-phase in the alloy as a controlling factor in improving the mechanical properties. As a result, the room temperature hardness and tensile strength have improved by 10% and 15%, respectively, due to a drastic reduction in grain size from ~ 906 nm to ~ 359 nm, which is in line with the well-established Hall–Petch equation. Basic finite element modeling has been studied as concerned with the sustainability and feasibility of the die setup to withstand the heavy metal forming forces involved in the ECAP of Ti-6Al-4 V. This success in processing Ti-6Al-4 V by a single pass of an ECAP using channel angle of 120° and corner angle of 10° under a controlled equivalent strain further opens doors for incorporating additional steps and criteria to achieve even higher grain refinement and strength enhancements thereby catering to the needs for manufacturing the assault vehicles and bioimplants.

2

Investigation on the microstructural and mechanical behavior of the friction stir welded RZ5/8 wt% TiB2 magnesium matrix composites

Meher Arabinda, Mahapatra Manas Mohan

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 4

art. no. e178, 2022

EN

Understanding the microstructural and mechanical behavior of the friction stir welded magnesium matrix composites is necessary for different applications in automobile and aerospace components such as fuel tanks, steering wheels, chassis, seat frames, etc. In the present study, friction stir welding of magnesium RZ5/8 wt% TiB2 metal matrix composites is carried out at different joining conditions. FESEM micrograph showed the refined equiaxed grains in the nugget zone and elongated grains in the thermo-mechanically affected zone. Better grain refinement with uniform distribution is achieved at the tool rotational speed of 931 rpm and traverse speed of 20 mm/min. During the joining of RZ5/8 wt% TiB2 composites, the maximum temperature measured in the nugget zone is 511 °C at the rotational tool speed of 1216 rpm and traverse speed of 20 mm/min. Hardness is maximum at the nugget zone, which is 30% higher than the base material. The heat-affected zone showed the lowest hardness due to the annealing induced grain growth. Tensile strength is maximum during the joining of the RZ5/8 wt% TiB2 composites at a tool rotational speed of 931 rpm because of the better grain refinement with uniform reinforcement distribution in the weld zone. The tensile residual stress is observed to be a maximum of 71.41 MPa at a depth of 2.5 mm from the top surface and compressive residual stress of 60.98 MPa at the bottom surface of the nugget zone. The residual stress increased with an increase in tool rotational speed due to the increase in shrinkage of the materials at the higher temperature.

3

Softening mechanism of P91 steel weldments using heat treatments

Pandey Chandan, Mahapatra Manas Mohan, Kumar Pradeep, Daniel F., Adhithan B.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 2

297--310

EN

The tungsten inert gas welded P91 steel welded joints were subjected to the two different type of heat treatments including the postweld direct tempering (PWDT) and re-austenitizing based tempering (PWNT) treatment. The microstructure of weld fusion and heat affected zone (HAZ) were characterized in different heat treatment conditions using optical microscope and scanning electron microscope. For as-welded joint, a great heterogeneity was observed in microstructure and mechanical properties across the weldments. The Charpy toughness of the as-welded joint was measured much lower than the minimum recommended value of 47 J and it was measured 8 ± 5 J. The PWHTs have found a beneficial effect in decreasing the microstructure heterogeneity across the welded joint and improving the mechanical properties. The PWDT resulted in a drastic improvement in the Charpy impact toughness of the welded joint and it was measured 59 ± 5 J which was higher than the minimum required value of 47 J but still inferior than the base metal. The δ ferrite still remained in overlap zone of the weld fusion zone. The PWNT treatment resulted in homogeneous microstructure and hardness variation across the welded joint in transverse direction and Charpy impact toughness (149 ± 6 J) exceeded than that achieved in base metal.

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An investigation into fabrication and characterization of direct reaction synthesized Al-7079-TiC in situ metal matrix composites

Sujith S. V., Mahapatra Manas Mohan, Mulik Rahul S.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 1

63--78

EN

The present study was attempted to highlight a novel direct reaction synthesis in which traditional casting plus rapid solidification techniques were implemented to produce Al-7079-TiC in situ composites with homogenous microstructure and improved dispersion strengthening by the reinforcing phases. Casted samples were effectively characterized by scanning electron microscopy followed by energy dispersive spectroscopy and X-ray diffraction. Ingot metallurgy showed a homogenous distribution of TiC particles inside the grain. This particle behavior acted as an excellent nucleation sites for the Al dendrites to grow unvaryingly. TiC reinforcements have semi coherent relationship with α-Al matrix. It was observed that eutectic boundary includes the second phases based on η (MgZn2) and Mg(Zn, Cu, Al)2. Almost 90% of the in situ reinforced TiC were homogenously distributed along the center of the grain. Thermal history conditions have shown an exothermic behavior during casting. Experimental results revealed the evolution of TiC particles in super-heated melt region, i.e. dissolution of titanium continued by reaction of titanium with diffused carbon in the Al matrix to form TiC particles. Further they acted as nucleation sites for the α-Al dendrites to grow homogenously. This study presents optimum process temperature for the Al-TiC in situ synthesis.