Cellular Precipitation Research Articles

Eutectoid transformations and precipitation in high carbon tool steels

Delta ferrite undergoes some rather complex solid-state transformations during solidification and cooling. These have been investigated in a series of alloyed high carbon steels. Solidification paths have been determined using the quenching during differential thermal analysis method (ODTA). The different phases produced were identified by scanning and transmission electron microscopy and were analysed by electron probe microanalysis. Four different types of transformation were identified: solid state precipitation, cellular precipitation, delta eutectoid transformation and plate formation followed by two further precipitation reactions. The latter transformation results in the development of very hard and complex structures in which four phases are intimately associated. An explanation has been proposed for the mechanism of their formation.

Cellular decomposition in a Cu-25Ni-15Co side-band alloy

The process of decomposition in a Cu-25 mass pct Ni-15 mass pet Co alloy has been investigated by X-ray diffraction, optical and electron microscopy, and hardness measurements. The alloy first decomposedvia spinodal decomposition, followed by a set of complex cellular-like reactions. X-ray diffraction results showed that side bands exist even after the spinodal microstructure has been completely replaced by the cellular-like microstructure. TEM showed that the cellular-like microstructure had a fiber-like appearance with high degree of periodicity. It is this structure which gives rise to the side bands in the X-ray diffraction pattern late in the transformation process. The primary cells engulfed the entire matrix after a short time of aging and were followed by secondary and tertiary cells. During these later reactions the fiber spacing increased and the composition of the phases reached their equilibrium values. This cellular-like transformation is different from the conventional cellular precipitation, and is interpreted as the preferential growth of part of the spinodal microstructure which is near the grain boundary, due to grain boundary migration. We call this type of cellular transformation in the spinodal alloys “cellular decomposition”.

Kinetics of Discontinuous Coarsening of Cellular Precipitate in Fe-Zn Alloys

Kinetics of Discontinuous Coarsening of Cellular Precipitate in Fe-Zn Alloys

Morphology of pseudophakic precipitates on intraocular lenses removed from human patients

Cellular precipitates on the surface of 52 intraocular lenses removed from human patients for various reasons from one week to five years following implantation were studied with cytologic techniques and scanning electron microscopy. A variety of cellular responses were characterized: mononuclear precipitates composed of lymphocytes and macrophages, multinucleated giant cells, and a fibroblastic proliferation. Polymorphonuclear leukocytes were encountered less frequently. Acellular membranous precipitates were also observed. Cellular response was related to clinical history to correlate temporal and possible etiopathogenic factors in the formulation of these precipitates and their possible relationship to implant failure.

Cellular precipitation and discontinuous coarsening of cellular precipitate in an Al-29 at.% Zn alloy

The morphology and growth kinetics of cellular precipitation and discontinuous coarsening of the cellular precipitate in an Al-29 at.% Zn alloy have been investigated at temperatures ranging from 323 to 523 K (50 to 250°C) by light microscopy, electron microscopy and X-ray diffraction. At all aging temperatures the alloy was observed to decompose completely by a cellular precipitation reaction which resulted in a fine lamellar structure of aluminium rich and zinc rich solid solutions. The first cell lamellar structure was then decomposed at all aging temperatures by a second cellular or discontinuous coarsening reaction. The discontinuous coarsening reaction occurred at a much slower rate than the first cellular reaction and resulted in a much coarser lamellar structure. Lattice parameter measurements showed the aluminum rich phase in the cellular precipitate to have a composition far from equilibrium while that in the product of discontinuous coarsening was close to equilibrium. Analysis of the growth kinetics of both the cellular precipitation and the discontinuous coarsening suggested that they were controlled by grain boundary diffusivity.

The high temperature low cycle fatigue behavior of the nickel base alloy IN-617

Fully reversed strain controlled LCF tests were performed on 4.5 mm thick sheet specimens IN-617 at 1033 K and 1144 K in air. The strain-life and cyclic stress-strain data were analyzed parametrically. While the inelastic strain amplitude-life relationships are similar at the two temperatures, the softer cyclic stress-strain relationship observed at 1144 K produces inferior fatigue resistance to that at 1033 K when comparisons are based on stress or total strain amplitude. Transmission electron microscope observations suggest that grain boundary sliding was the primary mechanism of deformation at 1144 K while at 1033 K intragranular slip produced a dense dislocation substructure which was stabilized by fine scale precipitation of M23C6. At 1144 K, grain boundary migration occurred within the specimen interiors, producing a cellular precipitation of M23C6 as well as the intragranular M23C6 observed at 1033 K. Cellular precipitation was not observed in the near surface regions. This is attributed to oxygen penetration along grain boundaries. Comparison of the data with mean stress-HCF data indicates that the mean load significantly reduces fatigue resistance at both temperatures.

