TO DEVELOP AND CHARACTERIZE Ni-BASED ODS ALLOY

Abstract

A superalloy is an alloy developed for elevated temperature service where relatively severe mechanical stressing is encountered and where high surface stability is frequently required. Super alloys are based on group VIII B elements and usually consist of various combinations of Fe, Ni, Co, and Cr as well as lesser amounts of W, Mo, Ta, Nb, Ti, and Al. The most important of these super alloys are long time strength at temperatures above 650°C and resistance to hot corrosion and erosion. To extend the good corrosion resistance and good strength values of conventional superalloys to even high temperatures, new processing techniques and new types of microstructure have been developed during the past two decades. Dispersion strengthened (ODS) superalloys form one of such new material groups, increasing the useful service temperature of gas turbines by almost 100°C. ODS alloys are usually manufactured by mechanical alloying (powder metallurgy route). Processing of these alloys involves high energy milling of elementary or pre- alloyed powders with stable oxide e.g. Y203, followed by pressure assisted consolidation at high temperature. The ODS alloys can be produced by powder metallurgy because conventional melting and casting techniques are not useful for production of dispersion strengthened materials because of the very high interfacial energy between the molten metal and oxide, which leads to flocculation and disparities between the matrix metals and dispersoids, lead to segregation in the melt. The Ni- based ODS alloys mainly consists of Ni of about 78% and the remaining of Cr, Al, Y203 as alloying elements. The important Ni- based ODS superalloy is MA754 which is mainly produced by M/S INCO ALLOY CO, USA. The present work aims to develop Ni- based ODS alloys economically with properties comparable with MA754 alloy through powder forging technique and to study the effect on rolling and their corrosion properties taking by commercially available a metal / alloy powder with even higher oxygen levels is the primary aim of present dissertation work.