A.K. Jena

Texture evolution during recrystallization in a boron-doped Ni76Al24 alloy

The evolution of recrystallization texture in the intermetallic compound Ni76Al24(B) has been investigated using the conventional pole figure as well as orientation distribution function (ODF) methods. The initial L12 structure which transforms to DO22 on cold rolling reverts back to the L12 during annealing. The annealing process can be divided into three stages: recovery, reordering and recrystallization. The moderately strong deformation texture resulting from cold rolling becomes very weak during the recovery and reordering processes by an ‘in-situ’ orientation change due to reordering that precedes recrystallization. The texture remains weak throughout recrystallization and grain growth stages. TEM investigations show evidence of twin like features during the reverse DO22→L12 transformation. This is expected to lead to fragmentation of the matrix grains resulting in a weak texture. The prominent recrystallization texture components are {025} and {011} , of which the latter component survives best with continued annealing.

On the nickel-rich nickel-germanium solid solution

La solution solide nickel-germanium riche en nickel a une large solubilite pour le germanium. Determination des parametres cristallins des solutions solides

Rolling texture in the intermetallic compound Ni76Al24(B)

The development of cold rolling texture in the intermetallic compound Ni3Al(B) has been investigated as a function of rolling reduction, using the conventional pole figure as well as the orientation distribution functions (ODF) method. The textures at low degrees of deformation have been found to be similar to the rolling texture of pure Ni cold rolled to similar levels. With increasing degree of deformation, the texture in Ni3Al(B) changes to alloy type at reductions greater than 45%. This texture is characterized by the presence of a remarkably strong rotated Goss component over and above the Brass (Bs) component. Transmission electron microscopy of thin foils of the material cold rolled by 65% and more shows evidence of twinning. X-ray diffraction analysis indicates a structural change in the material from L12 to DO22 with the progress of cold work. An attempt has been made to explain the texture development in terms of this structural transformation.

Effect of 0.23 wt.%Si on precipitation in the Al-1.52wt.%Cu-0.74wt.%Mg alloy

Abstract The precipitation behaviour of the Al-1.52wt.%Cu-0.74wt.%Mg-0.23wt.%Si alloy has been investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The DSC curves of solution-treated and quenched alloy give peaks like those of the silicon-free alloy as a result of GPB zone precipitation, GPB zone and GPB zone-dislocation complex dissolution, S′ precipitation and S′ dissolution. TEM studies show that the addition of silicon results in the precipitation of rod-shaped particles of the S′ phase. The kinetics of GPB zone formation are altered by the presence of silicon. The rate of zone formation is given by d Y/ d T = f(Y)k 0 × exp (−Q ∗ /RT) , where f ( Y ) = 1 − Y , Y is the transformed fraction, k 0 = 2.7 × 10 4 s −1 and the activation energy Q ∗ = 45.1 kJ mol −1 . The values of the activation energy and the frequency factor are appreciably lower than those observed in the silicon-free alloy.

Effects of heat treatment cycle on equilibrium between ferrite and austenite during intercritical annealing

Abstract A steel containing 0.2% C, 0.98% Mn, 0.46% Si and 0.47% Cr was intercritically annealed at 750, 770, 790 and 810 °C for 15 minutes and quenched to room temperature to produce dual-phase containing ferrite and martensite. Three heat-treatment cycles—IN aIQ and IA—were applied to the steel such that the structure at the beginning of intercritical annealing consisted of pearlite, martensite and austenite respectively. During intercritical annealing the steel first approaches partial equilibrium state is attained. The steel remains in that state uop to 770 °C, but above 770 °C departs from that state early during annealing because of partitioning of substitutional solutes. In the IN and IA cycles, the transformation rates are too slow for the partial equilibrium state to be attained in 15 minutes. In the case of the IA cycle, the departure from the partial equilibrium state increases with an increase in annealing temperature because of a decrease in the transformation rate with an increase in temperature.

