Effect of Nb Content on Martensitic Transformation Temperatures and Mechanical Properties of Ti-Ni-Nb Shape Memory Alloys for Pipe Joint Applications

Abstract

Several Ti-Ni-Nb shape memory alloys (SMAs) with various Nb contents (0$15 mol%) or Ni/Ti atomic ratios (1:0$1:1) were tested to investigate the martensitic transformation temperatures and mechanical properties. The martensitic transformation temperatures (M s , M f , A s and A f ) of the solution-treated Ti-Ni-Nb alloys at 1173 K for 300 seconds with Ni/Ti ratio of 1.0 decrease with increasing the Nb content. These transformation temperatures also depend on the Ni/Ti ratio, heat treatment condition and cold working rate. Furthermore, in the alloy with Nb content of 6 mol% and Ni/Ti atomic ratio being less than 1.05, the fracture stress and fracture strain reached about 1,000 MPa and over 20%, respectively. Based on the obtained results, several processing conditions such as the chemical composition, fabrication process and heat treatment are optimized for the Ti-Ni-Nb SMAs to develop SMA pipe joints.

Shape-memory NiTi–Nb foams

“…For both Ti 50 Ni 50-x Nb x and Ti 50-x/2 Ni 50-x/2 Nb x alloys (to which our alloy belongs), M s decreases by 20-40 C for a Nb content of 3 at.%. Uchida et al 32 reported a decrease in transformation temperature of $30 C after adding 3 at.% Nb to equiatomic NiTi produced by vacuum induction melting. This is in general agreement with the decline of M s by 23 C from NT0 to NTN0 and by 36 C from NT40 to NTN40 (Table II).…”

“…Also, it is known that the addition of Nb increases the local Ni/Ti ratio in the NiTi-rich B2 phase responsible for the recovery effect, and increases the proportion of the Nb-rich phase, which resists transformation of the B2 phase in the eutectic. 32,43 Therefore, transformation becomes more difficult, and transformation temperatures are decreased. Piao et al 43 studied the martensitic start temperature (M s ) in NiTi-Nb arc-melted alloys.…”

“…28) of such alloys used liquid processing approaches, such as arc-or induction-melting followed by casting. Although previous studies of these NiTi-Nb alloys have focused on the shape-memory properties for coupling/joint applications, [29][30][31][32][33] or more recently, on hydrogen dissolution and diffusion in membranes for hydrogen purification, [34][35][36] biomedical implant applications (such as stents 37,38 ) are another promising use for these alloys. In fact, a NiTi-Nb alloy with Ti 44 Ni 47 Nb 9 composition prepared by arc-melting was found to develop passive oxide layers imparting high corrosion resistance when tested in simulate body fluid.…”

On the replacement of steel by NITINOL as coupling agent in automobile shaft

“…The TiNiNbSMA has a high transformation temperature hysteresis and has thus been used in pipe joints and similar applications. Uchida et al (2007) manufactured the alloy in a high-frequency induction vacuum furnace and prepared two samples: One sample with Ni/Ti atomic ratio equal to 1, and Nb concentration between 0 and 15 mol%, whereas another sample contains Nb concentration 6 mol%, and the Ni/Ti ratio was changed from 1.025 to 1.1. Transformation temperature decreased with increasing Nb content in the first sample, and a huge deviation was recorded with Nb being 12 mol%, the second sample having Ni/Ti ratio is 1.088.…”

Processing Map of NiTiNb Shape Memory Alloy Subjected to Plastic Deformation at High Temperatures

“…In particular, when the soft β-Nb phase in the NiTiNb SMA suffers from plastic deformation, the relaxation of elastic strain in the martensite interface contributes to lowering the driving force of reverse martensite transformation and, hence, facilitating the stability of martensite [9]. Therefore, NiTiNb SMA has been a perfect candidate for pipe coupling because the large phase transformation temperature hysteresis plays a predominant role in guaranteeing the reliability of pipe coupling in engineering applications [10][11][12].…”