Preparation And Optimization Of Cu-Ni Alloy Thermoelectric Materials

Cu-Ni based alloys have the highest Seebeck coefficient among common alloys.In addition,they are stable at high temperature and have outstanding mechanical properties with low price.However,the large thermal conductivity hinders their application in thermoelectric field.Therefore,in this work,Cu-Ni alloys were prepared via different preparation techniques,including room-temperature rolling,melt spinning-spark plasma sintering and magnetron sputtering.Different scattering centers,such as grain boundaries,dislocations,and pores,etc.,are introduced to reduce the thermal conductivity of Cu-Ni alloys and improve their thermoelectric performance.The main research results are as the following:1)Cu-Ni alloys were prepared by melting combined with room-temperature rolling.With the rolling reduction increasing,the thermal conductivity of Cu-Ni alloys decreases.For the Cu-Ni alloy with 94%reduction ratio,the lattice thermal conductivity is dropped by nearly90%at 573 K,resulted from the increased scattering by refined grains and high dislocation density.This sample obtaines the highest z T of 0.138 at 573 K,which is 30.0%higher than the prinstine counterpart.Furthermore,fine grain and deformation strengthening also improve the room temperature hardness by 115.7%and reaches 198.9 HV in the 94%reduction Cu-Ni alloy.It is worth noting that room-temperature rolling is not only an effective way to improve the thermoelectric and mechanical properties of Cu-Ni alloys,but also a commercial technique with low cost and mass production.2)The porous Cu-Ni alloys were successfully prepared by melt spinning-spark plasma sintering(MS-SPS)techniques.Compared with the ball milled(BM)samples,the process without ball milling is beneficial to the optimized porosity,which is in favor of low thermal conductivity and high z T.In MS-SPS process,when the sintering temperature of SPS decreases from 500?to 400?and the pressure decreases from 35 MPa to 15 MPa,the thermal and electrical conductivities decrease by 65.8%and 48.0%at 573 K,respectively.With the 6.1%increased Seebeck coefficient,z T is eventually improved by 70.7%and reaches 0.239 at 573 K.In summary,MS-SPS can significantly improve the thermoelectric properties of Cu-Ni alloys by introducing various scattering mechanisms.The optimal sintering temperature and pressure are 400?and 15 MPa.3)The two-dimensional nanocrystalline Cu-Ni films with(111)preferred orientation and excellent thermoelectric properties were prepared by direct current magnetron sputtering on Si/Si O₂substrate.The power factor can reach 39.95 m W m^-1K^-2.Cu-Ni film shows a remarkably low thermal conductivity of 6.4 W m^-1K^-1,which is 80.1%lower than the bulk counterpart.It can be attributed to the grain boundary and interface scattering.As a result,the z T value reaches 0.165 at room temperature,which is more than 4 times higher than that of the bulk.Magnetron sputtering has the advantages of fast deposition rate and large production scale,which are promising for commercial application.This study investigates the strategies for thermal conductivity reduction in theremolectric Cu-Ni alloys.The improved thermoelectric performance promotes the application of the alloys in the self-powering devices,such as healthcare and direct tire pressure monitoring systems.