Effect of grain structure on the mechanical properties of a Monel alloy fabricated by laser-based directed energy deposition

Monel K-500 is a Ni–Cu alloy widely used in the marine and offshore industry due to their superior resistance to corrosion in seawater and hence easily degraded.To address this problem,laser-based directed energy deposition(LDED)is used to repair or refabricate these high-value worn parts.To optimize the mechanical properties of repaired parts,the commonly applied solution and aging is not ideal because it also changes the properties of the base materials.Consequently,in situ control of the grain structures during the LDED process becomes an effective approach for high-performance repair.In this study,we fabricated a duplex grain structure with small grain size and low texture intensity using low laser power and scanning velocity.The duplex microstructure consists of short columnar grains and zigzag-distributed fine equiaxed grains.The formation of this grain structure is dependent on both the solidification and recrystallization mechanisms.The strength of this grain structure is improved to 523.5 MPa without the sacrifice of ductility,which is instead 20%higher than that of the counterpart consisting of typical columnar grains due to the grain refinement and crack toughening.The mechanical properties of the alloy with the duplex grain structure are even comparable to heat-treated Monel K-500 fabricated by wire arc additive manufacturing.This work provides valuable insights into the in situ optimization of the microstructure and mechanical properties of LDED-fabricated parts.

Tribocorrosion behaviors of Ti-6Al-4V and Monel K500 alloys sliding against 316 stainless steel in artificial seawater

The tribocorrosion behaviors of Ti-6Al-4V and Monel K500 alloys sliding against 316 stainless steel were investigated using a ring-on-block test rig in both artificial seawater and distilled water. It is found that friction coefficients are in general larger in distilled water compared with seawater. The wear losses of Ti-6Al-4V and Monel K500 alloys are larger in seawater compared with distilled water. The mechanical action can destroy the passive film and increase the corrosion rate. The synergism effect between corrosion and wear occurs. The synergism action between corrosion and wear is related to the corrosion rate and with the increase of corrosion rate, the synergism becomes more important. 316 stainless steel suffers severe wear sliding against Monel K500 alloy compared with sliding against Ti-6Al-4V alloy in both distilled water and seawater.

A study on hot deformation behaviour of alloy Monel K-500

Thermal simulation tests were conducted at different deformation temperatures and degrees by a Gleeble simulator.The results show that the alloy has higher resistance to deformation;with an increase of the deformation temperature,the alloy’s flow stress and maximum value decrease;with an increase of the deformation degree,both the initial recrystallization temperature and the complete recrystallization temperature decrease sharply.When the deformation degree reaches 30%,60% and 80%,the initial recrystallization temperature is around 950℃,850℃ and 800℃,the complete recrystallization temperature is around 1 100℃,1 050℃ and 1 000℃ respectively.When the deformation temperature is higher than 1100℃,the deformation degree increases and the re-crystalized grains are significantly refined.The forging process parameters were established according to the regular pattern mentioned above.The microstructure of the bar forged in this pattern is uniform and the result is satisfying.