The Effect Of Trace Element On Microstructure And Properties Of Monel Alloy With Silicon

Monel alloys are the nickel alloys within main element of nickel and secondary element of copper.The alloys have better corrosion resistance,better mechanical property,etc.By means of vacuum melting,Monel alloys with addition Boron and Cerium is investigated into the microstructure and properties of the alloy in present paper.The following conclusions can be drawn from those investigations:1.The as-cast microstmcture of the Monel alloy with silicon consists of dendritic a matrix, dispersedβ-Ni₃Si phase and honeycomb-like eutectic(α+β-Ni₃Si)on grain boundary and in interdendritic regions.2.After individually adding B and Ce trace element in the alloy,the dendrites gradually refine with increasing B,Ce in the range of 0～0.10wt%,while the eutectic structure evolves from netlike shape to disconnected netlike shape slightly.When the B,Ce additive individually reaches 0.03wt%,the dendrites refine significantly and the eutectic structure has disconnected netlike shape.3.The corrosion potential of the alloy gradually shifts to positive value,while the corrosion current gradually decreases in the range of 0～0.10wt%B.When B additive is 0.03wt%,the corrosion potential of alloy is the highest and the corrosion current is the lowest and the passivating is the best compaction film.The corrosion potential of the alloy gradually shifts to positive value,while the corrosion current gradually decreases in the range of 0～0.10wt%Ce.When Ce additive is 0.03wt%,the corrosion potential of alloy is the higher and the corrosion current is the lower and the passivating is the better compaction film because of the film involving in Ce.With further increasing the content of Ce,the corrosion potential of alloy begins to gently shift positive value and the corrosion current gently decreases.4.With the increase of B and Ce,the hardness of the alloy firstly increases then decreases in the range of 0～0.10wt%.When the B additive reaches 0.03wt%,the alloys get the highest hardness 344HB.While the Ce additive reaches 0.03wt%,the alloys get the highest hardness 335HB.5.Trace B element plays a Strong inoculating role in the Monel alloy with silicon and the best addition is 0.03wt%.Trace Ce element plays a strong purifying role in the Monel alloy with silicon and the best addition is 0.03wt%.6.The alloy elements of 0.03wt%B and 0.03wt%Ce begin to diffuse uniformly and theβ-Ni₃Si phase decrease obviously on grain boundary with the increase of the solution temperature in the range of 820℃～1120℃.When the solution temperature is 1020℃,the dendritic segregation has been slaked wholly andβ-Ni₃Si phase are fully dissolved on grain boundary.With further increasing the solution temperature,the alloy appears burnt structure because of grain boundary melting.7.The alloy corrosion potential of 0.03wt%B and 0.03wt%Ce gradually shifts to positive value,while the corrosion current sharply decreases with the increase of the solution temperature in the range of 820℃～1120℃.When the solution temperature is 1020℃,the corrosion potential of alloy is the highest and the corrosion current is the lowest.8.The amount ofβ-Ni₃Si is strengthening phases of 0.03wt%B alloy and 0.03wt%Ce alloy with increasing of the aging temperature in the range of 500℃～700℃aging temperature. The largest quantity and the highest hardness can be got at 600℃,which is 361HB of the alloys with 0.03wt%B and is 357HB of the alloys with 0.03wt%Ce.Theβ-Ni₃Si phases begin to aggregate while aging at 700℃which result in decrease of hardness.9.From the experiments,it can be considered that the optimizational heat treatment technology is:solid solution treatment at 1020℃for 4h by oil cooling and then aging treatment at 600℃for 4h by air cooling.