F. Sczerzenie, G. Paul, C. Belden, SAES Smart Materials, New Hartford, NY; A. Fasching, Memry Corporation, Menlo Park, CA
Inclusion analysis to ASTM Standards has traditionally been preformed on optical microscopes with software to measure size and area. This study compared measurements obtained by using both optical and SEM – Backscatter Electrons Imaging (BEI) Inclusion Analyses of VIM - VAR Nickel-Titanium Alloy.Three binary nitinol alloys, with varying Af temperatures, were selected to be tested. Each sample tested was hot drawn to 0.250” diameter coil. The coil was then metallographically prepared to yield a sample in the longitudinal direction. This allowed the coil to be examined using both the optical and SEM-BEI method. The largest inclusion (carbide, intermetallic and oxide) and area fraction were recorded. In addition, the SEM-BEI was used to identify the chemistry of the noted inclusions.
A Zeiss M2 optical microscope and JOEL SEM were utilized throughout this study. These microscopes offer a highly accurate method of obtaining inclusion data. Understanding any differences between the two methods will ultimately give us a better understanding in selecting the method to be used.
Summary: Two different methods for inclusion analysis are compared in this study using samples from different VIM-VAR ingots of commercial binary NiTi alloys. The paper compares the traditional analysis according to ASTM standards by means of optical microscopy with the quantitative analysis in an SEM using backscattered electrons imaging. Besides the quantitative analysis the SEM method allows the identification of the chemistry of the inclusions.
