Anomalous Growth Behavior Research Articles

Anomalous kinetics, patterns formation in recalescence, and final microstructure of rapidly solidified Al-rich Al-Ni alloys

From thermodynamical consideration, rather a monotonically increasing crystal growth velocity with increasing undercooling is expected in the crystallization of liquids, mixtures, and alloys [P.K. Galenko and D. Jou, Physics Reports 818 (2019) 1]. By contrast to this general theoretical statement, Al-rich Al-Ni alloys show an anomalous solidification behavior: the solid-liquid interface velocity slows down as the undercooling increases [R. Lengsdorf, D. Holland-Moritz, D. M. Herlach, Scripta Materialia 62 (2010) 365]. It is also found that besides the anomalous growth behaviour, changes in the shape of the recalescence front as the growth front morphology occur. In the light of recent measurements in microgravity with an Al-25at.% Ni alloy sample onboard the International Space Station (ISS) results confirming this anomalous behavior as an unexpected trend in solidification kinetics are presented. The measurements show multiple nucleation events forming the growth front, a mechanism that has been observed for the first time in Al-Ni alloys [D. Herlach et al., Physical Review Materials 3 (2019) 073402; M. Reinartz et al. JOM 74 (2022) 2420] and summarized with detailed analysis in the present publication over a wider range of concentrations. Particularly, the experimental measurements and obtained data directly demonstrate that the growth front does thus not consist of dendrite tips (as in usual rapid solidifying samples), but of newly forming nuclei propagating along the sample surface in a coordinated manner. Theoretical analysis on intensive nucleation ahead of crystal growth front is made using the previously developed model [D.V. Alexandrov, Journal of Physics A: Mathematical and Theoretical 50 (2017) 345101]. Using equations of this model, quantitative calculations confirm the interpretation of experimentally observed propagation of the recalescence front and obtained data on the microstructure of droplets solidified in electromagnetic levitation facility (EML) on the Ground, under reduced gravity during parabolic flights, and in microgravity conditions onboard the ISS.

Molecular Passivation of Substrate Step Edges as Origin of Unusual Growth Behavior of 4,4′-Biphenyl Dicarboxylic Acid on Cu(001)

The structure and morphology of organic thin films on solid substrates influence their functional properties. Therefore, knowledge of molecular structure, orientation, diffusion, and involved interactions on particular surfaces is required to gain control over the growth process and prepare layers with the required functionality. However, the resulting morphology is dictated by the delicate interplay of several interactions, which in many cases results in novel and unexpected behavior. Here, we show that strong interaction of 4,4′-biphenyl dicarboxylic acid (BDA) with the step edges on Cu(001) results in the formation of densely packed molecular row, which causes the step edge passivation. The step edge passivation limits the BDA diffusion over the step edges and inhibits the attachment of additional BDA molecules preventing nucleation and growth of molecular islands on the step edges. Our results thus provide fundamental insight into the anomalous growth behavior exhibited by certain organic/inorganic sy...

Molecular-orientation-induced rapid roughening and morphology transition in organic semiconductor thin-film growth.

We study the roughening process and morphology transition of organic semiconductor thin film induced by molecular orientation in the model of molecular semiconductor copper hexadecafluorophthalocyanine (F16CuPc) using both experiment and simulation. The growth behaviour of F16CuPc thin film with the thickness, D, on SiO2 substrate takes on two processes divided by a critical thickness: (1) D ≤ 40 nm, F16CuPc thin films are composed of uniform caterpillar-like crystals. The kinetic roughening is confirmed during this growth, which is successfully analyzed by Kardar-Parisi-Zhang (KPZ) model with scaling exponents α = 0.71 ± 0.12, β = 0.36 ± 0.03, and 1/z = 0.39 ± 0.12; (2) D > 40 nm, nanobelt crystals are formed gradually on the caterpillar-like crystal surface and the film growth shows anomalous growth behaviour. These new growth behaviours with two processes result from the gradual change of molecular orientation and the formation of grain boundaries, which conversely induce new molecular orientation, rapid roughening process, and the formation of nanobelt crystals.

