Superalloys: What They Are and How to Machine Them
Industries such as aerospace machining are under increasing pressure to improve system efficiency, reduce cost, and reduce emissions. Due to this, the required materials must be constantly improved: for example, withstanding hundreds to thousands of degrees of temperature while retaining its original form, durability without too much mass, and the ability to be manufactured efficiently.
While there are an abundance of innovations developing new material alloys, the challenge is to integrate these new material technologies with manufacturing processes. A great example of this issue is with Superalloys.
Superalloys were manufactured to combat these issues—they are the perfect materials for use in high-stress, high-temperature places where even the smallest structural changes from creep are not tolerated. However, with this solution came other issues. These alloys have very challenging mechanical properties which create obstacles for conventional machining. The very properties that provide the desirable high-temperature properties, can limit the ability to form a chip in a milling or turning operation. This is due in part to mechanical and structural abnormalities—these alloys can appear brittle or soft at times, posing various machining problems.
A viable, but often overlooked, solution is utilizing electrochemical machining (ECM) to machine parts from Superalloys. ECM is a no-stress, no-contact method which can easily machine iron, nickel, or cobalt based materials. This process also creates low roughness surfaces without recast layer or heat affected zones – critical to fatigue and corrosion performance at high temperatures.
Superalloys are also known to wear down CNC machining tooling at a faster rate than most other alloys, but ECM eliminates this issue by simply never coming into direct contact with the workpiece. The ECM tool, a cathode, does not experience any wear, improving the repeatability of the process, and saves the manufacturer money on recurring tooling costs.
The name “Superalloy” began to be used around the 1920s, as Nickel, Titanium, and Aluminum were combined for the interior parts of early gas turbines. Most Superalloys today are nickel-based, although Copper and Cobalt-based Superalloys are occasionally used. Many Superalloys contain other metals such as Chromium, Titanium, Tungsten, Niobium, and Aluminum.
Superalloys perform best in extreme high-temperature environments. The largest market is commercial jet engines, but other similar usages are in solar thermal power plants, heavy-duty heat exchangers, corrosive industrial environments, and rocket engines. Many design engineers seek to eliminate the use of Superalloys due to their costs – especially the manufacturing and supply costs. However, utilizing techniques such as ECM can drive down costs, enabling the use of Superalloys in applications which were previously cost prohibitive with conventional machining methods.
Researchers are constantly seeking to develop new alloys with an even higher resistance temperature, as industrial needs for gas turbines and heat exchangers increases. Better processing techniques are yielding purer alloys, and researchers are increasingly introducing refractory elements like Tungsten and Molybdenum. Engineers currently estimate the average aircraft engine's weight is 40-50% composed of Superalloys.
As the capabilities and applications of these unique alloys are developed, most conventional machining methods will be unable to adequately match the increased expectations of machining Superalloys. Voxel Innovations offers ECM solutions and seeks to educate various industry leaders across aerospace, medical device manufacturing, and more about Electrochemical Machining and its unique applicability to machining precise parts out of Superalloys.
Voxel has assisted a wide array of organizations and is a specialized contract manufacturer with ECM technology.