J.H. Perepezko

• University of Wisconsin–Madison

The oxidation of a titanium (Ti)-modified Mo-Si-B alloy designed for aerospace applications was investigated. Test samples were produced using arc melting and laser powder bed fusion (LPBF) additive manufacturing methods. To address high-temperature oxidation, a three-step coating strategy was employed, comprising a Mo precoat, Si and B co-depositi...

Zn-based metallic glasses (Zn 40 Mg 11 Ca 31+x Yb 18-x , x = 0-4) are strong glass forming alloys with low glass transition temperatures. While the crystallization onset temperature is also low, the nucleation behavior has not been examined and analyzed quantitatively. For a Zn 40 Mg 11 Ca 31 Yb 18 metallic glass alloy, the crystallization behavior...

The surface diffusion kinetics on a Pd77.5Cu6Si16.5 metallic glass is measured using a scratch smoothing method in the range of 107–57 K below the glass transition temperature. Within this temperature range, the surface diffusion coefficients are determined to vary between (8.66 ± 0.80) × 10⁻¹⁹ and (5.90 ± 0.60) × 10⁻¹⁸ m² s⁻¹. The corresponding ac...

Radiation-induced segregation (RIS) is one of the most dramatic changes that can occur at grain boundaries (GBs) during irradiation. In ceramics, RIS has been rarely studied and the underlying mechanisms are not well understood. Here, we used a combination of experiments and simulations to demonstrate RIS in TiB2. Specifically, we found that radiat...

The current focus on the development of structural materials that can operate at temperatures beyond the current capability exposes materials to an extreme of enhanced oxidation attack. The emerging class of refractory multiple principal element alloys (RMPEA) offers superior structural performance at elevated temperature, but the alloys are suscep...

A Mo-Si-B based coating has been applied on a refractory multi-principal element alloy (RMPEA) using a two-step coating strategy and has endured more than 750 h of thermal cycling oxidation exposure between room temperature to 1300 • C with a minimal weight change. The formation of the Mo 5 SiB 2 diffusion barrier in the coating prevents the inward...

Traditionally, the formation of amorphous shear bands (SBs) in crystalline materials has been undesirable, because SBs can nucleate voids and act as precursors to fracture. They also form as a final stage of accumulated damage. Only recently SBs were found to form in undefected crystals, where they serve as the primary driver of plasticity without...

Bulk metallic glasses can exhibit novel material properties for engineering scale components, but the experimental discovery of new alloy compositions is time intensive and thwarts the rate of discovery. This study presents an experimental, high-throughput methodology to increase the speed of discovery for potential bulk metallic glass alloys. A we...

Traditionally, the formation of amorphous shear bands in crystalline materials has been undesirable, because shear bands can nucleate voids and act as precursors to fracture. They also form as a final stage of accumulated damage. Only recently were shear bands found to form in undefected crystals, where they serve as the primary driver of plasticit...

Future nuclear reactors and advanced power generators require materials with good stability and damage tolerance under harsh conditions, including high temperatures and high-dose radiation. Ti3SiC2 MAX phase has good physical properties and mechanical strength. It can remain crystalline under serious microstructure damage due to the nanolaminate st...

We use a random forest model to predict the critical cooling rate (RC) for glass formation of various alloys from features of their constituent elements. The random forest model was trained on a database that integrates multiple sources of direct and indirect RC data for metallic glasses to expand the directly measured RC database of less than 100...

Structural relaxation induced ductile to brittle transition seriously hampers the practical applications in metallic glasses. Although there have been many researches focusing on the hidden physical mechanism of ductile to brittle transition, the correlation between ductile to brittle transition and shear band nucleation kinetics is still unclear....

Refractory multiple-principal-element alloys (RMPEAs) are promising structural materials to enable increased power efficiency in high-temperature oxidation environments, but the oxidation behavior and microstructures of the oxides, especially at the beginning of the oxidation, have received limited attention. The oxidation mechanism in an equimolar...

