So you’ve heard the term, but what is it? Technically, it is a method in which an alloy’s structural matrix is altered on an atomic level by using temperature change to enhance the material’s mechanical properties – increasing the yield and tensile strength. Simply, it is a way to further strengthen a material. It is most often utilized on aluminum, magnesium, nickel, titanium and steel alloys to create extreme high-temperature strength.
The Process
Stage 1 – Solution treatment
Solute atoms are atoms that are irregularly dispersed outside of the structural matrix of a material. By heating the material to extremely high temperatures (called solutionizing), these solute atoms dissolved into the solid matrix forming a homogeneous solid solution. Now, the precipitates that were previously positioned amongst the structural matrix are now absorbed into the matrix making it saturated with these extra atoms.
Think about the sugar in your tea cup. If you put a teaspoon of sugar into a cool cup of tea, the sugar crystals (like solute atoms) float irregularly throughout the tea. If the tea is boiled (similar to solutionizing), the sugar crystals are dissolved into the tea and any segregation between the solute sugar and the “solid structure” of the tea are gone – you now have one uniform, homogeneous solution – sweetened tea.
Stage 2 – Quenching
Just like your thirst needs to be “quenched” to cool down on a hot day, so must the alloy as part of the precipitation hardening process. In this step, the material is rapidly cooled to form a to bring the some of the precipitates atoms out of solution.
Stage 3 – Aging
In the final phase, the material is heated a second time.This time it is heated only moderately, and kept below the solvus temperature. This causes the precipitates that are currently over-saturating the material structure, to move minutely, so that they are evenly distributed throughout the alloy matrix.
The Results: Extreme Alloys
Inconel 718
Developed in the 1960’s, 718 is still considered the go-to material for almost all aircraft engine components with service temperatures below 1200°F. It is the icing on the cake – the corrosion resistance of Inconel with the high strength of precipitation hardening.
- Exceptionally high yield, tensile and creep-rupture properties at temperatures up to 1300°F
- Excellent welding characteristics when compared to the nickel-base superalloys – especially in its resistance to post-weld cracking
Monel 500
Alloy K500 offers the same high corrosion protection as K400, but with added strength. Though in certain environments it can be more susceptible to stress corrosion cracking than K400, Monel 500 is ideal for sour gas environments. K500 also delivers low corrosion rates in sea water, though pitting may occur in stagnant waters.
- 3 times the yield strength and double the tensile strength as alloy 400
- Strong to 1200°F; pliable and tough to temperatures of 400°F
- Same high corrosion resistance as Monel 400
17-4PH
Alloy 17-4PH is a precipitation hardened steel with chromium, nickel and copper. This alloy is used where high strength and reasonablecorrosion resistance are required, as well as for applications requiring high fatigue strength, good resistance to galling, seizing and stress corrosion. Also, it is great for intricate parts that require extensive machining and welding.
- High strength and good toughness in both base metal and welds
- Reasonable corrosion resistance and mechanical properties at temperatures up to 600°F
How Does This Create a Stronger Materials
By changing the original phase matrix, the precipitate atoms not only create a second phase of the material, but they also strengthen the material. When these precipitates disperse in the alloy, they impede dislocation movement and defects in the crystal’s latice forcing the dislocations to either cut through the precipitated particles or go around them. By restricting dislocation movement during deformation, the alloy is strengthened.