Cellular Precipitation Research Articles

Inhibition of cyclic grain boundary migration through cellular precipitation in Pb-5 Pct Sn alloy

Inhibition of cyclic grain boundary migration through cellular precipitation in Pb-5 Pct Sn alloy

Numerical method of non-isothermal curve analysis by means of electrical resistance measurement during cooling

The temperature-dependence of the electrical resistance of Al-Zn 78 wt.% was measured during linear cooling of the samples in the range of eutectoidal decomposition. The resulting resistancevs. temperature curves were analysed by: deriving the temperature-dependence of the volume fractionx(T) of theη precipitate; fitting the theoretical functionx(T)=xh(T)+xc(T) following from numerical integration of the reaction rate equations for the simultaneously occurring homogeneous (H) and cellular (C) precipitation processes.

Influence of time and temperature dependent processes on strain controlled low cycle fatigue behavior of alloy 617

Strain controlled low cycle fatigue tests have been conducted in air to ascertain the influence of strain rate(e = 4 × 10-6'to 4 × 10-3 s-1) and temperature(T = 750/850/950 °C) on LCF behavior of Alloy 617. A strain range of 0.6 pct and a symmetrical triangular wave form were employed for all the tests. Crack initiation and propagation modes were studied. Microstructural changes that occurred during fatigue deformation were evaluated and compared with the results obtained on isothermal aging. Deformation and damage mechanisms which influence the endurance have been identified. A reduction in fatigue life was observed with decreasing e at 850 °C and with increasing temperature at e = 4 × 10-5 s-1. Cyclic stress response varied as a complex function of temperature and strain rate. Fatigue deformation was found to induce cellular precipitation of carbides at 750 and 850 ‡. Dynamic strain aging characterized by serrated flow was observed at 750 °C (e = 4 × 10-5 s-1) and in the tests at higher e at 850 °C. Strengthening of the matrix due to dynamic strain aging of matrix dislocations by precipitation of M23C6 carbides led to fracture of grain boundary carbide films formed at 750 °C, producing brittle intergranular crack propagation. At 850 °C transgranular crack propagation was observed at the higher strain rates e≥4× 10-4 s-1. At 850 and 950 °C even at strain rates of 4 × 10-5 s-1 or lower, life was not governed by intergranular creep rupture damage mechanisms under the symmetrical, continuous cycling conditions employed. Reduction of endurance at lower strain rates is caused by increased inelastic strain and intergranular crack initiation due to oxidation of surface connected grain boundaries.

Discontinuous precipitation and coarsening of lamellar cellular precipitate in Fe-Zn alloys

The initiation of cellular reaction, formation of cells, and their development have been studied in two Fe-Zn alloys containing 20 and 25 wt.% zinc. Optical microscopy was utilized to study the cellular structure developed during aging in the temperature range 400–520°C. Deflection of the grain boundary was observed to be associated with the nucleation of soluterich phase. From the observation of grain boundary migration into puckered configuration and nucleation of new lamellae at such positions of the boundary, it is evident that the cellular phase transformation occurs in this alloy by the pucker mechanism proposed by Tu and Turnbull [1]. Multiplication of the lamellae occurred by nucleation of the new lamellae in the recess of the grain boundary and by branching. Aging for longer periods resulted in a second cellular reaction or discontinuous coarsening, which decomposed the primary lamellar product into a coarse lamellar structure of the same two phases. The secondary cells were observed to nucleate at three different regions; namely, at the original position of the grain boundary, at the impinged region of two primary cells, and at the interface between the migrating cell boundary and original position of the grain boundaries.

Effects of B Additions on the Intragranular and Cellular Precipitations in a Cu–Be Alloy

Etude par des mesures de durete, par microscopie optique et par diffraction de rayons X des effets de l'addition de B (jusqu'a 0,1% en poids) sur les precipitations intergranulaires et cellulaires dans l'alliage Cu-2% poids Be lors d'un vieillissement a 523 et 623 K apres trempe a partir de 1093 K. L'addition de bore supprime la formation des zones de Guinier-Preston et retarde la precipitation de la phase γ'. Les parametres cristallins de la solution solide α augmentent avec l'addition de bore. La formation et la croissance des cellules aux joints de grains sont supprimees par addition de bore jusqu'a 0,05% et favorisees au-dela de cette concentration

Discontinuous Coarsening of the Cellular Precipitates in a Ni-Sn Alloy

Discontinuous Coarsening of the Cellular Precipitates in a Ni-Sn Alloy

The Effect of Thermal Cycling on the Kinetics of Cellular Precipitation in a Cu-In Alloy

The Effect of Thermal Cycling on the Kinetics of Cellular Precipitation in a Cu-In Alloy

