Department of Metallurgical & Materials Engineering

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The failure of a bearing-raceway assembly is governed by the spatial distribution of subsurface stresses at the vicinity of a bearing-raceway contact and the evolution of these stresses during rolling contact fatigue (RCF) loading. In this paper, we propose an experimental methodology that allows one to accurately measure the location and magnitude of the cyclically evolving elastoplastic von Mises stresses in terms of microhardness numbers. An M50NiL steel rod is subjected to RCF by three silicon nitride (Si3N4) balls for over several hundred million cycles at 5.5 GPa contact stress level. Microindentation hardness measurements within the subsurface RCF-affected regions of the rod revealed significant material hardening. A mechanistic methodology to construct a stress-life (S-N) diagram for RCF loading is proposed. S-N diagrams are constructed based on maximum von Mises stress amplitude and volume average von Mises stress amplitude. The effects of elastic modulus and yield strength gradient on stress fields are also considered in this analysis. Comparison of S-N diagrams based on both stress amplitudes indicates that the maximum von Mises stress amplitude overpredicts the fatigue strength of material in S-N diagrams. The experimental results obtained by following this methodology can help construct material hardening models for RCF, which may lead to an improved estimate of bearing fatigue life. Copyright © 2017 by ASTM International

World University root node

Materials Performance and Characterization

A new approach towards life prediction of case hardened bearing steels subjected to rolling contact fatigue

In the current emerging sustainable organic battery field, quinones are seen as one of the prime candidates for application in rechargeable battery electrodes. Recently, C6Cl4O2, a modified quinone, has been proposed as a high voltage organic cathode. However, the sodium insertion mechanism behind the cell reaction remained unclear due to the nescience of the right crystal structure. Here, the framework of the density functional theory (DFT) together with an evolutionary algorithm was employed to elucidate the crystal structures of the compounds NaxC6Cl4O2 (x = 0.5, 1.0, 1.5 and 2). Along with the usefulness of PBE functional to reflect the experimental potential, also the importance of the hybrid functional to divulge the hidden theoretical capacity is evaluated. We showed that the experimentally observed lower specific capacity is a result of the great stabilization of the intermediate phase Na1.5C6Cl4O2. The calculated activation barriers for the ionic hops are 0.68, 0.40, and 0.31 eV, respectively, for NaC6Cl4O2, Na1.5C6Cl4O2, and Na2C6Cl4O2. These results indicate that the kinetic process must not be a limiting factor upon Na insertion. Finally, the correct prediction of the specific capacity has confirmed that the theoretical strategy used, employing evolutionary simulations together with the hybrid functional framework, can rightly model the thermodynamic process in organic electrode compounds. (Graph Presented). © 2017 American Chemical Society.

The Journal of Physical Chemistry C

Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2: A High Voltage Organic Cathode for Sodium Rechargeable Batteries

In the current work friction stir processing of the Ti-6Al-4V alloy was carried out. Various process parameters (tool traverse speed and tool rotation speed) were studied for successful FSP of Ti-6Al-4V. The process parameters were identified using macrostructure observation on the surface of processed plate and microstructure evolution in the stir zone (SZ) of the FSP specimen. The effect of tool traverse speed and tool rotation speed on microstructure evolution in the SZ, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) were studied. The microstructure transformation from initial elongated α structure to prior β grains, with α layer grain boundary consisting of mixture of acicular α′ and very fine lamellar α/β colonies, was observed at SZ. This was the case for wide range of variations in parameters except for the tool rotation speed of 600 rpm and traverse speed of 60 and 100 mm/min. Under this combination of parameters, the bands of DRX α and transformed β structure were observed to evolve at SZ. © 2017, The Minerals, Metals & Materials Society.

