IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Table 1 : Relative comparison of sensitiveness of different NDE techniques for
characterization of ageing behaviour in maraging steel
N-Non sensitive
YY-More sensitive
complimentary information or
confirming the observation of
other techniques, this enhances
the use of multiple techniques
and adopting multi-parametric
approaches is very attractive
and is expected to enable very
effective characterization of
microstructures. In this study,
NDE parameters such as
ultrasonic velocity, magnetic
Barkhausen emission (MBE)
RMS voltage, eddy current (EC)
Fig.1 Variation in hardness,
ultrasonic wave velocity, and
positron annihilation life time
parameter with aging at 755 K.
impedance magnitude,
positron life-time and X-ray
diffraction based austenite
volume fraction have been
employed to develop a
comprehensive
NDE
Y-Sensitive
Y?-Sensitive but requries precise measurements
methodology
for
characterization of ageing
behaviour of M250 grade
maraging steel aged at 755 K
for different durations.
The variations in hardness,
ultrasonic longitudinal wave
velocity and positron
annihilation life time with aging
duration are shown in Fig.1.
The variations in hardness,
MBE rms voltage, volume % of
austenite (XRD based) and
impedance amplitude with
aging duration are shown in
Fig.2. Ultrasonic velocity
showed good promise in
characterizing the intermetallic
precipitation process and was
able to pick up the austenite
information to some extent. Its
drawback is with respect to
obtaining any information
about the defect structure and
early detection of initiation of
austenite reversion. Hence, this
technique is found to be very
sensitive to monitor only the
intermetallic precipitation
behaviour. Positron annihilation
studies were found to be very
sensitive to changes in defect
structure during initial aging
and precipitation to some
extent. Fig.3 shows the bright
field TEM image of defects
(dislocations) in solution
annealed condition. The
austenite reversion has
insignificant effect on positron
annihilation parameter. Hence,
this technique can be used for
high sensitive characterization
of defects such as vacancies or
dislocations. MBE study showed
good promise in identifying the
non-magnetic austenite phase
compared to the intermetallic
precipitation and defect
structure. EC technique had
shown good promise in
characterizing the austenitic
reversion ahead of ultrasonic
and almost on par with MBE.
As this technique is more
amenable to shop floor, it can
be used for quick and reliable
determination of volume % of
austenite on shop floor as well
as on components. The bright
field TEM image showing
Fig.1 Variation in hardness, MBE rms
voltage, EC amplitude and
volume % of austenite determined
by XRD with aging at 755 K.
120 ENABLING TECHNOLOGIES