摘要
本文的TiAl合金做钮扣炉实验,通过压缩实验确定不同成分钮扣锭的强度和塑性,从而计算出各钮扣锭的强塑值,根据强塑值的大小确定成分做定向凝固实验。本文从所配的6个类别的18种化学成分中选出Ti47Al5Nb0.3Y0.5Si做定向凝固实验,研究定向凝固的成形工艺对合金的宏观,微观组织和力学性能的影响。
26×26mm方形水冷铜坩埚定向凝固实验采取6种成形工艺分别制备了6件铸锭。铸锭的宏观组织可以分为三个区域:初生区,生长区和最后凝固区。通过实验发现固液界面的宏观形态对柱状晶的生长方向有直接的影响,而固液界面的宏观形态可以由成形工艺控制。固液界面其实质是由一个主动温度梯度和两个被动温度梯度的相互矛盾构成,主动温度梯度是电磁感应加热温度梯度,被动温度梯度是水冷铜坩埚冷却温度梯度和液态镓铟合金冷却温度梯度。主动温度梯度的存在是被动温度梯度存在的前提。通过对纵截面的金相照片和电子扫描发现:合金由α2,γ两相组成,而γ相有三种片层结构(和柱状晶的生长方向分别呈0°,45°,和90°),这说明发生了两种固态相变;对γ片层的厚度研究发现提高功率和抽拉速度均可以细化片层。这说明不仅要控制固液界面的形态还要尽可能地细化片层,因为柱状晶生长方向,片层方向和片层厚度对合金力学性能均具有重大的影响。对析出物的研究发现,工艺对Y和Si的析出相的分布和成分几乎没有什么影响,而Y和Si的析出相能细化晶粒。
室温和850℃的高温拉伸实验表明P=45kW,V=1.2mm/min的力学性能最优,而高温实验的力学性能优于室温实验的力学性能的机理尚待研究。实验断口扫描研究发现断裂方式主要是解理断裂和穿层断裂。
Compound multicomponents TiAl alloys in the button shape casting experiment,by compress experiment fix the intensity and the plasticity,acrrording to which work out the intensity and plasticity,calculate the multiplication of the intensity and the plasticity ,called the multiplication as IPF .according to IPF choose the best component Ti47Al5Nb0.3Y0.5Si of the 6 sorts and 18 kinds component to do directional solidification experiment .investigate the effect ion of the figuration technics of directional solidification to the macroscropic,microscropic structure and mechanics performance.
26 mm×26mm rectangular water-cooled copper crucible directional solidification experiment use 6 kind figuration technics to produce 6 pieces of casts .Divdid the macroscropic structure to three parts:beginning part ,directional growth part and last solidification part.By experiment find that the macroscropic conformation of the interface between solid and liquid acts important effection to the direction of growth of the pillar shape crystal.but the macroscropic conformation of the interface of between the solid and liquid can be contolled by figuration technics .The essence of the interface between solid and liquid is made up of one initiative temperature grads and two passivity temperature grads,the initiative temperature grads is the electromagnetic induction temperature ,the two passivity temperature grads contents the water–cooled copper crucible temperature grads and the GaIn alloys temperature grads.If there is not the passivity temperature without the initiative temperature.By the photo of metallography and electron scan researching:TiAl alloy microscropic structure made up ofα2 andγ,while theγhas three kinds lamellar structure( the angle of the growth of pillar shape crystaland lamellar is 0°,45°and 90°),show that two kinds solid state;increasing the power and ratio pulling can decrease the thickness of the lamellar .Controlling the conformation of the interface between solid and liquid and lameller thickness are very important to the mechanics performance of TiAl based alloy.figuration technics is invalid to the Y and Si separating out in the TiAl-based alloy but the separating of Y and Si can smallerize the lameller and crystal.
P=45kW,V=1.2mm/min is the best figuration technics by the room temperature stretch experiment and 850℃high temperature stretch experiment,but the mechanism that high temperature mechanics performance is better than the room terperature is unkown. Breaking along the way lamellar phase.of cleavage and wear layers along faults are the main ways of rupturing mechanism by electron scan.
引文
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