Process optimization for Ultra High temperature Sm2Co17
type magnets
R.K. Singh and R.P. Mathur
Advanced Magnetics Group, Defence Metallurgical Research Laboratory, Hyderabad – 500 058, India
*Corresponding author’s e-mail: ranjan@dmrl.drdo.in
Abstract
Sm2Co17 type magnets are age hardened to synthesize
fine cellular microstructure that imparts optimum
combination of coercivity and remanence. The effect of
quenching rate on aging kinetics has been studied and
correlated with the magnetic properties of the Ultra high
temperature magnets.
Keywords: Permanent magnet, Differential scanning
calorimeter, Age hardening, kinetics.
Introduction
Rare-earth permanent magnets (REPMs) play a
prominent role in the development of modern electrical
and electronic devices. The two most commonly known
REPMs are: Neodymium Iron Boron (Nd-Fe-B) and
Samarium Cobalt (SmCo5 & Sm2Co17 type) magnets.
The Ultra High Temperature (UHT) magnets are based
on Sm2Co17 type composition exhibiting outstanding
stability of magnetic properties at temperatures greater
than 300oC. These magnets find applications in strategic
devices such as BLDC motors for Navy, Traveling
Wave Tubes for microwave, magnetic bearings, etc.
Apart from remanence, high Curie temperature
(~930oC) coupled with low temperature coefficient of
intrinsic coercivity (~-0.1 %/oC) are the other critical
magnetic characteristics expected of an UHT magnet.
Experimental Procedure
An indigenous alloy with composition based
on Sm-Co-Fe-Cu-Zr quinary system was developed
which recorded Curie temperature of 930oC. The alloy
was melted using vacuum arc melting technique. Ascast alloy was processed through powder metallurgical
technique involving steps of ball milling, power
orientation and compaction in magnetic field press
followed by sintering. Sintered samples were
solutionized and then either water quenched or gas
quenched to get supersaturated high temperature phase.
Thermal analysis using DSC was carried out to study
kinetics of aging. After aging, magnetic properties were
studied using vibrating sample magnetometer (SQUIDVSM).
required to synthesize a fine cellular microstructure that
imparts high coercivity was studied and modeled to
obtain strong anisotropic magnet blocks. The
demagnetization curves for the indigenously developed
UHT magnet, measured at various temperatures are
shown in Fig. 1a. A linear BH curve up to 450 oC,
demonstrate that magnets are capable of performing
well at elevated temperature. The variation in magnetic
properties such as remnant induction Br , intrinsic
coercivity iHc and maximum energy product as a
function of temperature is shown in Fig. 1b. The aimed
temperature coefficient of intrinsic coercivity β(25400oC) of -0.11%/oC and Maximum energy product
(BH)max of 8-10MGOe at 400 oC have been realized.
Fig 1: a) Demagnetization curves at different
temperatures and b) Variation in magnetic properties as
a function of temperature.
Conclusions
Effect of quenching rate on aging kinetics has
been studied. The alloy composition and critical process
parameters involved in powder preparation, compaction
and sintering were optimized to enhance operating
temperature of Sm2Co17 type magnets.
Acknowledgment
The authors acknowledge keen interest shown
by Director DMRL in this activity. Authors are grateful
to Dr. SV Kamat Sc ‘H’ and Dr. S Pandian Sc ‘G’ for
their valuable suggestions.
References
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Martinek G, J. Magn. Magn. Mater.; 2002,242-245,1347.
Results and discussions
The critical process parameters involved in
powder preparation, compaction and sintering were
optimized. The solutionizing and aging treatment
Schobinger D, Gutfleisch O, Hinz D, Muller K-H, Schultz L,
[2]
Gopalan R, Hono K,
Mater.;2009,60 , 764.
Yan A,
Gutfleisch O, Scripta