SP-700鈦合金雷射銲件之熱處理及顯微組織研究

Abstract

本研究係針對SP-700鈦合金，探討母材之麻田散體相變態及其後續熱處理的組織變化。此外，藉由雷射銲接及不同條件之銲後熱處理，進行SP-700銲件顯微組織的探討，同時亦進行相關銲件之缺口拉伸及衝擊試驗，並分析試片之破斷面及顯微組織。 實驗結果顯示SP-700母材在β轉換溫度（900˚C）以上淬火，β將會完全變態為HCP的α′；固溶溫度略低於β轉換溫度（約890˚C）時，水淬後α′會與斜方晶格的麻填散體α″同時存在；當固溶溫度介於880˚C及800˚C之間時，β相在水淬後將會變態為α″相（或有部份β殘留）；若在低於800˚C固溶後水淬，β相不再變態為麻田散體，可完全殘存至室溫。α″相之晶體結構為Base-centered orthorhombic（底心原子位於垂直 軸的平面），其晶格常數為

The microstructural evolution and heat treatment of SP-700 titanium alloy, in particular the martensitic transformation, have been investigated. The emphasis of this study was also placed on the influence of the post-weld heat treatment (PWHT) on the microstructure and related mechanical properties of SP-700 laser welds. Notched tensile and impact tests of the laser welds with various PWHTs were evaluated. Detailed microstructural and fractographic analyses were conducted on distinct specimens and the results were discussed. Martensitic transformation studies of SP-700 titanium alloy indicated that β (BCC) was transformed completely into α′ (HCP martensite) after solution treating at a temperature higher than β-transus (approximately 900˚C) and water quenched. The co-existence of α′ and α″ (Orthorhombic martensite) could be observed upon quenching from a temperature which was slightly below β-transus, e.g. 890˚C, of the alloy. Quenching from the intermediate temperature range of 880˚C to 800˚C, the transformation of β to α″ with or without some retained β was resulted according to the solution temperature employed. For a solution temperature of less than 800˚C, β was remained unchanged after rapidly cooling to room temperature. The crystal structure of α″ has been identified as base-centered orthorhombic (centered on C-faces) with