Abstract
Several reviews have been written on various classes of titanium alloys including the high temperature titanium alloys. However, there is a gap in comprehensively putting together the research efforts on this important topic of low tensile ductility at room temperature in this class of high temperature titanium alloys used for critical applications in aeroengines. Thus, this review is aimed at bridging this gap. These alloys are designed based on exhausting the solid solubility of the alloying elements (mainly Al, Sn, Zr, Si) in titanium to improve the high temperature properties. Microstructural changes like precipitation of silicides and/or Ti3Al have been observed in these alloys depending upon their composition, thermomechanical processing, heat treatment and long exposures to service conditions. Several investigations have reported very low tensile ductility at room temperature in these alloys under certain conditions. This has been mainly attributed to either due to “silicides” or “silicides aided by Ti3Al” or “Ti3Al exacerbated by silicides” or “Ti3Al” and surface oxidation at the upper end of service temperatures. This low ductility is very pronounced in the lamellar than in the bimodal microstructures when silicides or Ti3Al or both occur. When Ti3Al precipitates are small (≤ ~6nm) and/or precipitation is only in the primary α in the bimodal microstructures, the impact on tensile ductility is very negligible. Alloy design and designing heat treatments are the methods found to be helping to mitigate the reduction in tensile ductility by either avoiding or controlling their size, volume fraction and location of the embrittling phases namely silicides and Ti3Al. Protective coatings are helping in reducing oxidation and help in avoiding the drop in tensile ductility. More research is required in these areas of alloy design, thermomechanical processing and coatings and also in optimizing the various conflicting requirements in these high temperature titanium alloys.

Keywords
titanium alloys; silicides; Ti3Al; ductility, microstructure, alpha case, embrittlement, coatings

Cite this paper
Ramachandra Canumalla, On the Low Tensile Ductility at Room Temperature in High Temperature Titanium Alloys , SCIREA Journal of Metallurgical Engineering. Volume 4, Issue 2, April 2020 | PP. 16-51.

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