Melting during heat treatment of a sheet of a niobium alloy - Failure analysis

• Published in: Materialwissenschaft und Werkstofftechnik 2009-08, Vol.40 (8), p.634-637
• Main Authors: Bhatia, D.N., Rao, M.N., Taneja, A.K.
• Format: Article
• Language: English
• Subjects: Annealing; Blech aus Niob-Legierung; Charge; Charge materials; Eutectic melting; eutektisches Schmelzen; Failure analysis; Heat treatment; Melting; Niobium alloy sheet; Niobium base alloys; Phase diagram; Phasendiagramm; Platte aus Superlegierung 600; Superalloy 600 plate; Titanium; Vacuum heat treatment; Wärmebehandlung unter Vakuum
• ISSN: 0933-5137; 1521-4052; 1521-4052
• DOI: 10.1002/mawe.200800453

The niobium alloy Nb‐5.4 At% Hf‐2 At% Ti is an important structural material used for high temperature applications. It is commonly produced in the form of sheet; however, it is also available in other mill forms. The sheets are vacuum‐annealed to improve the formability prior to fabricating different components out of them through metal forming. Annealing in vacuum is adopted in view of the high proneness to oxidation of niobium‐ base materials. In the present instance vacuum annealing of a sheet of the niobium alloy was carried out at 1175 oC; a plate of the nickel‐base superalloy 600 was used as charge support. It was noticed that the vacuum annealing resulted in melting of the charge as well as the charge support material. The plate of superalloy 600 was then replaced by a sheet of commercially pure titanium and next trial of annealing heat treatment carried out; there was no problem of melting. Failure analysis was carried out. The analysis brings out how phase diagrams can be used to choose the right material for supporting the charge in order to prevent melting during heat treatment. The failure is very expensive, if the material to be heat treated is costly, as it happens to be in the present case.