David Pye's series on normalizing forged aerospace components concludes with part 5.

 

Titanium Alloys

The titanium alloys can be successfully forged at the appropriate temperature, which is based on the specific titanium alloy. After forging, there are alternative heat-treatment processes that can be applied to the titanium alloy forging. These include annealing, solution treatment and precipitation hardening.

The process that is discussed in this presentation is that of annealing. There are, however, different interpretations of the procedure because the annealing procedure can vary considerably in the rate of cooling by furnace conditions, the rate of cooling by cross-sectional dimension variations and cooling-rate control.

This means that both the metallurgical and mechanical results can vary considerably with each successive load. The processes of solution treatment and precipitation hardening offer much tighter metallurgy and mechanical properties.

It should also be noted and considered that the titanium alloys will react adversely with the following gases: nitrogen, oxygen, carbon dioxide and hydrogen. This, once again, means that the post heat treatment needs to be conducted under closely controlled atmospheric conditions. The ideal atmosphere would be vacuum, of course. There is little to no risk of any adverse surface conditions with vacuum treatment.

 

Conclusion

Although normalize and anneal are relatively simple heat-treatment procedures, these two simple thermal-processing techniques are critical to the repeatable and consistent metallurgy demanded by the aerospace industry (commercial and military). Aside from repeatable dimensional control and tolerances demanded and imposed by the aerospace industry, the metallurgical consistency and repeatability is necessary to the mechanical strength and microstructure for the functionality of the forged part.

Any heat-treatment procedure is a very critical part of the total manufacturing process – aerospace, automotive or general – because the heat treatment will either make or break the product.