What is Precipitation Hardening?

Most metals and metal alloys receive treatment to give them special properties or to increase the properties they already have. Heat treatment is very effective for hardening metals, and there are several ways to do this. However, instead of baking the metal at high temperatures and then quickly quenching it to finish the job, precipitation hardening takes place over a specified time period. It’s also called age hardening and works well for many alloys today, including superalloys like nickel alloy 718. Here is more about the process and the role it plays in metal manufacturing and fabrication today.

Forming Precipitates

Precipitation hardening gets its name because the process forms precipitates. When you take two liquid salt solutions and combine them, it forms a solid which is insoluble. The precipitates formed from this kind of hardening are impurities. Once formed, they increase the grain structure of the metal. However, when age hardening metals like nickel alloy 718 the process is a little more complicated. There are three steps to typical age hardening processes:

1. Solution treatment – dissolved atoms turn into a solid. It can take a long heating process, depending on the metal.
2. Rapid cooling – the metal reaches room temperature quickly, and this requires quenching.
3. Precipitation treatment – precipitates form as tiny particles inside the grains. This is an aging process which takes places at lower temperatures. The aging allows for added tensile strength, but it’s a timed process. If not, the metal would eventually lose strength.

Benefits of Age Hardening

Precipitation hardening makes metals like nickel alloy 718 stronger without distortion. Parts are more resistant to wear and easier to cut and form. Extreme applications like jet engine turbine blades require hard metal capable of withstanding temperatures below -400 degrees and above 1300 degrees Fahrenheit. This is why 718 (inconel) is the perfect metal for these applications.