Alpha case

Abstract: Designed to support the need of engineering, management, and other professionals for information on titanium by providing an overview of the major topics, this book provides a concise summary of the most useful information required to understand titanium and its alloys The author provides a review of the significant features of the metallurgy and application of titanium and its alloys All technical aspects of the use of titanium are covered, with sufficient metals property data for most users Because of its unique density, corrosion resistance, and relative strength advantages over competing materials such as aluminum, steels, and superalloys, titanium has found a niche in many industries Much of this use has occurred through military research, and subsequent applications in aircraft, of gas turbine engines, although more recent use features replacement joints, golf clubs, and bicycles Contents include: A primer on titanium and its alloys, Introduction to selection of titanium alloys, Understanding titanium's metallurgy and mill products, Forging and forming, Castings, Powder metallurgy, Heat treating, Joining technology and practice, Machining, Cleaning and finishing, Structure/processing/property relationships, Corrosion resistance, Advanced alloys and future directions, Appendices: Summary table of titanium alloys, Titanium alloy datasheets, Cross-reference to titanium alloys, Listing of selected specification and standardization organizations, Selected manufacturers, suppliers, services, Corrosion data, Machining data

Abstract: The oxygen-enriched alpha case on titanium and alloys was successfully deoxygenated to satisfactory levels by electrolysis in molten CaCl2, in which the cathode was made from the metal to be refined. The oxygen distribution in the metal before and after electrolysis was characterized by microhardness tests, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The electrolysis has been carried out at voltages sufficiently below that for the decomposition of CaCl2, and the results obtained suggest that the alpha case deoxygenation follows a simple oxygen ionization mechanism in which the oxygen in the metal is simply ionized at the cathode/electrolyte interface, dissolves in the molten salt, and then discharges at the anode. It is shown that by applying the electrochemical method, the alpha cases on both commercially pure titanium (CP Ti) and the Ti-6Al-4V alloy can be effectively deoxygenated. In particular, due to the removal of oxygen, the original alpha case (single phase) on the Ti-6Al-4V alloy has been converted back to the two-phase microstructure.

Abstract: The aim of this study is to clarify of the alpha-case formation mechanisms for the economic net-shape forming of Ti and Ti alloys. The alpha-case formation reaction between Ti and Al 2 O 3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by electron probe micro-analyzer and transmission electron microscopy. The alpha-case generation between Ti and Al 2 O 3 mold could not be explained by the conventional alpha-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, from the experimental results and thermodynamic consideration, it could be confirmed that the alpha-case is formed by not only interstitial oxygen atoms but also substitutional metal atoms dissolved from mold materials.

Abstract: With a view to use titanium alloys more effectively at elevated temperatures, the oxidation and alpha case formation should be prevented. This can be achieved by the application of high performance oxidation resistant coatings on the titanium alloys. A high performance oxidation resistant coating, based on the combination of surface modification techniques, electro-deposition and pack aluminizing, has been successfully developed to protect the titanium alloy, IMI 834 from oxidation and alpha case formation. Negligible weight gain and elimination of the alpha case formation during the entire exposure period demonstrate the superior performance of platinum aluminide coating. The excellent behavior is due to the formation of a protective, adherent and continuous alumina scale on the surface of the coating. Based on the results obtained for both coated and uncoated alloys, the developed high performance coating can enhance the life of components fabricated from the titanium alloy, IMI 834 considerably by preventing oxidation and alpha case formation and thereby improve the efficiency of gas turbine compressor sections significantly