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首页> 外文期刊>Metallurgical and Materials Transactions, A. Physical Metallurgy and Materials Science >Fusion zone microstructure and porosity in electron beam welds of an α+β titanium alloy
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Fusion zone microstructure and porosity in electron beam welds of an α+β titanium alloy

机译：α+β钛合金电子束焊缝中的熔合区组织和孔隙率

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摘要

The effect of electron beam weldingparameters on fusion zone(FZ) microstructure andporosity in a Ti-6.8Al-3.42Mo-1.9Zr-0.21Si alloy(Russian designation VT9) has been investigated.It has been observed that the FZ grain widthincreased continuously with increase in heat inputwhen the base metal was in the β heat-treatedcondition, while in the α+β heat-treated basemetal welds, the FZ grain width increased onlyafter a threshold energy input. The difference isattributed to both the weld thermal cycle and thepinning effect of equiaxed primary alpha on graingrowth in the heat-affected zone (HAZ) of α+βheat-treated base metal. Postweld heat treatment(PWHT) in the subtransus and supertransus regionsdid not alter the columnar grain morphology in theFZ, possibly due to the lack of enough drivingforce for the formation of new grains by thebreaking up of the columnar grains and grainboundary movement for grain growth. As the PWHTswere conducted in a furnace, the role of thermalgradients can be ruled out. Intragranularmicrostructure in the as-welded conditionconsisted of hexagonal martensite. The scale ofthe martensite laths depended on welding speed.The highest porosity was observed at intermediatewelding speeds. At low speeds, a majority of poresformed at the fusion boundary, while at highspeeds, occurrence of porosity was maximum at theweld center. The trends on porosity can beexplained on the basis of solubility of hydrogenin titanium as a function of temperature and theinfluence of weld thermal cycle on nucleation,growth, and escape of hydrogen gas bubbles. Theporosity at slow welding speeds is low becausesufficient time exists for the nucleation, growth,and escape of hydrogen gas bubbles, whileinsufficient time exists for the nucleation of gasbubbles at high welding speeds. The effect ofpickling of joint surface, vacuum annealing of thebase metal, and successive remelting of the weldmetal has also been investigated.
机译：研究了电子束焊接参数对Ti-6.8Al-3.42Mo-1.9Zr-0.21Si合金（俄罗斯代号VT9）中熔合区（FZ）显微组织和孔隙率的影响。已观察到FZ晶粒宽度连续增加当母材处于β热处理状态时，热量输入增加;而在α+β热处理的母材焊接中，仅在输入能量阈值之后，FZ晶粒宽度才增加。该差异归因于焊缝热循环和等轴初生α对α+β热处理的母材热影响区（HAZ）中的晶粒长大的钉扎效应。亚熔区和超熔区的焊后热处理（PWHT）并没有改变FZ的柱状晶粒形态，这可能是由于柱状晶粒破裂和晶粒生长的晶界运动缺乏足够的驱动力来形成新晶粒所致。由于PWHT在炉中进行，因此可以排除热梯度的作用。焊接条件下的晶粒内显微组织由六角形马氏体组成。马氏体板条的尺寸取决于焊接速度。在中等焊接速度下，孔隙率最高。在低速下，大多数孔在融合边界处形成，而在高速下，在焊接中心的孔隙率最大。孔隙率的趋势可以根据氢气在钛中的溶解度与温度的关系以及焊缝热循环对氢气气泡的形核，生长和逸出的影响来解释。焊接速度慢时的孔隙率低，这是因为存在足够的时间使气泡成核，生长和逸出，而没有足够的时间使气泡在高焊接速度下成核。还研究了接头表面的酸洗，贱金属的真空退火以及焊缝金属的连续重熔的影响。

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