Phase equilibria and phase transformations in the Ti-rich corner of the Fe–Ni–Ti system
While the main features of the Fe-Ni-Ti system are well known at low Ti content, literature review of the Ti-rich corner revealed inconsistencies between experimental reports. This investigation presents new experimental results, defined to remove the uncertainties concerning melting behavior and solid-state phase equilibria of the (Ni,Fe)Ti2 phase with the adjacent (Fe,Ni)Ti (B2, CsCl-type structure) and Beta-Ti (A2, W-type) phases. Six samples have been prepared and examined by differential thermal analysis performed in yttria and alumina crucibles, and by scanning electron microscopy in the as-cast state as well as equilibrated at 900°C.
Thermodynamic modeling and optimization of the Fe–Ni–Ti system
Abstract A thermodynamic assessment of the ternary Fe–Ni–Ti system together with a partial reassessment of the binary sub-systems Ni–Ti and Fe–Ti was made following the CALPHAD method and using the compound energy formalism (CEF). Two and four sublattices were used to model the bcc and fcc phases respectively. This allows describing the order–disorder transformations occurring not only in the ternary Fe–Ni–Ti system, but also in the quaternary Al–Fe–Ni–Ti system. The description of the C14 Laves phase TiFe2 was modified to three sublattices in order to be consistent with other Al–Fe–Ni–Ti sub-systems in which a three sublattice model is needed. Thermodynamic parameters were optimized using the available experimental data. On the basis of this optimization the stable phase diagram is calculated. Moreover stable and metastable equilibria between ordered and disordered phases based on fcc and bcc respectively are calculated.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.