Cellular precipitation and overaging in an As-cast PbSnSrAl alloy

The aging behavior of an as-cast lead alloy containing tin, strontium and aluminum has been investigated over the temperature range 298–423 K. After casting, the lead-rich dendritic grains of the alloy age harden to a peak Meyer hardness of 19.5 kgf mm −2 at room temperature (298 K) in about 50 h. Hardening presumably results from the general precipitation of coherent (Pb, Sn) 3Sr. The general precipitate responsible for age hardening the grains appears to be stable at temperatures ranging from 298 to 373 K; however, at these temperatures the grains are gradually decomposed by cellular precipitation into a lamellar structure of depleted solid solution and a precipitate having about half the hardness of the age-hardened grains. This behavior results in the gradual overaging of the alloy and has been observed in other lead-base alloys such as PbSnCa and PbNa. The growth rate and lamellar spacing of the cells have been determined by quantitative metallography and analyzed according to existing thepry. The analysis suggests that the cell growth is controlled by the grain boundary diffusion of strontium in the advancing cell interface. At temperatures above 373 K the alloy overages primarily by the overaging of the general precipitate structure in the dendritic grains although some cellular precipitation is observed.

Cellular precipitation in austenitic stainless steel containing aluminium and titanium

This paper presents a detailed investigation of a complex cellular transformation in an Fe-25Ni-20Cr-2Al-2Ti alloy. Convergent beam electron diffraction and energy dispersive X-ray spectroscopy are used to monitor the reaction, including the precipitation on existing grain boundaries which precedes the cellular transformation. It is shown that growth of this cellular precipitation involves the volume diffusion of solute such that the growth rate decreases with aging time. The consequences of this decrease of reaction rate are discussed with particular reference to the types of cellular transformation product formed.

Cu-Ni-Si合金の粒界反応型析出とそれにおよぼすB, P添加の影響

Cu-Ni-Si合金の粒界反応型析出とそれにおよぼすB, P添加の影響

Effects of Addition of B and P on the Cellular Precipitation in Ni–Sn and Cu–Ni–Sn Alloys

Etude par metallographie quantitative de l'influence d'additions de B et P sur la precipitation cellulaire et intergranulaire dans les alliages Ni-8 et 15% masse Sn et Cu-80% masse Ni-8% masse Sn. Les additions de B et P retardent legerement la precipitation intergranulaire et suppriment la precipitation cellulaire

Mesoscale and Convective Structure of a Hurricane Rainband

Abstract The mesoscale thermodynamic, kinematic, and radar structure of a Hurricane Floyd rainband observed on 7 September 1981 is presented. Data are from 26 aircraft passes through the rainband from 150 to 6400 m. A composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km. In the direction parallel to rainband orientation, radar reveals cellular reflectivity structure on the upwind and central portions of the rainband; the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall. In the radial direction, a decrease of 12 K in θe, is observed across the rainband in the subcloud layer. Convective scale up- and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subc...

A study of a cellular phase transformation in the ternary Ni- Ai- Mo alloy system

Orthorhombic Ni3Mo has been observed as a product of a cellular precipitation reaction occurring at grain boundaries in both Ni-12Al-15Mo and a ternary eutectic Ni-12.8Al-22.2Mo (compositions in at. pct) when heat treated at intermediate temperatures (600 to 850 °C). Convergent beam electron diffraction and energy dispersive X-ray spectroscopy techniques have been employed to characterize the structure and composition of this phase in these alloys. Since this phase is usually heavily faulted, the diffraction symmetries are reduced, causing ambiguities in analysis. Therefore, a binary (nominally) stoichiometric Ni3Mo alloy was produced and heat treated in a manner designed to minimize faulting. Convergent beam patterns obtained from this material exhibited symmetries that identify it as having the mmm point group; further analysis of the diffraction patterns led to the conclusion that the space group is Pmmn. These patterns were then used to aid in the interpretation of those taken from the ternary alloys. Orthorhombic Ni3Mo was also observed within the grains of the ternary eutectic alloy following prolonged aging treatments; the orientation relationship between the Ni3Mo and the fee matrix was determined to be identical with that in the cellularly transformed regions.

Aging behaviour of 18Mn–18Cr high nitrogen austenitic steel for end rings

AbstractThe end windings of electrical generators are held in place by end rings which are heated to over 300°C during the fitting process. A new non-magnetic 18Mn–18Cr–0·6N steel has recently been developed for this application and the possibility of sensitization during service has been investigated. Precipitation of grain boundary nitrides is slow and from observations between 400 and 800°C the extrapolated time at 300°C for 10% of the boundaries of the as-received material to contain precipitates is 105 h. Cellular precipitation occurs at high temperatures but is only detected at 600°C after 32 h. A re-solution treatment for 1 h at 1080°C reduces the subsequent rate of precipitation, whereas prior cold work accelerates precipitation. The precipitates are Cr rich but contain Mn and Fe. Below 700°C only the M23X6 structure forms, but above 700°C (CrMnFe)2N is also observed. Both structures coexist for up to 68 h at 800°C. At temperatures above 550°C the rate of precipitation appears to be governed by Cr...

