Needle-like Phase Research Articles

Investigation of interfacial interaction between uncoated and coated carbon fibres and the magnesium alloy AZ91.

Unidirectionally reinforced metal-matrix composites with a fibre volume content between 63 and 68% were processed by squeeze casting using T800 H carbon fibres and the magnesium alloy AZ91. The surface of the fibres was prepared by thermal desizing of the fibres or by deposition of a pyrolytic carbon (pyC) coating. Different interfacial conditions could be identified by transmission electron microscopy (TEM) and the single-fibre push-in test. TEM confirmed the formation of needle-like phases at the fibre surface or, for coated fibres, within the pyrolytic carbon coating. During loading by the Vickers type indenter an intense response was observed for composites of coated fibres and the magnesium alloy. This could by caused by stick-slip effects within the pyrolytic carbon coating.

Study of precipitates due to the addition of silicon in yttrium modified Ni–Al–Mo–B alloy IC6

The effect of adding 0.10–0.30 wt% Si on the microstructure of the yttrium modified alloy IC6 was examined by scanning electron microscopy (SEM). The chemical compositions of phases precipitated due to the presence of silicon were analyzed by the energy dispersive spectrum (EDS) technique of electron probe micro-analyser (EPMA). The crystal structures of precipitates were studied by transmission electron microscopy (TEM). The results show that two blocky-shaped phases, Mo 1.24Ni 0.76 and Mo 6(Ni 0.75Si 0.25) 7 are formed in the interdendritic area in the alloy with the addition of 0.10–0.20 wt% Si and 0.12 wt% Y, and that a needle-like phase named Y–NiMo precipitates in the interdendritic area in the alloy with addition of 0.30 wt% silicon and 0.12 wt% yttrium besides the formation of the blocky-shaped phases mentioned above.

Untersuchungen zum Gefügezustand von Verbunden aus Kohlenstofffasern (T 800H) und der Magnesiumlegierung AZ91 / Investigations into the Microstructures of Carbon Fibre (T 800H)/ Magnesium Alloy (AZ91) Composites

Composites of T 800H carbon fibres and the Magnesium alloy AZ91 were produced by Squeeze Casting. As a result of this method of casting and the presence of the carbon fibres, segregation of the Magnesium alloy occurs whereby an intermetallic zone of Mg 17 AL 12 is precipitated around the carbon fibres. Electron beam microscopic investigations confirm the formation of needle-like phases of different morphology at the fibre-matrix interface, which differ from one another in their geometry and orientation. Needle-like phases with a length to diameter ratio UD of between 4 and 6 are found orientated parallel to the surface of the T 800H fibres, whilst needles with an UD ratio of between 20 and 25 are found positioned at angles between 45 and 135° to the fibre surface.

Effects of gravity on the microstructure of Zr41Ti14-Cu12.5Ni10Be22.5 bulk glass forming alloy

The ZrTiCuNiBe alloy is melt and solidified by Bridgman unidirectional solidification on two gravity field orientations (the gravity field orientation is parallel and opposite to solidification direction). Effects of gravity on morphology and microstructure are investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). When gravity field orientation is parallel to solidification direction, less needle-like primary phase is embedded in a matrix eutectic; when gravity field orientation is opposite to solidification direction, a large amount of coarser needle-like primary phases were observed.

Magnetic analysis of Pr 80Fe 15(B 1− xC x) 5 alloys (0.85⩽ x⩽1.00)

A magnetic study of Pr 80Fe 15(B 1− x C x ) 5 alloys with low B-content (0.85⩽ x⩽1.00) in the as-cast state and annealed at 600°C has been performed. In as-cast samples, a metastable eutectic phase A 1 is present in all samples. For x=1.00 in as-cast state, coarse and quite corrosive carbides are also present. With thermal treatment at 600°C for 2 h, these phases disappear and a hard needle-like magnetic phase, known as D 1, with T C=224°C and I H C=2.4 kOe at room temperature, is the only phase observed. The coercivity of the annealed Pr 80Fe 15C 5 alloy strongly increases with decreasing temperature ( I H C=44.6 kOe at 4.2 K), confirming the high magnetocrystalline anisotropy of D 1. A comparison of the χ AC(T) curves for Pr 80Fe 15X 5, X=B, C, indicates that D 1 is different from the ternary carbide RE 2Fe 14C.

