本研究的主要目的在於利用電鍍法製備鎳磷合金，並將部份試片經過400℃熱處理一小時，探討不同磷含量之鎳磷合金在熱處理前及熱處理過後，兩者在鍍層顯微結構上的差異(磷含量0 wt % ~ 14 wt %)，並從結構的觀點出發，討論初鍍之鎳磷合金及經熱處理過後鍍層硬度值的改變與硬化機構(Hardening mechanism)。本實驗使用X光繞射儀(XRD)分析鍍層結晶結構、掃描式電子顯微鏡(SEM)和原子力顯微鏡(AFM)觀察表面形貌、並使用穿透式電子顯微鏡(TEM)觀察微觀組織以及能量散佈分析儀(EDS)探討化學成分之變化，最後利用微式硬度計(Vickers micro-hardness tester)測量鍍層之微硬度值。

從TEM/EDS結果顯示，鎳磷合金鍍層結構並不是均勻分布，而是以奈米晶相(nanocrystalline)及非晶相(amorphous)之兩相結構共同存在，隨著整體鍍層之磷含量的上升，非晶相基地面積提升，而奈米晶相的數量下降且晶粒大小有下降之趨勢。從fcc晶粒之晶格常數(Lattice constant)計算可知，隨著磷元素之添加，磷元素會固溶(solid solution)進入鎳晶格之中，並造成晶格曲變，為了降低晶格能(lattice relaxation)，故形成奈米晶叢聚(nanoclustering)於非晶相之中之不均勻分布的現象。另外從EDS分析可知，奈米晶相及非晶相兩相之化學成分並不相同，奈米晶相有較低的磷含量，而非晶相有較高之磷含量。從鍍層硬度值分析結果顯示，隨著磷含量的上升，微硬度呈現先上升後下降之趨勢，並在4 wt% P達到最高峰值，根據以上結果歸納出初鍍鎳磷合金硬化機構包含了過飽合之固溶強化(super-saturated solid solution strengthening)、分散強化(dispersion hardening)、以及非晶質原子排列受壓之軟化現象(atomic spacing relaxation)。並將部份試片進行400 oC 熱處理一小時後，從TEM結果觀察得知，原先的非晶相發生再結晶，形成更均勻之等軸晶N(P)與Ni3P相，且隨著整體鍍層磷含量的上升，等軸晶N(P)平均晶粒大小隨之下降，而Ni3P在數量上以及平均半徑則有上升的趨勢。另外在鍍層中有發現針狀之Ni3P析出相，此析物亦隨著整體鍍層磷含量的上升，數量和平均半徑有增加的趨勢。從微式硬度值之數據結果可知，經過熱處理過後之鎳磷合金，其硬度值明顯大於未經熱處理之試片，而最高硬度值(1100 Hv)大約是在整體磷含量為8 wt% 時，然而在本研究指出，經過熱處理過後之鎳磷合金強化之機構並不同於初鍍鎳磷合金，其硬化機構為Ni(P)相之細晶強化、Ni3P之析出硬化(precipitation hardening)與Ni3P之細晶強化現象。

本研究即針對鎳磷合金之三項部分進行討論，第一項探討隨著磷的添加，造成鎳磷合金鍍層顯微組織的連續變化。第二項嘗試利用電鍍液中鎳離子以及亞磷酸(H3PO3，磷提供者)的濃度分佈曲線，來解釋奈米晶相如何叢聚於非晶相基地之中。最後，討論熱處理前以及熱處理過後之鎳磷合金之顯微組織，探討組織變化對於兩者硬化機構帶來之影響。

Effect of phosphorous addition on the microstructural evolution and hardening mechanism of as-deposited and heat-treated electroplating Ni-P alloys were studied respectively in this work. The microstructure and properties of these films were measured using X-ray diffractiometry, energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy and Vickers micro-hardness tester. TEM/EDS analyses indicated that microstructure was not distributed uniformly in the as-deposited Ni-P film. Nanocrystals were formed in the electroplated Ni film. The addition of P results in the formation of amorphous solid solution phase and causes a decrease in the number of nanocrystals as the P content increases. The grain size of the nanocrystalline phase also decreased with increasing P content. The lattice constant calculated from the Ni crystal with the variety P content also shows that the formation of fcc solid solution of P in Ni. Furthermore, the characteristic feature of nanoclustering either with amorphous phase dispersed in crystalline matrix or vice versa is a result of lattice relaxation caused by P addition. Furthermore, chemical composition analysis showed that the crystalline phase had a low P content while that in the amorphous phase was enriched.

For the as-deposited Ni-P alloys, a peak micro-hardness was found with the alloy containing about 4 wt% of P, indicating the solid solution hardening was not the sole factor affecting the strengthening mechanism of the as-deposited Ni-P alloys. The solid solution strengthening, dispersion hardening mechanism and atomic spacing relaxation play important roles for the changes in micro-hardness for the deposits containing different amount of P.

For the heat-treated Ni-P alloys, prepared at 400 ℃ for 1 hr, led to recrystallization of the amorphous phase and gave rise to a more uniform chemical composition within the Ni-P deposit. The recrystallized Ni(P) grain size decreased with increasing total P content in the deposit. The Ni3P phase was also found in the heat-treated deposit, with its amount and grain size increased with total P content. The micro-hardness values of heat-treated deposits with various P content are higher than as-deposited Ni-P alloy and peak at 8 wt% of P. This means that precipitation is not the chief determinant of high hardness in the electrodeposited Ni-P alloys. For the heat-treated Ni-P electrodeposits, precipitation hardening is responsible for the substantial increase in micro-hardness. At a high P content, a large Ni3P grain size leads to softening of the Ni-P electrodeposits.

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