For high temperature applications Mo base alloy requirements include both superior structural performance and environmental resistance. To address these requirements alloys in the Mo-Si-B system and refractory multi- principal element alloys (RMPEA) are being developed that exhibit a promising potential, but also have some remaining challenges to i...

The high density of aluminum nanocrystals (>10 ²¹ m ⁻³ ) that develop during the primary crystallization in Al-based metallic glasses indicates a high nucleation rate (∼10 ¹⁸ m ⁻³ s ⁻¹ ). Several studies have been advanced to account for the primary crystallization behavior, but none have been developed to completely describe the reaction kinetics....

The isothermal and cyclic oxidation behavior of Mo-6Si-12B-(1, 2, 4, 8)Al samples was investigated from 800 to 1300℃. With increasing Al content, the isothermal oxidation resistance is enhanced and the pesting behavior is suppressed at 800℃. The Mo-6Si-12B-4Al alloy with an oxide layer of both an alumino-borosilicate glasses and mullite has the bes...

Glassy materials under external stimuli usually display multiple and complex relaxations. The relaxations and the evolution paths of glassy materials significantly affect their properties and are closely related to many key issues in glass physics, such as glass transition and thermoplastic forming. However, until now, the relaxation dynamics in th...

We have investigated the radiation tolerance of Cr-B binaries and Cr-Al-B ternary MAB phases using a combination of ab initio calculations and experiments. One key discovery is that Cr3AlB4 has excellent resistance to radiation-induced amorphization, and therefore it is a promising material for applications in extreme environments. We also demonstr...

Surface diffusion is vastly faster than bulk diffusion in some glasses, but only moderately enhanced in others. We show that this variation is closely linked to bulk fragility, a common measure of how quickly dynamics is excited when a glass is heated to become a liquid. In fragile molecular glasses, surface diffusion can be a factor of 10^{8} fast...

Under intense deformation of metallic multilayer samples, a nanometer-scale layer thickness and grain size develops during repeated cold-rolling. Along with the evolution of the highly refined microstructure, a nanoscale interfacial alloying occurs that can result in an amorphization reaction. The deformation of multilayers exhibits driven system b...

Refractory multiple-principal-element alloys (RMPEAs) are promising structural materials to enable increased power efficiency in high-temperature oxidation environments, but the oxidation behavior and microstructures ofmthe oxides, especially at the beginning of the oxidation, have received limited attention. The oxidation mechanism in an equimolar...

We have developed models of metallic alloy glass forming ability based on newly computationally accessible features obtained from molecular dynamics simulations. Since the discovery of metallic glasses, there have been efforts to predict glass forming ability (GFA) for new alloys. Effective evaluations of GFA have been obtained but generally relied...

The advent of chip calorimetry has enabled an unprecedented extension of the capability of differential scanning calorimetry to explore new domains of materials behavior. In this paper, we highlight some of our recent work: the application of heating and cooling rates above 10⁴ K/s allows for the clear determination of the glass transition temperat...

We have developed models of metallic alloy glass forming ability based on newly computationally accessible features obtained from molecular dynamics simulations. In this work we showed that it is possible to increase the predictive value of GFA models by using input features obtained from molecular dynamics simulations. Such features require only r...

Strategies to change the properties of metallic glass by controlling the crystallization and the glass transition behavior are essential in promoting the application of these materials. Aside from changing the composition approaches to stabilize the glass and frustrate the nucleation and growth of crystals, new strategies at a fixed glass compositi...

A new class of Al‐based metallic glasses is identified, which exhibits polymer‐like thermoplastic formability near the boiling point of water. To satisfy the requirements for thermoplastic behavior, a series of AlSm‐based metallic glasses are examined by Flash DSC to determine the glass transition temperature, Tg. Viscosity measurements confirm tha...

Differential thermal analysis (DTA) and microstructural and microprobe measurements of DTA and as-cast Ni-Re alloys with compositions between 0.20 and 0.44 mass fraction Re provide information to resolve differences in previously published Ni-Re phase diagrams. This investigation determines that the peritectic invariant between liquid, Re-rich hexa...

