Semenov D. The effect of alloying and impact ultrasonic surface treatment on physical and mechanical properties of the f.c.c. Fe-Ni-C Invar alloys

The mechanical tensile testing in the temperature range 100-300 K of the alloyed with the С, Mn, Сo Y, Tb austenitic f.c.c. Fe-Ni alloys as well as the low cyclic fatigue tests at the room temperature of the alloyed Fe-Ni-C alloys have been carried out. The increment of yield stress due to the effect of magnetic heterogeneities in the alloys was estimated within the framework of the magneto-precipitation hardening model. The improvement of mechanical properties of Invar alloys due to carbon was shown under the static and low cyclic sign variable loading. The cyclic softening under fatigue loading, which is attributed to austenitic steels was not revealed. The studies of changes of surface structure, microhardness, thermal expansion and elastic properties of the Fe-Ni-C alloys caused by UST with the impacts amplitude of 20-28 mkm was carried out. The gradually hardening of the bulk-samples under UST accompanying with the atomic redistribution in a solid solution without any changes of Invar and elasticproperties. Unlike the surface IST resulting in martensitic transformation and in such a way worsens the Invar effect the UST is the efficient technique of a hardening since according to Mossbauer data it does not change the phase composition and magnetic state.