Crystal nucleation and dendrite growth of metastable phases in undercooled melts

An undercooled melt possesses an enhanced free enthalpy that opens up the possibility to crystallize metastable crystalline solids in competition with their stable counterparts. Crystal nucleation selects the crystallographic phase whereas the growth dynamics controls microstructure evolution. We apply containerless processing techniques such as electromagnetic and electrostatic levitation to containerlesss undercool and solidify metallic melts. Owing to the complete avoidance of heterogeneous nucleation on container-walls a large undercooling range becomes accessible with the extra benefit that the freely suspended drop is direct accessible for in situ observation of crystallization far away from equilibrium. Results of investigations of maximum undercoolability on pure zirconium are presented showing the limit of maximum undercoolability set by the onset of homogeneous nucleation. Rapid dendrite growth is measured as a function of undercooling by a high-speed camera and analysed within extended theories of non-equilibrium solidification. In such both supersaturated solid solutions and disordered superlattice structure of intermetallics are formed at high growth velocities. A sharp interface theory of dendrite growth is capable to describe the non-equilibrium solidification phenomena during rapid crystallization of deeply undercooled melts. Eventually, anomalous growth behaviour of Al-rich Al–Ni alloys is presented, which may be caused by forced convection.

Growth Morphology of Perylene-3,4,9,10-tetracarboxylic Dianhydride (PTCDA) Thin Films: Influence of Intermolecular Interactions and Step-Edge Barriers

The growth evolution of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) thin films on glass substrates has been studied using atomic force microscopy measurements and scaling analysis. The results are consistent with an upward mound growth mechanism, with the measured scaling exponents indicating anomalous growth behavior. Simulation of one-dimensional surface lateral diffusion models and calculation of the intermolecular interaction energies indicate that the observed growth mode arises from the preference for deposited molecules to attach at the minimum energy position within the same PTCDA layer rather than in a lower layer, based on the existence of high step-edge barriers. The results highlight the important role played by the microscopic molecular properties in determining the macroscopic thin film morphology.

542 Zr基バルクアモルファス合金の疲労破面における結晶化(OS7-2 微視構造を有する材料の変形と破壊,OS7 微視構造を有する材料の変形と破壊)

The present study has investigated deformation-induced crystallization on fatigue fracture surfaces in a Zr-based bulk amorphous alloy. Fatigue crack growth tests were performed on center-cracked plate specimens of 55at%Zr-10at%Al-5at%Cu-30at%Ni bulk amorphous alloy at room temperature in air. Tension to tension fatigue loads were applied at stress ratios of R=0.05 to 0.3 at a loading frequency of 5Hz. The plastic replication technique was used for observing crack growth behavior. Crack branching, crack deflection and non-propagating branches frequently observed at specimen surfaces of the amorphous alloy. Thus, the crack growth rate vs. stress intensity factor range diagrams in which projected crack length was used fluctuated widely. This anomalous growth behavior of cracks can be attributed to the fact that internal crack surfaces were very rough. Roughness-induced crack closure was observed at stress ratios lower than 0.3. Scanning electron microscopy revealed striation-like patterns in some portions of the rough crack surfaces. Spot X-ray diffraction analysis with a focal diameter of 30 micrometer of crack surfaces were also made and detected localized crystallization in the form of Zr_2Cu. The localized crystallization may have been brought about by severe deformation in the vicinity of crack tips. The striation-like patterns were produced in some portions of crack surfaces so crystallized.

Rapid solidification of highly undercooled Si and Si–Co melts

We present direct experimental observations of growth velocity and morphology in undercooled melts of pure Si and dilute Si100−xCox alloys (x=0.1, 0.5, and 2.5at.%). An anomalous behavior in the growth velocity-undercooling relation of the Si–Co alloys is found, exhibiting an abrupt break at a critical undercooling ΔT* which depends on Co concentration. In contrast to pure Si, the anomalous growth behavior in Si–Co alloys cannot be described by current dendrite growth theory even if nonequilibrium effects at the interface as solute trapping are taken into account. The growth morphology changes essentially with increasing undercooling and Co concentration.