Structure characterization of a laser-processed Al–Mo alloy

The surface structure of a laser-processed Al–Mo alloy has been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractory (XRD). The alloy was prepared by first laser alloying a mixture of Al and Mo powders into an Al substrate and then laser remelting the alloyed surface. Following the first laser alloying process, the needle-like equilibrium phases (Al5Mo(h) and Al5Mo(r)) are formed with a broad size ranges and distribute inhomogeneously in the α-Al solid solution matrix. This coarse structure is replaced by a finer, uniform dispersion of dendrites after the subsequent laser remelting. Four basic types of solid states precipitates are observed: (1) irregularly shaped particles constructing the dendrites and having a nearly Al5Mo stoichiometry; (2) needle-like particles which is the Al5Mo (r) phase; (3) Faceted particles having a cubic structure with a stoichiometry close to Al7Mo; (4) tiny, equi-axed particles, with a rather narrow particle size distribution and a cubic structure. © 1998 Chapman & Hall

Aqueous Pb sorption by hydroxylapatite; applications of atomic force microscopy to dissolution, nucleation, and growth studies

Other| February 01, 1998 Aqueous Pb sorption by hydroxylapatite; applications of atomic force microscopy to dissolution, nucleation, and growth studies Steven K. Lower; Steven K. Lower Kent State University, Department of Geology, Kent, OH, United States Search for other works by this author on: GSW Google Scholar Patricia A. Maurice; Patricia A. Maurice Search for other works by this author on: GSW Google Scholar Samuel J. Traina; Samuel J. Traina Search for other works by this author on: GSW Google Scholar Ernest H. Carlson Ernest H. Carlson Search for other works by this author on: GSW Google Scholar Author and Article Information Steven K. Lower Kent State University, Department of Geology, Kent, OH, United States Patricia A. Maurice Samuel J. Traina Ernest H. Carlson Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online Issn: 1945-3027 Print Issn: 0003-004X GeoRef, Copyright 2004, American Geological Institute. American Mineralogist (1998) 83 (1-2): 147–158. https://doi.org/10.2138/am-1998-1-215 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Steven K. Lower, Patricia A. Maurice, Samuel J. Traina, Ernest H. Carlson; Aqueous Pb sorption by hydroxylapatite; applications of atomic force microscopy to dissolution, nucleation, and growth studies. American Mineralogist 1998;; 83 (1-2): 147–158. doi: https://doi.org/10.2138/am-1998-1-215 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract A combination of atomic force microscopy, scanning election microscopy, transmission electron microscopy, energy dispersive spectroscopy, electron diffraction, and X-ray diffraction were used to study reactions of 0.5-500 mg/L aqueous Pb with Ca 5 (PO 4 ) 3 OH, hydroxylapatite (HAP), at pH 6 and 22 degrees C. Following 2 h reaction time, concentrations of Pb aq ([Pb aq ]) decreased from 500 mg/L to <100 mg/L, and from 0.5-100 mg/L to <15 mu g/L. This loss of Pb aq from solution (i.e., sorption) resulted partially from simultaneous dissolution of HAP and precipitation of Pb 5 (PO 4 ) 3 OH, hydroxypyromorphite (HPY), or another solid Pb phase. The initial saturation state with respect to HPY (defined as the ratio of the ion activity product to equilibrium solubility product) influenced strongly precipitation processes. At a high degree of saturation (initial [Pb aq ]>100 mg/L), small nuclei or aggregates of poorly crystalline HPY precipitated homogeneously in solution. At intermediate saturation (initial [Pb aq ] approximately 10-100 mg/L), large, euhedral needles of HPY precipitated homogeneously in solution. At a low degree of saturation (initial [Pb aq ]<10 mg/L), a needle-like Pb-containing phase grew heterogeneously on HAP. These results agree well with concepts derived from nucleation and growth theories and demonstrate that initial saturation state influences strongly the sorption process. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Metastable and stable magnetic phases in as-cast and annealed Pr 80Fe 15(B 1− xC x) 5 alloys (0.0≤ x≤1.0)

In as-cast Pr 80Fe 15(B 1− x C x ) 5, samples metastable A 1 ( T c=225 °C) was the predominant magnetic phase in the whole composition range, with intrinsic properties that were not affected with increasing C content. Up to x=0.75 this phase coexists with an additional minor magnetic phase having T c=263 °C which has been labelled by us to as A 3. Upon annealing at 600 °C A 1 dissolves and the following stable phases were observed: a) Pr 2Fe 14B and A 3 for 0.0≤ x≤0.75, and; b) an unknown stable phase D 1 with coercivity around 2.1 kOe and Curie temperature of 230 °C for x=1.0. D 1 is the predominant phase for annealing times less than 8 h while for 8 and 16 h annealing an additional phase with T c=17 °C appears. The latter has been tentatively identified as Pr 2Fe 17. SEM and X-ray microanalysis studies were performed on Pr 80Fe 15C 5 samples in the as-cast state and after 16 h of annealing. The as-cast sample shows large Pr-rich grains immersed in a fine eutectic microstructure consisting of Pr and Fe. In annealed samples, both large square or polygonal grains and a needle-like phase are formed. The latter is believed to be D 1.

