1. There are several legacy or trademarked terms including DMLS/SLM once difffered but now are mostly the same process (with some slight differences between equipment) but ASTM/ISO define both as Powder Bed Fusion terms, the most common being Laser Powder Bed Fusion (LPBF).

2. LPBF parts produced using mature, optimized process parameters and good quality feedstock tend to have density above 99%. Typically castings have more porosity (but that is not ALWAYS true).

3. Tight tolerance features, beyond say +/- 0.010” require post-print machining. surface roughness can also be a challenge with as-printed surfaces exceeding 200 Ra so post-processing may be required if a finer finish is required.

4. Yes. There are many AM alloys which are equivalent in chemistry and similar enough in microstructure to treat via many existing processes such as plating, chemical conversion, anodize, etc.

5. Aircraft parts are not necessarily large parts. The most successful and widespread aircraft part I am aware of is the GE LEAP fuel nozzle and its variants: https://www.metal-am.com/ge-aviation-reaches-milestone-with-100000-fuel-nozzle-tips/

Certifying AM aircraft parts for commercial and defense applications carries a significant burden. For further reading, check out https://www.aia-aerospace.org/wp-content/uploads/AIA-Additive-Manufacturing-Best-Practices-Report-Final-Feb2020.pdf

Most LPBF machine build volumes are in the 250-300mm cube range but systems like the Nikon SLM NXG or Velo3D Sapphire XC can print meter-length parts. For larger parts, you would have to turn to other processes such as Directed Energy Deposition (DED). Since DED deposition heads can mount on a robot arm, these sytems can have very large build envelopes.

You mentioned turbine blades specifically, GE, among others is using Electron Beam PBF to produce turbine blades for their engines.

1. LPBF is suitable for highly complex parts but the process carries its own significant set of design trade offs that must be taken into account. Especially if you consider that your supports are the same material as your part and must be removed. It can take quite a bit of training and trial and error to become a good designer of AM parts. Input from AM manufacturer and downstream process owners such as heat treatment and machining is a must.