Effect of initial pH and temperature of iron salt solutions on formation of magnetite nanoparticles

This study describes the relative effect on the permanent magnet characteristics viz. remanence (Br), intrinsic coercivity (Hci), Curie temperature (TC), and rectangularity of the intrinsic demagnetization curve, when Al, Cu, Ga, and Nb are added individually to NdFeB. Each elemental addition causes significant improvement in Hci but the level of improvement differs from one additive element to the other. The addition of Nb is favored over other elements for realizing maximum enhancement in Hci and rectangularity of the demagnetization curve. The microstructural features of the sintered samples of NdFeB with elemental addition show the formation of a new phase, in addition to the phases (φ,η, and Nd-rich) generally found in the ternary sample. The factors influencing the permanent magnet characteristics of sintered samples are the distribution of the Nd-rich phase in the intergranular region, the size and distribution of the minor phases at the grain junctions, the formation and distribution of new phases...

Effect of Al, Cu, Ga, and Nb additions on the magnetic properties and microstructural features of sintered NdFeB

Tribological characteristics of nickel based composite coatings

The effect of grain size on the oxidation of a 2
 4
 1
 Cr-1Mo steel has been studied at 823 K in air. The oxidation rate was found to decrease with increasing grain size (varied form 16 to 59 μm). The decrease in oxidation rate with increasing grain size is attributed to the smaller grain-boundary area which results in a decrease in the short-circuit-diffusion paths. The enhancement in the oxidation rate with decreasing grain size has been confirmed further by acoustic emission (AE) tests which show more AE activity for smaller-grain-size specimens during oxidation as well as during cooling following the oxidation, indicating a faster oxidation rate and thicker scale, leading to more cracking and spailing.

Influence of grain size on the oxidation resistance of 2 4 1 Cr-1Mo steel

Effect of Co, Dy and Ga on the magnetic properties and the microstructure of powder metallurgically processed Nd-Fe-B magnets

Sintered samples of (Nd14.9 Dy1.9) (Fe65 Co8 Cu1.0 Ga1.0 Nb0.7)B7.5 were prepared and subjected to stepwise annealing in the temperature range 875 K–675 K. The XRD and metallographic (optical and electron microscopy) studies reveal a multi-phase microstructure with each phase showing different solubility of the alloying additions. This alloy has T
C of 705 K with an intrinsic coercivity of 1000 kA/m and energy product of ∼250 kJ/m3 at RT. Solubility of Co into the matrix phase and that of Ga and Cu into the Nd-rich grain boundary phase are considered to be the main contributing factors for the significant enhancement in T
C and H
ci respectively of the multi-component alloy when compared to those of ternary NdFeB, wherein H
ci = 720 kA/m and T
C = 585 K.

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

In this work AE events and cumulative AE events have been measured during oxidation of 2.25 Cr-1 Mo steel at 773, 873, 973 and 1073 K and the results are compared with a corresponding thermogravimetric study

Correlation of acoustic emission events with parabolic oxidation behaviour of 2.25Cr-1Mo steel

Fatigue behaviour of nickel-flyash composite coatings

The onset of breakaway oxidation and cracking of the oxide scale formed on 2.25Cr-1Mo steel in air at 1173 K have been studied by the acoustic emission (AE) technique. AE parameters, i.e. events, ring-down counts, rise time, event duration and root mean square voltage show negligible increase during isothermal heating at this temperature, until a point where a sudden increase in AE activity is found. This point corresponds to the onset of breakaway oxidation. An enormous increase in AE activity after the start of cooling from the oxidation temperature has been attributed to separation of the oxide scale from the matrix. The peak amplitude distribution is measured and a derived b parameter is calculated. This has helped in distinguishing the phenomena of isothermal oxidation at 1173 K and internal cracking of oxide scale during cooling from 1173 K.

Acoustic emission as a technique to study breakaway oxidation and spalling behaviour of 2.25Cr-1 Mo steel

The retained austenite content of a quenched case of a low alloy steel was examined with and without ultrasonic vibrations. Results obtained are particularly promising and indicate the possibility of reducing the amount of retained austenite in a quenched case-carburized steel by ultrasonic treatment which is of considerable industrial importance. The activity of the austenite to form more martensite has been attributed to the increase in dislocation density and point defects which enhance the number of martensite nucleation sites on ultrasonic treatment.

K. J. L. Iyer

Papers

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

Correlation of acoustic emission events with parabolic oxidation behaviour of 2.25Cr-1Mo steel

Fatigue behaviour of nickel-flyash composite coatings

Acoustic emission as a technique to study breakaway oxidation and spalling behaviour of 2.25Cr-1 Mo steel

Enhanced activity of austenite resulting from ultrasonic vibration in a low alloy case-hardened steel