- 學位論文
鈦合金Ti-6Al-4V及真空硬銲後固溶時效熱處理的研究
The Study of Solution and Aging Treatment of Ti-6Al-4V and its Post-Vacuum-Brazing
摘要
鈦金屬比強度比所有金屬都高，加上優越的耐蝕性及耐熱強度，適合航太及國防材料的需要，使用量仍提升中，成為重要的金屬材料。其中最常被使用的是雙相α-β型鈦合金Ti-6Al-4V，占45%鈦金屬。其真空硬銲後熱處理大多經退火，為了提升強度，本研究探討真空硬銲後熱處理固溶時效的效果，並且與真空硬銲後的退火狀態做比較。 首先利用田口方法獲得鈦合金Ti-6Al-4V固溶和時效熱處理的最佳參數條件，以期獲得最大硬度及抗拉強度，實驗結果顯示最佳製程組合為時效溫度482℃、固溶時間60分、淬火延遲時間、時效時間6小時、固溶溫度960℃、使用風扇、冷卻水靜止、氣氛乾燥空氣，固溶時效熱處理後硬度均高於HRc43以上，抗拉強度圓桿1,165MPa、板材1,082MPa以上，比退火處理硬度HRc36，抗拉強度990Mpa更好。 接著探討Ti-6Al-4V使用鈦基、銀基二種填料真空硬銲後固溶時效熱處理，鈦基填料Ti-15Cu-15Ni真空硬銲溫度和保持時間970℃x15/30/60min，硬銲後熱處理固溶和時效的銲道接合界面平均剪力強度476MPa，剪力強度範圍474±47MPa；銀基填料Ag-26.7Cu-4.5Ti真空硬銲溫度和保持時間900℃x30min、960℃x 5min/10min，銲道接合界面剪力強度平均470MPa，剪力強度範圍464.5±23.5MPa，比較文獻Ti-15Cu-15Ni真空硬銲後退火的剪力強度411Mpa，及銀基填料Ag-26.7Cu-4.5Ti真空硬銲後無熱處理的200Mpa，超過分別為16%及240%。 硬銲填料Ti-15Cu-15Ni初始成分15Cu-15Ni合併組成30wt.%，硬銲溫度保持時間若不足，銲道中心殘留連續帶狀化合物偏析組成約在共晶點，Ti-(Cu, Ni)硬銲銲道填料組成分佈如擬相圖，從本研究發現硬銲後熱處理，無論是退火或是固溶時效，都足以消除銲道中央連續帶狀介金屬化合物，βTi在共晶溫度最大固溶度12wt.%，甚至可以獲得≦6wt.%共析點或亞共析組織，無論硬銲參數是否選擇使用消除銲道中央連續帶狀介金屬化合物的條件，硬銲後熱處理的Ti-(Cu, Ni)組成範圍，必然因為稀釋於母材的關係，有朝著αTi增加，亦即Ti2(Cu, Ni)減少的擴散趨勢，因此會持續縮小範圍。硬銲後熱處理退火或固溶時效，實驗結果都是破壞於費德曼組織，也因此影響硬銲的剪力強度，其間最大的差異是在於費德曼組織和晶粒的尺度大小。 銀基填料Ag-26.7Cu-4.5Ti真空硬銲後熱處理EDS分析結果，在Ti-Cu二元相圖觀察Cu成分範圍8.64wt.%至13.22wt.%，因此銲道組成成分如同鈦基填料真空硬銲後熱處理之縮小範圍，此乃證實真空硬銲後熱處理產生均質化的結果。
並列摘要
In this research, the popular alloy Ti-6Al-4V was used to investigate the optimization process parameters of heat-treatment by using Taguchi method. The hardness after aging and tensile strength was chosen as the quality characteristics. Eight controllable factors were selected including fan, solution temperature, duration time of solution treatment, protective gas, quench delay time, cooling rate, temperature and duration time of aging treatment. The experiment was performed using orthogonal array of L18(21×37). The best combination condition of process parameters was obtained after Taguchi quality analysis. The quality reproducibility was verified to be excellent via the confirmation experiments. The results showed that the hardness after aging was above HRc 43, the tensile strength of rod material all above 1,165Mpa(169ksi), and that of plate material all above 1,082Mpa(157ksi) while using the optical heat-treatment condition. They all met the specification of AMS-4965 for the quality requirement of alloy Ti-6Al-4V. Using the optimal solution and aging treatment for Ti-6Al-4V brazed by Ti-15Cu-15Ni and Ag-26.7Cu-4.5Ti fillers, the average shear strengths of the lap-joint interface are 427 to 521MPa and 441 to 488Mpa, respectively. When compared to the reference, the shear strength has improved by 16% and 240%. And the average grain sizes of post-brazed solution and aging treatment are approximately between 6.6 μm to 8.1μm and 5.3 μm to 6.1 μm, and the average lengths of Widmanstätten structure are approximately between 37μm to 40μm and 25 μm to 35 μm with ≦ 1μm in width, which are significantly smaller than that of post-brazed annealing. Both Ti-base and Ag-base fillers specimens are examined to indicate the improving mechanism for shear strength of brazed joints is by optimal post-brazed solution and aging treatment, as it is an effective way to homogenize the microstructure of Ti-6Al-4V joint to simultaneously enhance the strength of joint braze and substrate.