Tantalum-Free Nickel Superalloy Gradient Microstructure
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Solution Overview
Problem
Current nickel-based superalloys for high-temperature turbine disc applications face limitations in achieving a balance between mechanical properties and temperature resistance, with existing chemical compositions not optimized for gradient microstructure treatments, leading to suboptimal performance at temperatures above 760°C.
Innovation Solution
A nickel-based superalloy with a specific composition devoid of tantalum, characterized by ranges of chromium, cobalt, molybdenum, tungsten, aluminum, titanium, niobium, hafnium, zirconium, carbon, and boron, which allows for a dual- or gradient-microstructure through tailored heat treatments, enhancing mechanical properties and temperature resistance up to 850°C without increasing density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional chemical compositions are used for nickel-based superalloys, then homogeneous microstructure can be achieved with balanced mechanical properties, but temperature capability is limited to 760°C with peaks to 800°C
Solution Approach 1:
The patent applies local quality by creating a gradient microstructure where different regions of the turbine disc have different grain sizes optimized for their specific functional requirements. The rim region has coarse grains for creep resistance at high temperatures, while the bore region has fine grains for tensile and fatigue strength at medium temperatures. This is achieved through controlled non-uniform heat treatment processes that create spatial variations in microstructure within the same component.
Solution Approach 2:
The patent segments the turbine disc into distinct microstructural zones (coarse-grain rim region and fine-grain bore region) that can be independently optimized. This segmentation allows each region to have tailored mechanical properties suitable for its specific operational conditions, resolving the contradiction between high-temperature creep resistance and medium-temperature tensile strength.
2Reliability
If gradient heat treatment is applied to existing conventional alloys, then dual microstructure can be produced for improved high-temperature performance, but the chemical composition is not optimized for gradient treatment configuration
Solution Approach 1:
The patent modifies the chemical composition parameters of the nickel-based superalloy to be specifically optimized for gradient heat treatment. This includes adjusting the content of alloying elements such as chromium, cobalt, molybdenum, tungsten, aluminum, titanium, and niobium to achieve the desired microstructural evolution during non-uniform heat treatment. The composition is tailored to enable controlled grain growth in the rim region while maintaining fine grains in the bore region.
Solution Approach 2:
The patent applies preliminary action by pre-optimizing the chemical composition before the gradient heat treatment process. The alloy composition is designed in advance to respond predictably to the intended non-uniform thermal processing, ensuring that the desired dual microstructure is achieved during manufacturing. This preliminary composition optimization simplifies the subsequent heat treatment process and improves manufacturing consistency.
3Temperature
If tantalum is added to improve high-temperature creep resistance, then temperature capability increases, but density increases which is undesirable
Solution Approach 1:
The patent applies the taking out principle by removing tantalum from the alloy composition. Instead of using tantalum to achieve high-temperature creep resistance, the patent relies on the optimized gradient microstructure (coarse grains in the rim region) and the carefully balanced composition of other alloying elements. This extraction of the heavy element achieves the desired high-temperature performance without the penalty of increased density.
Solution Approach 2:
The patent changes the compositional parameters by eliminating tantalum and adjusting the levels of alternative alloying elements. This parameter change maintains or improves high-temperature creep resistance through microstructural control while reducing the alloy density, thereby resolving the contradiction between temperature capability and weight.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The alloy achieves improved mechanical properties, including controlled density, metallurgical stability, and oxidation resistance, with a gamma prime solvus temperature difference suitable for supersolvus treatment, enabling effective performance at high temperatures with reduced density and enhanced creep and cracking resistance.
Implementation Method 1
The thermal treatment method enabling alloys having such a dual structure to be obtained is known, as described in patent application FR3043410. This application presents a method for producing the structure gradients on a disc-type part via a heat treatment which itself has a gradient.
Implementation Method 2
in the zones in which the temperature exceeds the solvus temperature of the gamma prime phase, the grains will increase in size in order to form a structure favourable to the creep and cracking properties
Implementation Method 3
in the hottest region, the temperature is greater than the dissolution temperature of the phase blocking the grain boundaries, also called the solvus temperature (for gamma-gamma prime nickel-based alloys; the is phase in question is the gamma prime phase).
Implementation Method 4
The alloy achieves improved mechanical properties, including controlled density, metallurgical stability, and oxidation resistance
Data Source
AI summary
A Nickel-based superalloy, whose composition includes, in percent by weight of the total composition: Chromium: 10.0-11.25; Cobalt: 11.2-13.7; Molybdenum: 3.1-3.8; Tungsten: 3.1-3.8; Aluminium: 2.9-3.5; Titanium: 4.6-5.6; Niobium: 1.9-2.3; Hafnium: 0.25-0.35; Zirconium: 0.040-0.060; Carbon: 0.010-0.030; Boron: 0.01-0.030; Nickel: remainder as well as unavoidable impurities; the composition being free of tantalum.