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- 저자 : Gokuldoss, Prashanth Konda (검색결과 3 건)
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Shin, Jinkyung,Yi, Seonghoon,Pradeep, Konda Gokuldoss,Choi, Pyuck-Pa,Raabe, Dierk Materials Research Society of Korea 2013 한국재료학회지 Vol.23 No.3
Spatial distributions of alloying elements of an Fe-based amorphous ribbon with a nominal composition of $Fe_{75}C_{11}Si_2B_8Cr_4$ were analyzed through the atom probe tomography method. The amorphous ribbon was prepared through the melt spinning method. The macroscopic amorphous natures were confirmed using an X-ray diffractometer (XRD) and a differential scanning calorimeter (DSC). Atom Probe (Cameca LEAP 3000X HR) analyses were carried out in pulsed voltage mode at a specimen base temperature of about 60 K, a pulse to base voltage ratio of 15 %, and a pulse frequency of 200 kHz. The target detection rate was set to 5 ions per 1000 pulses. Based on a statistical analyses of the data obtained from the volume of $59{\times}59{\times}33nm^3$, homogeneous distributions of alloying elements in nano-scales were concluded. Even with high carbon and strong carbide forming element contents, nano-scale segregation zones of alloying elements were not detected within the Fe-based amorphous ribbon. However, the existence of small sub-nanometer scale clusters due to short range ordering cannot be completely excluded.
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Morteza Alizadeh,Saba Khoramkhorshid,Amir Hossein Taghvaei,Prashanth Konda Gokuldoss 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.4
Devitrified Al84Gd6Ni7Co3 glassy particles have been used to reinforce Al-matrix composites through repeated rollbonding (RRB) process. Microstructural characterization of the produced composites after various rolling cycleswas performed by scanning electron microscopy. Mechanical properties of the fabricated composites were evaluatedby the tensile and microhardness tests. The results indicate that the RRB process is successful to producecomposites with the negligible amount of flaws and porosity, and it is followed by homogeneous distribution ofAl84Gd6Ni7Co3 particles in the Al matrix after nine rolling passes. Elongation of the composites improves significantlyupon RRB cycles and the tensile strength and microhardness of them increase more than two times comparedto unreinforced Al. According to fractography results, the enhanced mechanical properties are correlatedwith formation of excellent bonding at the interface of Al84Gd6Ni7Co3 particles and Al matrix. The theoretical valuesof composites hardness and yield strength calculated based on iso-strain model show a good agreement withrespect to the experimental results.
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Effect of boron addition on thermal and mechanical properties of Co-Cr-Mo-C-(B) glass-forming alloys
Kim, Jeong Tae,Hong, Sung Hwan,Bian, Xilei,Gokuldoss, Prashanth Konda,Song, Kaikai,Eckert, Jü,rgen,Park, Jin Man,Kim, Ki Buem Elsevier 2018 INTERMETALLICS Vol.99 No.-
<P><B>Abstract</B></P> <P>In this work, we investigated the effect of boron addition on glass-forming ability and mechanical properties of Co-Cr-Mo-C alloys. The starting alloy was (Co<SUB>0.65</SUB>Cr<SUB>0.13</SUB>Mo<SUB>0.22</SUB>)<SUB>80</SUB>C<SUB>20</SUB> derived from the Co<SUB>65</SUB>Cr<SUB>13</SUB>Mo<SUB>22</SUB> ternary eutectic composition. This alloy is almost fully crystalline and exhibits brittle mechanical properties. Replacing carbon with boron allows obtaining bulk metallic glasses (BMGs) and bulk metallic glass composites. The designed alloys show very high strength (∼4100 MPa), wide super-cooled liquid region (∼100 K) and large endothermic enthalpy of the supercooled liquid region (∼35 J/g), indicating high thermal stability. The electronegativity difference and supercooled liquid region of the present alloys are comparable to rare-earth elements containing BMGs. The physical properties of the present alloys corresponded well with the alloy design strategy based on the unified parameter using the glass transition temperature, fracture strength, and molar volume. Furthermore, we propose the optimum compositional condition for glass formation by controlling the carbon-to-boron ratio and the influence of carbon on phase formation in this alloy system is discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of boron/carbon ratio on the glass formation, fracture strength, and thermal stability of Co-Cr-Mo eutectic alloy. </LI> <LI> The wide supercooled liquid region of 100 K when carbon to boron ratio is 2:1. </LI> <LI> The excellent thermal stability of supercooled liquid can offer a wide enough processing window for thermoplastic forming. </LI> <LI> The electronegativity difference is an indicator dominating the extension of the supercooled liquid region. </LI> </UL> </P>
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