The Measurement of Total Inclusion Content In Nickel-Titanuim Alloys

Inclusion content is important for the performance of Nickel-Titanium alloys particularly in fatigue rated devices.  In commercial products, inclusion content is most often rated by maximum inclusion size and maximum area fraction pursuant to the ASTM standards.  This paper presents work done to measure the total inclusion population of wire products.  Inclusion size was characterized by frequency versus size from the minimum to the maximum observed size.  Area fraction of inclusions was characterized by frequency versus area percent for all fields of view analyzed.  Work presented at SMST 2010 showed that carbide inclusions and intermetallic oxides behave differently in cold drawing of wires.  Therefore, carbides and oxides were measured separately.   Inclusion populations in binary alloys were also found to vary with the nickel to titanium ratio.  Data will be presented for standard products at low and high Ni:Ti ratios. Inclusion size and area fractions distributions will be presented as a method to assess potential new products and process improvements.