Recrystallization and grain growth in metastable beta III titanium alloy

The progress of recrystallization and subsequent grain growth has been systematically investigated in a metastable beta titanium alloy (Ti-11.5 Mo-6 Zr-4.5 Sn). Quantitative evaluation of the kinetics of these processes over a wide range of temperature, deformation, and initial grain sizes has been performed. For a given deformation, the average grain boundary velocity, decreasing with the reciprocal of annealing time, suggests the occurrences of recovery with second order kinetics concurrent with the recrystallization. The amount of deformation, varying from 20 to 80 pct cold reduction and proportional to the stored energy of deformation in the alloy, increases the average grain boundary migration rate during recrystallization by three orders of magnitude. The temperature dependence of the recrystallization rate, however, remains unaffected by the amount of deformation at 83 kcal/mole (347 kJ/mole). The isothermal grain growth kinetics follow the power law such that the time exponent of the process remains at a value of 0.35 at most annealing temperatures. The excellent agreement between the driving force exponent of recrystallization and the time exponent of grain growth based on a model which relates the driving force dependence of the rates of both processes, clearly suggests that the kinetics of these processes are controlled by a single mechanism,i.e. impurity dependent boundary migration. This paper is based on a presentation made at a symposium on “Recovery, Recrystallization and Grain Growth in Materials” held at the Chicago meeting of The Metallurgical Society of AIME, October 1977, under the sponsorship of the Physical Metallurgy Committee.     

Recrystallization and grain growth of Co3Ti

Polycrystalline Co₃Ti (Ll₂ structure) was cold-rolled to several strain levels, and isochronally and isothermally annealed at temperatures up to 1100°C. Hardness measurements and microstructural observations were used to determine the kinetics of recrystallization and grain growth as functions of composition. Recrystallization was primarily responsible for the large reductions in hardness and the kinetics obeyed the Avrami equation. The grain growth rate obeyed the expression, d = Btⁿ, (where d is the grain diameter, and B and n are experimental parameters). The time exponent, n, is less than 0.5 and was approximately independent of temperature. The effects of composition on recrystallization and grain growth were interpreted in terms of excess solute atoms. The “apparent” activation energies for the two processes showed approximately the same values, suggesting the same diffusion-controlling mechanism. These results suggest Co₃Ti as a possible candidate for new heat-resistant materials.     

Recrystallization and grain growth of cold-rolled gold sheet

Recrystallization and grain growth of a cold-rolled gold sheet with 98 pct reduction in area (RA) were investigated with electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Gold with some dopants (Be, Ca, and La) was used in this research and its recrystallization temperature was 320 °C. Isothermal annealing experiments at 400 °C, 500 °C, and 600 °C were carried out for the cold-rolled gold sheet, and recrystallization texture was examined. In the cold-rolled gold sheet, α- and β-fibers were measured mainly and some shear texture components were found on the surface. Shear texture components remained on the surface for 2 hours at 400 °C and were consumed by other recrystallized grains after 24 hours at 400 °C. Microstructure and texture evolution during in-situ annealing at 400 °C were investigated from the cold-rolled state to the fully recrystallized state using EBSD. Most of the newly, recrystallized grains came from the deformed β-fiber regions and consisted of β-fiber, cube, and other random orientations.     

