Carbide precipitates in Ni-based superalloys are often desirable phases that can improve high-temperature properties as well as aid in microstructural refinement of the material; however, they can also serve as crack initiation sites during fatigue. To date, the knowledge on carbide formation has mostly originated from assessments of cast and wrought Ni-based superalloys. As powder-processed Ni-based superalloys are becoming increasingly widespread, understanding the different mechanisms by which they form becomes increasingly important. In the present work, we performed detailed characterization of MC carbides present in two experimental high Nb-content powder-processed Ni-based superalloys and revealed that Hf additions affect the resultant carbide morphologies. This morphology difference was attributed to a higher magnitude of elastic strain energy along the interface associated with Hf being soluble in the MC carbide lattice. The characterization results of the segregation behavior of Hf in the MC carbides and the subsequent influence on their morphology were compared to density functional theory calculations and found to be in good agreement, suggesting that computational modeling can successfully be used to predict carbide features.
"MC carbide characterization in high refractory content powder-processed Ni-based superalloys", Metallurgical and Materials Transactions A, 49, 2340-2351 (2018) [PDF]
The standard enthalpy of formation is a fundamental thermodynamic property that determines the phase stability of a compound, which can be coupled with other thermodynamic data to calculate phase diagrams. Calorimetry provides the only direct method by which the standard enthalpy of formation is experimentally measured. However, the measurement is often a time and energy intensive process. We present a dataset of enthalpies of formation measured by high-temperature calorimetry. The phases measured in this dataset include intermetallic compounds with transition metal and rare-earth elements, metal borides, metal carbides, and metallic silicides. The dataset contains 1,276 entries on experimental enthalpy of formation values and structural information. Most of the entries are for binary compounds but ternary and quaternary compounds are being added as they become available.
The dataset also contains predictions of enthalpy of formation from first-principles calculations for comparison. We compared DFT formation enthalpy values from the Materials Project and OQMD, and identified problematic systems that show substantial discrepancies between experiments and PBE-DFT.
The most recent database can be queried from our website:
The data file can be accessed from Figshare:
Experimental formation enthalpies for intermetallic phases and other inorganic compounds", Scientific Data, 4, 170162 (2017) [PDF]
Glad to be a member of a team that received the 2017 National Energy Research Scientific Computing Center (NERSC) Award for High-Impact Scientific Achievement:
A team of researchers from Lawrence Berkeley National Laboratory, University of California Berkeley and Caltech was honored in this category for using NERSC resources to speed up the discovery of commercially viable materials that can be used to produce solar fuels. The group gathered a list of potentially useful compounds and then were able to rapidly screen and test the best materials with NERSC. This process would normally take an immense amount of time to conduct all the tests and experiments by hand. The researchers were able to go through 174 compounds containing vanadium and oxygen, called vanadates, and were able to identify 12 useful materials. These materials will be very useful for developing solar fuels, which are a clean and renewable alternative to fossil fuels. The work was led by Berkeley Lab's Jeff Neaton, John Gregoire and Qimin Yan. Other members of the team were Jie Yu, Santosh Suram, Lan Zhou, Aniketa Shinde, Paul Newhouse, Wei Chen, Guo Li and Kristin A. Persson.
We are glad to receive a 3-year award from the Solid State & Materials Chemistry Program of National Science Foundation (DMR-1709959) to study mechanical activation enhanced solid-state reaction and electrochemical properties of the NaCrO2 cathode. The work will be in collaboration with Prof. Leon Shaw.
Dr. Chen received a 3-year award from the Metals & Metallic Nanostructure program of National Science Foundation (DMR-1607943) to study the thermodynamic properties of binary and ternary intermetallic compounds using experimental and computational methods. This work will be in collaboration with Prof. Philip Nash.