F. H. Sam Froes

Structure of mechanically alloyed Ti-Al-Nb powders

Ti-Al-Nb ternary powder mixtures containing 24Al-11Nb, 25Al-25Nb, 37.5Al-12.5Nb, and 28.5Al-23.9Nb (at. pct) were mechanically alloyed in a SPEX 8000 mixer mill using a ball-to-powder weight ratio of 10:1. The structural evolution in these alloys was investigated by X-ray diffraction and transmission electron microscopy techniques. A solid solution of Al and Nb in Ti was formed at an early stage of milling, followed by the B2/body-centered cubic (bec) and amorphous phases at longer milling times. The stability of these phases and their transformation to other phases have been investigated by heat treating these powders at different temperatures. The B2/bcc phase transformed into an orthorhombic (O-Ti2AlNb) or a mixture of the orthorhombic (O) and hexagonal close-packed (α2-Ti3Al) phases, the proportion of phases being dependent on the powder composition. Milling beyond the amorphous phase formation resulted in the formation of an fee phase in all the powders, which appears to be TiN, formed as a result of contamination of the powder.

Precipitation of Ti5Si3 phase in TiAl Alloys

Abstract The nucleation, growth and interface structure of Ti5Si3 precipitates in Ti52Al48–3Si, Ti52Al48–3Si2M (M=Cr, V), and Ti52Al48–3Si2Cr2V (at.%) alloys were studied. It is found that nucleation of Ti5Si3 precipitates depends on the dislocation types, γ domain boundary or γ/γ lamellar boundaries. Most of the Ti5Si3 nucleates at 1/2[10 1 ] super-dislocation networks, particularly at the extended nodes of [10 1 ], where stacking faults exist, while some Ti5Si3 precipitates at 1/2[1 1 0] dislocations. In addition, most Ti5Si3 are precipitating out heterogeneously at pseudo-twin type γ/γp* and 120°-rotational order-fault type γ/γR* lamellar boundaries, but no Ti5Si3 is found to precipitate at true-twin type γ/γT* lamellar boundaries. The growth mechanism of Ti5Si3 in TiAl is also studied.

Cost Effective Developments for Fabrication of Titanium Components

The major reason that there is not more widespread use of titanium and its alloys is the high cost. In this paper, developments in one cost effective approach to fabrication of titanium components - powder metallurgy - will be discussed under various aspects of this technology. The aspects to be discussed are the blended elemental approach, pre-alloyed techniques, additive layer manufacturing, metal injection molding, spray deposition and microwave sintering. A brief review of a number of low cost powder production processes is also presented.