Analysis on the Suitability of Powder Metallurgy Technique for Making Nickel Based Superalloys

Abstract

Nickel based superalloys are of a typical class of materials with an exceptional capability of retaining strength and toughness at high temperatures. Also, they have high resistance to degradation in corrosive environments. These properties of superalloys make them ideal materials for gas turbine engines used in power generation, marine engineering and aircraft applications. Earlier, researchers studied about the suitability of cast and wrought superalloys for their applicability in gas turbines. Superalloys are developed from polycrystalline to directionally solidified alloys and finally single crystal alloys by investment casting process for making turbine blade. In this work, the powder metallurgy technique is analysed for determining its appropriateness for making nickel based superalloys in gas turbines. This technique includes powder blending, compaction and sintering with or without post heat treatment for making a product. This process can offer high performance applications, where unique microstructural and mechanical characteristics are required. Refractory material can be easily alloyed by this technique, to enhance heat bearing capabilities. In this work, the development of nickel based superalloys by powder metallurgy technique, their composition as well as the influence of various elements on mechanical properties is analysed. Major defects like prior particle boundary (PPB) precipitation, thermally induced porosity (TIP), and non-metallic inclusion have to be taken care, in order to see that the mechanical properties are not deteriorated. It is observed that alloys like IN100, Rene95, and N18, Rene 88DT, ME3 and R1000 developed by powder metallurgy technique have sufficient temperature bearing capability for 1000 hr service life at 630 MPa. Alloys like U720 Li, IN 718 plus and U 720, made by casting technique and alloys like ME3, IN 100, and U720, made by powder metallurgy technique are compared on the basis of stress and temperature bearing capability. It is found that ME3 alloy prepared by powder metallurgy technique is the efficient nickel based superalloy with maximum heat bearing capability.