The Effect of Alloying Elements and Impurities on the Composition and Formation of Intermetallic Particles in Titanium and Titanium Alloys

ABSTRACT

The corrosion resistance of alpha and near‐alpha titanium alloys has resulted in their widespread application in extreme environments. Their corrosion behavior is often influenced by their microstructure, particularly intermetallic particles (IMPs), and even slight compositional variations can produce significant differences in microstructure and corrosion performance. This study examines the microstructure of two different source materials for each of ASTM Grade‐2 titanium (Ti‐2), ASTM Grade‐7 titanium (Ti‐7), and ASTM Grade‐12 titanium (Ti‐12). Field emission scanning electron microscopy coupled to energy‐dispersive X‐ray spectroscopy (FESEM/EDX) and a field emission scanning Auger microprobe (FESAM) were used to investigate the relationship between the nominal composition and microstructure of each material. The IMPs on Ti‐2 were found to be enriched in Fe, with average compositions of Ti _4.6 Fe and Ti _5.5 Fe in the two Ti‐2 materials, respectively. For Ti‐7, no IMPs formed in the lower‐iron material, and Pd was distributed evenly through the Ti matrix. In the alloy with higher Fe content, the IMPs were predominantly composed of Fe and were only slightly enriched in Pd relative to the matrix. Pd was detected but could not be accurately quantified by AES due to low enrichment levels. The average IMP composition was Ti _4.8 FePd _x . For Ti‐12, Ni, Mo, and Fe were present in the IMPs. The average IMP compositions for the Ti‐12 materials were Ti _5.2 NiMo _0.17 and Ti _3.4 NiFe _0.16 Mo _0.11 . Across all materials, an increase in Fe content was associated with an increase in average IMP size; Fe played a unique role that was not shared by other elements in driving IMP formation.