Dissolution of High Density Inclusions in Titanium Alloys

Abstract

This paper deals with the presence of High Density Inclusions (HDI) in VAR melted titanium ingots. For performance and economical reasons, the elimination of these inclusions is of utmost importance for the titanium industry. However, very few studies have considered dissolution aspects of HDIs and accurate data on their dissolution rates still lack in the literature. In the present study, we investigate the mass transport driven dissolution of some HDIs (tungsten and molybdenum) in CPTi, Ti64 and Ti17 baths. This has been done by allowing the partial dissolution of cylindrical rods in molten titanium for various controlled periods of time. Dissolution rates have been determined by measuring the dimensions of these samples before and after the experiments. In some cases, the chemical composition of the solidified bath near the sample has also been measured by Scanning Electron Microscope. It has been evidenced that the dissolution kinetics depends highly on the liquid metal agitation and temperature. The results also revealed that the dissolution of both tungsten and molybdenum is higher in pure titanium than in the investigated alloys. A numerical model describing the mass transport driven dissolution was used to determine dissolution rates numerically and to compare them to experimental results.

Laser Powder Bed Fusion (PBF-LB/M) Process Strategies for In-Situ Alloy Formation with High-Melting Elements

“…While, according to literature, a high volumetric energy proved to be beneficial [15], the present results demonstrate that this is only one aspect of many and that more complex interdependencies affect the dissolution of high melting particles in the meltpool during PBF-LB/M. Vacuum arc furnace melting experiments and theoretical considerations by Ghazal et al [30] identify the dwell time, the temperature, and the velocity of the surrounding melt as key factors for dissolution of high melting inclusions in Ti-alloys. Quantifying these parameters for a specific PBF-LB/M parameter combination is complex and requires elaborate numeric simulations that would exceed the scope of this manuscript.…”

An examination of the factors influencing the melting of solid titanium in liquid titanium

“…In order to keep S M bounded, a limiting value for f s of 0.99 was imposed on the calculation of Eq. (5). Note: f s equals 0.99 corresponds to a large value of the term l Kperm in Eq.…”

“…Turning to the titanium system, some relevant investigations have been carried out on the dissolution behavior of HDIs and HIDs in liquid titanium. For example, Ghazal et al [5] dipped cylinders of tungsten and molybdenum (metals that result in HDIs) into various molten titanium alloys melted in a small EBBF to quantify their dissolution rates. In another study on HDIs, Yamanaka and Ichihashi [6] investigated the dissolution of tungsten, tantalum and vanadium particles in a molten pool by utilizing a Vacuum Arc Remelting (VAR) furnace.…”

Present stage and future prospects of development of compressor material

“…The diameter of a VAR ingot at Toho Titanium Co. Ltd varies from 510 to 1250 mm . One conventional issue of the VAR process is that melt‐related defects such as hard α inclusion (LDI), like TiC and TiN, and high‐density inclusion (HDI) can be included in an ingot . HDI can be formed by non‐melted refractory elements such as tungsten or the accidental mix of fragments of tools.…”