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 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.     

High temperature grain growth during slab reheating of oriented 3 pct Si-Fe made using continuous casting

Studies were made into the process behind the excessive grain growth which is observed in continuous cast slabs of both regular and high permeability oriented 3 Pct Si-Fe during reheating from 1230 °C to 1400 °C. These large grains are undesirable because of the greater difficulty incurred in obtaining the suitably uniform and fine primary grain size desired prior to the final high temperature anneal during which the (110) [001] texture is developed. It was found that the driving force for the growth is the subgrain structure which develops due to the strains of solidification and cooling during continuous casting; however, the temperature at which growth initiates is related to the austenite-ferrite phase relationship. The grain growth begins when the austenite which forms during slab reheating decomposes to form highly perfect ferrite which then grows by consuming the strained preexisting (as-cast) ferrite matrix. Data summarizing studies into the energy storage and recrystallization processes which occur with the use of slab breakdown (or prerolling) prior to reheating from 1230° to 1400 °C are also discussed. This paper is based on a presentation made at the symposium “Physical Metallurgy of Electrical Steels” held at the 1985 annual AIME meeting in New York on February 24–28, 1985, under the auspices of the TMS Ferrous Metallurgy Committee.     

3%取向硅钢中MnS沉淀析出动力学的计算

利用第二相相关理论计算分析薄板坯连铸连轧3%取向硅钢中MnS沉淀析出的动力学行为。沉淀析出计算结果显示在薄板坯连铸连轧生产工艺中以铁素体位错线上形核为主导,MnS在铁素体中的析出量最大,其有效沉淀温度范围约为700~900℃,临界形核尺寸约为0.7~1.5 nm;相变完成时MnS颗粒的半径约为30 nm,可以起到抑制剂的作用。终轧温度应在800℃以上。     

Breakdown of primary grain boundary inhibition in 3 pct si-fe sheet

Grain boundary inhibition in 11-mil cold rolled decarburized 3 pct Si-Fe sheet was observed to break down by isothermal annealing at temperatures in excess of 1075°C. Small MnS particles (-r < ~260Å) responsible for inhibiting primary grain growth in this material were observed to undergo complete dissolution within 3 min at temperatures of 1100°C and higher. Calculated dissolution rates were in good agreement with this observation. The dissolution of these particles produced appreciable primary grain growth during the early stages of (110)[00l] secondary recrystallization which was responsible for an overall reduction in the volume percent of (H0)[00l] grains produced on prolonged isothermal annealing at temperatures above 1075°C.     

Effect of uniaxial stress on coarsening of precipitate clusters

The influence of moderate applied uniaxial stresses (σ_app/C ₄₄ ≈ 10⁻³) on the coarsening behavior of misfitting coherent precipitates in binary alloys has been studied. Three-dimensional (3-D) computer simulations of the coarsening have been performed for elastically homogeneous systems with tetragonal misfit strain and elastically heterogeneous systems with dilatational misfit strain. Precipitate shapes are restricted to spheres. Results depend on the sign of the misfit strain, the sign of the applied field, and the character of the elastic heterogeneity: precipitates softer than the matrix phase with positive (negative) misfit strain align along the direction of the applied stress for compressive (tensile) fields and arrange in planes perpendicular to it for tensile (compressive) fields. Precipitates harder than the matrix behave in the opposite way. This article is based on representation made during TMS/ASM Materials Week in the symposium entitled “ldAtomistic Mechanisms of Nucleation and Growth in Solids,” organized in honor of H.I. Aaronson’s 70th Anniversary and given October 3–5, 1994, in Rosemont, Illinois.     

Observation of cold-rolling texture and partially recrystallized texture in polycrystalline 3 pct Si-Fe by high-resolution electron backscattered diffraction

Cold-rolling texture and partially recrystallized texture of polycrystalline 3 pct Si-Fe were investigated using high-resolution electron backscattered diffraction (EBSD) method. From the measurement on a deformed grain with {211}〈011〉∼{111}〈011〉 orientations, deformation bands with {12 4 1}〈014〉 orientation were found. It turned out that the orientation rotation relationship between deformation bands and surrounding deformed grain can be explained by the activation of the slip system, which has a common slip plane with an adjacent grain. Oriented nucleation of recrystallized grains with {12 4 1}〈014〉 orientation was observed in a deformed grain with {211}〈011〉∼{111}〈011〉 orientation. Exactly the same orientation relationship that was observed between deformed grain and the deformation bands was also observed between the deformed grain and the recrystallized grain. A hypothesis that recrystallization nuclei are generated directly from the deformation bands formed by an activation of the slip system that has a common slip plane of neighboring deformed grains was proposed from the present experimental results.     