Microstructure study of a γ-TiAl based alloy containing W and Si

The phase transformations and modulated microstructures in the cast alloy Ti-47Al-2W-0.5Si(at.%) have been studied. It has been shown that microstructure is sensitive to heat treatment and composition. The structure in the alloy heat treated at 1300 degrees C mainly consists of coarse lamellar, fine lamellar, equiaxed gamma grains and beta phase. Homogenizing treatment at 1400 degrees C results in nearly fully-lamellar structure which shows colony-boundary gamma phase grains. The observations showed that small increases in W content result in changes in the amount and morphology of beta phase. For the alloy containing 2.1 at.% W, the beta phase has been observed in three types of morphology: blocky beta phase containing gamma needles and fine silicide particles inside; rod-like beta phase and fine needle-like beta phase. For the alloy variant containing 1.5 at.% W, only a very small amount of rod-like beta phase appeared. Different mechanisms are proposed to explain the occurrence of three types of beta phase, in that W may stabilize it by extending the primary beta phase to lower temperature as well as by yielding new phase zones. A few primary silicide particles have been found in the interdendrite region in the alloys containing more than 0.5 at.% Si, while coherent secondary silicides generally nucleated at the interfaces. (C) 1997 Elsevier Science S.A.

The Crystallization of Fluorapatite in the Presence of Hydroxyapatite Seeds and of Hydroxyapatite in the Presence of Fluorapatite Seeds

The kinetics of growth of crystals induced by hydroxyapatite (HAP) seed crystals in supersaturated solutions of fluorapatite and of fluorapatite (FAP) seed crystals in supersaturated solutions of hydroxyapatite have been studied using the constant composition method. The reactions were investigated at relative supersaturations ranging from σFAP= 0.99 to 12.0 at pH 6.5 and for HAP, σHAP= 3.6 to 12.6 at pH 7.4. In FAP-supersaturated solutions, this phase was nucleated at the HAP surfaces and underwent growth at a rate more than three times greater than that on FAP seed crystals of equivalent surface area. Transmission electron microscopy (TEM) and electron diffraction imaging clearly demonstrated that the new needle-like HAP phase originated at the FAP surface with the 002 planes of HAP growing on FAP. In contrast, the mutual orientation of FAP crystallization on HAP seed crystals could not be established. Interfacial energies of FAP, HAP, and octacalcium phosphate (OCP) microcrystals against aqueous solutions were obtained by using a thin-layer wicking technique. The interfacial energy values measured in pure aqueous solutions were 18.5, 9.0, and 4.3 mJ m−2for FAP, HAP, and OCP, respectively. The much smaller value for OCP as compared with the other phases may explain why this phase has been so frequently implicated as a possible precursor to the formation of apatite, especially in biological mineralization reactions.

Effect of copper addition on the β-phase formation rate in FeSi2 thermoelectric materials

The transformation kinetics of the β-phase from an as-solidified structure composed of α and e in the Fe–Si system was investigated by using rapidly, unidirectionally or conventionally solidified FeSi2 alloys containing a small amount of Cu (0.1–1 at%). The addition of Cu decreased the size of primary e and slightly changed the solidified eutectic morphology. The solubility of Cu in the α-Fe2Si5 phase was estimated to be less than 0.2 at%. A needle-like Cu enriched phase was newly formed in the conventionally solidified alloys containing more than 0.2 at % Cu. Microdifferential thermal analysis (DTA) clearly showed that the addition of Cu drastically accelerated β-phase formation. X-ray diffraction analysis and microstructural observation of the isothermally heat-treated specimens showed that Cu addition was effective in increasing the rate of eutectoid decomposition (α → β + Si) and the initial stage of the peritectoid reaction (α + e → β). For complete β formation, heat treatment for a long time was still required because it took a long time for the coarse e-phase in the slowly solidified alloy to be eliminated by peritectoid reaction. The effect of Cu depended on the annealing temperature. The decomposition rate of α in the Cu-added cast specimen was about 15 times higher at 1073 K than that of the binary cast specimen and exceeded more than 30 times at 873 K.

