Selective Laser Melting of a bronze propeller with superior mechanical properties

Room-temperature stress–strain curves under tensile loading for the cast and SLM Cu–10Sn bronze and (inset) Cu–10Sn bronze propeller fabricated by SLM. [1]

What happens when the oldest alloy known to mankind meets the latest trend in laser-based manufacturing? Superior. Mechanical. Properties. [1]

Given its electrical conductivity and its excellent resistance to salt and water corrosion, bronze is still widely relevant in marine applications as well as in water propulsions and handling systems [2].

The mechanical properties at room temperature of Cu-10Sn bronze samples are presented that were built by selective laser melting using gas-atomized powders with average particle size 85+/-15 μm [1]. They are compared to the benchmark characteristics of samples produced using casting. Using an SLM 250HL machine, samples built under argon atmosphere (using the following optimized processing parameters [1]: scanning speed 210mm/s, laser power  271W, powder layer thickness 90μm and hatch distance 90μm) exhibit 99.7% density, measured using the Archimedes technique. The mechanical properties of Cu-10Sn depend directly of the microstructure formed during solidification [3] with no need for post-heat treatment.

SEM micrographs for the Cu–10Sn fabricated by (left) SLM and (right) casting showing the (α+δ)-eutectoid (bright phase) and α-dendrites (dark phase). [1]

Although the phases available are essentially similar – both microstructure exhibit dendrites of the alpha-Cu(Sn) phase along with an interdendritic (alpha+delta)-eutectoid - the refined SLM microstructure compared to the coarser cast microstructure is due to the faster cooling rate during solidification and significantly affects the mechanical properties:

SLM Cu-10S tensile properties [1]

• Yield strength: 220MPa
  
• Ultimate strength: 420Mpa
  
• Fracture strain: 17%
  

Cast Cu-10Sn tensile properties [4]

• Yield strength: 120MPa
  
• Ultimate strength: 180Mpa
  
• Fracture strain: 7%
  

These SLM properties are comparable to those of Cu-10Sn-2Zm-1.5Fe bronze cast alloys strengthened by iron nanoparticles [5].

References
[1] S. Scudino, C.Unterdörfer, K.G.Prashanth, H.Attar, N.Ellendt, V.Uhlenwinkel, J. Eckert, Additive manufacturing of Cu–10Snbronze - Materials Letters, May 2015,  http://dx.doi.org/10.1016/j.matlet.2015.05.076
[2] BarikRC,WhartonJA,WoodRJK,TanKS,StokesKR.Wear2005;259:230–42.
[3] Davis JR. Copper and copper alloys. Materials Park: ASM International; 2001.
[4] InoueA.ActaMater2000;48:279–306.
[5] ChenX,WangZ,DingD,TangH,QiuL,LuoX,etal.MaterDes2015;66:60–6.