本文選題：TZM合金 + 電子束焊接��； 參考：《哈爾濱工業(yè)大學(xué)》2017年碩士論文

【摘要】：TZM合金作為一種最有前途的鉬合金,具有彈性模量高、蒸氣壓低、抗蝕性強以及高溫力學(xué)性能良好的特點,因此在航空航天、核電等領(lǐng)域得到了廣泛的應(yīng)用。本文為滿足TZM合金高溫下的連接需求,研究了不同的焊接工藝對接頭組織及性能的影響,揭示了焊接接頭的組織轉(zhuǎn)變及接頭脆化的機理。分析了焊縫中沉淀相的形成對TZM合金接頭力學(xué)性能的影響,并提出了焊縫冶金元素調(diào)控的新方法。首先進行了TZM合金對接試驗的有限元數(shù)值模擬,研究了不同的焊接工藝參數(shù)對接頭溫度場及應(yīng)力場的影響,確定了電子束焊接工藝參數(shù)范圍。采用該參數(shù)范圍進行焊接工藝試驗,研究了電子束焊接工藝參數(shù)對接頭表面成形及力學(xué)性能的影響。得出了試驗條件下優(yōu)化的工藝參數(shù):聚焦束流為581m A,焊接速度為350mm/min,焊接束流為35m A。該參數(shù)下的焊接接頭強度為403MPa。由組織分析的結(jié)果可知,TZM合金電子束焊縫區(qū)晶界容易富集低熔點的Mo O_2及Ti O_2,而沉淀相在晶界上的偏析會造成晶界上共格關(guān)系的改變,進而引起晶界處的應(yīng)力集中,在應(yīng)力加載過程中造成焊縫區(qū)沿晶斷裂的產(chǎn)生。而Zr O_2及Mo2C在焊縫晶粒內(nèi)的彌散強化,使焊縫區(qū)硬度高于熱影響的硬度。采用Ti作為焊縫冶金調(diào)控元素時,接頭的抗拉強度無明顯提升。向焊縫中添加適量的Zr元素時,Zr元素會優(yōu)先與O元素發(fā)生反應(yīng),生成高熔點的Zr O_2彌散分布于焊縫晶粒內(nèi)部。因此焊縫區(qū)晶界得到凈化,晶界上應(yīng)力集中得到緩解。接頭的斷裂形式由解理與沿晶斷裂的混合斷裂形式轉(zhuǎn)變?yōu)橥耆慕饫頂嗔?接頭的抗拉強度提高到452MPa。進行添加Re中間層的TZM合金電子束焊接試驗,焊接接頭的抗拉強度隨焊縫中Re元素的增加而提高。這主要是由添加Re元素后,富錸相在晶界附近聚集,提高晶界結(jié)合能力,抑制了接頭沿晶斷裂的發(fā)生。并且在焊縫區(qū)的晶粒內(nèi)部形成大量的小角度晶界,提高了位錯開動的門檻值,阻止焊縫區(qū)穿晶裂紋的形成。因此,當焊縫區(qū)Re元素的質(zhì)量分數(shù)為48.7%時,接頭的抗拉強度達到524MPa,焊接接頭在熱影響區(qū)產(chǎn)生斷裂。
[Abstract]:As one of the most promising molybdenum alloys, TZM alloy has been widely used in aerospace, nuclear power and other fields because of its high modulus of elasticity, low vapor pressure, strong corrosion resistance and good mechanical properties at high temperature. In order to meet the requirements of TZM alloy joining at high temperature, the effect of different welding processes on the microstructure and properties of the joint was studied, and the mechanism of microstructure transformation and embrittlement of the welded joint was revealed. The influence of precipitate phase formation on the mechanical properties of TZM alloy joint was analyzed, and a new method for adjusting metallurgical elements of weld metal was proposed. Firstly, the finite element numerical simulation of TZM alloy docking test was carried out. The influence of different welding parameters on the temperature field and stress field of the joint was studied, and the range of electron beam welding parameters was determined. The effects of electron beam welding parameters on the surface forming and mechanical properties of the joints were studied. The optimized process parameters are obtained as follows: the focused beam is 581m A, the welding speed is 350 mm / min, and the welding beam current is 35 Ma. The strength of welded joint under this parameter is 403 MPA. The results of microstructure analysis show that the grain boundary of electron beam weld zone of TZM alloy is easy to enrich Mo / O _ 2 and TIO _ 2 with low melting point, while segregation of precipitated phase at grain boundary will result in the change of coherent relation at grain boundary, which will lead to stress concentration at grain boundary. The intergranular fracture occurred in the weld zone during stress loading. However, the diffusion strengthening of Zr O _ 2 and Mo2C in the weld grain makes the hardness of weld zone higher than that of heat-affected. When Ti is used as the adjusting element of weld metal, the tensile strength of the joint does not increase obviously. When the proper amount of Zr element is added to the weld, the Zr element will react with O element in priority, and the high melting point Zr O _ 2 will be distributed in the weld grain. Therefore, the grain boundary in the weld zone is purified and the stress concentration at the grain boundary is alleviated. The fracture form of the joint changed from the mixed fracture form of cleavage and intergranular fracture to the complete cleavage fracture, and the tensile strength of the joint was increased to 452 MPA. The electron beam welding test of TZM alloy with re interlayer was carried out. The tensile strength of the welded joint increased with the increase of re element in the weld. This is mainly due to the accumulation of rhenium rich phase near grain boundary after the addition of re element, which improves the binding capacity of grain boundary and inhibits the occurrence of intergranular fracture of the joint. In addition, a large number of small angle grain boundaries are formed in the grain interior of the weld zone, which increases the threshold of dislocation starting and prevents the formation of transgranular cracks in the weld zone. Therefore, when the mass fraction of re in the weld zone is 48.7, the tensile strength of the joint reaches 524 MPA, and the welded joint breaks in the heat-affected zone.
【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】：TG407
，

本文編號：1973362