A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 6 1 SMJ HIGHLIGHTS applications such as fracture healing and joint fusion. Orthopaedic medical devices that have incorporated Nitinol are increasing in number, with two noted examples including staples and intramedullary nails. Early Nitinol devices utilized shape memory Nitinol, but the logistical difficulties with maintaining a cold state in the clinic or limited force- generation for materials warmed from room temperature to body temperature have led to pseudoelastic Nitinol devices dominating clinical usage. Both pre-clinical biomechanical and clinical studies have shown that these devices do exert sustained compression beyond the abilities of competing static devices, and largely have resulted in superior clinical outcomes, such as higher fusion rates and faster times to fusion. Given these results, continued adoption of existing Nitinol devices and future development of new orthopaedic devices utilizing the material should continue (Fig. 2). EFFECT OF C/O RATIO ON PHASE CHANGE AND STABILITY OF INCLUSIONS IN Ti–Ni ALLOYS FABRICATED BY A COMMERCIAL PRODUCTION PROCESS Fumiyoshi Yamashita, Yasunori Ide, Hiroshi Akamine, Kouji Ishikawa, and Minoru Nishida The effects of carbon/oxygen concentrations in Ti-51 at.% Ni on the morphology and phase changes of inclusions in a commercial wire manufacturing process were investigated. Whereas, cast material fabricated with a carbon to oxygen mass concentration ratio (C/O ratio) of 1.0–1.5 were found to contain single-phase Ti(C,O), when hot working was performed, some of the Ti(C,O) exhibited a phase change to Ti2Ni(O), and a mixed phase structure was found in specimens with a C/O ratio of less than 1.5. On the other hand, single-phase Ti(C,O) was found to remain in the wire produced from the specimens with a C/O ratio of 1.5 (Fig. 3). PROCESSING AND SCALABILITY OF NiTiHf HIGH-TEMPERATURE SHAPE MEMORY ALLOYS O. Benafan, G.S Bigelow, A. Garg, R.D. Noebe, D.J. Gaydosh, and R.B. Rogers Development of melting and processing techniques for NiTiHf high-temperature shape memory alloys at the laboratory scale has resulted in pronounced success and repeatability for actuation purposes. Even the Ni-rich NiTiHf formulations, which are more challenging from a compositional control standpoint since small changes in chemistry can result in large transformation temperature variations, are reproducibly processed at the laboratory scale. Since properties of the slightly Ni-rich NiTiHf alloys have proved promising, large-scale production of such alloys now requires renewed attention. In this work, several melting techniques were used to process NiTi-20Hf (at.%), ranging from vacuum induction melting to plasma arc melting, with heats ranging in size from 0.4 to 250 kg with a target composition of Ni50.3Ti29.7Hf20 (at.%). All cast ingots were subsequently hot extruded into bar. The resulting chemistries, microstructures, and inclusion types and sizes were evaluated as a function of melting technique. Finally, the thermophysical, mechanical and functional properties were measured for a number of material heats that varied in size and primary processing technique. The results indicated that variousmelting techniques could result in alloys with slightly different end compositions that can affect the mechanical and functional Fig. 2 — Intramedullary nail incorporating pseudoelastic Nitinol element. Recovery of the stretched element during the joint fusion process can be observed and quantified using longitudinal x-rays. Fig. 3 — Scanning electron microscopy (SEM)-secondary electron (SE) images of inclusions extracted from cast specimen with C/O ratio of 1.3 by the selective potentiostatic etching by electrolytic dissolution (SPEED) technique. 1 3
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