Ni-Sn, Cu-Ni-Sn合金の粒界反応型析出におよぼすB, P添加の影響

Ni-Sn, Cu-Ni-Sn合金の粒界反応型析出におよぼすB, P添加の影響

Coercivity of precipitation hardened cobalt rare earth 17:2 permanent magnets

The influence of the microstructure on the coercivity has been investigated by means of transmission electron microscopy. It is shown that a thin coherent (CoCu) 5Sm-cell boumdary phase, separating cells of 17:2-crystal structure, acts as a pinning centre for magnetic domain walls. The attractive interaction force is interpreted in terms of a micromagnetic theory for domain wall pinning. The coercive force is determined by the domain wall energy gradient and by the magnetoelastic coupling energy between domain wall stresses and lattice deformation strains. The calculated coercive force due to the lattice mismatch, originated by the cellular coherent precipitation structure, is comparable to the experimentally obtained values.

Phase Transformations and Ageing Phenomena in Copper-Nickel-Manganese Alloys

The pseudo-binary alloy system extending between copper and the intermetallic NiMn was first shown by Dean et al. [1,2] to yield a series of age hardenable alloys. The alloy containing 20% each of Ni and Mn has the best combination of strength and toughness and has been the subject of more recent studies [3,4]. The phase transformation associated with ageing in quenched Cu-NiMn alloys is precipitation of the ordered tetragonal (Llo) phase, (⊖) based on NiMn, from an fcc solid solution. Generally three modes of transformation occur depending on composition and temperature. An intragranular precipitate of fine coherent particles of ⊖, or a cellular or discontinuous precipitation reaction emanating from the grain boundaries, or heterogeneous precipitation of ⊖ at the grain boundaries.

Is discontinuous (cellular) precipitation an effect of a structural transformation in the migrating phase boundary?

The discontinuous precipitation reaction in the CuAg-system was investigated by means of light microscopy, electron microscopy and X-ray diffraction studies. The observations suggest that a discontinuous precipitation reaction can occur only at a pre-existing (static) grain boundary if the structure of the static boundary is converted into a structure of high mobility by a structural transformation.

炭化物，窒化物を析出相とするセル状析出の成長挙動

To study cellular precipitations with carbide or nitride as the precipitate, high chromium-high nickel austenitic steels with 0.4 per cent nitrogen were chosen as a model system. Two austenitic steels with the composition of 25%Cr-28%Ni-0.40%N and 25%Cr-20%Ni-0.41%N were aged at 1073 K and growth characteristics of cellular precipitation of Cr2N were investigated.All the following growth characteristics are quite different from the well known growth characteristics of cellular precipitations in binary substitutional systems. (A) Average migration rate of the free interface between untransformed matrix and cell decreases with reaction time. Cell growth stops even when the large portion of the specimen still remains untransformed with substantial supersaturation. This leads to the result that only a part of the specimen decomposes into cell. The rest remains untransformed even after a prolonged aging. (B) The observed volume fraction of Cr2N precipitates inside the cell is much larger than the calculated one based on the matrix-precipitate equilibrium in the original solid solution. Average nitrogen concentration inside the cell becomes higher than that of the original solid solution. In contrast to this, nitrogen concentration in the untransformed matrix outside the cell decreases with reaction time. (C) The volume fraction of Cr2N precipitates inside the cell decreases with reaction time.These unusual characteristics can be ascribed to the long range diffusion of nitrogen. It is suggested that the redistribution of solutes accompanying the cellular precipitation of Cr2N takes place through grain boundary diffusion of chromium and long range volume diffusion of nitrogen. The present behaviors are expected to be generally observed in any cellular precipitation of carbide or nitride.

The cellular reaction in dilute copper-titanium alloys

A review is made of the various mechanistic models for the initiation of the cellular reaction. Observations of the production of theβ phase in dilute copper-titanium alloys are reported, and it is noted that the Widmanstatten product and small, recently nucleated intermediate cellular plates adhere strictly not only to the (111)α//(010)β [ 110]α //[001]β orientation relationship, but also to the favorable (111)α//(010)β habit plane. The plates in cellular colonies developed at lower transformation temperatures (and thus higher supercoolings) show appreciable deviations from the latter interface plane, though the orientation relationship is still obeyed. Three different initiation mechanisms for cellular precipitate are observed. The ‘pucker’ and the ‘conventional’ routes are found to operate, and in addition a mechanism relying on the preexistence of Widmanstatten plates has been identified. The intermediate level of crystallographic specificity displayed by the coppertitanium system is suggested, therefore, to give rise to a high.probability of cellular precipitation. It is shown that the reaction can proceed under the action of very low driving forces.

Some ordering phenomena in the β Cu4Ti phase

SUMMARYThis paper presents further evidence concerning the structure of the β phase which forms as Widmanstätten or cellular precipitates in dilute copper‐titanium alloys. The effect of deformation in producing faults in this ordered phase is considered, and illustrations are provided of the resultant dislocation structures. The observation of some intrinsic disorder is discussed in terms of the influence of a simultaneous phase transformation on the order‐disorder transition.