Adjustment of Aging Temperature for Reaching Superelasticity in Highly Ni-Rich Ti-51.5Ni NiTi Shape Memory Alloy

Abstract

In this research, the effects of aging temperature on the phase transformation, mechanical properties, and superelasticity of Ti-51.5 at.% Ni alloy were investigated. For this purpose, samples were solution annealed and then aged at different temperatures ranging from 300 to 700ºC. The results showed that the change of aging temperature has a great influence on the behavior of the alloy. Aging at 300 and 400ºC led to the occurrence of the austenite to R phase (A↔R) transformation. By aging at these temperatures, the ultimate tensile strength and elongation did not change significantly compared to the solution annealed sample. Aging at 500 and 600ºC lead to the appearance of B19´ phase during cooling cycle of differential scanning calorimetry tests. Samples aged at 500ºC and 600ºC showed the best mechanical properties, in comparison to the other aging temperatures. Maximum tensile strength of 1250 MPa and the elongation of 25% were obtained by aging at 500 and 600ºC, respectively. Solution annealed sample showed no superelastic property. Complete superelasticity was observed by aging at 400 and 500ºC.The sample aged at 700ºC showed the transformation behavior and mechanical properties similar to the solution annealed sample.

Development of Nickel-Rich Nickel–Titanium–Hafnium Alloys for Tribological Applications

“…High hardness in nickel-rich binary NiTi alloys is mainly attributed to nanoscale Ni4Ti3 precipitates [12][13][14][15][16] and to a lesser degree anti-site defects or Ni clustering due to excess Ni atoms within the matrix [17][18][19]. Moreover, coherency strain fields surrounding the Ni4Ti3 precipitates within the matrix can further enhance the hardness [13,20].…”

The machining characteristics and surface integrity of Ni-rich NiTi shape memory alloy using wire electric discharge machining

“…[1][2][3][4][5] Ni-rich SMAs are being widely used in various areas, namely robotics, biomedical, aerospace, and other important industries due to their outstanding properties. [6][7][8][9] Nevertheless, conventional machining of SMAs is extremely difficult, which creates low surface quality, high machining time, and high dimensional deviation. Therefore, to overcome these defects, the advanced machining process such as electrochemical machining, laser machining, water jet machining, electric discharge machining, and wire electric discharge machining (WEDM) process can be utilized for efficient and economic machining of SMAs.…”

Tuning the temperature range of superelastic Ni-Ti alloys for elastocaloric cooling via thermal processing

“…In terms of the A f temperature for these samples, it appears to be optimal for the samples aged at 400 • C for 5-10 min and annealed at 500 • C-550 • C for achieving elastocaloric materials for operation near room temperature. However, several studies revealed that superelastic properties, especially the recoverable and plateau stresses of Ni-Ti wires annealed at temperatures above around 500 • C-600 • C, decreased significantly, likely due to the plastic deformation of the austenite phase occurring before the stress-induced martensite transformation or due to the formation of large Ni 4 Ti 3 precipitates in the NiTi matrix [20,26,27]. It also should be noted that we might have achieved optimal A f temperature, but not necessarily optimal fatigue behavior depending on the size, morphology, and distribution of the precipitates.…”