Solidification of the Sm-rich Al–Sm alloys has been studied using a newly developed Al–Sm embedded atom model potential by molecular dynamics (MD) simulations. We use descriptors for glass forming ability that have been previously validated for Al-rich Al–Sm alloys, and we predict that among the Sm-rich alloys the best glass formers have compositio...

The isothermal nucleation kinetics in Al-Sm metallic glasses with low Sm concentrations (xSm) was studied using molecular dynamics simulations in order to calculate time-temperature-transformation curves. The average delay time of Al nanocrystal nucleation was found to increase exponentially with xSm, whereas the estimated critical cooling rate nec...

YB4/YB6 two-phase alloys were prepared by arc-melting of high purity elemental materials. The Young's moduli of YB4 and YB6 were evaluated by nanoindentation technique. During loading of nanoindentation, pop-in events were clearly observed for YB4 and YB6, suggesting that both have some capability of dislocation emission at room temperature. TEM ob...

Diffusion couple experiments between Ni and Re at 1200 and 1350 °C were performed. These experiments established the limits of the two-phase FCC + HCP region. No intermediate phase was observed at these temperatures. Composition-dependent interdiffusion coefficients and associated uncertainties were estimated by three methods. The first employed fi...

The early stage of crystallization in amorphous phases is a key step in the overall microstructural evolution. In a Zr-based amorphous alloy the formation of metastable nanophase was observed at the earliest crystallization stage, with an ultra-high nucleation density of 6.5 × 10²⁴ m⁻³ and a size of ∼1–2 nm. The nanophase has an icosahedral structu...

The main recent advances in Al-based amorphous alloys are discussed in three areas: crystallization behavior, glass-forming ability and minor alloying effects. First, as a brief introduction, the special features and structure-property relationships are presented for the Al-based amorphous alloys. The different models for the nucleation behaviors,...

During the solidification of Al-Sm metallic glasses the evolution of the supercooled liquid atomic structure has been identified with an increasing population of icosahedral-like clusters with increasing Sm concentration. These clusters exhibit slower kinetics compared to the remaining clusters in the liquid leading to enhanced amorphous phase stab...

The three-phase, (Mo,Nb)ss/(Mo,Nb)5Si3/(Mo,Nb)5SiB2, Bcc/T1/T2 microstructures that develop in Mo–Nb–Si–B alloys have been examined in arc cast and directionally solidified samples to identify the phase sequencing during solidification. A Mo-32.6Nb-19.5Si-4.7B (at.%) alloy was directionally solidified using an optical floating zone (OFZ) furnace in...

Multiphase Mo-Si-B alloys comprised of Mo(ss), Mo3Si (A15), and Mo5SiB2 (T2) phases offer attractive high temperature mechanical properties with some capability to resist oxidation via production of a borosilica surface layer. In previous work, Fe additions into Mo-rich Mo-Si-B alloys appreciably limited transient oxidation, where the major mass ch...

While melt undercooling is often observed during solidification, the study of nucleation is challenging due to the numerous possible heterogeneous sites present in even high-purity melts. Identification of active nucleation sites requires developing well-planned experimentation. In samples with well-defined and controlled undercooling the identific...

Repeated cold rolling was performed on multilayers of Cu60/Ni40 and Cu40/Ni60 foil arrays to study the details of driven atomic scale interfacial mixing. With increasing deformation, there is a significant layer refinement down to the nm level that leads to the formation of a solid solution phase from the elemental end members. Intriguingly, the co...

During the cold rolling of multilayers of Ni and V with an average composition Ni70V30, Ni30V70 and Ni57V43, deformation induces phase transformation and an interfacial mixing. After repeated cold rolling at room temperature, X-ray diffraction (XRD) and scanning transmission electron microscope (STEM) results demonstrate that between pure Ni and V...

To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings were applied on Mo–9Si–8B (in at.%) alloy substrates by Si–B co-pack cementation. Subsequently, the samples were conditioned at 1450 °C for 8 h in air to develop an outer 10 μm thick aluminoborosilicate scale. A multilayered microstructure of MoSi2, Mo5Si...