Kinetics of cellular dissolution in an AlZn alloy

Dissolution of the lamellar precipitate by cell boundary migration has been studied in an Al-18.9at.% Zn alloy in the temperature range 554–637 K. Microstructural observations have revealed that the process of dissolution in this alloy is cellular mode of transformation in the early stages. The boundary diffusivities were calculated by using the theory of Petermann and Hornbogen modified for cellular dissolution. The diffusivities calculated from the experimental data are four orders of magnitude higher than the volume diffusivities. From the Arrhenius plots, activation energies of 51.5 ± 2 and 47.5 ± kJ mol −1 were obtained from the temperature dependence of diffusivity and mobility respectively. These values are about half the activation energy required for volume diffusion of Zn in Al and compare very well with the activation energy of 60 kJ mol −1 for the cellular precipitation in this alloy system. There exists a range of temperature between 502 and 532 K where the two kinetic processes, cellular precipitation and dissolution, are equally probable. The forward migration of the grain boundary during cellular precipitation is acted upon by the back pull of dissolution and the migrating grain boundary remains motionless.

Kinetics of discontinuous coarsening of cellular precipitate in a Ni-8.5 at.% Sn alloy

The morphology and growth kinetics of the cellular precipitate and discontinuous coarsening of the cellular precipitate have been studied in the temperature range 815–995 K by utilizing optical microscopy and X-ray diffraction. The Ni-Sn alloy was observed to decompose completely by cellular precipitation reaction into a lamellar structure consisting of alternate lamellae of the α and β phases at all aging temperatures. The fine lamellar structure of the primary cells decomposed into a coarse lamellar structure in two stages. In the first stage, the secondary cells with larger interlamellar spacing decomposed the primary cells. In the second stage, the tertiary cells with a much larger inter-lamellar spacing decomposed the secondary cells. The tertiary cells also decomposed the primary cells. The primary cell growth data were analysed by using theories of Petermann and Hornbogen, Turnbull and Cahn. The secondary and tertiary cell growth data were analysed by assuming that these also follow the theory of Petermann and Hornbogen of primary cell growth. From the diffusivity values, it has been concluded that the growth of primary, secondary and tertiary cells occurs by diffusion of tin along the migrating grain boundaries.

Cu-Be合金の時効析出におよぼすB添加の影響

Effects of B addition on the intragranular and cellular precipitations in a Cu-2 mass%Be alloy on aging at 523 and 623 K after quenching from 1093 K were investigated by means of hardness measurements, optical and electron microscopic observations, and X-ray analysis. The results obtained are as follows: The addition of 0.02-0.1 mass%B suppressed the formation of G.P. zones and retarded the precipitation of γ′ phase. The lattice parameter of the α solid solution of the B added alloy increased with the B addition. This result suggests that B exists interstitially in the α solid solution and suppresses the formation of G.P. zones and retards the precipitation of γ′ phase as a result of the strong interaction with vacancies. The formation and growth of grain boundary cells were suppressed by the addition of 0.02-0.05%B, but promoted by the excess addition of B, 0.1%.

Cu-Ni-Feスピノーダル合金におけるセルラー析出

Cu-Ni-Feスピノーダル合金におけるセルラー析出

Analytical Electron Microscope Study of High- and Low-Coercivity SmCo 2:17 Magnets

ABSTRACTSintered, precipitation hardened SmCo 2:17 magnets contain a multiphase microstructure. Our electron microscopic investigations reveal that the size of the rhombic, cellular precipitation structure and the formation of cell interior and cell boundary phases is determined by the nominal composition of the alloy and the postsintering heat treatment conditions and primarily control the intrinsic coercivity of the magnet. Selected area electron diffraction together with high resolution electron microscopy showed a high density of basal stacking faults (microtwinning) of the cell interior phase of low coercivity (iHc < 700 kA/m) magnets with a (c/a)*- ratio of the basic structural unit of > 0.843. High coercivity magnets (iHc>) 1000 kA/m), containing a high density of the platelet phase perpendicular to the c-axis, exhibit cell diameters up to 200 nm with a (c/a)*-ratio of the basic structural unit of the cell interior phase of < 0.843.

Kinetics of cellular dissolution in a CuIn alloy

The dissolution of lamellar precipitates by cell boundary migration has been studied in a Cu-15 wt.% In alloy in the temperature range 778–853 K, primarily by optical microscopy. Microstructural observations indicated that the process of dissolution in this alloy is a cellular mode of transformation. By approximating the tip radius at the α-δ interface as equal to half the width of a δ lamella, the interface composition during dissolution was determined using the Gibbs-Thomson relation. The boundary diffusivities were calculated using the theories of Tu and Turnbull and of Petermann and Hornbogen modified for dissolution and a formulation applying balance of fluxes at the edge of a receding cell boundary similar to the formulation of Aaronson and Liu for the cellular precipitation reaction. The diffusivity values calculated from the experimental data fall within a range of two orders of magnitude for these theories but in all cases are four to five orders of magnitude higher than the volume diffusivity. For this alloy, there exists a critical temperature at which the driving forces for cellular precipitation and dissolution are equal. The value lies approximately 23 K below the equilibrium solvus temperature. An activation energy in the range 148–159 kJ mol −1 for different models has been obtained which agrees well with the Q values reported for cellular precipitation in CuIn alloys.

