Shape Memory NiTi and NiTiCu Alloys Obtained by Spark Plasma Sintering Process

Abstract

Abstract. The addition of Cu to near equiatomic NiTi shape memory alloys (SMAs) can provide some modifications of their shape memory properties by affecting their transformation behavior. The same effect was obtained in the case of Ni 3 Ti 2 and Ni 4 Ti 3 precipitates presence in the microstructure of NiTi. Also the substitution of Cu to NiTi alloys increases the hardness of the materials. This paper presents the microstructural and mechanical investigations of NiTi and NiTiCu alloys obtained by spark plasma sintering (SPS) process that represents a great potential for researchers as a new process for the fabrication of intermetallic compounds.

Thermodynamic and Kinetic Simulations Used for the Study of the Influence of Precipitates on Thermophysical Properties in NiTiCu Alloys Obtained by Spark Plasma Sintering

“…The investigated NiTiCu samples with the compositions Ni 45 Ti 50 Cu 5 and Ni 40 Ti 50 Cu 10 (at.%) were made at INCDIE ICPE-CA in previous studies [ 3 , 6 ] by powder technology with and without MA up to 15 h. The samples were made from Ni (with 10 µm particle size), Ti (with 150 µm particle size) and Cu (with <63 µm particle size) elemental powders, acquired from Merck, Darmstadt, Germany. Four samples with different processing and alloying methods are compared: without MA and with 5 at.% Cu alloyed (Ni 45 Ti 50 Cu 5 with notation HT-P0), without MA and with 10 at.% Cu (Ni 40 Ti 50 Cu 10 with notation HT-S0), with MA and with 5 at.% Cu alloyed (Ni 45 Ti 50 Cu 5 with notation HS-P1), and with MA and with 10 at.% Cu alloyed (Ni 40 Ti 50 Cu 10 with notation HS-S1).…”

“…The EDX and XRD showed the presence of the minority austenite phase and martensite as the majority phase. Moreover, they have confirmed that Ni 2 Ti/(Ni, Cu) 2 Ti, NiTi 2 /(Ni, Cu)Ti 2 and Ni 3 Ti/(Ni, Cu) 3 Ti phases exist, that the samples were properly compacted and the density calculated by Archimedes' method was 5.041 ÷ 6.664 g/cm 3 [6]. The densification of NiTiCu materials is higher in the high-Cu samples' content.…”

“…Also, the sintering by spark plasma combined with heat treatment offers the possibility to obtain materials’ bulk outside thermodynamic equilibrium, enabling the formation of metastable phases in the microstructure or partial amorphous structure. Cirstea et al [ 1 , 3 , 6 ] investigated the influence of the microstructure of Ni 45 Ti 50 Cu 5 and Ni 40 Ti 50 Cu 10 with MA and without MA in SPS-processed material on the mechanical properties. From the analysis of the results obtained from XRD and EDX measurements, the existence of austenite and martensite phases, Ni or Ti phases and precipitates was observed.…”

“…In recent years, a very fast method of obtaining advanced materials has been the powder technology that uses the spark plasma sintering (SPS) as one of the modern compaction methods. SPS allows for the realization of high sintering rates by uniaxial pressing accompanied by the passage of an electric current through the sample [1][2][3]. This results in the rapid heating of the sample and, moreover, the discharges between powder particles can cause the local welding of the particles and thus contribute to even more rapid sintering [3][4][5][6][7].…”

“…SPS allows for the realization of high sintering rates by uniaxial pressing accompanied by the passage of an electric current through the sample [1][2][3]. This results in the rapid heating of the sample and, moreover, the discharges between powder particles can cause the local welding of the particles and thus contribute to even more rapid sintering [3][4][5][6][7]. These experimental improvements together with smart alloying set a suitable base for optimized NiTi-based shape memory alloys.…”