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Based on the results of experiments performed at temperatures T ≳ 613 K, a thermodynamic model was recently proposed to explain: (i) the origin of a metastable liquid miscibility gap (MLMG) in Pd-Ni-P, an alloy system with a negative heat of mixing. It originates from the superposition of two distinct liquid Gibbs free energy blades; and (ii) a liquid-liquid phase transition (LLT) just outside the MLMG. Since Gibbs free energy is a function of T, the MLMG was revisited in this work for its T dependence, but this time with T ≲ 613 K. It was found that the MLMG has the shape of a truncated right angle prism, instead of a right angle prism as suggested previously. It is similar to, but not the same as an immiscibility loop in a binary liquid mixture. The revised MLMG is in good agreement with the predictions of the thermodynamic model.

Recently, for the first time, a metastable liquid miscibility (MLMG) in a metallic alloy system was found and determined (Z. D. Wu et al. J. Non-Cryst. Solids 410 (2015) 51–57 and W. Z. Zhou et al., J. Non-Cryst. Solids, 432 (2016) 420–425). According to thermodynamics, a MLMG consists of two decomposition reactions, which are liquid state nucleation and growth (LNG) and liquid state spinodal decomposition (LSD). However, in all of the results reported so far, only LSD was found. In this work, by using Porod's law, decomposition by LNG was found, confirming the existence of the LNG regime in the MLMG.

Polyamorphic transition is the transition between two amorphous states or two liquid states (LLT) at a fixed composition of a substance. Experience in LLT is limited. Besides, its nature remains largely unknown as it occurs under the experimental conditions of high pressure/temperature (P/T) or high undercooling. In this study, we found that some undercooled Pd Ni P melts undergo a LLT. Contrary to all earlier studies, Pd Ni P specimens that contain the structural changes that occur at different stages of the LLT can be prepared for electron microscopy. HRTEM (high resolution transmission electron microscope) establishes that it is a first-order phase transition. From thermodynamics, a first-order phase change is accompanied by a latent heat. Here it was measured by a DSC (differential scanning calorimeter). A first-order LLT has important thermodynamic implications. First, it reconfirms that a liquid has different kinds of short-range-orders (SROs). Second, the first-order LLT implies that the SROs of a liquid are divided into distinct groups, each containing either a SRO or a number of different SROs, but not all. Physically, each group represents a real liquid. Third, the SRO(s) in a group can be assigned an independent Gibbs free energy, G SRO (P, T, c = composition) and the thermodynamics of the liquids can be described in terms of these G SRO .

Despite having a negative heat of mixing, a metastable liquid/amorphous miscibility gap (MLMG) was found below the liquidus of the alloy system, Pd–Ni–P. Earlier, a direct determination of the complete MLMG was not possible because it lies in the undercooling regime. It is known that the morphology of an alloy system that has undergone a spinodal mechanism is interconnected. In this work, a morphological transition, from eutectic to interconnectedness, was used to determine the complete MLMG of the alloy system, Pd–Ni–P.

Recently, it was found that undercooled molten Pd–Ni–P undergoes amorphous/liquid spinodal decomposition or equivalently the alloy system has a metastable liquid miscibility gap (MLMG) in its undercooling regime. This is unusual because the alloy system has a negative heat of mixing. In this work, a portion of the MLMG was determined, at 613 and 593 K. The incomplete MLMG obtained differs fundamentally from that of an alloy system with a positive heat of mixing. EDX and X-ray studies show that the MLMG is due to two unique short-range orders.

Pd41.25Ni41.25P17.5 bulk metallic glasses (BMGs) undergo phase separation despite the fact that the alloy system has a negative heat of mixing. By employing the techniques of small angle X-ray scattering (SAXS), it was found that the phase separation is consistent with a spinodal mechanism. Its occurrence is attributed to unique short-range orders in the amorphous (or liquid) state of the BMGs. (C) 2013 Elsevier B.V. All rights reserved.

Phase-separated Pd41.25Ni41.25P17.5 bulk metallic glasses (BMGs) were subjected to isothermal annealing at 613 K (340 °C) for different time periods, t, in the range of 0 ≤ t ≤ 8 hours. For 0 ≤ t ≲ 5 hours, crystalline precipitates, in the shape of spheres, appear and its density is more or less a linear function of t. They are randomly distributed in the amorphous matrix. For t ≳ 5 to 6 hours, the number density of the spherical crystalline precipitates increases rapidly. In addition, they are no longer distributed randomly in the phase-separated amorphous matrix. Clustering is displayed. Experimental results suggest that the clustering is due to cubic crystalline precipitates that start to appear when t ≈ 5 to 6 hours.

