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.
Microstructural investigations of laser welded dissimilar Nickel- Titanium-steel joints
Nickel-titanium based shape memory alloys are used in a variety of applications. These applications desire joining techniques that provide only local degradation of the functional properties and are compatible to the special mechanical properties of shape memory materials. Laser welding of nickel-titanium based shape memory alloys is an established process in medical application. Similar and especially dissimilar joints of nickel-titanium shape memory alloys, in particular joints of nickel-titanium and steel, are requested combinations to open additional fields of applications. A detailed investigation of the microstructural changes of laser welded parts is necessary to provide a good weld quality and to consider the related changes of the mechanical properties in the design process for certain applications. The formation of phases in the heat-affected zone as well as in the fusion zone was investigated by means of optical microscopy, scanning electron microscopy, electron backscatter diffraction and X-Ray diffraction. Focused ion beam was used for aim preparation of transmission electron microscopy samples at the interface nickel-titanium/fusion zone, the center of the fusion zone and the interface fusion zone/steels.
Activities in dilute solutions of chromium and iron in nickel at 1600° by mass spectrometry
Binary and ternary alloys of chromium and iron with nickel were studied. The total solute content ranged from 1 to 10 at. pct. The first-order interaction coefficients for chromium are εCr(Cr)= 1.8 ±2.0, and εCr(Fe) = 0.6 ± 5.0 (twice standard deviation). The relative partial molar enthalpy of liquid chromium in nickel at 1550° and at 5 pct chromium is −2200 cal per g-atom. An unusual result was obtained for iron in the form of a minimum in the experimental ln(IFeNNi/INiNFe)-curve.