ACOUSTICAL AND RESISTIVITY PROPERTIES OF PERSPECTIVE
FOR ATOMIC ENGINEERING g-AUSTENITIC
IN THE TEMPERATURE REGION 5 – 325 К
Semerenko Yu.A., Pal-Val L.N., Skibina L.V.
B.Verkin Institute for Low Temperature
Physics and Engineering,
In the temperature range 5¸325
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.