Earlier, it was shown that molten Pd 41.25 Ni 41.25 P 17.5 alloys can be cast into BMGs (bulk metallic glasses) of different microstructures, which are: (i) homogeneous BMGs (A-type), (ii) homogeneous BMGs embedded with crystalline precipitates (B-type), and (iii) phase-separated BMGs (C-type). Their crystallization behaviors were studied in this paper. At low annealing temperatures, the crystallization is characterized by spherical precipitates, each of which consists of a nanocrystalline core and a eutectic crust. The cores of the three types of BMGs are not of the same composition. At high annealing temperatures, there are cubic precipitates in addition to the spherical precipitates. For reference purposes, the crystallization of amorphous Pd 40 Ni 40 P 20 , a widely studied BMG, was examined. It was found that spherical precipitates, with a core composition different from those of Pd 41.25 Ni 41.25 P 17.5 BMGs, appear, but cubic precipitates are absent.

Molten Fe79.5B6.5C14 melts can be cast into ingots of networklike microstructure. According to microstructural classification, a Fe79.5B6.5C14 network specimen can be divided into three zones. Zone A is occupied by a random network, zone B by a uniformly aligned network, and zone C by a severely aligned network that exhibits network patterns.

Experimental arrangements were made to study the spinodal mechanism occurring in undercooled molten Pd 41.75 Ni 41.75 P 17.5 alloys as a function of time. It can be estimated from the experimental results that the lower bound of the duration (or completion time) of the spinodal mechanism at a temperature of ≈ 625 K is about 200 s. Simple kinetic analysis shows that the time constant τ of the spinodal decomposition at a temperature of ≈ 625 K is ~ 0.002 s − 1 . Both quantities are useful indicators for other metallic glasses and bulk metallic glasses (BMG) that also undergo spinodal decomposition.

Recently, phase separation was found to occur in Pd41.25Ni41.25P17.5 bulk metallic glasses (BMG), which have a negative heat of mixing among the constituent elements. In this work, Pd40 + 0.5xNi40 + 0.5xP20 − x BMG with x = 0 to 3.5, were studied for amorphous phase separation. It occurs for x ≳ 1, but absent for x ≲ 1. In addition, in phase-separated specimens, the characteristic sizes or wavelengths of the decomposed phases were measured. It was found that they obey the lever rule. The experimental results suggest the existence of a metastable liquid/amorphous miscibility gap. Its origin is attributed to unique short range orders in the undercooled Pd–Ni–P melts.

The alloy system, Pd 41.25 Ni 41.25 P 17.5 , has a negative heat of mixing among its constituent elements. By using high resolution transmission electron microscopy, high angle annular dark field in scanning transmission mode, and energy dispersive X-ray spectroscopy, it was found that phase separation occurs in Pd 41.25 Ni 41.25 P 17.5 glassy alloys. For a clear exhibition of the amorphous phase separation reaction, it is desirable to introduce intermediate thermal annealing before an undercooled Pd 41.25 Ni 41.25 P 17.5 melt is cooled down to become a solid amorphous specimen. The results suggest that there may be unique short range orders in amorphous/liquid Pd 41.25 Ni 41.25 P 17.5 , which are responsible for the phase separation.

Fe100–x C x melts (x = 18 to 24) can be cast under B2O3 flux into solids of interconnected network morphology, with a wavelength in the submicron range. There are two major constituent subnetworks, which are a brittle Fe3C subnetwork and a ductile αFe subnetwork. The Fe100–x C x network alloys, therefore, are white cast iron of novel microstructure. Fe100–x C x specimens of x = 18 to 21 are ductile and the yield strength can be as large as ~3200 MPa. Fe100–x C x specimens of x = 22 to 24 are in the regime of a ductile-to-brittle transition. The compressive strength is high, at ~2700 MPa. Microstructural analysis indicates that the ultrafine network morphology and the ductile αFe subnetwork are responsible for the ductility exhibited in Fe100–x C x network alloys of x = 17 to 21. They are also responsible for the high compressive strength in Fe100–x C x network alloys of x = 22 to 24.

The thermoluminescence (TL) properties of yttrium fluorides K2YF5 and KYF4 singly doped with Ce3+, Tb3+, Dy3+ or Tm3+ have been studied in the range from 30 °C to 500 °C after α or β irradiation. It has been found that K2YF5 doped with 5.0 at% Ce3+, K2YF5 doped with 1.0 at% Tb3+ and KYF4 doped with 5.0 at% Tb3+ show TL sensitivity of the same order as that of the well known TLD-100 (LiF:Mg,Ti) phosphor. Strongly different TL response to α or β irradiation has been found for Tb3+ doped K2YF5 crystals. The TL mechanism in these phosphors is discussed by taking into account the TL emission spectra from irradiated samples, which are identical to the emission spectra of the appropriate doping rare earth ions, and the kinetics parameters obtained with the method of various heating rates.