3341 Zrバルクアモルファス合金の疲労き裂進展挙動(S18-5 アモルファス合金,S18 材料の強度と組織)

The present study has investigated fatigue fracture behavior and deformation-induced crystallization in a Zr-based bulk amorphous alloy. Fatigue crack growth tests were performed on center-cracked plate specimens of 55at%Zr-10at%Al-5at%Cu-30at%Ni at room temperature in air. Tension to tension fatigue loads were applied at stress ratios of R=0.05 to 0.3 at a loading frequency of 5Hz. The plastic replication technique was used for observing crack growth behavior. Crack branching, crack deflection and non-propagating branches frequently occurred at specimen surfaces of the amorphous alloy. Thus, the crack growth rate vs. stress intensity factor range diagrams in which projected crack length was used fluctuated widely. This anomalous growth behavior can be attributed to the fact that internal crack surfaces were very rough. Roughness-induced crack closure was observed at stress ratios lower than 0.3. Scanning electron microscopy revealed striation-like patterns in some portions of the rough crack surfaces. Spot X-ray diffraction analysis with a focal diameter of 30 micrometer of crack surfaces were also made and detected localized crystallization in the form of Zr_2Cu. The localized crystallization may have been brought about by severe deformation in the vicinity of crack tips. The striation-like patterns were produced in some portions of crack surfaces so crystallized. Sparks were observed emitted from growing fatigue cracks just before fracture by the high-speed camera.

Anomalous growth behaviour of Pd-Au and Ag-Au alloy particles during vapour deposition on carbon substrates at elevated temperatures

Anomalous growth behaviour of Pd-Au and Ag-Au alloy particles during vapour deposition on carbon substrates at elevated temperatures

Corrosion fatigue of a 2024-T3 aluminum alloy in the short crack domain

It is well accepted that the steady-state fatigue crack growth rates of long cracks depend uniquely on AK for a fixed load ratio R and test environment. Anomalous growth behavior of short cracks in either inert or deleterious environments that has been reported [1-7], however, calls into question the validity of using only long-crack results in evaluating the service life of a structural component and argues for the need for considering the effects of crack size. Crack-size effects have been extensively studied from the perspectives of mechanical, metallurgical and chemical principles. Microstructurally and mechanically short cracks [1-3] are associated with the influences of fine-scale microstructure, the limitation of continuum mechanics (or LEFM-linear elastic fracture mechanics), or crack closure. Chemically short cracks [4-7], on the other hand, normally extend to longer lengths and are attributed to the differences in local crack-tip chemistry (e.g., pH, [Oz], potential) between the long and short cracks and also, perhaps, from the bulk solution. The objective of this study is to explore the effect of crack size in various environments and to identify the key variables that affect crack growth behavior. The crack size investigated herein was chemically short but microstructurally and mechanically long. A 1.6 mm thick 2024-T3 (bare) aluminum alloy was used and its chemical composition (in wt%) is as follows: 4.24 Cu, 1.26 Mg, 0.65 Mn, 0.15 Fe, 0.08 Zn, 0.06 Si, 0.031 Ti, <0.01 Cr and balance A1. The elongation, 0.2% offset yield strength and tensile strength are 17.0%, 355 MPa (51 ksi) and 480 MPa (70 ksi), respectively. The specimens were cut in the L-T orientation as dog-bone shaped, center-pin-loaded, single-edge-cracked specimens with a 31.75 mm wide and 76.2 mm long (final dimension) mid-section. A 1.6 mm long electro-discharge machined (EDM) starter notch was introduced at the center of one edge of each specimen. The specimens were precracked by fatigue in air to a crack length of 3.42 mm (including the notch). Extra material (2.92 mm wide) was included on the notched side, and was removed by EDM to produce the final specimen, with a symmetrical test section and an approximaely 0.5 mm long edge crack. The following K calibration equation was used:

Anomalous growth behaviour of Pd-Au and Ag-Au alloy particles during vapour deposition on carbon substrates at elevated temperatures