Discontinuous coarsening of the cellular precipitate in a NiSn alloy

Discontinuous coarsening of the cellular precipitate in a NiSn alloy

Kinetics of Discontinuous Coarsening of Cellular Precipitate in an AI-20 at.% Zn Alloy

Kinetics of Discontinuous Coarsening of Cellular Precipitate in an AI-20 at.% Zn Alloy

Evidence of Long Range Diffusion of Nitrogen in Cellular Precipitation of Cr2N in Cr-Ni Austenitic Steel

Evidence of Long Range Diffusion of Nitrogen in Cellular Precipitation of Cr2N in Cr-Ni Austenitic Steel

Kinetics of discontinuous coarsening of cellular precipitate in a Cu-15 wt% in alloy

The morphology and growth kinetics of the cellular precipitate and discontinuously coarsened cellular precipitate have been studied in the temperature range 573–731 K by utilizing optical and scanning electron microscopy and X-ray diffraction. In order to avoid precipitation of the Widmanstatten precipitate phase, which has a retarding effect on the rate of growth of primary cells, isothermal aging of the alloy was preferred. The Cu-In alloy was observed to decompose completely by cellular precipitation reaction into a lamellar structure consisting of alternate lamellae of the α and δ phases at all aging temperatures. The fine lamellar structure of the primary cells decomposed into a coarse lamellar structure consisting of the same two phases by a discontinuous coarsening or secondary reaction. Lattice parameter measurements indicated that whereas the depleted matrix was richer in solute than the equilibrium solvus during the primary reaction, it was very close to the equilibrium solvus during the secondary reaction. Analysis of the growth kinetics both of the primary and secondary cellular reaction indicated that the transformations are controlled by diffusion through the cell boundaries.

Kinetics of Discontinuous Coarsening of Cellular Precipitate in a Cu-2 at.% Cd Alloy

Kinetics of Discontinuous Coarsening of Cellular Precipitate in a Cu-2 at.% Cd Alloy

Fe基超合金の時効組織と極低温における機械的性質に及ぼす添加元素の影響

A study has been made on effects of C, B, Al, and Mo on cellular precipitation, grain-boundary and intragranular microstructures, and mechanical properties at 4 K of an A286-type iron-base superalloy. Base composition was low C (≤0.005) and Si (≤0.1) Fe-25Ni-15Cr- (2.4 and 3) Ti (mass%), and 0.06C, 0.006B, 1Al, 1-1.5Mo, and 1.4Mo+0.006B were independently added to the alloy in order to explicitly examine the effects of the respective elements.The independent addition of C, B, Mo and Mo+B suppressed the cellular precipitation in the alloy aged at 973 K after solution-treatment at 1373 K for 3.6 ks followed by water quenching. Particularly, C and Mo completely retarded the precipitation for times up to 720 ks. Aluminum, however, showed no retarding effects on the cellular reaction.Microstructural observations and fractographs revealed that there were three metallurgical factors which degraded the low temperature ductility (reduction of area and total elongation in tensile tests) and toughness (Charpy absorbed energy) of the nearly peak-aged alloy: (a) Cellular precipitates, (b) grain-boundary precipitates such as TiC and Fe2B which are responsible for intergranular fracture, and (c) coarse intragranular precipitates which consist mainly of TiC and act as nucreation sites for intragranular voids or cracks. The C addition can only suppress (a), but introduces (b) and (c). The B bearing alloys of which ductility and toughness are higher than those of the C bearing alloys are free from (a) and (c), but not from (b). The Mo addition to low C alloys eliminates these three factors, which results in marked enhancement in ductility and toughness at 4 K.

Precipitation in a liquid phase sintered WNiFe alloy

The precipitate phases formed within samples of a W-5 wt% Ni-5 wt% Fe alloy following sintering and controlled, post-sintering heat treatments have been characterized using techniques of transmission electron microscopy. Interphase boundary precipitation of a complex eta carbide has been confirmed in an as-sintered, commercial alloy of high impurity carbon content, and reproduced on a reduced scale in an experimental alloy of reduced carbon content by isothermal ageing (10 h, 900–950°C of solution treated (1 h, 1350°C) and quenched specimens. The experimental alloy contained no evidence of third phase precipitation in the as-sintered condition, but fine particles were noted along tungsten grain boundaries in solution treated and quenched specimens and were found to have a structure similar to that of the matrix γ phase. Isothermal ageing of solution treated specimens at temperatures of 750–850°C produced local colonies of cellular precipitation within the matrix phase, the discontinuous phase of essentially pure tungsten arising in response to a retained supersaturation of tungsten in matrix solid solution in the quenched material. A competitive precipitation of the eta carbide, (Ni, Fe) 6W 6C, was observed in the matrix phase under similar heat treatment conditions, with the most common form of the precipitate being Widmanstätten laths of (111) 7 habit plane. The present study produced no evidence for the formation of an intermetallic phase in the WNiFe alloy containing a weight ratio of Ni:Fe of 1:1.