It was demonstrated that bulk nanostructured materials can be prepared by rapidly solidifying a eutectic alloy melt. Prior to solidification, the undercooled melt has to undergo liquid phase spinodal decomposition. Although the average grain size of an as-prepared bulk nanostructured alloy can be as small as 3–6 nm, there is actually little control over its grain size. It turned out that by introducing intermediate isothermal annealing to the rapid solidification process, bulk nanostructured alloy ingots of diameter >1 cm can be synthesized with controllable grain size.

In this paper, the microstructures of undercooled Ni that solidified at various initial bulk undercoolings are examined in detail in order to understand the mechanism of grain refinement in metallic systems. Molten Ni contracts on solidification. In the experiment, since it was covered by molten glass flux, upon crystallization cavities had to form to accommodate the rapid volume change if the undercooled specimen remained in contact with the glass flux, which could not flow so readily. The adhesiveness between Ni and glass flux was confirmed by removing them from a furnace after the whole system had been cooled down to room temperature. Furthermore, it was clear from the micrographs that after a cavity had formed, it did not collapse. It can therefore be concluded that smaller grains are found to concentrate near the void along the minor axis. At still higher undercoolings, the effect was so violent that the voids took irregular shapes. Again, the grains near the cavity are somewhat smaller than those further away. Accordingly, the authors conclude that grain refinement in undercooled Ni was brought about by dynamic nucleation as the cavities formed.

The microstructures of 〈110〉 twin dendrites were studied in detail. It was found that the periphery surfaces of the dendrite are all {111} planes. A 〈110〉 twin dendrite model was constructed to explain the growth morphology. The model predicts the absence of branching except ion the initial stage, which has indeed been observed experimentally. From the model, it turns out that the 〈110〉 growth is in fact a combination of two 〈211〉 twin dendritic growths if the latter can maintain their coherency. Finally, the 〈110〉 to 〈211〈 dendritic transition is attributed to the break-up of the coherent growth of the two 〈211〉 dendritic growths.

Undercooled molten Ge was allowed to solidify at initial bulk undercoolings, ΔT , from 10 to 200°C under dehydrated boron oxide flux. It turned out that in addition to the 〈211〉 twin dendrite found by Billig and the 〈100〉 twin-free dendrite discovered by Devaud and Turnbull, there is a third novel twin dendrite, the 〈110〉 twin dendrite. The twin planes in a 〈110〉 dendrite always appear in multiple numbers and the orientation is {111}. These different kinds of dendrites exist at different initial interfacial undercoolings and the transition temperatures for 〈110〉 to 〈211〉, 〈211〉 to 〈100〉 are †T = 61 and 93°C, respectively.

Liquid Ge drops (diameter 7 mm) have been undercooled 60−342±°C below Tm in dehydrated boron oxide with a cooling rate of 6°C/min. They always crystallized to the diamond cubic phase and the resulting grain size decreased with increasing undercooling. During crystallization, audible sound was emitted whenever the undercoolings were ⪸ 258° C . It was determined that cracks were responsible for sound emission while grain refinement gave rise to cracks. Optical and SEM micrographs showed that for undercoolings ⪸ 200° C , dendrites formed first and they were seeds for the subsequent crystallization. The micrographs also illustrated that grain refinement was due to multiplication of dendrites. During crystallization, the compressive wave (Ge expands on solidification) set up by the rapid dendritic growth recoiled from the liquid germanium-boron oxide interface would be minimized by the surrounding B2O3. It is likely then that dynamic nucleation was not the origin of grain multiplication. The multiplication of grains is therefore attributed to dendritic break-up during solidification. It is further suggested that stress is the origin of dendritic break-up.

When an undercooled specimen crystallizes, its microstructure depends on the initial bulk undercooling, {Delta}T = T{sub m} {minus} T where T{sub m} is its thermodynamic melting temperature. At {Delta}T near but smaller than 200 K, a typical undercooled Ge specimen exhibits an ordered and connected structure, in which the various dendrites are arranged side by side in a very orderly way. Indeed, the entire surface of this specimen is covered with this regular dendritic pattern. Another undercooled specimen with {Delta}T = 206 K, on the other hand, illustrates a small region inside which the grains are more or less randomly oriented. It appears that these grains are fragments of dendrites scattered all over the region where contact had been made with the fused silica rod. Furthermore, the size of the grains near this region is smaller than those further away indicating grain refinement has just occurred in this region. Summing up, it can therefore be concluded that the onset of grain refinement in undercooled Ge lies between {Delta}T = 201 and 206 K which is substantially smaller than the previous value, 230 K. For simplicity, the onset of grain refinement temperature is chosen to be 203 K.