【摘要】：鈦及鈦合金具有高強(qiáng)度、低密度、耐高溫、耐腐蝕、無(wú)磁性和良好生物相容性等優(yōu)點(diǎn)被廣泛應(yīng)用于各個(gè)領(lǐng)域,然而傳統(tǒng)的鈦及鈦合金成型工藝需要真空熔煉、鍛造及大量切削等后續(xù)處理,使得材料利用率降低,增加了生產(chǎn)成本,采用增材制造技術(shù)可以縮短工藝,提高鈦合金材料的利用率,配以合金成分優(yōu)化,可以提高鈦合金的力學(xué)性能�；诖�,本文研究了鈦合金添加微量硼元素結(jié)合絲材電弧增材制造技術(shù),并對(duì)鈦合金絲材電弧增材制造過(guò)程中快速凝固組織的演變進(jìn)行了模擬。首先,采用高真空非自耗熔煉及吸鑄方法制備不同硼含量的Ti6Al14V-xB(wt%,x為0,0.05,0.1,0.5)合金,研究了不同微量硼元素添加對(duì)Ti6Al4V-xB的鑄造顯微組織及力學(xué)性能的影響;其次,采用Ti6Al4V及Ti6Al4V-0.05B絲材為原料,以電弧為熱源,將鈦合金絲材熔融并逐層堆積實(shí)現(xiàn)快速增材制造,研究了鈦合金絲材電弧增材制造的凝固過(guò)程、組織形貌和力學(xué)性能等;最后,采用元胞自動(dòng)機(jī)-有限元法對(duì)Ti6Al4V及Ti6Al4V-0.05B合金絲材電弧增材制造的快速凝固過(guò)程進(jìn)行模擬計(jì)算,進(jìn)一步探究了絲材電弧增材制造不同階段的固-液轉(zhuǎn)變、初始β晶形核及生長(zhǎng)等機(jī)理。通過(guò)以上研究,得出以下結(jié)果:(1)微量B的添加影響了鈦合金初始β晶生長(zhǎng),在固-液前沿富集B元素阻礙初始β-Ti長(zhǎng)大,有效細(xì)化晶粒,當(dāng)硼含量超過(guò)0.1wt%時(shí),則有明顯的TiB相析出。Ti6Al4V-xB合金的抗拉強(qiáng)度極限隨硼含量的增加單調(diào)上升,這是細(xì)晶強(qiáng)化和析出強(qiáng)化共同作用的結(jié)果;合金的塑性則是先升高后降低,Ti6Al4V-0.05B的塑性提高了 15%,而Ti6Al4V-0.1B與Ti6Al4V-0.5B的塑性則降低超過(guò)了 40%,因?yàn)槲龀龃嘈缘腡iB相,形成脆性斷裂敏感帶。(2)在Ti6Al4V絲材電弧增材制造過(guò)程中,由于電弧具有高的熱量輸入,使得每個(gè)堆積區(qū)-熔合區(qū)-堆積區(qū)得到了有效的冶金結(jié)合,沒(méi)有明顯的堆積分界面和鈦馬氏體存在,各區(qū)域的顯微組織均為穩(wěn)定的α+β片層組織以及接近的顯微硬度值。與鑄態(tài)Ti6Al4V相比,電弧增材制造的鈦合金不僅初始β晶粒細(xì)小,而且α+β片層間距也較小,其抗拉強(qiáng)度與延伸率相比鑄態(tài)均有所提高,拉伸斷口為細(xì)小韌窩狀的韌性斷裂。(3)在Ti6Al4V-0.05B絲材電弧增材制造過(guò)程中,獲得了更加細(xì)小晶粒的組織,同時(shí)有少量不規(guī)則針狀TiB析出;相比較于鑄態(tài)Ti6Al4V-0.05B合金,晶粒尺寸有所減小并且更加趨于枝狀晶形貌,其抗拉強(qiáng)度提高了 6.2%,延伸率增加了 28.7%。(4)在Ti6Al4V絲材電弧增材制造的凝固組織演變模擬結(jié)果中發(fā)現(xiàn),初始階段β晶取向雜亂且晶粒尺寸細(xì)小;隨著增材高度的增加,溫度梯度變緩,平均固-液轉(zhuǎn)變糊狀區(qū)域?qū)挾仍黾?初始β晶平均晶粒尺寸增加,晶體取向趨于熱流傳遞方向(垂直于冷基板方向);其模擬結(jié)果與實(shí)際增材制造的初始β晶組織形貌相一致;此外,Ti6Al4V-0.05B合金的模擬結(jié)果表明,0.05 wt%的硼含量添加提高了形核率與生長(zhǎng)速率,從而使得初始β晶粒表現(xiàn)出更多的枝晶生長(zhǎng)。
[Abstract]:Titanium and titanium alloys are widely used in various fields because of their high strength, low density, high temperature resistance, corrosion resistance, non-magnetic and good biocompatibility. However, the traditional forming process of titanium and titanium alloys requires follow-up treatment such as vacuum melting, forging and a large number of cutting, which reduces the material utilization rate and increases the production cost. Manufacturing technology can shorten the process, improve the utilization rate of titanium alloy materials, and optimize the alloy composition, which can improve the mechanical properties of titanium alloy. Based on this, this paper studies the manufacturing technology of titanium alloy with trace boron and wire arc augmentation, and the evolution of rapidly solidified microstructure in the process of titanium alloy wire arc augmentation. Firstly, Ti6Al14V-xB (wt%, x 0, 0.05, 0.1, 0.5) alloys with different boron contents were prepared by high vacuum non-consumptive melting and suction casting. The effects of different trace boron addition on the casting microstructure and mechanical properties of Ti6Al4V-xB were studied. Secondly, Ti6Al4V and Ti6Al4V-0.05B wires were used as raw materials and arc as heat source. The solidification process, microstructure and