SEMIPRODUCT SHAPE-MEMORY MATERIALS OF NITI TYPE AND PROCESS FOR PREPARING THE SAME

• Main Authors: SBÂRCEA BEATRICE GABRIELA, CÎRSTEA CRISTIANA DIANA, ION IOANA, LUNGU MAGDALENA-VALENTINA, STANCU NICOLAE
• Format: Patent
• Language: English; Romanian
• Published: 26.02.2021
• Subjects: ALLOYS; CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS ANDNON-FERROUS ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; METALLURGY; TREATMENT OF ALLOYS OR NON-FERROUS METALS

The invention relates to semiproduct shape-memory materials of the NiTi type, intended to be used for applications in motor vehicle industry, aeronautical industry, medicine and electrical engineering, and to a process for preparing the same. According to the invention, the materials have cylinder shape, they consisting of Ni and Ti alloys having Ni content in the range of 50.8...51.5% atomic mass and, for the remainder, Ti, a density in the range of 5.8...6.45 g/cm, Vickers hardness in the range of 406...709 HV, Young's modulus ranging between 42...98 GPa and conversion temperatures ranging between 2...50°C, the materials being meant to be used in applications at temperatures of less than 80°C. The process, as claimed by the invention, comprises a mechanical alloying of pure Ni and Ti powders having a particle size of 10 μm for Ni and 150 μm for Ti, for 8...15 h, in a stainless steel ball mill, where the ball diameter varies between 4...16 mm, the ratio between the mass of the grinding bodies and the mass of the powder mixture is 7:1, the grinding rate is 250 rpm in wet petroleum ether medium and 99.9% pure Ar protected atmosphere, an amount of 8...36 g being sampled from the so-obtained mixture and introduced into a cylindrical high-density graphite mould having a diameter of 20...40 mm, being sintered in plasma by spark in a vacuum of 10Torr, at a pressing pressure of 40...50 MPa and a temperature of 800...900°C, at a temperature growth/drop rate of 100°C/min and maintained in the sintering plateau for a period of time of 5 min, under the action of 12 direct current pulses, at a pulse duration of 3.3 ms, with an interval of 2ms between the pulses, after which the sintered material is thermally treated in argon or vacuum, in a pipe furnace, at 400°C and maintained in the plateau for 30 min, at a heating rate of 20°C/min, followed by cooling in iced water, when the furnace temperature has reached 100°C.