A Mo–Si–B based coating was prepared on an NbSS/Nb5Si3 composite by a two-step process consisting of the initial deposition of Mo followed by pack cementation co-deposition of Si and B. After a conditioning treatment, an aluminoborosilica layer fully covered the sample. Following oxidation at 1300 °C for 24 h, the coated sample demonstrated a weigh...

In the present study, the crystallographic features of bcc/T1/T2 three-phase microstructure in a directionally solidified Mo–32.2Nb–19.5Si–4.7B (at.%) alloy have been examined by electron back-scattering diffraction (EBSD) analysis. The alloy was directionally solidified using an optical floating zone (OFZ) furnace in a flowing Ar gas atmosphere at...

The transition from blunt leading edges to sharp leading edges on re-entry aircrafts is necessary to increase both maneuverability and safety. However, the oxidation resistance of current materials is inadequate for the extreme conditions experienced by sharp leading edge re-entry vehicles. The Mo–Si–B alloy system has been utilized to design a mul...

A Mo–Si–B based coating was applied to niobium that produced a coating structure composed of molybdenum and niobium silicides. Oxidation tests at 1000 °C and 1200 °C showed that the Mo–Si–B coating provided enhanced oxidation protection of niobium due to the formation of a protective aluminosilica layer. The coating performance was identified to be...

For vitrification of an alloy melt during cooling there is a kinetic competition with the nucleation and growth of metastable and stable crystalline phases. Many of the measures of glass forming ability (GFA) attempt to capture some of the features of the kinetic competition, but the GFA metrics are static measures and the kinetic processes are dyn...

Ultrastable glasses and nanoglasses are two emerging materials with novel properties that have been investigated separately. In order to explore the combined effect of ultrastable character and a nanoglass with a nanoglobular microstructure on the kinetic behavior, the glass transition and crystallization behaviors of an ultrastable nanoglass and a...

A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of compositio...

Nanocalorimetry offers new capabilities to explore previously inaccessible domains of reaction kinetics due to the expanded heating and cooling rates compared to conventional calorimetry methods. With this capability it is now possible to explore ranges of alloy metastability and to examine rapid kinetic reactions such as melting and the competitio...

The degree of overheating of a melt often plays an important role in the response of the melt to subsequent undercooling, it determines the nucleation and growth behavior and the properties of the final crystalline products. However, the dependence of accessible undercooling of different bulk melt samples on prior liquid overheating has been report...

Significance A shear band is a region of highly localized plastic flow that develops during loading in both crystalline and amorphous materials. Shear bands directly determine the ductility of an amorphous phase, but relatively little is known about their nucleation. We use nanoindentation to probe shear band nucleation by measuring the first pop-i...

Aluminide coating of steels enables more efficient power generation through higher operating temperatures. Low-temperature (T < 660 °C) pack cementation aluminide coatings form an Al5Fe2 phase which allows for the development of a large Al flux, but the mechanism is not clear. The coating structures and resultant oxides were examined in both austen...

Molten CMAS (calcia–magnesia–aluminosilica) deposits penetrate and interact with thermal barrier coatings (TBCs) in gas-turbine engines to degrade the zirconia-based TBCs and the overall TBC performance. To address the CMAS attack some approaches have been advanced based upon sealing the TBC or altering the TBC composition. A new strategy is presen...

We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe...

We review and discuss methods for including the role of point defects in calculations of the free energy, composition and phase stability of elements and compounds. Our principle aim is to explain and to reconcile, with examples, the perspectives on this problem that are often strikingly different between exponents of CALPHAD, and others working in...

During the repeated cold rolling of Cu/Ni and Ag/Pd multilayers, a solid solution forms at the interfaces as nanoscale layer structure with a composition that replicates the overall multilayer composition. The interfacial mixing behavior was investigated by means of X-ray diffraction and scanning transmission electron microscopy. During deformation...

For high temperature application beyond the range of Ni-base superalloys, multiphase Mo–Si–B alloys with compositions, that yield the ternary intermetallic Mo5SiB2 (T2) phase as a key microstructure constituent together with the Mo and Mo3Si phases, offer an attractive balance of high melting temperature, oxidation resistance and mechanical propert...

