High yield strength bulk Ti based bimodal ultrafine eutectic composites with enhanced plasticity

Misra, D. K.,Rakshit, R. K.,Singh, M.,Shukla, P. K.,Chaturvedi, K. M.,Sivaiah, B.,Gahtori, B.,Dhar, A.,Sohn, S. W.,Kim, W. T.,Kim, D. H. BUTTERWORTH - HEINEMANN 2014 MATERIALS AND DESIGN Vol.58 No.-

Ti-based bulk metallic glass (BMGs) and their bimodal composites are linked with the pronounced strain hardening after yielding but with much low value of strength. Therefore, developing Ti-based alloys with high yield strength and high plasticity is the current challenge. Here, we report the synthesis of ultra-fine grained bulk (UFG) (Ti0.705Fe0.295) 100 Ga-x(x) (0 <= x <= 2) bimodal eutectic composites with not only high strength and larger plasticity but also with high yield strength which is one of the important mechanical property for structural application. Reasonably high strength, high yield strength, strain to failure ratio, and enhanced plasticity of similar to 7 +/- 0.8% was observed in (Ti70.5Fe29.5)(98)Ga-2 composite which is superior than Ti-based BMGs and bimodal composites. Modification of degree of eutectic structure refinement and volume fraction of constituent phases with the addition of Ga are the crucial factors in enhancing the mechanical properties of Ti-Fi-(Ga) composites. (C) 2014 Elsevier Ltd. All rights reserved.

Constitutive Modeling and Dynamic Softening Mechanism During Hot Deformation of an Ultra-Pure 17%Cr Ferritic Stainless Steel Stabilized with Nb

Fei Gao,Zhenyu Liu,R. D. K. Misra,Haitao Liu,Fuxiao Yu 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.5

The hot deformation behavior of an ultra-pure 17%Cr ferritic stainless steel was studied in the temperaturerange of 750-1000 °C and strain rates of 0.5 to 10 s1 using isothermal hot compression tests in a thermomechanicalsimulator. The microstructural evolution was investigated using electron backscattered diffractionand transmission electron microscopy. A modified constitutive equation considering the effect of strain onmaterial constant was developed, which predicted the flow stress for the deformation conditions studied, exceptat 950 °C in 1 s1 and 900 °C in 10 s1. Decreasing deformation temperature and increasing strain was beneficialin refining the microstructure. Decreasing deformation temperature, the in-grain shear bands appeared inthe microstructure. It is suggested that the dynamic softening mechanism is closely related to deformationtemperature. At low deformation temperature, dynamic recovery was major softening mechanism and no dynamicrecrystallization occurred. At high deformation temperature, dynamic softening was explained in terms ofefficient dynamic recovery and limited continuous dynamic recrystallization. A drop in the flow stress wasnot found due to very small fraction of new grains nucleated during dynamic recrystallization.

Extending the Boundaries of Mechanical Properties of Ti-Nb Low-Carbon Steel via Combination of Ultrafast Cooling and Deformation During Austenite-to-Ferrite Transformation

Xiangtao Deng,Tianliang Fu,Zhaodong Wang,Guohuai Liu,Guodong Wang,R. D. K. Misra 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.1

We underscore here a novel approach to extend the boundaries of mechanical properties of Ti-Nb low-carbon steel via combination of ultrafast cooling and deformation during austenite-to-ferrite transformation. The proposed approach yields a refined microstructure and high density nano-sized precipitates, with consequent increase in strength. Steels subjected to ultra-fast cooling during austenite-to-ferrite transformation led to 145 MPa increase in yield strength, while the small deformation after ultra-fast cooling process led to increase in strength of 275 MPa. The ultra-fast cooling refined the ferrite and pearlite constituents and enabled uniform dispersion, while the deformation after ultra-fast cooling promoted precipitation and broke the lamellar pearlite to spherical cementite and long thin strips of FexC. The contribution of nano-sized precipitates to yield strength was estimated to be ~247.9 MPa and ~358.3 MPa for ultrafast cooling and deformation plus ultrafast cooling processes. The nano precipitates carbides were identified to be (Ti, Nb)C and had a NaCl-type crystal structure, and obeyed the Baker-Nutting orientation relationship with the ferrite matrix.

High performance bifunctional electrocatalytic activity of a reduced graphene oxide-molybdenum oxide hybrid catalyst

Chandrasekaran, Sundaram,Kim, Eui Jung,Chung, Jin Suk,Bowen, Chris R.,Rajagopalan, Balasubramaniyan,Adamaki, Vaia,Misra, R. D. K.,Hur, Seung Hyun The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.34

