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Tuesday, May 9, 2006 - 8:30 AM
MEM6.1

Fabrication of Single-Phase NiTi-Based SMA by Vapor Phase Calciothermic Reduction (VPCR) Process

F. Sczerzenie, SAES Smart Materials, New Hartford, NY; B. Bertheville, Nickel Industrial Titanium Innovative Group, NITIG, Sion, Switzerland

The use of a highly reducing atmosphere, i.e. calcium reducing vapor, during the NiTi compound forming reaction allows obtaining directly a single-phase microstructure by a PM basic single-step sintering procedure. It was successfully applied for synthesizing equiatomic NiTi, Ti-rich NiTi, NiTi1-xZrx and NiTi1-xHfx shape-memory alloys. Furthermore, controlling sintering parameters (heating rate, sintering temperature) make possible adjustments of porosity rate. Thus, porous single-phase NiTi alloys for used as biomaterials were also obtained using this alternative powder metallurgical route. X-ray diffraction (XRD) and electron scanning microscopy/energy dispersive (SEM/EDS) analyses show that the generated microstructure of NiTi-based alloys is comparable to that of melt-cast alloys. Furthermore, composition shifts usually observed in alloys processed by other powder metallurgical routes do not occur. By using the VPCR process, the formation of Ti-consuming oxides, that shifts the transformation temperatures in a poorly controlled manner, is avoided.

 

Summary: The use of a highly reducing atmosphere, i.e. calcium reducing vapor, during the NiTi compound forming reaction allows obtaining directly a single-phase microstructure by a PM basic single-step sintering procedure. It was successfully applied for synthesizing equiatomic NiTi, Ti-rich NiTi, NiTi1-xZrx and NiTi1-xHfx shape-memory alloys. Furthermore, controlling sintering parameters (heating rate, sintering temperature) make possible adjustments of porosity rate. Thus, porous single-phase NiTi alloys for used as biomaterials were also obtained using this alternative powder metallurgical route. In the present work, processing and mechanism of generation of a single-phase microstructure are presented.