Fabrication and characteristics of porous NiTi shape memory alloy synthesized by microwave sintering

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-07, Vol.528 (18), p.6006-6011
• Main Authors: Tang, C.Y., Zhang, L.N., Wong, C.T., Chan, K.C., Yue, T.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Elasticity. Plasticity; Exact sciences and technology; Intermetallics; Martensitic transformations; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Microwave sintering; Nickel base alloys; Nickel compounds; Nickel titanides; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase transformation; Physics; Porous NiTi; Powder metallurgy. Composite materials; Production techniques; Shape memory alloys; Sintering (powder metallurgy); Technology; Titanium compounds
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.04.040

► A novel microwave sintering method to fabricate porous NiTi shape memory alloy was developed. ► Porous NiTi SMA was fabricated without using any pore forming agents. ► Characteristics of the microwave sintered porous NiTi SMA were investigated. Porous nickel titanium (NiTi) shape memory alloy (SMA) was successfully fabricated by microwave sintering method. This method allows formation of porous structures without using any pore-forming agents. Moreover, microwave sintering of NiTi SMA can be successfully performed at a relatively low sintering temperature of 850 °C and a short sintering time of 15 min. The pore characteristics, microstructure, phase transformation and stress–strain behavior of the porous NiTi SMA were investigated. The porous NiTi SMA exhibited porosity ratios from 27% to 48% and pore sizes range from 50 to 200 μm when using different sintering temperatures and holding times. The predominant B2 (NiTi) and B19′ (NiTi) phases were identified in the porous NiTi SMA. A multi-step phase transformation took place on heating and a two-step phase transformation took place on cooling of the porous NiTi SMA. The irrecoverable strains decreased with increasing sintering temperature, but the holding time had little effect on the stress–strain behavior at 60 °C.