In the temperature range 5¸325
K, the
temperature dependences of decrement d, dynamic Young's
modulus Е and a resistivity r in a perspective
for cryogenic and atomic engineering alloys
Fe100-x-yCrxMny (x=5; 10 and y=30; 35; 40) are investigated.
The main impurities are: C, N, S, P < 0.1% and Si < 0.3%. Samples of two
types were investigated: 1) rods cut from cold-rolled wires ~ 1 mm in diameter;
2) rectangular parallelepipeds cut out from massive swaged ingots. Samples had
g-austenitic
structure that was formed during 1 hour annealing at 1273 K and subsequent
quenching into water.
Acoustic measurements were
carried out by two methods: 1) two-component composite vibrator technique on
longitudinal standing waves at frequencies f ~75 kHz (the ultrasonic
strain amplitude had a value e0 ~ 10-7
corresponded to the amplitude-independent region); 2) flexural vibration
technique at frequencies f ~3 kHz. dc-resistivity
measurements were carried out using four-point method at two opposite
directions of a transport current. For all measurements, temperature was
stabilized to <50 mK using a thermocouple and AsGa thermometer and resistive
heater. The temperature changes rate during thermocyclings was ~ 1 K/min.
Experimental
results can be divided into two groups concerning to samples with fixed Cr content:
5% and 10%, accordingly. In the alloys with 5% Cr, a series of internal
friction peaks P1, P2 and P3 is recorded in
dependences d (T) which are localized at
temperatures TP1 » 20 К, TP2 » 155 K and TP3
» 255 K. When increasing Mn concentration, peak height of P1
is reduced and peak is transformed to a plateau Parameters of peaks P2
and P3 change unsignificantly and the changes are not systematic. In
samples with 10% Cr, internal friction peaks on dependences d (T) are
also registered and are localized at 
» 140 К and 
» 220 К. The greatest peak height is observed in samples with
40% Mn, and the least - in samples with 35% Mn. The nature of these peaks
remains unknown.
Alloys investigated are
characterized by low values of decrement d < 6×10-4 and the
considerable magnitude of a dynamic Young's modulus
Е ~ 180 GPa which increases monotonically
by 7% when temperature decreases from 325 down to
5 K.
Temperature dependences of a Young's modulus may be described by analytical
expressions in the assumption of additivity of the electronic and phonon
contributions. Variation of Mn concentration in an irregular manner changes absolute
value Е and practically does not
influence a shape of dependences Е (Т).
There is a series of the
distinct differences in the results obtained for wires and massive samples. In
massive samples over the whole temperature interval values of decrement are
much lower than those recorded in wire samples. At the same time values of a
dynamic Young's modulus appeared to be noticeably higher. Supposed reason of
these differences may be difference in initial defect structures of the massive
and wire samples.
The alloys investigated are
characterized by the considerable residual resistance r(T=0K) » 50 ¸ 70 mW·cm. In samples
with 5% Cr r increases systematically when Mn content is increased.
In alloys with 10% Cr the regular resistivity change with change in Mn and Fe
concentration is not observed.
It is known that 
transition is accompanied by
jump of electroresistance and occurrence of absorption peak. The temperatures
of direct and reverse transition do not coincide and on temperature dependences
of electroresistance and Young's modulus the hysteresis loops is observed. On
the dependences received by us similar features are absent that testifies to
stability of structure of the investigated alloys in the investigated
temperature interval. However, observable in alloys with 10 % Cr not regular character of change of acoustic and
resistive properties can be connected to insignificant inclusions of a e-martensite phase formed during reception of a sample. It is
correlated with X-ray structure investigations.