mechanical properties of arc augmented titanium alloy wire were studied. Finally, the rapid solidification process of arc augmented Ti6Al4V and Ti6Al4V-0.05B alloy wire was simulated by cellular automata-finite element method. The mechanism of solid-liquid transition, initial beta nucleation and growth in different stages of wire arc augmentation is studied. The results are as follows: (1) The addition of trace B affects the initial beta crystal growth of titanium alloy. The enrichment of B in the front of solid-liquid hinders the initial beta-Ti growth and refines the grain effectively. When the boron content exceeds 0.1wt%, the grain size is obviously refined. The tensile strength limit of Ti6Al4V-xB alloy increases monotonously with the increase of boron content, which is the result of fine grain strengthening and precipitation strengthening; the plasticity of Ti6Al4V-0.05B alloy increases by 15%, while the plasticity of Ti6Al4V-0.1B and Ti6Al4V-0.5B alloy decreases by more than 40% because of precipitation brittleness. (2) In the arc augmentation process of Ti6Al4V wire, due to the high heat input of the arc, effective metallurgical bonding is achieved between each deposited area, fusion area and deposited area, without obvious deposited interface and titanium martensite, and the microstructure of each area is stable a + beta lamella. Compared with as-cast Ti6Al4V, the titanium alloy made by arc augmentation has not only fine initial beta grain, but also small interlamellar spacing of alpha+beta. Its tensile strength and elongation are higher than that of as-cast titanium alloy, and the tensile fracture surface is fine dimple-like toughness fracture. (3) The titanium alloy made by arc augmentation of Ti6Al4V-0.05B wire has been fabricated. In the process, finer grains were obtained with a small amount of irregular acicular TiB precipitation. Compared with as-cast Ti6Al4V-0.05B alloy, the grain size was reduced and tended to dendrite morphology. The tensile strength increased by 6.2% and the elongation increased by 28.7%. (4) Simulation of solidification microstructure evolution in arc augmented Ti6Al4V wire The results show that the orientation of the initial beta crystal is disordered and the grain size is small; with the increase of the height of the augmented material, the temperature gradient slows down, the width of the average solid-liquid transition paste region increases, the average grain size of the initial beta crystal increases, and the orientation of the crystal tends to the direction of heat transfer (perpendicular to the direction of the cold substrate); the simulation results and the initial production of the actual augmented material. In addition, the simulation results of Ti6Al4V-0.05B alloy show that the addition of 0.05 wt% boron improves the nucleation rate and growth rate, which makes the initial beta grain show more dendritic growth.
【學(xué)位授予單位】：西安理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG146.23

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