Recrystallization and grain growth of cold-drawn gold bonding wire

Recrystallization and grain growth of gold bonding wire have been investigated with electron back-scatter diffraction (EBSD). The bonding wires were wire-drawn to an equivalent strain greater than 11.4 with final diameter between 25 and 30 μm. Annealing treatments were carried out in a salt bath at 300 °C, and 400 °C for 1, 10, 60 minutes, and 1 day. The textures of the drawn gold wires contain major 〈111〉, minor 〈100〉, and small fractions of complex fiber components. The 〈100〉 oriented regions are located in the center and surface of the wire, and the complex fiber components are located near the surface. The 〈111〉 oriented regions occur throughout the wire. Maps of the local Taylor factor can be used to distinguish the 〈111〉 and 〈100〉 regions. The 〈111〉 oriented grains have large Taylor factors and might be expected to have higher stored energy as a result of plastic deformation compared to the 〈100〉 regions. Both 〈111〉 and 〈100〉 grains grow during annealing. In particular, 〈100〉 grains in the surface and the center part grow into the 〈111〉 regions at 300 °C and 400 °C. Large misorientations (angles >40 deg) are present between the 〈111〉 and 〈100〉 regions, which means that the boundaries between them are likely to have high mobility. Grain average misorientation (GAM) is greater in the 〈111〉 than in the 〈100〉 regions. It appears that the stored energy, as indicated by geometrically necessary dislocation content in the subgrain structure, is larger in the 〈111〉 than in the 〈100〉 regions.     

Recrystallization and grain growth phenomena in a particle-reinforced aluminum composite

Recrystallization and grain growth in a 2219/TiC/15p composite were investigated as functions of the amount of deformation and deformation temperature. Both cold and hot deformed samples were annealed at the normal solution treatment temperature of 535 °C. It was shown that large recrystallized grain diameters, relative to the interparticle spacing, could be produced in a narrow range of deformation for samples cold-worked and those hot-worked below 450 °C. For cold-worked samples, between 4 to 6 pct deformation, the recrystallized grain diameters varied from 530 to 66 μm as the amount of deformation increased. Subsequent grain growth was not observed in these recrystallized materials and noncompact grain shapes were observed. For deformations greater than 15 pct, recrystallized grain diameters less than the interparticle spacing were observed and subsequent grain growth produced a pinned grain diameter of 27 μm. The pinned grain diameter agreed well with an empirical model based on three dimensional (3-D) Monte Carlo simulations of grain growth and particle pinning in a two-phase material. Tensile properties were determined as a function of grain size, and it was shown that grain size had a weak influence on yield strength. A maximum in the yield strength was observed at a grain size larger than the normal grain growth and particle-pinned diameter.     

Grain size and grain growth in an equiaxed alpha-beta titanium alloy

Methods of revealing grain size in a two-phase α-β titanium alloy have been examined and observations on beta grain growth in the presence of alpha have been carried out. The technique proposed by Greenfield and Margolin¹ for revealing β matrix grain sizes has been shown not to produce grain growth. However, for grain sizes of about 10 μm the G.M. technique does not reveal all the grains because of the similarity in orientation in neighboring grains. These clusters of similarly oriented grains are shown to persist as grain growth takes place but the misorientation between grains within a cluster decreases. Both the beta grain growth and alpha particle coarsening follow the same time dependency from which it is shown that a linear relationship exists between α particle size and β grain size. It is proposed that α particles must dissolve from theβ grain edges for β grain growth to occur. The linear dependency between beta grain size,D _β, and alpha particle size,d _α, can be rationalized either on the basis of geometrical or surface tension considerations. Formerly with New York University. Formerly Graduate Student with New York University.     

Recrystallization of low-carbon titanium stabilized steel

The recrystallization kinetics and microstructure of a low-carbon titanium stabilized steel, cold rolled and annealed in the temperature interval between 800° and 1750°F, were investigated. Recrystallization followed the normal sigmoidal relationship at all temperatures; however, compared to low-carbon steel without the addition of titanium, recrystallization was severely retarded. The longer time required for recrystallization is believed to have occurred primarily as a result of the titanium in solution and to a lesser degree because of the presence of numerous stable precipitate particles. No precipitation occurred during recovery prior to recrystallization to alter the recrystallization kinetics as has been observed in aluminum killed steels. Annealing studies showed that the addition of titanium altered the recrystallization texture in a manner highly favorable for enhanced drawability (high \(\bar R\) values) resulting from an increase in the intensity of the {111～ component. Heating rate and annealing temperatures were found to exert only a small influence on the recrystallization texture. The influence of titanium on the recrystallization kinetics and grain morphology is discussed in terms of improved properties compared to rimmed and aluminum killed steel.     

