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

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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.