Phase equilibrium between the α-Nb5Si3 and β-Nb5Si3 phases has been studied in the Nb–Mo–Si ternary system. The high temperature β-Nb5Si3 phase is stabilized by Mo additions to yield a relatively narrow α/β two-phase field in the Nb–Mo–Si ternary system. The enthalpy of the α–β phase transformation has been evaluated from the experimentally determi...

Thermal spray methods offer a versatile and flexible approach to the manufacture of coatings as a final product. A novel application of thermal spray coating is demonstrated by incorporating a plasma-sprayed Mo layer coating as a precursor step within an integrated costing design. The effectiveness of the two-step design is illustrated for aluminob...

Nanoparticles were shown to catalyze nucleation of primary and secondary phases in metal matrix nanocomposites (MMNCs). This catalysis is important as it contributes to the mechanical property enhancement in the MMNCs. Primary aluminium grain refinement was demonstrated in A356 matrix nanocomposites. Various types and sizes of nanoparticles (SiC, T...

Thermodynamic and phase diagram data in the Pb-Cd system are reevaluated. A substitutional solution model is used for the liquid and fcc and hcp phases. The stable and metastable equilibria of this system are calculated using the thermodynamic equations derived from equilibrium data. Besides the well-established eutectic reaction at 521 K (248 °C),...

Magnesium-based metallic glasses (MMGs) show intriguing potentials for application as implantable biomaterials owing to their disordered atomic structure, good biodegradability, low elastic modulus, high strength, and large elasticity. However, despite of all these advantages, their brittleness is their Achilles’ heel, which severely limits their a...

The degree of overheating of a melt often plays an important role in determining its solidification behavior and the quality of the final product. However, the relationship between the level of melt overheating and the resulting undercooling is far from being understood, especially in rapid cooling processes. The undercooling dependence on overheat...

A new class of materials: Au-based nanograined metallic glasses (NGMGs) were synthesized using magnetron sputtering with powder targets. A detailed study by x-ray diffraction and high-resolution transmission electron microscopy (TEM) documents the unique nanoscale granular structure of the Au-based NGMG. This material inherited the good mechanical...

The degree of overheating of a melt often plays an important role in determining its solidification behavior and the quality of the final product. However, the relationship between the level of melt overheating and the resulting undercooling is far from being understood, especially in rapid cooling processes. The undercooling dependence on overheat...

Multiphase Mo-Si-B alloys composed of Mo, Mo 3Si and Mo 5SiB 2 phases offer excellent high-temperature mechanical properties with the ability to resist oxidation via production of a borosilica surface layer. In the current study the effects of Fe addition were examined on the oxidation performance of Mo-2Si-1B and Mo-3Si-1B (wt.%) alloys. The analy...

The oxidation performance of ZrB2–SiC ultra-high temperature ceramics with SiC content ranging from 20 to 80 vol% has been evaluated at 1773 K for 50 h and at 2073 K for 20 min. Oxidation reaction pathways were interpreted using volatility diagrams of the ZrB2–SiC system. At 1773 K for 50 h, all ZrB2–SiC composites from 20 to 80 vol% SiC formed a p...

Nucleation reactions play a central role in the synthesis of both bulk metallic glasses and nanostructured materials. For nanostructured materials it is necessary to promote a high nucleation density without significant growth or coarsening. Beyond crystallization reactions nucleation of shear bands is critical for promoting a homogeneous flow and...

Crystallization of highly undercooled materials either from the melt during cooling or from an amorphous phase during heating can yield novel phases with useful properties, but a reliable control of phase selection has been elusive. In bulk volumes fluxing is a common method to promote high undercooling due to nucleant removal or deactivation, but...

The development of robust high temperature oxidation resistant coatings for tungsten was evaluated for a Mo–Si–B coating system that was applied by a two step process. The synthesized coating shows a graded structure composed of various amounts of molybdenum and tungsten disilicide as well as an aluminoborosilica top layer. Oxidation tests conducte...