Analysis of grain growth in a two-phase gamma titanium aluminide alloy

Microstructure evolution during annealing of a wrought near-gamma titanium aluminide alloy, Ti-45.5Al-2Nb-2Cr (at. pct), in the temperature range 1200 °C to 1320 °C was investigated. The mean grain size of the alpha phase as well as the volume fraction and size of the gamma particles were evaluated as a function of annealing temperature and time. Isothermal annealing at temperatures above the alpha transus, T _α=1300 °C, led to rapid grain growth of the alpha phase, the kinetics of which could be described by a simple power-law type expression with a grain growth exponent p=2.3. Alpha grain growth was significantly retarded during annealing at subtransus temperatures (1200 °C≤T≤1300 °C) by the pinning influence of gamma-phase particles. Limiting grain size values predicted by computer simulation models applicable for high-volume fractions of precipitates/particles were in good agreement with experimental findings. The kinetics of alpha grain growth in the presence of gamma particles were analyzed, and the results showed that a grain growth exponent of p≈2.6 could satisfactorily account for the experimental results.     

Recrystallization during the sintering of niobium and titanium carbide powders

Summary During the sintering of loosely poured niobium and titanium carbide powders in their homogeneity regions at temperatures above 1600°C, collective recrystallization takes place. The observed changes in the rate constants of grain growth and in the energy of activation for collective recrystallization are related to changes in the electronic structures of the carbides in their homogeneity regions.Translated from Poroshkovaya Metallurgiya, No. 7 (79), pp. 30–35, July, 1969.     

析出粒子对钛微合金化高强钢奥氏体晶粒长大的影响

通过析出粒子与奥氏体晶粒尺寸的定量关系,建立奥氏体晶粒长大模型,计算TiN和TiC析出粒子共同作用下钛微合金化钢奥氏体晶粒尺寸.根据析出相质点理论计算结果表明:随着加热温度的升高,析出粒子体积分数逐渐减少,粒子半径逐渐增大,TiC粒子强烈阻止奥氏体晶粒长大,TiN粒子对奥氏体晶粒长大钉扎效果一般.采用实验测试手段测量不同加热温度下保温30 min后实验钢的奥氏体晶粒尺寸,与理论计算结果吻合较好.     

The influence of acceleration forces on dendritic growth and grain structure

The results of experiments on the tin-15 wt pct lead system are presented, showing the effects on microstructure of solidification in presence of acceleration forces from 10^-4 to 5g* for three cooling rates. An increase in the acceleration level is shown to drive fluid flow and cause dendrite remelting, fragmentation, and macrosegregation. The cooling rate impacts the final structure through its control of dendrite arm spacings and permeability to fluid flow. At the low (10^-4 g) acceleration, dendrite arm spacings deviated from the predicted relationship to cooling rate. An explanation for this anomaly is given which considers the temperature and concentration gradients in the low-gravity environment.     

Structure of the welding zone between titanium and orthorhombic titanium aluminide for explosion welding: I. Interface

The structures of the interfaces and transition zones of bimetallic metal-intermetallide joints produced by explosion welding under various conditions have been studied. The welded materials were commercial-purity titanium and orthorhombic titanium aluminide of two alloying schemes. The specific features of the structure and substructure of the zones under study are discussed. Wave formation and formation of isolated vortex zones, as well as tracks of particles related to the transfer of particles of one metal into the other one, were observed. A possible scenario of formation of interfaces, depending on the composition of titanium aluminide and welding conditions, is proposed.     