Annealing atmosphere,magnetic induction,and the number of {110} grains in inhibitor-free 3 pct Si-Fe alloys

Under flowing hydrogen of a lower flow rate or a vacuum, a high magnetic induction, which arises from the decrease in the number of {110}〈uvw〉_≠〈001〉 grains, was obtained from annealed strips. This is due to the surface segregation profile of sulfur that is broadened to the longer annealing time range.     

Kinetics Simulation of MnS Precipitation in Electrical Steel

In this work, the solid‐state precipitation kinetics of manganese sulfides (MnS) particles in ferrite during continuous deformation of electrical steel is investigated. Thermokinetic simulations are carried out on basis of the software package MatCalc. The results are compared with independent experimental results from literature. The mean radius evolution of second phase MnS precipitates is numerically simulated as a function of the heat treatment parameters time and temperature. The calculated results show good agreement with the experimental measurements using a single set of simulation input parameters.     

Crystallography and interphase boundary of (MnS+VC) complex precipitate in austenite

Crystallography and interphase boundary of (MnS+VC) complex precipitates formed in austenite (γ) matrix are studied by transmission electron microscopy (TEM) in an austenitic Fe-36 mass pct Ni alloy containing small amounts of manganese, sulfur, vanadium, and carbon. When VC is formed directly within the γ matrix grain, it displays a cube-cube orientation relationship (OR) with respect to γ. When VC is formed on MnS, which precipitated in γ with a cube-on-edge OR, three distinctive VC/γ ORs are found: (1) (111)_γ‖(001)_VC, , (2) the cube-cube OR, and (3) the cube-on-edge OR. The MnS/γ OR becomes irrational after γ recrystallization. When VC forms on such incoherent MnS particles, which hold irrational ORs with respect to γ matrix, a wide variety of VC/γ ORs are observed. Geometrical analysis by near coincidence site lattice (NCS) model achieves reasonable success in explanation of the observed planar facets for VC precipitates having rational ORs with respect to γ. However, as for the VC formed on the incoherent MnS with irrational ORs, there is rather poor agreement between observation and prediction. T. KIMORI, formerly Graduate Student, Department of Materials Science and Engineering, Kyoto University This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committeee.     

Crystallography and interphase boundary of (MnS + VC) complex precipitate in austenite

Crystallography and interphase boundary of (MnS + VC) complex precipitates formed in austenite (γ) matrix are studied by transmission electron microscopy (TEM) in an austenitic Fe-36 mass pct Ni alloy containing small amounts of manganese, sulfur, vanadium, and carbon. When VC is formed directly within the γ matrix grain, it displays a cube-cube orientation relationship (OR) with respect to γ. When VC is formed on MnS, which precipitated in γ with a cube-on-edge OR, three distinctive VC/γ ORs are found: (1) , (2) the cube-cube OR, and (3) the cube-on-edge OR. The MnS/γ OR becomes irrational after γ recrystallization. When VC forms on such incoherent MnS particles, which hold irrational ORs with respect to γ matrix, a wide variety of VC/γ ORs are observed. Geometrical analysis by near coincidence site lattice (NCS) model achieves reasonable success in explanation of the observed planar facets for VC precipitates having rational ORs with respect to γ. However, as for the VC formed on the incoherent MnS with irrational ORs, there is rather poor agreement between observation and prediction. This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee.     

Crystallography and interphase boundary of (MnS+VC) complex precipitate in austenite

Crystallography and interphase boundary of (MnS+VC) complex precipitates formed in austenite (γ) matrix are studied by transmission electron microscopy (TEM) in an austenitic Fe-36 mass pct Ni alloy containing small amounts of manganese, sulfur, vanadium, and carbon. When VC is formed directly within the γ matrix grain, it displays a cube-cube orientation relationship (OR) with respect to γ. When VC is formed on MnS, which precipitated in γ with a cube-on-edge OR, three distinctive VC/γ ORs are found: (1) (111)_γ‖(001)_VC, , (2) the cube-cube OR, and (3) the cube-on-edge OR. The MnS/γ OR becomes irrational after γ recrystallization. When VC forms on such incoherent MnS particles, which hold irrational ORs with respect to γ matrix, a wide variety of VC/γ ORs are observed. Geometrical analysis by near coincidence site lattice (NCS) model achieves reasonable success in explanation of the observed planar facets for VC precipitates having rational ORs with respect to γ. However, as for the VC formed on the incoherent MnS with irrational ORs, there is rather poor agreement between observation and prediction. T. KIMORI, formerly Graduate Student, Department of Materials Science and Engineering, Kyoto University This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committeee.     