Effects of silicon addition on the first stage of

The influence of silicon on the precipitation kinetics of Al-Cu-Mg alloys is not yet understood, although its effect on the improvement of mechanical properties is well established. In this study, the kinetics of the first stage of precipitation in Al-1.52 pct Cu-0.75 pct Mg alloy con-taining 0.49, 0.76, and 1.03 pct Si were investigated by differential scanning calorimetry. From the calorimetric data, the extent of reactionY and the reaction rate(dY/dt) were evaluated as functions of the reaction temperature. The rates are expressible by the relation(dY/dt) = (1 —Y)k0 exp(— Q*/RT), whereK0 is the frequency factor andQ* is the activation energy. For the alloys containing 0.49, 0.76, and 1.03 pct Si, the activation energies are 76.7, 70.1, and 64.6 kJ/mole, respectively, andk0 changes systematically with silicon content. Critical analysis of these results and those available in the literature on the silicon-free and 0.23 pct Si containing alloys shows that GP zones precipitate in the 0.49, 0.76, and 1.03 pct Si alloys, while only GPB zones precipitate in the silicon-free and 0.23 pct Si containing alloys. The sudden change in the precipitation behavior occurs due to the preferential removal of magnesium from the matrix by the insoluble particles which are present in 0.49, 0.76, and 1.03 pct Si alloys. The alteration of the matrix composition is also responsible for systematic decrease in the activation energy.

Lattice parameters and bonding characteristics of boron-doped hafnium containing trinickel aluminide alloys

Abstract The lattice parameters of boron-doped γ ′ phase (Ni 3 Al) containing hafnium were measured at room temperature after quenching from 1130°C. The lattice parameter a in angstroms is given by the following best fit expression: a =6.9987−7.52 X Ni −3.785 X Al +4.47 X Ni 2 +4.38 X Al 2 +2.00 X Ni X Al . The composition dependence of the partial volumes of Ni, Al and Hf calculated from lattice parameters suggest that in alloys containing 75 at.% Ni, the boron atoms occupy the edge centered octahedral sites. Hafnium atoms tend to occupy the aluminium sites when the hafnium content is low while they start occupying nickel sites also when the hafnium content is increased. In nickel-rich alloys containing 77 at.% Ni, the boron atoms tend to occupy some of the body centered octahedral sites in addition to the edge centered octahedral sites. The lattice parameters of the binary stoichiometric γ ′ phase measured as a function of quenching temperature show an unusual temperature dependence. The lattice parameter tends to increase with increase in quenching temperature up to about 1000°C and then tends to decrease slightly beyond 1000°C.

Lattice parameters and bonding characteristics of hafnium containing trinickel aluminide alloys

Abstract The lattice parameters of the γ′ phase (Ni3Al) in a number of alloys containing hafnium were measured at room temperature after quenching from the equilibration temperature of 1130 °C. The lattice parameter a in angstroms could be expressed by the following best fit expression: a = 4.839725 − 2.492 X Ni − 1.295 X Al + 1.54 X Ni 2 + 3.89 X Al 2 − 0.98 X Ni X Al where XNi and XAl are the atom fraction of nickel and aluminium in the alloy respectively. The partial volumes of the components calculated from the above data shows that the partial volume of aluminium changes significantly with changes in the composition compared with the partial volumes of nickel and hafnium. The results indicate that hafnium has considerable covalent character and the covalent characteristics of aluminium have the tendency to increase appreciably with increase in hafnium content. The lattice parameters of the binary stoichiometric γ′ phase measured as a function of quenching temperatures show unusual temperature dependence. This has been attributed to the changes in the defect concentration of Ni3Al.

Nucleation and recrystallization kinetics in boron doped Ni76Al24 deformed to small strains

Abstract Nucleation and recrystallization behaviour of boron doped Ni 76 Al 24 nickel aluminide, cold rolled upto small reductions of 25% has been examined at temperatures in the range of 850 to 925°C. Microstructural observations showed that nucleation and recrystallization occurred preferentially at grain boundaries, triple points and deformation bands. The presence of serrated grain boundaries in the microstructure, suggested strain induced grain boundary migration as a mechanism of nucleation and recrystallization. Using standard metallographic measurements, the average nucleation rates were calculated at a range of temperatures. As expected, the average nucleation rate increased with increasing temperature. The usual Arrhenious equation was used to determine activation energy of nucleation. The recrystallization kinetics were analysed using the Johnson-Mehl-Avrami relationship. The results have been found to be consistent with the recrystallization studies performed on ordered intermetallics.