本文選題：高鈮TiAl合金　切入點：Ti_2AlNb合金　出處：《哈爾濱工業(yè)大學(xué)》2017年碩士論文

【摘要】：高鈮TiAl合金和Ti_2AlNb合金作為新興輕質(zhì)高溫Ti-Al合金,是航空航天等領(lǐng)域應(yīng)用的理想材料。本文對高鈮TiAl合金自身以及高鈮TiAl與Ti_2AlNb合金進行直接擴散連接,研究了擴散連接工藝對接頭微觀組織和力學(xué)性能的影響,獲得最佳連接工藝參數(shù),分析了接頭的斷裂位置和斷口形貌,綜合探究了接頭組織,力學(xué)性能,斷裂位置以及斷口形貌之間的聯(lián)系,闡述了擴散連接接頭的形成機理。對高鈮TiAl合金進行直接擴散連接連接,連接界面處主要為再結(jié)晶的轉(zhuǎn)變,隨著連接溫度的升高及保溫時間的延長,將其分為六個階段。孔洞閉合階段,隨著原子不斷擴散,孔洞消失;再結(jié)晶形核前期,隨著位錯在連接界面處不斷堆積,畸變程度小的一側(cè)的晶粒邊界向大的一側(cè)延伸;再結(jié)晶形核后期,隨著位錯的進一步堆積,邊界向畸變程度小的一側(cè)延伸,再結(jié)晶形核完成;再結(jié)晶長大階段,隨著連接溫度的升高或保溫時間的延長,再結(jié)晶晶粒不斷長大,位錯不斷減少;連續(xù)動態(tài)再結(jié)晶發(fā)生及物相轉(zhuǎn)化階段,當(dāng)達到一定溫度時,連接界面處發(fā)生連續(xù)動態(tài)再結(jié)晶。當(dāng)連接溫度達到1125°C時,母材及接頭內(nèi)部出現(xiàn)物相轉(zhuǎn)化,造成連接界面處α2相增多,不利于接頭性能提高;接頭完全形成階段,連接界面處再結(jié)晶晶粒尺寸不斷增大,數(shù)量不斷增多,此時接頭剪切強度達最大值為154.3MPa。保溫時間和壓力對再結(jié)晶的影響與溫度有相似之處,但過大的壓力,會抑制再結(jié)晶晶粒的長大。不同連接工藝參數(shù)下,斷裂形式以脆性斷裂為主。在高鈮TiAl合金和Ti_2AlNb合金直接擴散連接過程中,隨著連接溫度的升高或者保溫時間延長,連接界面處主要表現(xiàn)為物相的轉(zhuǎn)化,其可分為四個階段�？锥撮]合階段,兩側(cè)母材原子擴散更加充分,連接界面處孔洞消失;(Al(Ti,Nb)_2+Ti_3Al)混合層以及Ti_3Al層形成階段,由于Nb原子在連接界面處的積累及Al原子的擴散,在連接界面處生成Al(Ti,Nb)_2相和Ti_3Al相,此時界面結(jié)構(gòu)為Ti_2AlNb合金/Al(Ti,Nb)_2+Ti_3Al/Ti_3Al/高鈮TiAl合金;O相形成階段,Al原子穿過混合層進入Ti_2AlNb母材中,致使O相形成,此時界面結(jié)構(gòu)為Ti_2AlNb合金/Ti_2AlNb/O/Al(Ti,Nb)_2+Ti_3Al/Ti_3Al/高鈮TiAl合金形成;Ti_3Al過渡層形成階段,隨著原子進一步擴散,Al(Ti,Nb)_2相逐漸消失,O相層變?yōu)椴贿B續(xù)狀態(tài),連接界面處形成Ti_3Al過渡層,界面結(jié)構(gòu)為Ti_2AlNb合金/Ti_3Al/高鈮TiAl合金,此時接頭強度達到最大值為66.1MPa。不同連接工藝參數(shù)下接頭的斷裂形式均為脆性斷裂。
[Abstract]:High niobium TiAl alloy and Ti_2AlNb alloy as new lightweight high temperature Ti-Al alloys are ideal materials for aerospace applications.In this paper, the direct diffusion bonding of high niobium TiAl alloy and high niobium TiAl and Ti_2AlNb alloy is carried out. The effect of diffusion bonding process on the microstructure and mechanical properties of the joint is studied, and the optimum bonding process parameters are obtained.The fracture location and fracture morphology of the joint were analyzed. The relationship among the microstructure, mechanical properties, fracture location and fracture morphology of the joint was investigated. The formation mechanism of the diffusion joint was described.In the direct diffusion bonding of high niobium TiAl alloy, the interfacial transition is mainly recrystallization. With the increase of bonding temperature and the prolongation of holding time, it is divided into six stages.In the closing stage of the cavity, the cavity disappears with the diffusion of atoms, and in the early stage of recrystallization, the grain boundary of the side with small distortion extends to the larger side as the dislocation accumulates at the junction interface, and the later stage of recrystallization nucleation,With the further accumulation of dislocation, the boundary extends to the side with small distortion degree, and the recrystallization nucleation is completed, at the stage of recrystallization, the recrystallization grain grows and the dislocation decreases with the increase of joining temperature or the prolongation of holding time.Continuous dynamic recrystallization occurs in the phase of phase transformation. When the temperature reaches a certain temperature, continuous dynamic recrystallization occurs at the interface.When the bonding temperature is up to 1125 擄C, there is a phase transformation between the base metal and the joint, which results in the increase of 偽 _ 2 phase at the interface, which is not conducive to the improvement of the joint properties, and the recrystallization grain size at the interface increases continuously at the stage of the complete formation of the joint.The maximum shear strength of the joint is 154.3 MPA.The effect of holding time and pressure on recrystallization is similar to that of temperature, but excessive pressure will inhibit recrystallization grain growth.Brittle fracture is the main fracture form under different connection parameters.In the process of direct diffusion bonding between high niobium TiAl alloy and Ti_2AlNb alloy, with the increase of bonding temperature or the prolongation of holding time, the interfacial transition of the interface is mainly material-phase transformation, which can be divided into four stages.In the closing stage of the cavity, the diffusion of the base metal atoms on both sides is more complete, and the holes disappear at the connection interface, and the mixed layer of NbTiTiTi2Ti3Aland the formation stage of the Ti_3Al layer are formed, due to the accumulation of NB atoms at the junction interface and the diffusion of Al atoms.Ti_3Al phase and Ti_3Al phase are formed at the junction interface. At this time, the interface structure is Ti_2AlNb alloy / AlTiTiTiNbTi2 Ti_3Al/Ti_3Al/ high niobium TiAl alloy O phase formation stage, the Al atom passes through the mixing layer into the Ti_2AlNb base metal, resulting in O phase formation.At this point, the interface structure is Ti_2AlNb alloy Ti2AlNb / O / AlTiNb / Ti_3Al/Ti_3Al/ Ti_3Al/Ti_3Al/ high niobium TiAl alloy to form Ti3Al transition layer. With the further diffusion of atoms, the O phase layer gradually disappears and the O phase layer becomes discontinuous, and the Ti_3Al transition layer is formed at the junction interface.The interface structure is Ti_2AlNb alloy / Ti3Al / high niobium TiAl alloy, and the maximum strength of the joint is 66.1 MPA.The fracture form of the joint is brittle fracture under different process parameters.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG457.1
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本文編號：1701528