Effects of VIM frequency on chemical composition, homogeneity and microstructure of NiTi shape memory alloy

Abstract

The concentration distribution and microstructure of NiTi shape memory alloys produced in vacuum induction furnaces operating at high and medium frequencies are compared with those of materials melted in vacuum resistance furnaces. The production procedure consisted of charging pure metals into a graphite crucible; raising the temperature to 1450°C under vacuum; holding the materials in high and medium frequency induction and resistance furnaces for 3, 5, and 120 min under vacuum; and allowing alloys to solidify in the crucibles under the same vacuum. The procedures in each of the three furnaces were made as similar as possible. Chemical composition, microstructure, and surface hardness of alloys were determined at different locations along the length of solidi ed specimens. Standard deviations in chemical analyses and hardness numbers were taken as criteria for specimen homogeneity. Results indicate that a high vacuum induction furnace operating at medium frequency is an appropriate equipment for melting NiTi shape memory alloys of the desired homogeneity, microstructure, and hardness.MST/5915

Optimum temperature for recovery and recrystallization of 52Ni48Ti shape memory alloy

“…Sponge titanium particles together with cathodic nickel plates were melted to produce NiTi ingots. Details of the production procedure were described elsewhere [9]. Particle induced X-ray emission (PIXE) [10] analyses were used to determine the analysis of the as-cast samples.…”

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“…SEM/EDS analysis revealed an equiatomic proportion of Ni and Ti in accordance with the requisites for shape memory effect. 8 Alloys with more than 51.6at%Ni became hard and friable. 8 Besides alloys enriched with Ni present the best SE and SME characteristics.…”

Nitinol Spinal Vertebrae: A Favorable New Substitute

“…NiTi monophase is, however, both flexible and rigid depending on the temperature. Superelasticity, biocompatibility, shock damping, fatigue restraint, restricted erosion, biofunctionality, wear opposition, corrosion resistance, shape memory, and stiffness similarity to the bone are some extraordinary behaviors of the Ni-Ti alloy [9,18,[24][25][26][27][28][29][30][31][32][33][34][35]. That these characteristics make it superior to other alloys qualifies Nitinol usage for making orthopaedic implants, especially for high loading/reloading regions.…”

“…Precise composition control has a crucial role in the structural characteristics of the Nitinol [61,62]. Method of production influences homogeneity and chemical composition of the alloy, drastically [26]. Any impurity can affect both transformation temperatures and the movementlocking precipitates which substantially deteriorate the alloy performance [53].…”