Polycrystalline Superalloy Membranes Produced by Load-Free Coarsening of Incoherent γ′-Precipitates: Microstructure Evolution and Mechanical Properties

Nanoporous superalloy membranes are a functional extension of the use of nickel-based alloys. The material, which is usually used for high-temperature applications, consists mainly of the two phases γ and γ′. Through coarsening of the precipitates and thus forming of a bicontinuous γ/γ′ network, membranes can be produced by removing either of these phases. From the single-crystalline alloy CMSX-4, the bicontinuous network can be formed either thermo-mechanically by directional coarsening of coherent precipitates or by load-free coalescence of incoherent precipitates. Recent investigations have shown that membranes also can be produced from polycrystalline starting material in both ways. In this article, the process route for membranes by load-free coarsening of incoherent γ′ precipitates from a carbon-free version of the polycrystalline alloy Nimonic 115 is presented. This manufacturing method has the advantage of its simplicity and in comparison to single-crystalline membranes it can be realized in larger scales. We discuss the microstructure and show the mechanical properties by means of tensile tests. Despite the grain boundaries as a mechanical weak link, polycrystalline membranes show promising mechanical properties. Their strength even exceeds that of the single-crystalline membranes despite the significantly higher pore volume content.

Empirical Modeling and Analysis of Surface Roughness in Milling Process of Nickel-Based Super Alloy Nimonic 115 through Response Surface Methodology

Nimonic 115 is one of the essential Nickel-based super alloys is known as one of the most difficult-to-cut materials because of its unique properties. Appropriate selection of the machining parameters in milling of this material is so vital for improving the machining efficiency. This paper discusses the use of response surface methodology for modeling of surface roughness in milling of Nimonic 115 with coated carbide tools. The machining parameters used in this study, are cutting speed, feed rate, axial and radial depth of cut. Average Surface roughness was measured in different conditions and analysis of variance (ANOVA)was performed. Then, quadratic model for predicting the surface roughness is established. The results show that the most significant parameter which affects surface roughness is feed rate.

Practical Experience With the Development of Superalloy Rejuvenation

Material degradation is one of the primary causes of gas-turbine hot section component retirement. This is characterized by microstructural aging and subsequent loss of creep strength. Under the same temperature conditions, the longer components remain in service, the more microstructural degradation occurs. This can be evaluated both through microscopy and stress-rupture tests, quantifying the material strength under high temperature, constant load creep conditions. In an effort to extend component life and reduce replacement part costs, material rejuvenation processes have been developed and implemented over the past few decades. In total over 35 commercial superalloy rejuvenation processes were studied and it was found that many alloys can be successfully rejuvenated but others pose a greater challenge. Issues of grain growth in forged turbine components and recrystallization in single crystal components impose limits on rejuvenation processes and are areas of ongoing development. The feasibility, successes and limitations of material rejuvenation are reviewed in this paper with a particular focus on the following superalloys: GTD111, IN738, and Nimonic 115. Examples of microstructure and stress-rupture life of turbine components in both the service-exposed and rejuvenated condition are presented. Component microstructure is shown to be restored, and the stress-rupture life following rejuvenation is returned to a condition fit for continued service.

NIMONIC ALLOY 115

NIMONIC alloy 115 is a nickel/chromium/cobalt based alloy developed as a vacuum processed creep resisting alloy for service at temperatures up to about 1010 C (1850 F) as a turbine blade material for aircraft turbines. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on heat treating. Filing Code: Ni-104. Producer or source: INCO Alloys Limited. Originally published as Nimonic 115, August 1965, revised November 1991.