The condensation of Pd-Au and Au-Ag alloy particles from vapour beams of the components on amorphous carbon substrates was investigated by TEM, mostly in-situ. At substrate temperatures in the range from 623 to 723 K, condensation was found to be virtually complete for all components, but nucleation densities of pure Pd or Ag were significantly lower than of Au, under similar conditions, while particle growth speeds were high for Pd and Ag, and low for Au. For the case of Au alloys, rich in Pd or Ag, respectively, two sorts of particles were found to grow simultaneously: relatively few crystallites with high growth speed, and many slowly growing particles in between. After interruptions of the vapour beam, the large crystallites exhibited a significant delay of the order of minutes in resuming growth, depending on composition. Electron diffraction analysis as well as observations of some catalytic activity under oxygen revealed that the large species were rich in Pd, whereas most of the gold was contained in the small particles. It is shown that this complex nucleation and growth behaviour can be explained by differences in the interaction of the metals with each other and in combination with peculiar properties of the a-C substrate. These include the existence of at least two binding states for the metal atoms with energies of around 1 eV for “regular” states and in the range from 1.5 to 1.7 eV with abundance of 10 13 to 10 14 cm −2, probably at porosities in the substrate surface, where metal atoms can temporarily be trapped without acting as nucleation centers. In the case of alloy depositions, these “active sites” are initially preferentially occupied by Au atoms, while Pd or Ag adatoms exhibit relatively low binding energies not only to the substrate but also to alloy particles, possibly induced by the presence of the carbon. In particular, the binding energy of Pd seems to be lower on the small particles rich in Au at their surfaces than on the large crystallites rich in Pd. These combined effects would explain selective clustering of Pd adatoms, and the simultaneous growth of small alloy particles. Qualitatively similar results were found for Ag-Au alloys, with Ag behaving like Pd.

Observation of the crystallization of amorphous FeCuSiB alloy by in situ transmission electron microscopy

Observation of the crystallization behavior of an amorphous FeCuSiB alloy by in situ transmission electron microscopy (TEM) is reported. It was found that the crystallization process of FeCuSiB amorphous foil occurred in two separate steps with the formation of α-Fe(Si) and Fe 2B phases respectively. Two nucleation regions were observed for the α-Fe(Si) phase. One is close to the edge of an ion-thinning region, in which the α-Fe(Si) phase nucleates at first; the other is the inner area. No such phenomenon was observed for the Fe 2B phase. At T=813 K, anomalous growth behavior was observed. Both the nucleation and growth of particles depended on the thickness of the foil. TEM results were found to be in good agreement with the results of isothermal differential scanning calorimetry.

Small Fatigue Crack Behavior in 7075-T651 Aluminum as Monitored with Rayleigh Wave Reflection

Small fatigue crack growth in 7075-T651 aluminum is periodically monitored with an ultrasonic Rayleigh wave technique. The wideband reflection signals are digitized and stored in the computer memory to permit the signal processing in the frequency domain. With the help of the constructed three-dimensional (3-D) reflection coefficient, the reflection amplitude spectra yield the measurements of the crack depth, if larger than 0.062 mm, and the crack closure stress. Acoustically obtainedda/dN-ΔK eff relations describe the anomalous growth behavior of small surface crack, extending from the late small crack regime to the large crack regime passing through the minimum growth rate. The split spectrum processing proves to be useful in removing the grain noises to illuminate the target echoes, which is necessary to detect the nucleation and characterize the cracks smaller than 0.1 mm in depth. Discussions on the computer-controlled, automated,in situ monitoring system are provided.

Subcritical Crack Growth Characteristics on Compact Type Specimens and Indentation Cracks in Glass

For the purpose of comparing crack growth characteristics on small indentation cracks with those for long cracks, subcritical crack growth data on soda-lime glass were obtained using the compact type (CT) specimens with long cracks and the indentation cracks. It was found that there is apparently a small crack effect in the as-indented cracks which increases crack growth. However, the annealed indentation crack shows the same trend of crack growth as that for the CT specimens. A residual stress effect can be used to explain this anomalous growth behavior of the as-indented cracks.

Influence of Sputtering and Redeposition on Compound Layer Growth during Plasma Nitriding

Apparently anomalous surface compound layer growth is observed during plasma nitriding, and this has previously been ascribed to the removal of surface material by sputtering. Previous work has produced results which clearly indicated that during plasma nitriding non-uniform sputtering of material occurs on the workpiece and that this gives rise to a net loss of material from high sputtering sites such as edges and corners and to a net redeposition of material on flat faces. In the present work, the γ’–Fe4N compound layers on the flat faces of pure iron workpieces were found to display anomalous growth behaviour, in which the compound layer initially increases and subsequently decreases in thickness. This observation cannot be explained by the removal of layer material by sputtering. The nature of the redeposition of material was examined and it was found that there is a time delay associated with its onset. In addition, examination of the redeposited material by quantitative scanning Auger microprobe depth profiling revealed that oxygen accumulation occurs in the redeposited material. The anomalous growth behaviour of the compound layer can be ascribed to the formation of the redeposited material layer which inhibits further nitriding of the substrate.