Minerals, Metals and Materials Series

Investigation of Process Parameters for Friction Stir Processing (FSP) of Ti-6Al-4V Alloy

Shape memory alloys (SMAs) are known for their exotic shape memory properties. These properties are obtained through diffusionless austenite to martensite phase transformation. The phase transformation is induced through two ways: (1) stress (pseudo elasticity) and (2) temperature (one or two way shape memory effect). Among the various Cu or Ni-Ti based SMAs, a Ni-Ti-Fe combination is unique because of its phase transformation temperature (sub-zero range), large hysteresis, and high reversion stress (>450 MPa). These properties are useful in aerospace applications such as actuators, pipe couplings, vibration dampeners and variable area fan nozzle and medical instruments such as Simon filter and spinal vertebra spacer. In this paper, the complete process flow chart of the Ni-Ti-Fe alloy is outlined in detail. The phase transformation, one and two way shape memory effects, and pseudo elasticity behaviour of this alloy are explained based on the DSC curves and crystallographic orientations. Properties such as corrosion, tensile, fatigue strength and wear resistance of the Ni-Ti-Fe alloy are critically reviewed. © 2017 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Processing, properties and applications of Ni-Ti-Fe shape memory alloys

High temperature tensile flow behavior of aluminum-boron carbide (Al-B4C) composites of 0, 5 and 15% B4C, hot rolled to ~88% with intermediate annealing at 350 °C, was investigated by constant initial strain rate (CIS) (έ=1×10-2s-1) test technique at 500 °C and strain rate jump (έ=5×10-2s-1) test technique over the temperature range of 400–500 °C. In the as-cast condition, the flow stresses obtained between CIS and strain rate jump test techniques were found to be significantly different at 500 °C. The strain rate sensitivity index (m) was found to be ~0.1 over (έ=4×10-2s-1) for all the composites in both as-cast as well as hot rolled condition. Tensile elongations were found to be 0.36 in both as-cast and hot rolled aluminum, whereas the same reduced in Al-5% B4C composite to 0.35 and 0.27, respectively. The values of activation energy (Q) for deformation of rolled aluminum and Al-5% B4C composite were determined to be 194.2 and 73.4 kJ/mol, respectively. The microstructural examination, using SEM and EBSD techniques, revealed cavitation in aluminum upon differential strain rate test, and grain refinement upon rolling, which increased later during tensile test. © 2016 Japan Society for Composite Materials, Korean Society for Composite Materials and Informa UK Limited, trading as Taylor & Francis Group.

Advanced Composite Materials

Comparison of flow behavior of as-cast and hot rolled Al-B4C composites by constant and differential strain rate tests

A novel, “active-active-inactive” type Tin-Antimony-Nickel alloy with dendritic morphology electrodeposited on 3D interconnected microporous Nickel foam (∼8 μm pore diameter) as a potential high capacity anode for Li-ion batteries is reported. The multiphase composition comprising of SnSb and Ni3Sn4“reactant” intermetallics dispersed in Sn “matrix”, alleviates the volumetric stress generated during cycling by lithiating at different step potentials (0.84, 0.66, 0.57, 0.42, 0.40, and 0.38–0.25 V vs. Li/Li+). Nickel foam was synthesized by template-free hydrogen bubble-assisted electrodeposition and it successfully acts as a stress buffer preventing delamination. This combination of properties for Tin-Antimony-Nickel anode impregnated into Nickel foam results in 2nd cycle discharge capacity of 845 mAh/g, superior rate capability and stable cycle retention with a capacity loss of 16% in the last 50 cycles at a rate of 430 mA/g (0.5 C), while preserving its structural integrity and micro-architecture in comparison to a Tin-Antimony-Nickel anode deposited on a planar Nickel film as a current collector. © 2017 Elsevier B.V.

Journal of Alloys and Compounds

3D microporous Sn-Sb-Ni alloy impregnated Ni foam as high-performance negative electrode for lithium-ion batteries

Phase diagram of Mg-Sn-Y ternary alloy systems were constructed thermodynamically using calculation of phase diagram (CALPHAD) approach. The thermodynamically calculated isothermal section of Mg-Sn-Y ternary alloy at 400 °C was validated by comparing with results reported in the literature and few selected key experiments. The calculated results matched well with the experimental results. Vertical section phase diagram of Mg-1Sn-xY and Mg-3Sn-xY alloys were constructed on the basis of solidification analysis and compared with thermodynamically calculated phase diagram. The thermodynamically calculated liquidus temperature for Mg-1Sn-xY system matched well with the experimental results. However, significant differences in solidus temperature and solubility limit were observed for Mg-1Sn-xY alloys. This difference is attributed to the shift in composition and temperature for L→L+α-Mg + Sn3Y5and L→α-Mg + Sn3Y5+Mg24Y5phase transformations. In Mg-3Sn-xY phase diagram, a gradual decrease in liquidus temperature is experimentally observed up to 13 wt % Y and further addition of Y leads to increase in liquidus temperature. The increase in liquidus temperature is attributed to the formation of MgSnY intermetallic compound which is not predicted by thermodynamic model. The lack of experimental data on the enthalpy of formation of ternary MgSnY compound is one of the major reasons for the discrepancy between the thermodynamic calculation and experimental results. © 2016 Elsevier B.V.