Dislocation/precipitate interactions during coarsening of a plastically strained high-misfit nickel-base superalloy

The effects of dislocations on the coarsening of γ’ precipitates have been studied in INCONEL* X-750. Using a thermomechanical treatment that includes solution treatment, the addition of approximately 3 pct plastic strain at room temperature, followed by aging at 845 °C for 100 hours, a unique banded microstructure is obtained. The plastic strain results in the formation of intense planar slip bands, and the dislocations in these bands act as preferred coarsening sites by relieving γ’ misfit strains. Precipitates grow on only one side of a slip band, and hexagonal arrays of mixed a/2〈110〉 dislocations form on the precipitate faces in the plane of the slip band. The resulting microstructure consists of interconnected networks of dislocations and precipitates, separated by bands of the γ matrix phase that are relatively free of γ’. The equilibrium dislocation structure has been determined for the γ/γ’ interface by an O-lattice construction. Comparisons with experimental results have been made and interphase boundary dislocation reactions analyzed. A model has also been proposed by which matrix dislocations are incorporated into the hexagonal networks of mixed character. Some fundamental insight into the probable role of dislocations in stress coarsening can be gained from the study.     

The Kinetics of the Nitriding of Ternary Fe-2 at pct Cr-2 at pct Ti Alloy

The mechanism and the kinetics of growth of the nitrided zone of ternary Fe-2 at pct Cr-2 at pct Ti alloy was investigated by performing gaseous nitriding experiments at temperatures of 833 K and 853 K (560 °C and 580 °C) and at nitriding potentials r _N = 0.004 atm^−1/2 and 0.054 atm^−1/2. The microstructure of the nitrided zone was investigated by transmission electron microscopy and the elemental compositional variation with depth was determined by employing electron probe microanalysis. Fine platelet-type mixed Cr_{1 – x} Ti _x N nitride precipitates developed in the nitrided zone. To describe the evolution of the nitrogen concentration depth profile, a numerical model was developed with the following parameters: the surface nitrogen content, the solubility product(s) of the alloying elements and dissolved nitrogen in the ferrite matrix, and a parameter defining the composition of the inner nitride precipitates. These parameters were determined by fitting model-calculated nitrogen depth profiles to the corresponding experimental data. The results obtained demonstrate that the type of nitride formation (i.e., whether Cr and Ti precipitate separately, as CrN and TiN, or jointly, as mixed Cr_{1 – x} Ti _x N) as well as the amounts of mobile and immobile excess nitrogen taken up by the specimen considerably influence the shape and extent of the nitrogen concentration profiles.     

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 Structure and Kinetics of the Nanoscale Precipitation Processes in Al-1.0 wt pct Mg2Si-0.4 wt pct Mg-0.5 wt pct Ag Alloy

The influence of addition of 0.4 wt pct Mg on the precipitation sequence in the balanced Al-1.0 wt pct Mg₂Si bearing 0.5 wt pct Ag has been investigated during the continuous heating of the quenched alloy from the solid solution state. Differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy techniques have been used. The DSC experiments showed that all processes occurred are thermally activated. The activation energies of the precipitation processes have been determined and hence the kinetics of these precipitates have been determined. The obtained results have shown that the existence of excess Mg inhibits the formation of the early stage clusters of solute-vacancy clusters. These clusters can be assisted by the binding energies between solute Si, Mg, and Ag atoms and the excess vacancies. On the other hand, excess Mg accelerates the precipitation of random, β′-phase and β-phase precipitates.     

Kinetics of Z-Phase Precipitation in 9 to 12 pct Cr Steels

The Z-phase nitride is seen as a detrimental phase in 9 to 12 pct Cr steels as it is in competition with the beneficial MX particles. Two model steels, with 9 pct Cr and 12 pct Cr content, respectively, were designed to study the effect of Cr on Z-phase precipitation kinetics. The steels were isothermally aged at 873 K, 923 K, and 973 K (600 °C, 650 °C, and 700 °C) for up to 30,000 hours in order for Z-phase to replace MX. X-ray diffraction (XRD) analysis of extracted precipitates was used to quantitatively follow the evolution of the nitrides population. It was found that the 12 pct Cr steel precipitated Z-phase 20 to 50 times faster than the 9 pct Cr steel. Transmission electron microscopy (TEM) was applied to follow the Z-phase precipitation, using energy-dispersive X-ray spectroscopy (EDS) line scans and atomic resolution imaging.