Status of powdered high-temperature alloys

Status of Powdered High-Temperature Alloys

A number of powdered high-temperature alloys are currently being developed and used. These materials have a wide range of properties that make them useful for various industrial applications.

These alloys are normally designed to minimize the oxidation, hot corrosion, creep and microstructural changing that occur at high temperatures. However, a large number of research studies have shown that some alloys experience significant degradation when exposed to hot environments.

Developments

The most common high temperature alloys are nickel base superalloys with braze powder that provide a combination of strength, corrosion and oxidation resistance at temperatures from 500degF (260degC) to 2200degF (1205degC). These alloys can be used in a variety of applications including gas turbines, turbocharger rotors and other energy and aerospace components.

However, these alloys have a number of limitations that limit their use. For example, a metal's strength starts to drop at around 600degC and the microstructure reverts to a less useful equilibrium structure.

A number of approaches have been developed to address this problem. Among them, the addition of alloying elements at elevated solid solubility levels can increase the stability of the microstructure and thus improve the performance of a metal at high temperatures.

Moreover, several other alloying elements can also enhance the performance of a material by improving its corrosion/oxidation properties. In the case of iron-based materials, the inclusion of elemental powder blends can offer an opportunity to achieve a combination of mechanical and functional properties that are difficult to obtain with conventional alloys.

Applications

Powdered high-temperature alloys are applied in many applications where components are exposed to extremely high temperatures and oxidation. This includes aero engines, gas turbines and power plants.

Alloys used for this purpose typically form protective chromia scales that can withstand thermal cycling and reduce the likelihood of oxide scale failure. These alloys are typically nickel base alloys.

They also exhibit good corrosion resistance at elevated temperatures and are able to withstand repeated exposure to corrosive environments. They can be found in components such as compressor rotors, high and low pressure turbine blades, exhaust and combustor areas.

In order to enhance these materials' properties, new powder processing methods are being developed. Some of these techniques, like advanced powder processing, can produce very fine particles and a dense microstructure.

Costs

The cost of powdered high-temperature alloys has been a key concern for many aerospace OEMs and suppliers. They are keen to improve part properties at an affordable with stainless steel metal powder price point, but this is not always possible when compared to traditional machining or precision casting.

One method used for the production of metal AM parts is electron beam powder bed fusion (EB-PBF). This process uses an electron beam to fuse metal particles in a vacuum chamber, based on a CAD model that has been sliced into section layers.

Another method used to produce AM parts is laser powder bed fusion (L-PBF). In this technique, a molten metal alloy is sprayed onto a build platform and then fusing occurs in a heated vacuum chamber.

A new study investigated the fatigue behavior of EB-PBF fabricated Alloy 718 degC at 650 degC. It found that EB-PBF specimens with their center axis parallel to the build direction failed transgranular. Similarly, those with their center axis transverse to the build direction failed intergranular.

Markets

Powdered high-temperature alloys are being used in the industries of aerospace, defense, medical and electronics. Their characteristics make them ideal for various conditions, such as high temperatures and corrosive environments.

There are several types of powdered alloys available, with a variety of particle sizes and distributions. They are produced to meet customer-specific requirements, including the lubrication and corrosion resistance required in certain applications.

Among the most commonly used alloys are Inconel 600, 625 and 718. These are nickel-iron-cobalt alloys, which are durable, strong and resistant to a wide range of environments with copper powder.

They are also highly oxidation and corrosion resistant. These properties are crucial for aircraft gas turbine engines and other critical applications. This combination of features makes them highly suitable for many different components, including gas turbine casings, duct segments, nozzles and seal rings.