| Summary: | 碩士 === 義守大學 === 材料科學與工程學系 === 92 === Change of melting conditions under constant chemical composition of nickel-based alloys lead to changes of shape, amount, size and distribution; the properties of nickel-based hardfacing alloys in addition will also show improvement. Differing melting temperature and melting times and influence on microstructure of nickel-based hardfacing alloys and AISI 4140 steel is also discussed. Hardness of nickel-based hardfacing alloys are investigated. The relationship between melting condition and the characteristic of diffusion layer are also investigated.
The nickel-based powder (3.1B-0.75C-4.3Si-14.8Cr-3.7Fe-bal.Ni wt%) was put in AISI 4140 steel crucible and then heated to 917~1180oC. After the nickel-based powder was completely melted then holding temperature was effected for 0~10 minutes respectively, the crucible were furnace-cooled to 700 oC followed by cooling in ambient room temperature. Resultant microstructures, chemical compositions, phase identifys and situation were then investigated by X-ray diffractometer (XRD), optical microscopy (OM), scanning electron microscopy (SEM), electron probe micro analysis (EPMA), transmission electron microscopy (TEM) and hardness measurement.
Whether the temperature is hold or not, γ-Ni, Ni31Si12, Ni3B, CrB, and Ni2.9Cr0.7Fe0.36 would be found in 917oC~1060 oC. The microstructure of nickel-based hardfacing alloy would be transformed into γ-Ni, FeNi, rich in B、Cr、Fe, rich in C、Cr、Fe at 1120 oC when held for 7.5minutes. Phases of γ-Ni+Ni31Si12 ,CrB ,and Cr7C3 would become coarser with increasing temperatures by metallographic observations. The hardness of γ-Ni+ Ni3B is Hv947~1202.The hardness of γ-Ni+ Ni31Si12 is Hv388~502 .The hardness of CrB and Cr7C3 is Hv1486~1913. The hardness of FeNi is Hv292~310. The hardness of rich in B、Cr、Fe and rich in C、Cr、Fe is Hv870~1020.
The influence of melting conditions on the interface between nickel-based alloy and AISI 4140 steel, the phases of γ-Ni、rich in Ni、Si, rich in Ni、B,rich in Cr、C,rich in Cr、B existed at 917oC~1060oC by EPMA . After holding time, phases would transform into γ-Ni, C0.12Fe1.88and Fe23(CB)6 at 1180oC. With increasing holding time, γ-Ni+ rich in Ni、Si, rich in Cr、B and rich in Cr、C are coarsened as well.
At 1180 oC there is much influence on hardness across the layer of nickel-based alloys. Hardness would be change from 650Hv~820Hv to 250~380Hv after effecting holding times. I predict that wear resistance would also be much poorer with increasing holding time.
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