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RISS 인기검색어
- 검색키워드
- 저자 : Gwalani, B. (검색결과 4 건)
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Experimental investigation of the ordering pathway in a Ni-33 at.%Cr alloy
Gwalani, B.,Alam, T.,Miller, C.,Rojhirunsakool, T.,Kim, Y.S.,Kim, S.S.,Kaufman, M.J.,Ren, Yang,Banerjee, R. Elsevier 2016 Acta materialia Vol.115 No.-
<P>The present study involves a detailed experimental investigation of the concurrent compositional clustering and long-range ordering tendencies in a Ni-33 at.%Cr alloy, carried out by coupling synchrotron-based X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT). Synchrotron-based XRD results clearly exhibited progressively increasing lattice contraction in the matrix with increasing isothermal aging time, at 475 degrees C, eventually leading to the development of long-range ordering (LRO) of the Pt2Mo-type. Detailed TEM and APT investigations revealed that this LRO in the matrix is manifested in the form of nanometer-scale ordered domains, and the spatial distribution, size, morphology and compositional evolution of these domains have been carefully investigated. APT results also revealed the early stages of compositional clustering prior to the onset of long-range ordering in this alloy and such compositional clustering can potentially be correlated to the lattice contraction and previously proposed short-range ordering tendencies. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>
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Gwalani, B.,Choudhuri, D.,Soni, V.,Ren, Y.,Styles, M.,Hwang, J.Y.,Nam, S.J.,Ryu, H.,Hong, S.H.,Banerjee, R. Elsevier 2017 ACTA MATERIALIA Vol.129 No.-
<P>A detailed investigation of precipitation of the ordered L1(2) (gamma') phase in a Al0.3CrCuFeNi2 high entropy alloy (HEA), more generally referred to as a complex concentrated alloy (CCA), reveals the role of copper (Cu) on stabilization and precipitation of the ordered L1(2) (gamma') phase. Detailed characterization via coupling of scanning and transmission electron microscopy, and atom probe tomography revealed novel insights into Cu clustering within the face-centered cubic matrix of this HEA, leading to heterogeneous nucleation sites for the gamma' precipitates. The subsequent partitioning of Cu into the gamma' precipitates indicates their stabilization is due to Cu addition. The gamma' order-disorder transition temperature was determined to be similar to 930 degrees C in this alloy, based on synchrotron diffraction experiments, involving in situ annealing. The growth and high temperature stability of the gamma' precipitates was also confirmed via systematic scanning electron microscopy investigations of samples annealed at temperatures in the range of 700-900 degrees C. The role of Cu revealed by this study can be employed in the design of precipitation strengthened HEAs, as well as in a more general sense applied to other types of superalloys, with the objective of potentially enhancing their mechanical properties at room and elevated temperatures. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>
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Gwalani, Bharat,Pohan, Rizaldy M.,Waseem, Owais Ahmed,Alam, Talukder,Hong, Soon Hyung,Ryu, Ho Jin,Banerjee, Rajarshi Elsevier 2019 Scripta materialia Vol.162 No.-
<P><B>Abstract</B></P> <P>The high-entropy alloy (HEA) composite Al<SUB>0.3</SUB>CoCrFeMnNi based on the face-centered-cubic (FCC) system and reinforced with 0–3 vol% Y<SUB>2</SUB>O<SUB>3</SUB> was processed by mechanical alloying followed by spark plasma sintering (SPS). The compressive yield strength of the Al<SUB>0.3</SUB>CoCrFeMnNi high-entropy alloy (HEA) increased phenomenally, from 0.98 GPa (0 vol% Y<SUB>2</SUB>O<SUB>3</SUB>) to 1.76 GPa (3 vol% Y<SUB>2</SUB>O<SUB>3</SUB>). A quantitative analysis by atom probe tomography (APT) suggested the in-situ formation of complex oxide resulting from the reaction of Y<SUB>2</SUB>O<SUB>3</SUB> with the HEA matrix during processing, enhancing the strength. Using the dispersion-barrier hardening model, the strengthening by dispersoids in Al<SUB>0.3</SUB>CoCrFeMnNi with Y<SUB>2</SUB>O<SUB>3</SUB> was calculated, and closely matched the experimental results.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Pohan, Rizaldy M.,Gwalani, Bharat,Lee, Junho,Alam, Talukder,Hwang, J.Y.,Ryu, Ho Jin,Banerjee, Rajarshi,Hong, Soon Hyung Elsevier 2018 Materials chemistry and physics Vol.210 No.-
<P><B>Abstract</B></P> <P>The present study focuses on phase evolution in Al<SUB>0.3</SUB>CoCrFeMnNi high entropy alloys (HEAs) during mechanical alloying and after spark plasma sintering. Aluminium addition hardens and induces ordered precipitates in a soft <I>fcc</I> alloy based on CoCrFeMnNi. Mechanical alloying of the alloy powders resulted in a single <I>fcc</I> phase. However, ordered B2 precipitates and chromium carbide precipitates were observed after spark plasma sintering. Sintering temperature optimization was done and maximum densification and hardness were obtained at 900 °C. High compressive yield strength of 979 ± 20 MPa and compressive ductility of 39 ± 3% were observed for the SPS processed alloy. Significant contributions from grain boundary strengthening coupled with dispersion strengthening via carbides and B2 particles appear to be major contributors to alloy strengthening. These hard intermetallic particles not only keep the grain growth in check but also increase the cumulative (fcc + B2) strength of the material.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Al<SUB>0.3</SUB>CoCrFeMnNi high entropy alloy was prepared using Spark Plasma Sintering. </LI> <LI> Optimum density and grain size is obtained at 900 °C sintering temperature. </LI> <LI> Microstructure consisted of fcc matric, ordered bcc (B2) and chromium carbides. </LI> <LI> Alloy showed high compressive strength of 979 MPa and failure strain of 39%. </LI> </UL> </P>
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