The outstanding efficiency of Fe-based metallic glass powders in degrading organic water contaminants is reported. While the glassy alloy contains 24% chemically inactive metalloid elements, the powders are capable to completely decompose the C32H20N6Na4O14S4 azo dye in aqueous solution in short time, about 200 times faster than the conventional Fe...

Refractory metal cermets have attractive mechanical properties for high temperature applications, but exhibit poor resistance to oxidation attack. A two-step coating process has been developed in order to provide an effective high temperature oxidation resistance. W–HfN and Mo–ZrN cermet samples were initially coated with a layer of Mo through a Mo...

Silicon carbide conversion coated carbon/carbon composites (SiC–C) are promising materials for high temperature engine, aircraft and aerospace applications. However, the inherent coating cracks in SiC–C composites due to processing and rapid degradation of silica and SiC in corrosive combustion environments demand a protective external coating to p...

The lack of new functional applications for metallic glasses hampers further development of these fascinating materials. In this letter, we report for the first time that the MgZn-based metallic glass powders have excellent functional ability in degrading azo dyes which are typical organic water pollutants. Their azo dye degradation efficiency is a...

The formation of Al nanocrystals from an amorphous Al92Sm8 alloy involves kinetic phenomena with very different characteristic length and timescales, including initial nucleation and later growth and coarsening. Insight into these processes can be derived from the evolution of the sizes of nanocrystals as a function of time. Synchrotron small angle...

Multiphase Mo-Si-B alloys with compositions which yield the ternary intermetallic Mo5SiB2 (T2) phase as a key microstructure constituent together with the Mo and Mo3Si phases, offer an attractive balance of high melting temperature, oxidation resistance, and mechanical properties. The investigation of reaction kinetics involving the T2 phase enable...

The next generation of infrared remote sensing missions, including the climate benchmark missions, will require better absolute measurement accuracy than now available, and will most certainly rely on the emerging capability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation designed...

The next generation of infrared remote sensing satellite instrumentation, including climate benchmark missions will require better absolute measurement accuracy than now available, and will most certainly rely on the emerging capability to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentat...

Different types of nanoparticles in aluminum (Al) alloy A356 nanocomposites were shown to catalyze nucleation of the primary Al phase. Nanoparticles of SiC β, TiC, Al2O3 α, and Al2O3 γ were added to and dispersed in the A356 matrix as nucleation catalysts using an ultrasonic mixing technique. Using the droplet emulsion technique (DET), undercooling...

A novel Mg42Li23Cu25Y10 nanostructure-bcc ductile phase composite containing a Mg2Cu phase and amorphous zones has been obtained by injection casting. This alloy exhibits a large plastic engineering strain of 83% and plastic true strain of 177% with a flow stress at 4.3% deformation of 425 MPa. During compression, the deformation of the nanometer s...

The deformation behaviour of Zr65Cu20Fe5Al10 bulk metallic glass has been studied at room temperature under uniaxial compression conditions at the strain rate of 5×10−4s−1 and performing jump tests for the strain rates (SR) ranging between 5×10−6s−1 and 5×10−2s−1. The alloy always shows the formation of shear bands and exhibits serrated flow. In th...

The effect of serrations initiated in the elastic deformation region before macroscopic yielding on the mechanical behaviour of Zr65Fe 5Cu20Al10 bulk metallic glassy rods was analysed using a large number of samples. The apparent work-hardening-like behaviour and the plasticity tend to increase with the number of shear bands in the pre-yield region...

The microstructure and compression response of a quaternary Mo-Nb-Si-B alloy has been examined in in the temperature interval 1200°C-1600°C and in the strain rate regime 10–4 s–1 to 10–6 s–1 and compared to earlier results on the ternary Mo-Si-B alloys The microstructure is composed of a three-phase microlamellar eutectic composed of the Mo-Nb soli...

Mo-Si-B alloys respond to high temperature oxidation in two distinct stages. First, there is a transient stage with an initial high recession rate that corresponds to the evaporation of volatile MoO3 due to the oxidation of the molybdenum rich phases. The steady state stage of the oxidation begins when a borosilica layer that initiated in the trans...