Faculty Publications

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Development and mechanical characterization of novel polymer-based flexible composite and optimization of stacking sequences using VIKOR and PSI techniques
(SAGE Publications Ltd, 2021) Mahesh, V.; Joladarashi, S.; Kulkarni, S.M.
The development of natural fiber-reinforced polymer composites is becoming prominent in numerous engineering applications over the synthetic fiber-reinforced composites mainly because of their environment-friendly characteristics. This article deals with comparative study on selection of optimal stacking sequence (jute/rubber/jute (JRJ), jute/rubber/rubber/jute, and jute/rubber/jute/rubber/jute) of the jute/natural rubber-based completely biodegradable flexible composite using multi-attribute decision making (MADM) approaches namely hybrid entropy-VIse Kriterijumska Optimizacija kompromisno Resenja (VIKOR) and preference selection index (PSI) methods. Tensile strength, tear strength, specific impact strength, and specific wear rate are used as attributes for MADM methods. The results show good agreement between hybrid entropy-VIKOR and PSI methods used for stacking sequence selection. Scanning electron microscope analysis is carried out to study the failure mechanisms of the proposed flexible composite. The findings of the present study led to the choice of JRJ as the preferred stacking sequence among all the three stacking sequences considered as it exhibited the best overall properties compared to other two configurations of the flexible composite. © The Author(s) 2019.
Phase evolution and high-temperature wear behavior of non-equiatomic metastable CoCrNiTiMox HEA coatings fabricated by high-velocity oxy-fuel technique
(Elsevier Ltd, 2023) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.
The current research aims to enhance the tribological performance of maraging steels at high temperatures by surface modification techniques. CoCrNiTiMox (x; molar fraction, x = 0.5, 1.5) high-entropy alloy (HEA) coatings with dense lamellar microstructures were deposited onto maraging steels using high-velocity oxy-fuel spray (HVOF). In order to achieve a uniform distribution of constituent elements for thermal spray deposition, mechanical alloying was employed to synthesize the HEA feedstock. The phases and microstructure of the synthesized HEA powder, as-sprayed coatings, and worn surfaces were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-sprayed HEA coatings exhibited metastability, with a BCC phase solid solution, NiTiO3 spinel, and an intermetallic MoNi phase for CoCrNiTiMo0.5 and Co2Mo3 phase for CoCrNiTiMo1.5. The average microhardness of CoCrNiTiMo0.5 and CoCrNiTiMo1.5 HEA coatings were 841 ± 62 HV0.3 and 952 ± 23 HV0.3, respectively. The specific wear rate and friction coefficients of CoCrNiTiMox HEA coatings exhibited a decreasing trend with an increase in temperature, owing to the formation of tribofilms on the worn surface. X-ray diffraction studies revealed the formation of NiMoO4 spinel for CoCrNiTiMo0.5 and MoO2, Co3O4 phases for CoCrNiTiMo1.5 HEA at a wear temperature of 600 °C. The investigation of worn surfaces showed a transformation in wear mechanisms from abrasive wear at room temperature to oxidative wear with mild fatigue at elevated temperatures. © 2023 Elsevier Ltd
Elevated temperature tribological performance of non-equiatomic CoCrNiTiWx high entropy alloy coatings developed by mechanical alloying and high-velocity oxy-fuel spray
(Elsevier B.V., 2024) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.
High entropy alloys (HEA) have applications in multiple fields owing to their exceptional mechanical and physical properties. In the current study, mechanical alloyed CoCrNiTiWx (x; a molar fraction, x = 0.5 and 1.5) HEA feedstock powders were deposited on maraging steel substrate using high-velocity oxy-fuel spray (HVOF). The phase evolution and the microstructure of the milled powders and as-sprayed coatings were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The tribological behaviour of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings at elevated temperatures was studied extensively using a Pin-on-Disc tribometer. The CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings retained the BCC solid solution phases formed during the milling stage. However, additional oxide and intermetallic phases were formed owing to the in-flight oxidation and high temperatures experienced during the HVOF deposition. The deposited coatings exhibited a lamellar structure and good mechanical bonding with the substrate. The porosities of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings were found to be 1.69 ± 0.32 % and 1.51 ± 0.37 % respectively.Consequently, the CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings displayed average microhardness values of 863 ± 52 HV0.3 and 1025 ± 39 HV0.3, respectively. Further, the wear rates of coatings exhibited a significant reduction at elevated temperatures, owing to the formation of TiO2, NiCr2O4 oxide tribofilms for CoCrNiTiW0.5, and CoCr2O4, NiWO4, WO3 oxides for CoCrNiTiW1.5. The specific wear rate of CoCrNiTiW0.5 HEA coating dropped by 73.6 % from 22.7 ± 2.6 × 10−6 mm3/N-m to 5.99 ± 1.9 × 10−6 mm3/N-m, while CoCrNiTiW1.5 dropped by 78.8 % from 11.86 ± 3.5 × 10−6 mm3/N-m to 2.51 ± 1.5 × 10−6 mm3/N-m, with a rise in the temperature from RT to 600 °C. Likewise, The frictional coefficients of CoCrNiTiW0.5 HEA dropped from 0.504 ± 0.015 to 0.397 ± 0.005, while CoCrNiTiW1.5 HEA dropped from 0.578 ± 0.025 to 0.471 ± 0.004, with a rise in temperature from RT to 600 °C. At room temperature, the wear mechanisms of the as-sprayed CoCrNiTiWx coatings were dominated by adhesive wear. However, at elevated temperatures, a shift towards oxidative wear was observed. © 2023 Elsevier B.V.

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