Laser Processing of Net-Shape NiTi Shape Memory Alloy

Abstract

Fabrication of bulk NiTi alloy parts by conventional processing contains undesirable intermetallic phases in varying proportions depending on the composition and requires postfabrication heat treatments, which necessitate development of new processing routes. We have fabricated net-shape samples, with and without designed porosity, from equiatomic NiTi alloy powders using laser engineered net shaping (LENS), a commercially available rapid prototyping technique. Laser-processed NiTi samples retained the desired phases of initial powder and showed higher hardness due to the retention of high-temperature cubic B2 phase. Thermally induced stresses and defects, due to high cooling rate in laser processing, increased the reverse transformation temperatures of laser-processed samples. LENS-processed samples also showed high compressive strengths (plastic flow stress) in the range of 890 to 1,050 MPa due to finer grain size. This article discusses the influence of laser parameters on microstructure, mechanical properties, and phase transformation behavior of fully dense NiTi parts produced via LENS.

In Situ Synthesis and Characterization of Shape Memory Alloy Nitinol by Laser Direct Deposition

“…More recently, investigations for direct laser metal deposition (DMD), [17] laser engineered net shaping, [18,19] and selective laser melting [20] have been carried out to fabricate near-net shape components using prealloyed nitinol powder. However, to the best of the authors' knowledge, no attempts have been made to fabricate components directly from elemental nickel and titanium powder using any of the previously stated additive manufacturing techniques.…”

Multiple Memory Shape Memory Alloys

“…Specific methods previously attempted included, direct electric resistance heat treatment (DERHT), [10,11] direct hot air heat treatment (DHAHT), [10] powder metallurgy (PM), [12][13][14][15] gradient annealing, [16] laser annealing, [17] and joining of multiple alloys. [18] All of these techniques aimed to enable designs that utilize more than one set of functional properties in a monolithic component.…”

“…[10,11,16,17] PM methods exhibited issues with porosity, poor surface finish, and composition inhomogeneity leading to undesirable intermetallic compound (IMC) formation. [13][14][15] In contrast, joining of multiple alloys showed to be relatively effective for simple devices. [18] However, challenges associated with joining dissimilar SMAs (i.e., IMC formation) and more complex designs again limit application.…”

Effect of surface modification by nitrogen ion implantation on the electrochemical and cellular behaviors of super-elastic NiTi shape memory alloy

“…Furthermore, excellent mechanical properties and close similarity of stress-strain behavior between NiTi and human bone made NiTi a suitable choice for permanent implant applications [18].…”