METHOD FOR EVALUATING THE EFFECTIVENESS OF A COMPACTION PROCESS TO FRACTURE NITRIDED TITANIUM SPONGE PARTICLES
Publication Date: 2010-Jul-23
The IP.com Prior Art Database
A method for evaluating the effectiveness of a compaction process to fracture nitrided titanium sponge particles is disclosed. Nitrided seeds containing varying nitrogen contents are immersed in colored liquids, which make the nitrided seeds visually detectable, before being added to the melt process. As a result, when a puck is broken to determine the effectiveness of the compaction process, the nitrided seeds are easily distinguishable from the non-nitrided sponge particles.
The present invention relates to titanium melt processes. More specifically this disclosure relates to a method for evaluating the effectiveness of a compaction process to fracture nitrided titanium sponge particles.
Titanium alloys are used to manufacture rotating parts (e.g. disks, shafts, spools, etc). Titanium alloys are ideal for high speed rotating aircraft parts that require high-strength metals. Generally, titanium is extracted from ore by the production of titanium tetrachloride and its subsequent reduction to titanium by reaction with either magnesium or sodium. Electrolytic reduction may also be used. The reduction product is a porous, spongy material, which is referred to as titanium sponge. Titanium sponge is typically converted to titanium alloy products by a series of consumable electrode melting operations. Initially, the titanium sponge with either alloy particles mixed therewith or unalloyed in particle form is typically pressed to compact the particles to form compacts that are joined by welding to produce an electrode. Alloying elements may be introduced in admixture with the sponge particles in desired amounts for producing titanium-base alloys. The electrode is then vacuum arc melted to produce an ingot that typically is then re-melted once or twice to produce a final ingot. The ingot resulting from either double or triple vacuum arc melting is then processed by a series of forging and annealing steps to form ingot products such as a billet or shaped products that are machined to desired final product configurations.
During the production of titanium sponge, interaction with the ambient atmosphere may cause a reaction of particles of the titanium sponge with air to form nitride or oxynitride particles, which ultimately can result in defects known as low density inclusions in the ingot and products made therefrom. These nitrogen-rich particles are highly refractory and thus do not melt during the conventional vacuum arc melting steps incident to the production of a titanium ingot. Typically, the nitride or oxynitride particles slowly dissolve during the vacuum arc melting operation. As the particles dissolve slowly, they tend to sink to the bottom of the molten metal pool formed during vacuum arc melting. If not completely dissolved when they sink to the bottom of the pool the titanium solidifies above these undissolved particles to entrap them in solid titanium. Because the dissolution of the particles is by a solid-state reaction process, the dissolving of the particles is impeded. Consequently, these particles result in defects in the form of highly refractory, hard, porous particles that are contained within the solidified ingot.
During subsequent reduction of the titanium ingot as by forging and/or rolling to the desired shapes, such as billet, bar and plate, the low-density inclusions remain with...