Evaluation of Low Cost Titanium Alloy Products

Abstract

Titanium has extremely attractive properties for air vehicles ranging from excellent corrosion resistance to good compatibility with graphite reinforced composites and very good damage tolerance characteristics. At current Buy to Fly ratios, the F-35 Program will consume as much as seven million pounds of titanium a year at rate production. This figure is nearly double that of the F-22 Program, which has a much higher titanium content. Lockheed Martin has initiated “Project Black Ti” to reduce the cost of titanium parts by reducing the titanium consumption but not the quantity of titanium parts. Ultimately, we want to reduce the inherent waste in the current processing of titanium alloy products. The Kroll process, by which most titanium product is made today, is nearly 60 years old. Kroll himself predicted the process would be replaced within 15 years due to inherent inefficiencies – in 1950. Titanium is also mis-characterized as a precious metal, which it is not. It is the ninth most abundant element on the earth’s surface. Aluminum by comparison is the third most abundant but has a much more efficient method to convert it to a usable form. Until the turn of the 20th century, aluminum was considered to be as precious as platinum until the Bayer Process brought prices down from $1200/kg to $0.60/kg. Regarding titanium, one way to improve efficiency and buy less material to make the same parts is via Powder Metallurgy (PM). Until recently, titanium alloy powder was very expensive. However, new methods of producing titanium alloy have been developed which generate powder as an output versus massive ingots, which require multiple melts to achieve homogeneity. With powder, in theory, we should be able to get much closer to net shape and reduce the initial buy and reduce significant machining costs. These low cost titanium powders are becoming commercially available, which has the potential to initiate a paradigm shift in the applications of titanium. PM technologies and the consolidation of these new powders are now economically viable with the potential cost of the new powders running approximately an order of magnitude less than conventional PM grade powders. This paper will present the current status of “Project Black Ti” and its potential impact to the F-35 program.

Powder metallurgy of titanium – past, present, and future

“…The initial rapid pressurisation has been called an 'air hammer', which is achieved by opening a valve between the pressure chamber and a pre-pressurised gas reservoir. Super-transus (>1000°C) GIF treatments of Ti-6Al-4V have also been reported [252]. A simple schematic showing the primary steps of the GIF process is shown in Figure 28.…”

“…Gaseous isostatic forging (GIF) technology, also known as pneumatic isostatic forging (PIF), is a post-sintering process to increase the density of a sintered article [252][253][254][255]. GIF is similar to HIP, in that it uses isostatic pressure at elevated temperatures to close pores.…”

Sintering of Titanium with Yttrium Oxide Additions for the Scavenging of Chlorine Impurities

“…The sintered density was determined by the Archimedes method as per Metal Powder Industries Federation Standard 42, with the exception that H-Galden ZT-180 high-density fluid (1.693 g/cm 3 at 298 K [25°C]) was used instead of water. The theoretical (or pore-free) density of alloys was calculated [26] using information from the phase diagram (i.e., the mass fraction of phases) and the density of the phases.…”

“…The appeal of PM methods is associated with potential cost and energy savings compared to traditional methods of manufacture based on repeated ingot metallurgy. [1][2][3][4] Such potential savings are derived principally from more efficient processing conditions, reduced material wastage, and the benefits of avoiding bulk melting of titanium.…”

Sintering of HDH Ti Powder

“…Therefore there is a great loss of expensive material. Currently the aerospace industry buys about eight times more Ti as it finally uses in the aircrafts finished parts [3]. Machine ability of Ti is worse than other metals because its surface becomes brittle due to oxygen and nitrogen [4].…”