Experimental investigation and thermodynamic calculation of the phase equilibria in the Mg-rich region of Mg-Sn-Y alloys

Metallic glasses are ideal candidates for functional applications. Mg-Zn-Ca amorphous alloy powders are found to exhibit significant enhancement in degrading azo dyes. In this work, an attempt has been made to study the dye degradation behavior of partially amorphous powders of one of the best corrosion resistant composition. For the first time, partially amorphous Mg-Zn-Ca alloy powders are synthesized through a single step ball milling (BM) process and their dye degradation capacity has been systematically evaluated. The results clearly demonstrate that Mg-Zn-Ca powders synthesized through single step ball milling process exhibit superior reaction efficiency in degrading azo dyes. The work has implications in arriving at an easy and efficient method for functional applications of partially amorphous Mg-Zn-Ca alloy powders. © 2016 Elsevier B.V.

A facile and efficient single step ball milling process for synthesis of partially amorphous Mg-Zn-Ca alloy powders for dye degradation

High-strength copper alloys are used extensively in the regenerative cooling parts of aerospace structures. Transient liquid phase (TLP) bonding of a Cu-Cr-Zr-Ti alloy was attempted in the present study using thin layers of elemental Ni and Mn coatings applied by electroplating. One of the base metals was given a Ni coating of 4 µm followed by a Mn coating of 15 µm, while the other base metal was given only the Ni coating (4 µm). The bonding cycle consisted of the following: TLP stage—heating to 1030 °C and holding for 15 min; homogenization stage—furnace cooling to 880 °C and holding for 2 h followed by argon quenching to room temperature. Detailed microscopy and electron probe microanalysis analysis of the brazed joints were carried out. The braze metal was found to undergo isothermal solidification within the 15 min of holding time at 1030 °C. At the end of TLP stage, the braze metal showed a composition of Cu-17Ni-9Mn (wt.%) at the center of the joint with a steep gradient in Ni and Mn concentrations from the center of the braze metal to the base metal interfaces. After holding for 2 h at 880 °C (homogenization stage), the compositional gradients were found to flatten significantly and the braze metal was found to develop a homogeneous composition of Cu-11Ni-7Mn (wt.%) at the center of the joint. In lap-shear tests, failures were always found to occur in the base metal away from the brazed region. The copper alloy base metal was found to undergo significant grain coarsening due to high-temperature exposure during brazing and, consequently, suffer considerable reduction in yield strength. © 2017, ASM International.

Journal of Materials Engineering and Performance

Transient Liquid Phase Bonding of Cu-Cr-Zr-Ti Alloy Using Ni and Mn Coatings: Microstructural Evolution and Mechanical Properties

Spinel ferrite NiFe2O4 thin films have been grown on three isostructural substrates, MgAl2O4, MgGa2O4, and CoGa2O4 using pulsed laser deposition. These substrates have lattice mismatches of 3.1%, 0.8%, and 0.2%, respectively, with NiFe2O4. As expected, the films grown on MgAl2O4 substrate show the presence of the antiphase boundary defects. However, no antiphase boundaries (APBs) are observed for films grown on near-lattice-matched substrates MgGa2O4 and CoGa2O4. This demonstrates that by using isostructural and lattice-matched substrates, the formation of APBs can be avoided in NiFe2O4 thin films. Consequently, static and dynamic magnetic properties comparable with the bulk can be realized. Initial results indicate similar improvements in film quality and magnetic properties due to the elimination of APBs in other members of the spinel ferrite family, such as Fe3O4 and CoFe2O4, which have similar crystallographic structure and lattice constants as NiFe2O4. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim