鋯合金702 (UNS R60702)具備優良的抗中子性和抗蝕性，廣泛用於核能電廠和化學工業，且隨著國防材料鎳、鉻、鉬、鈷、鎢等元素之國際價格節節昇高，更造成使用鋯合金有利的地位，且有取代鎳基合金的趨勢。鋯合金702為一種極活潑之金屬，在真空中施銲較易進行，但因銲件尺寸受限於真空施銲室，實際應用並不廣泛。
本論文主旨在探討鋯合金702施以惰性氣體鎢極電弧銲(GTAW)及CO2雷射銲接(LBW)之影響，以進行銲後機械性質之研究。研究之進行是透過微硬度試驗、拉伸試驗、光學顯微鏡組織觀察及掃瞄式電子顯微鏡(SEM)觀察，探討鋯合金702銲件之機械性質，並分析銲件微觀金相組織結構。同時以能量散佈光譜儀(EDS)、X光繞射分析(XRD)、電子探測微分析儀(EPMA)分析銲道中合金元素分佈情形，以提升國內對鋯合金的銲接技術與分析，提高工業製造技術之品質。
研究結果顯示，利用GTAW與LBW可成功銲接鋯合金702，經由金相觀察，母材為粒狀之等軸晶，經銲接後，銲道先凝固成BCC的β相柱狀晶，當冷卻溫度低於鋯合金702之β轉換溫度(871C)時，HCP的針狀α相組織從β相中成核成長，室溫下即呈現α相的Widmanstatten組織。經微硬度試驗發現，無論是GTAW銲後或是LBW銲接後銲道硬度均比母材高，銲道均呈現較高硬度值，此為銲道顯微組織中具有較細緻針狀α相所致。另外，再與微硬度測試曲線對照，也可以發現LBW其銲道硬度比GTAW高，因為雷射冷卻速度較快，生成之針狀α相較GTAW銲道更細小，故可以發現LBW銲道硬度比GTAW銲道高。實施GTAW與LBW銲後，強度皆與母材相近，其銲接參數所施銲之試片具有良好的機械性質。將銲件施以拉伸試驗，其破斷的地方均在母材區域，且破壞處兩端皆有頸縮現象。再將銲件之破斷面由SEM觀察，可以發現酒窩狀的組織，綜合兩種方法可推薦此破斷屬於延性破壞。
經由EDS、XRD、EPMA等實驗鑑定，GTAW銲道與LBW銲道並無其他析出元素含量，由此可證明鋯合金702是一種純淨度非常高的純金屬材料。

關鍵字：鋯合金702 (UNS R60702) 、惰性氣體鎢極電弧銲、CO2雷射銲接、機械性質、X光繞射分析、電子探測微分析儀

Zirconium alloy 702 (UNS R60702) has excellent neutron and corrosion resistance and it is widely used in the nuclear power and chemical industry. Owing to the international price of defense industrial material such as Ni, Cr, Mo, Co, W,etc, is hiking gradually, it has caused a beneficial position to use Zirconium alloy and also there is a tendency to replace the use of Nickel-base alloy.
Zirconium alloy 702 is a pretty active metal. It is easy to proceed under the vacuum chamber to do welding. However, its practical application is not so popular because the base metal dimensions are limited by the vacuum chamber.
The objective of this research is to compare the mechanical properties of the Zirconium alloy 702 weldments using two different welding processes, Gas Tungsten Arc Welding (GTAW) and CO2 Laser Beam Welding (LBW). Mechanical properties test including microhardness test and tensile test were conducted. OM and SEM were also used for microstructure analysis. The content of alloy elements within the fusion zone was analyzed by EDS, XRD and EPMA analysis. The research mentioned above would enhance the internal welding technology of Zirconium alloys and improve the quality of industrial manufacturing technology.
The result shows that Zirconium alloys 702 can be successfully welded by GTAW and CO2 LBW. The microstructure of Zirconium alloy 702 has been phase transformation (871°C), from α phase (HCP) transfer to β phase (BCC) and became Widmanstatten structure.
In the hardness test, the hardness of fusion zone of GTAW and LBW was higher than base metal. All tensile test specimens were fracture at the base metal, According to the SEM observation, the ductile fracture feature was observed in all specimens.
According to the EDS, XRD and EPMA analysis, the weldments of GTAW and CO2 LBW are no other elements in precipitation. It can be seen that Zirconium alloy 702 is a pure metal with very high purity.

Keywords: Zirconium alloy 702 (UNS R60702), GTAW, CO2 LBW, Mechanical properties, EDS, XRD, EPMA

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