Physiological characterization of mBSA antigen induced arthritis in the rat. I. Vascular leakiness and pannus growth

OBJECTIVE: To study the temporal relation between vascular inflammatory activity and synovial hyperplasia during the development of methylated bovine serum albumin (mBSA) antigen induced arthritis (AIA) in the rat, and to correlate these variables to changes in knee diameter. The influence of a single dose of indomethacin and methotrexate (MTX) on these measures was also determined. METHODS: Vascular inflammatory activity was assessed as extravasation of radiolabelled albumin. Synovial hyperplasia was followed by measurements of the increases in wet and dry weight of the anterior part of the periarticular soft tissue and by routine histology. RESULTS: The vascular inflammation peaked on Day 3 after antigen challenge. The pannus weight increased at a slower pace, peaking on Day 7. No major difference between the sexes was found in these responses. Both variables were attenuated by MTX or indomethacin, suggesting a dependence between them. The water content of the pannus increased in tandem with the tissue growth but did not correlate to vascular leakiness, and is thus explained by the structural properties of the pannus rather than by the formation of inflammatory edema. In histological sections, ingrowth of pannus and destruction of cartilage was visible from Day 3 until the end of the experiment. CONCLUSION: Proliferative response follows the inflammatory vascular inflammation over time. The knee diameter, which is the most commonly used clinical measurement, seems mainly to be a reflection of the former variable. The effects of MTX and indomethacin suggest that the pannus formation is induced by the inflammatory activity in this model.     

Dendritic solidification of Cu-Ni alloys: Part I. Initial growth of dendrite structure

Small Cu-Ni melts were furnace cooled at different rates and with different "nucleation" temperatures. Thermal analysis showed that the thermal arrests associated with the formation of the dendrite skeletons showed a significant supercooling below the liquidus temperatures. This supercooling increased with increased rates of heat extraction,i.e. higher cooling rates and lower "nucleation" temperatures; and was associated with higher dendrite growth velocities. The solute content of the dendrites measured on samples quenched during the thermal arrest quantitatively supported these observations. The magnitude of the supercooling for a given rate of heat extraction varied directly with the freezing range of the alloy but remained finite (although small) for unalloyed copper. The approximate measurements of dendrite growth velocities for one alloy (40 wt pet Ni) at different supercoolings agreed well with the predictions of Trivedi’s theory of dendrite growth. E. A. FEEST, formerly Graduate Student, University of Sussex K. HOLM, formerly Visiting Research Student, University of Susses     

Techniques for the study of group structure and behavior: I. Analysis of structure.

Recent advances in the development of mathematical techniques growing out of sociometry are described. Applications of these techniques are described. Applications of these techniques in assessing status, group structure, and the assignment of individuals to subgroups are suggested. Further use of these procedures should clarify the requirements for adequate explanatory systems and perhaps provide the variables to be incorporated in more comprehensive theories. 47-item bibliog. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure and properties of rapidly solidified dispersion-strengthened titanium alloys: Part I. Characterization of dispersoid distribution,structure, and chemistry

The feasibility of developing dispersion-strengthened powder metallurgy Ti alloys was determined in Ti-RE (RE = Ce, Dy, Er, Gd, La, Nd, or Y) alloys prepared by rapid solidification processing. The alloys were produced by electron-beam melting and splat quenching. Dispersoid precipitation and growth were studied as functions of annealing temperature, 700 to 1000 °C, for annealing times between 5 and 50,000 minutes. Dispersoid diameters, spacings, compositions, and crystal structures were characterized by transmission and scanning electron microscopy, X-ray and electron diffraction, energy-dispersive X-ray analysis, and scanning Auger microscopy. Two classes of dispersoid coarsening behavior at temperatures below theβ-transus were identified. In Ti-Ce, Ti-Gd, and Ti-Nd alloys, equilibrium rare earth sesquioxide (RE₂O₃) dispersoids form early in the annealing process and coarsen rapidly to > 1 μm diameter. The Ti-Nd alloys additionally contain large volume fractions of small (< 100 nm diameter) dispersoids. In the other Ti-RE alloys, dispersoids identified as Ti-RE-O-C compounds coarsen relatively slowly. Ti-Er is the most promising of the investigated systems for application in a multicomponent dispersion-strengthened alloy because long-time annealing at 700 to 800 °C produces stable dispersoids of 50 to 150 nm average diameter and 300 to 600 nm inter-particle spacing.