Effect of Fe and/or Cu contents on the intrinsic coercivity of Sm2Co17-type coercive powders for the bonded magnet application

The microstructure of conventionally cast Sm(CobalFe0.28CuvZr0.022)8.0 alloys, where v=0.043–0.092, were examined by optical microscopy and scanning electron microscope with energy dispersed analytical x ray in the as-cast state. In addition to the regular 2:17 matrix phase, the Sm-rich grain boundary phase and the needle-like Zr-rich phases are present in most commercial Sm(Co,Fe,Cu,Zr)z alloys. A grayish Sm- and Cu-rich grain boundary phase was found in alloys with v≥0.07. Attention was focused on the impact of increasing Cu content to the microstructure and process parameters required to produce coercive powder for bonded magnets. An increase of the Cu content from the v value from 0.043 to 0.092 shifts the liquid+2:17→TbCu7-type transformation temperature from slightly above 1180 to approximately 1140 °C. The Hci of optimally prepared magnet was found to increase significantly while the Br remained relative constant when the Cu content is increased. When the Cu content was increased to beyond v=0.07, a slight decrease in the BHmax was noticed. A magnetizing field of 15 kOe and more than 50 kOe were determined to be necessary to charge magnets with a Hci of 12 and 25 kOe, respectively, to about 90% of their full potential. For a composition of Sm(CobalFeuCu0.07Zr0.022)8.0, a slight increase in Fe concentration from u=0.22 to 0.28 was found to increase the Br of an optimally prepared magnet from 8.07 to 8.28 kG and decrease the Hci from 11.8 to 9.7 kOe. A BHmax of 15 MGOe was obtained on a bonded magnet with a composition of Sm(CobalFe0.28Cu0.07Zr0.022)8.0 when the data are normalized to a specific density of 7.0 g/cm3.

Casting and HIPping of Al-based metal matrix composites (MMCs)

The commercially available Al (trade mark A-356 Al) alloy, with approximately 7 wt% Si, 0.4 wt%Mg and other small amount of elements, is the most common type of Al foundry alloy due to its excellent castability. The needle-like Si phase embedded in the Al matrix is the most typical structural feature of this alloy system and the morphology of the Si phase has been shown to be important in determining the mechanical properties of this alloy. Much work has been done to modify the Si phase morphology by heat treatment or addition of grain refiners such as Sodium and Strontium. The present work describes the microstructural changes by the addition of alumina particles into molten Al, focusing on the effect of the alumina particle on the location, amount and morphology of the Si or eutectic phase in the matrix. Since the alumina particles are not wettable by molten Al, small amount of reactive agent such as Li was added to the Al. Reasonable alumina particle distribution within the matrix Al was achieved by low temperature mixing and gravity casting technique under open atmosphere. The cast MMC bars were processed by Hot Isostatic Pressing (HIPping) in order to densify the MMCs. The cast and HIPped MMCs were examined and mechanically tested. Results show that the 0.2% Yield Strength was improved over the unreinforced Al alloy.

The microstructures and magnetic properties of some cast and annealed PrFeCuB alloys

This paper reports the results of investigations of the microstructures and magnetic properties of some cast and annealed PrFeCuB alloys represented by the formulae, Pr x Fe 94.3− x Cu 2.0B 3.7, Pr 20.5Fe 75.8− x Cu x B 3.7 and P i 20.5 Fe 77.5− x Cu 2.0B x . Microstructural examination of these alloys showed that most of them exhibited Pr 2Fe 14B plate-like grains with the c-axis perpendicular to the plate surface and there was c-axis alignment in the plane perpendicular to the predominant cooling direction. Scanning electron microscopy examination of the alloys showed that the copper was concentrated in the inter-crystalline regions and only trace quantities (<0.4at.%) of copper were detected in the Pr 2Fe 14B phase. A eutectic mixture and a needle-like phase were observed in the inter-crystalline regions. The permanent magnet properties of the alloys, subject to various casting conditions and heat treatments, were investigated and enhanced properties were observed perpendicular to the predominant cooling direction. The largest (BH) max value (70 kJ m −3) was achieved for the Pr 20.5Fe 73.8Cu 2.0B 3.7 alloy after annealing at 1000 °C for 5 h to remove the free iron. An improvement in the intrinsic coercivity of 73% was observed for this alloy on annealing for 3 h at 500 °C. Attempts have been made to correlate the permanent magnetic properties of the alloys with their corresponding microstructures.

