Research On Microstructure Optimization Of High Silicon Nickel-copper Alloy NCu30-4-2-1

High silicon nickel-copper alloy NCu30-4-2-1is the Ni-Cu-Si-Fe-Mn dispersionhardening alloy, which have lots of excellent performance like high hardness,high-intensity, good abrasion resistance and adhesion resistance. The alloy is widelyused in making aircraft fuel devices and other precision grinding parts. But domestichigh silicon nickel-copper alloy has some problems such as poor center quality resultfrom microstructure uniformity. Indication the properties of the extrusion bars should beimproved. This paper researched the casting method, hot extrusion deformation and heattreatment and so on several aspects to optimize bars microstructure.Casting microstructure optimization using four methods which are non-vacuumsmelting, vacuum smelting, electroslag casting with the binary slag system andelectroslag casting with the quaternary slag system. A chemical analyzer, ametallographic microscope, a scanning electron microscope(SEM) were used. Fourkinds of as-casting high silicon nickel-copper alloy microstructures from differentcasting methods were compared and analysed. The true stress-true strain curves ofNCu30-4-2-1alloy are got under the thermal simulation experiment by the technique ofGleeble—3800．The rheological stress equation of the NCu30-4-2-1alloy has beenestablished using the parameters of Zener-Holloman. The thermal deformationactivation energy and material parameters of NCu30-4-2-1alloys were obtained.Combining with the analysis of the microstructure after hot extrusion, optimizingextrusion temperature and rate were obtained. Through the standard solution treatmentprocess, then changed aging treatment parameters for microstructrue optimization. Theaging state was evaluated by ultrasonic velocity.Studies have shown that High silicon nickel copper alloy NCu30-4-2-1ingotcasting should use electroslag casting with the quaternary slag system. Hot extrusiondeformation temperature is1050℃and the strain rate is5s-1. the optimizational heattreatment parameters for NCu30-4-2-1alloy is930℃40min of solution treatment，640℃8h of aging heat treatment and then cooled in air to room temperature.(peak-aged stage). The microstructure for the as-casting is that the dendrite structure isfine and fairly homogeneous, and the secondary β phase which is tiny and dispersive inmatrix phase. The macrosegregation of NCu30-4-2-1alloy is alleviated and have noobvious macroscopic defects. Hot extrusion deformation microstructure is the completely dynamic recrystallization microstructure. The β-Ni3Si precipitates haveuniform size and uniformly distributed after heat treatment. Nickel-copper alloy has aoptimal size for the dispersoid particles. It’s about25nm. At this time NCu30-4-2-1alloy’s hardness is HB404.The ultrasonic velocity were be higher in peak aging.The application of above research results is that domestic high siliconnickel-copper alloy parts instead of imported components, greatly improving theproperties and pass rate of domestic parts, the slider, worm, gear friction device madefrom domestic high silicon nickel-copper alloy can be used in a multi-models aviationengine fuel accessories, and has been widely used in chemical, aerospace, shipbuildingand other military field.