Precipitation Strengthening in Ni-Cu Alloys Fabricated Using Wire Arc Additive Manufacturing Technology

Two Ni-Cu alloys, Monel K500 and FM60, with various contents of Ti, Mn, Al, Fe and C were deposited in the form of plates on a metal base plate using wire arc additive manufacturing technology. Three deposition speeds have been applied: 300, 400 and 500 mm/min. To modify the as-welded microstructure and properties, the deposited walls/plates have been subjected to two heat treatment procedures: annealing at 1100 degrees C for 15 min, slow cooling to 610 degrees C, ageing at this temperature for 8 h and either (i) air cooling to room temperature or (ii) slow cooling to 480 degrees C, ageing at this temperature for 8 h and air cooling to room temperature. The microstructure characterisation and mechanical properties testing have been conducted for each of the 18 chemistry/processing conditions. The dependences of the precipitate's parameters (size, number density and chemistry), mechanical properties and wear resistance on the alloy composition, deposition speed and heat treatment have been obtained. In Monel K500, the precipitates were mainly of the TiC/TiCN type, and in FM60, they were of the MnS and TiAlMgO types. Monel K500 has shown higher hardness, strength, toughness and wear resistance in all studied conditions. Ageing at 610 degrees C improved properties in both alloys following the precipitation of new particles. Ageing at 480 degrees C could result in a properties loss if the particle coarsening (decrease in number density) took place.