Study on the formation mechanism of superconducting phases during annealing of sputtered BiSrCaCuO thin films

In order to understand the formation mechanism of the superconducting phases, amorphous BiSrCaCuO films prepared by RF magnetron sputtering were rapidly cooled after various annealing processes. The 2201 phase began to grow at 600°C and the 2212 phase with c-axis orientation was grown up to 870°C. Two kinds of needle-like secondary phases which were rich in Ca and Cu were also observed from 870°C, along with a partial melting in the matrix. After holding at 880°C and 890°C for 6 h, the matrix was mostly liquefied and transformed to the 2201 phase after rapid cooling. However, when slowly cooled at 1°C/min, the 2212 phase with the c-axis orientation was obtained. On the other hand, when slowly cooled after holding at 870°C for 6 h, the remaining 2212 phase and the co-existing liquid phase within the matrix could also produce the 2223 phase.

Long-period stacking-fault structure of the needle-like phase in a duplex FeMnAlC alloy

The purpose of this investigation was to study the crystal structure of the needle-like phase which appears in b.c.c. regions of water-quenched Fe-27.3 wt% Mn-6.7 wt% Al-0.22 wt% C alloy. The morphology, crystal structure, transformation mechanism and microstructure of the needle-like phase have been studied by transmission electron microscopy and electron diffraction. A structure change from the b.c.c. (matrix) to the 18R (5 l ) 3 needle-like phase is proposed to occur by shearing in the <110 > b.c.c. directions of the {110} b.c.c. planes in a five-to-one sequence repeated three times. Since we find a close relationship between the {110} b.c.c. and {111} f.c.c., we can utilize an existing description of 18R (5 l ) 3 as a stacking sequence of ABCABC −BCABCA −CABCAB −A in terms of {111} f.c.c. planes.

Phase transformation in a duplex FeMnAlC alloy

Precipitates with various shapes and crystal structures produced during cooling an Fe-27.3wt.%Mn-6.8wt.%Al-0.22wt.%C alloy at various rates from 1300°C were investigated by light microscopy, scanning electron microscopy, transmission electron microscopy, and electron diffraction. Morphological, microstructural, and crystallographic information is presented for each precipitate type. Based on precipitate shape and location, the γ phase developed can be classified into the following types: (1) needle-like phase (18R(5 1 ) 3), (2) grain-boundary allotriomorphs (f.c.c.), (3) Widmanstätten sideplates (f.c.c.) and (4) intragranular phase (f.c.c.). Electron diffraction studies verify that the f.c.c. (γ) phase precipitates from the b.c.c. matrix in Femnal alloys. A Kurdjumov-Sachs orientation relationship holds between the b.c.c. matrix and the precipitates, i.e. the needles, Widmanstätten sideplates, and intragranular phase.

Metastable Alumina Structures in Melt‐Extracted Alumina–25 wt% Zirconia and Alumina–42 wt% Zirconia Ceramics

Microstructures are examined of rapidly solidified hypoeutectic Al2O3–25 wt% ZrO2 and eutectic Al2O3–42 wt% ZrO2 ceramic alloys by using transmission electron microscopy and scanning transmission electron microscopy. Structures observed in the hypoeutectic alloy were dendritic. Three different types of dendrite morphologies were observed. These are believed to be the stable α‐ and metastable γ‐ and δ‐ modifications of alumina. The cores of the γ‐alumina dendrites were somewhat richer in ZrO2 than those of α‐alumina dendrites; δ‐alumina dendrites were substantially enriched in ZrO2. The lamellar structure of the eutectic in the Al2O3–42 wt% ZrO2 alloy became increasingly finer with increasing cooling rate and at the highest cooling rates was replaced by a fully amorphous structure (except in some instances a ZrO2‐rich needlelike phase identifiable as δ‐alumina was found in the amorphous matrix). An interpretation is given of the results obtained, based on assumed metastable free energy curves and dendrite growth theory.

Carbon-induced nucleation (CIN) mechanism of the needle-like phase in duplex Fe-Mn-Al-C alloys

Carbon-induced nucleation (CIN) mechanism of the needle-like phase in duplex Fe-Mn-Al-C alloys

Orientation relationship of the needle-like phase in a duplex Fe/1bMn/1bAl/1bC alloy

Orientation relationship of the needle-like phase in a duplex Fe/1bMn/1bAl/1bC alloy