Development of Cu added FeSi thrmoelectric material and production of burnar type module by investment casting

在873K和1173K温度范围内，获得了少量Mn和Cu缓慢凝固Fe_2Si_5合金共析分解（α * β + Si）的时间-温度转变图。二元Fe_2Si_5合金的熔点温度约为1023K，添加Cu合金的熔点温度约为50K。少量Cu的加入极大地缩短了图表的时间。在高温下，加Cu合金的共析分解开始速度比不加Cu合金快240倍以上。共晶分解形成的Si分散体由无Cu合金中的片状变为添加Cu合金中的粒状。在FeSi2合金中，Cu的加入也增强了准晶反应（α + epsilon * β）。这些结果表明，Si的存在对β的形成没有显著的加速作用。基于Johnson-Mehl-Avrami方程的β相变动力学分析表明，Cu的加入可能不会改变相变机理，但会改变生长动力学。在1023K以下加热时，Si分散体的尺寸很细。将Fe_2Si_51Mn0.2Cu和Fe_2Si_51Co0.2Cu合金铸入外径4mm、长30mm的管中。它们在1073K下退火30min进行β，并组合成一对热模组。燃料气体在管道内流动，并在管道的顶端燃烧。在350K的温差下，得到了220mV左右的稳定热电力。

The time-temperature-transformation diagrams for the eutectoid decomposition ( alpha * beta + Si) in slowly solidified Fe_2Si_5 alloys with small amount of Mn and Cu were obtained in the temperature range of 873K and 1173K.The shape of the diagrams was typically described as a character C.The nose temperature in a binary Fe_2Si_5 alloy was about 1023K and it raised about 50K for Cu added alloy.The addition of small amount of Cu drastically shifted the diagram to shorter time.The start of the eutectoid decomposition in Cu added alloy was more than 240 times faster than that in Cu free alloy at nose temperature.The shape of the Si dispersoids formed by the eutectoid decomposition changed from lamella in Cu free alloy to granular in Cu added alloy.In FeSi2 alloy, the peritectoid reaction (alpha + epsilon * beta ) was also enhanced by the addition of Cu.These results suggested that the existence of Si was not significant for the acceleration of beta formation.The kinetic analysis of beta phase transformation based on Johnson-Mehl-Avrami equation suggested that the addition of Cu may not change the transformation mechanism but change the growth kinetics.The size of Si dispersoids was quite fine by heating below 1023K.The alloys of Fe_2Si_51Mn0.2Cu and Fe_2Si_51Co0.2Cu were cast into tubes with 4mm in outer diameter and 30mm in length.They were annealed at 1073K for 30min for beta and combined as one pair of thermo-module.The fuel gas flowed inside of the tubes and burned at their top end.About stable thermoelectric force of 220mV was obtained for the temperature difference of 350K.