A rationale for the “apparent anomalous” growth behavior of short fatigue cracks

The anomalous growth behavior of short fatigue cracks in a Ni-based superalloy is examined. Experimental and analytical work is presented which clearly demonstrates the break-down of linear elastic fracture mechanics (LEFM) in the “so-called” short crack regime. Short crack data only appear anomalous when correlated in terms of the stress intensity factor. When short and long crack data are analyzed in terms of a more valid driving force (e.g. strain energy density criteria), no anomalous short crack behavior is observed.

A mutant of Saccharomyces cerevisiae lacking catabolic NAD-specific glutamate dehydrogenase Growth characteristics of the mutant and regulation of enzyme synthesis in the wild-type strain

NAD-specific glutamate dehydrogenase (GDH-B) was induced in a wild-type strain derived of alpha-sigma 1278b by alpha-amino acids, the nitrogen of which according to known degradative pathways is transferred to 2-oxoglutarate. A recessive mutant (gdhB) devoid of GDH-B activity grew more slowly than the wild type if one of these amino acids was the sole source of nitrogen. Addition of ammonium chloride, glutamine, asparagine or serine to growth media with inducing alpha-amino acids as the main nitrogen source increased the growth rate of the gdhB mutant to the wild-type level and repressed GDH-B synthesis in the wild type. Arginine, urea and allantoin similarly increased the growth rate of the gdhB mutant and repressed GDH-B synthesis in the presence of glutamate, but not in the presence of aspartate, alanine or proline as the main nitrogen source. These observations are consistent with the view that GDH-B in vivo deaminates glutamate. Ammonium ions are required for the biosynthesis of glutamine, asparagine, arginine, histidine and purine and pyrimidine bases. Aspartate and alanine apparently are more potent inducers of GDH-B than glutamate. Anabolic NADP-specific glutamate dehydrogenase (GDH-A) can not fulfil the function of GDH-B in the gdhB mutant. This is concluded from the equal growth rates in glutamate, aspartate and proline media as observed with a gdhB mutant and with a gdhA, gdhB double mutant in which both glutamate dehydrogenases area lacking. The double mutant showed an anomalous growth behaviour, growth rates on several nitrogen sources being unexpectedly low.

CHEMICALLY DEFINED MEDIA FOR CULTIVATION OF LONG-TERM CELL STRAINS FROM FOUR MAMMALIAN SPECIES.

Abstract A number of new cell lines have been grown in chemically defined medium NCTC 109 free of any exogenous protein. The list in this laboratory now includes fibroblast-like and epithelial-like cells, normal and malignant, and in origin from the mouse, hamster, monkey and human. The lines growing in medium NCTC 109 were then tested for their growth in simpler media of the NCTC series: 117, 126, 131, 132 and 133. Medium 117 lacks the six coenzymes and deoxyguanosine, deoxyadenosine, 5-methyl-cytosine, and sodium acetate present in medium 109. Media 126, 131, 132 and 133 lack all of these except sodium acetate; nine vitamins, glutathione, cysteine and sodium glucuronate were also omitted. Medium 131 is identical with medium 126 except that the former contains vitamin B 12 . Media 132 and 133 are identical with medium 126 except that 132 contains inositol and 133 contains both inositol and vitamin B 12 . Two human lines grew readily in media 117 and 126, as did also the monkey kidney cells and some of the mouse cell strains. All mouse cells tested grew in medium 117 except the mouse liver cells. Hela and mouse liver cells showed anomalous growth behavior in media 117, 126, 131 and 132; these two strains are still under test. When mouse cells did not growin media 126 and 131 it was usually because they required inositol. Of all of the cell strains conclusively tested only one strain of mouse cells and the one Chinese hamster strain required vitamin B 12 for continuous growth at least when thymidine and deoxycytidine were included. This report, timely because of the increased significance and more widespread use of various chemically defined media, also describes improvements in quality control and simplified preparation methods for the NCTC series of media. Our experience strongly emphasizes the necessity for high quality in the chemicals and for the meticulous preparation and storage of such media when used without any protein supplements.