<P>The advances in cost effective, highly active and stable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remain the major issues for the commercialization of metal air-batteries and alkaline fuel cells. In this aspect, a facile hydrothermal route was developed to prepare nonprecious metal electrocatalysts including pristine MoO3rods, nanospheres, and their hybrids with reduced graphene oxide (rGO). This is the first report of the use of rGO coupled with hexagonal MoO3nanocrystals that act as both ORR and OER catalysts. The rGO-MoO3sphere hybrid catalyst exhibited excellent catalytic activity toward both the ORR and OER compared to pristine MoO3rods, MoO3spheres and rGO-MoO3rods. In addition, the rGO-MoO3nanosphere hybrid exhibited excellent catalytic activity, long-term durability, and CO tolerance compared to a high quality commercial Pt/C catalyst. This makes the GMS hybrid composite a highly promising candidate for high-performance non-precious metal-based bi-functional electrocatalysts with low cost and high efficiency for electrochemical energy conversion. The enhanced activity of the rGO-MoO3nanosphere hybrid is due mainly to the enhanced structural openness in the tunnel structure of the hexagonal MoO3when it is coupled with rGO.</P>

Favorable Modulation of Microstructural Constituents in Governing Low Temperature Toughness Induced Through a Three-Stage Cooling Trajectory

Y. Tian,X. N. Xu,Q. B. Ye,R. D. K. Misra,Z. D. Wang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10

Low temperature toughness continues to be a major challenge and significant efforts are being made in this regard. Weaddress the challenge of scientific and technological gap through the design of a novel process involving a three-stage coolingtrajectory during thermo-mechanical controlled processing to process high strength low alloy heavy plates with highlow temperature toughness. Interestingly, in contrast to the conventional continuous cooling process, the three-stage coolingtrajectory enabled us to obtain a favorable acicular ferrite toughening enhancing microstructure. On the other hand, martensite–austenite islands were characterized by small dot morphology in the three-stage cooling trajectory that restrict cracknucleation and prevent debonding from the matrix. The low temperature impact toughness at − 80 °C exceeded ~ 500% inrelation to the conventional process. The mechanism of formation of acicular ferrite and its impact on toughness is criticallyanalyzed experimentally via electron microscopy and electron back scattered diffraction analysis and theoretically discussedin the context of toughening and crack arresting mechanism.

Micro-scale to nano-scale generators for energy harvesting: Self powered piezoelectric, triboelectric and hybrid devices

Chandrasekaran, Sundaram,Bowen, Chris,Roscow, James,Zhang, Yan,Dang, Dinh Khoi,Kim, Eui Jung,Misra, R.D.K.,Deng, Libo,Chung, Jin Suk,Hur, Seung Hyun Elsevier 2019 Physics reports Vol.792 No.-

<P><B>Abstract</B></P> <P>This comprehensive review focuses on recent advances in energy harvesting of micro-scale and nano-scale generators based on piezoelectric and triboelectric effects. The development of flexible and hybrid devices for a variety of energy harvesting applications are systematically reviewed. A fundamental understanding of the important parameters that determine the performance of piezoelectric, triboelectric and hybrid devices are summarized. Current research directions being explored and the emerging factors to improve harvester functionality and advance progress in achieving high performance and durable energy conversion are provided. Investigations with regard to integrating flexible matrices and optimizing the composition of the piezoelectric and triboelectric materials are examined to enhance device performance and improve cost-effectiveness for the commercial arena. Finally, future research trends, emerging device structures and novel materials in view of imminent developments and harvesting applications are presented.</P>

Effect of Vanadium on the Microstructure and Mechanical Properties of 2100 MPa Ultra-High Strength High Plasticity Spring Steel Processed by a Novel Online Rapid-Induction Heat Treatment

Qi‑Lei Dai,Kun Li,Kai‑Ren Meng,Zhou Fang,Wen Chen,Tian‑Bao Yang,Chi Feng,Jin‑Ming Wu,R. D. K. Misra 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.4

Advanced automotive industries generate large demand for the next generation of high strength and high toughness springsteels. Vanadium-containing 55SiCrV spring steels subjected to rapid-induction heating treatment can fulfil such requirements. However, the effect of vanadium microalloying under online rapid-induction heat treatments is rarely reported. Acomparative study of the microstructure and tensile properties of 55SiCr and 55SiCrV spring steel wires subjected to a novelonline rapid induction heat treatment has been demonstrated herein. It is found that the tensile strength of the 55SiCr springwire decreases with the decrease in the wire speed in online rapid-induction heating, and the plasticity increases. Whereas,the tensile strength of the 55SiCrV steel wire increases with the decrease in the wire speed with the retained high plasticity,which is attributed to the strengthening effect of the dislocations. Through the optimized rapid-induction heating/coolingthermal cycles and intermediate-temperature tempering treatment, the tensile strength of the 55SiCrV steel wire approaches2106 MPa with total elongation of 9.7%. Compared with the 55SiCr spring steel, the addition of V in 55SiCrV spring steelchanges the strengthening and toughening mechanisms via the grain refinement and enhancement in the hardenability andtempering resistance. The finely dispersed V-containing secondary phases are rarely found in the matrix, which indicates thatthe precipitation effect stemming from the addition of V is not the dominant strengthening factor in the online rapid-inductionheat process. The proposed novel online rapid-induction heat treatment provides a promising pathway for the mechanicalproperty improvement of the spring steel.