Effects Of Cu Addition On Microstructure And Properties Of Fe-Ni-P Alloy

Fe-Ni based alloys with BCC structure are the typical high-strength alloy systems with a martensitic transformation,and have great applications in precise transmission parts and electromagnetic devices.However,the inability of conventional Fe-Ni binary alloys with single phase structure to achieve a breakthrough in their strength has caused the strategy of multi-component and multi-phase to appear in the study of designing Fe-Ni based alloys.On basis of our previous studies,a novel idea that combines Ni-P chemical deposition with semi-liquid phase sintering?SLPS?has been utilized to develop a type of novel high-strength Fe-Ni-P-Cu alloys.Firstly,in order for the obvious strengthening effect of Cu doping on Fe-Ni-P alloys,nano Cu powders were mechanically milled with Fe-Ni-P composite powders prepared by chemical deposition,to obtain Fe-Ni-P-Cu mixed powders.The Fe-Ni-P-Cu alloys were prepared by SLPS at 950^oC and 30min under vacuum and pressureless condition.The effects of Cu content on microstructure and mechanical properties of as-prepared Fe-Ni-P-Cu alloys were investigated in detail.The results show that the low-temperature sintering at L+?dual-phase region can effectively avoid the formation of phosphorus eutectics.The doping of Cu is an effective approach to increase the hardness of Fe-Ni-P alloy,whilst maximum Vickers micro-hardness of 371HV is available in Fe-Ni-P-Cu alloy containing 2wt.%Cu.Then,in order to obtain a high purity?-?Fe,Ni?matrix in Fe-Ni-P-Cu alloys,the proportion of Ni-P in Fe-Ni-P composite powders varied by adjusting the chemical deposition process.The Fe-Ni-P-Cu alloys were prepared by rapid SLPS at 950^oC and20min under atmospheric and pressureless condition,followed by cooling in air.The effects of Ni-P content on microstructure and mechanical properties of sintered alloys were studied in detail.The results show that an appropriate amount of Ni-P?25.3wt.%?contributes to the full diffusion and interface growth during the sintering.The optimal Vickers micro-hardness?465.4HV0.1?,ultimate compressive strength?1920MPa?and yield strength?1223MPa?are available in the Fe-25.3wt.%?Ni-P?-Cu alloy.Additionally,in order to eliminate the agglomeration of ultra-fine Cu powders during sintering,a novel method that combines Fe-Cu substitution reaction and Ni-P chemical deposition had been utilized to prepare Fe-Cu-N-P multi-layered composite powders.The Fe-Cu-Ni-P alloys were fabricated by SLPS at 950^oC and 30min under atmospheric and micro-pressure condition.The effects of Cu content on microstructure and mechanical properties of as-prepared Fe-Cu-Ni-P alloys were investigated in detail.The results show that excessive Cu middle layer?>10wt.%?obstructs the precipitation of bulk?Fe,Ni?₃P phase,whereas appropriate amount of Cu layer contributes to an impressive ultimate compressive strength?2711MPa?and yield strength?1538MPa?in Fe-1wt.%Cu-Ni-P alloy.On basis of previous experimental mechanical results,this work characterized the fine and diffuse distribution feature of Cu precipitates in Fe-Ni-P-Cu alloys.The experimental results show that the yield strength increment contributed by Cu precipitates coincides with theoretical arithmetic.It is found that Ni promotes the formation of Cu clusters by reducing the critical energy for nucleation of Cu precipitates,whilst P induces the phase transition of Cu precipitates from G.P.to?-Cu phase by forming transition phase?-Cu₃P with Cu atoms.