The samples were produced at S.C. R & D Consultancy and Services Bucharest, with which a service contract was concluded, in the form of ingots. The ingots were developed by the supplier in a FIVES CELES levitation induction furnace with a power of 25 kW, a melting temperature above 2000 0C, a primary vacuum of 10-4 mbar; secondary vacuum 3 x 10-8 mbar, vacuum-melting, with direct injection into the ingot mold (diameter 20 mm).
After receiving, the ingots were subjected to various thermal treatments in accordance with the experimental procedure used in other similar cases (Tseng et al., 2016).
Fig.1 presents two examples of electroerosion cut samples, with Mo wire (Ø 0.18 mm), with a DEM 320 machine, from samples 1 and 7.
Fig.1 Wire cutting examples of hot rolled samples: (a) Cutting the ingots for sample no. 1 (Fe41Ni28Co17Al11.5Ta2.5); (b) cutting the ingots for sample no. 1 (Fe43.5Mn34Al15Ni7.5)
Fig.2 Macrographs of cracked samples after hot rolling: (a) sample 1.1 of Fe41Ni28Co17Al111.5Ta2.5; (b) sample 7.2 of Fe43.5Mn34Al15Ni7.5, with a detail of the cracks
1.2. Samples thickness reduction (t)
Reduction of samples thickness was first performed by hot rolling with an experimental hot rolling device (800W), equipped with an electric furnace quartz tube which can heat up to 11000C. In order to avoid cracks due to quenching, after each rolling step, the samples were reinserted in the quartz tube, while the furnace was always on (Suru, et al., 2015).
1.3. Edge chamfering
After hot rolling, the edges presented a series of cracks which, after following plastic deformation After hot rolling, the sample edges exhibited a series of cracks which, in subsequent plastic deformation processes performed in order to reduce the thickness, may evolve, risking to destroy the integrity of the sample. Fig.2 shows two examples of cracks after hot rolling.
After a new mechanical grinding, followed by edges chamfering, the annealed samples were cold-rolled with the help of an experimental rolling device at the Faculty of Engineering at "Dunarea de Jos" University from Galati.
2.3 Determining the average grain size
AA thermomechanical treatment was applied to induce abnormal growth of crystalline grains. In order to determine the average grain size, special vices were designed and made to "bundle" the obtained samples. Sample grain size was determined using the OPTIKAM B5 software, provided by the OPTIKA XDS-3 MET microscope.
Fig.3 Optical micrographs of sample 9.2 of Fe43.5Mn34Al16.5Ni6 in a completely thermally treated state, chemically etched with a 4% Nital solution: (a) incomplete growth grain area; (b) measurement detail of three grains