Production of thermoelectric materials by mechanical alloying - extrusion process

The extrusion process offers one of the greatest prospects for the industrial production of Bi/sub 2/Te/sub 3/-based thermoelectric alloys. When coupled with mechanical alloying, this process promises substantial cost savings because of its ability to deliver net shape components, leading to a reduction in the so-called kerf losses and higher material yields. It is also well known that materials produced using one of the various powder processing routes have greater mechanical strength when compared to conventionally grown alloys, leading to an improved reliability. We have produced both p-type (Bi/sub 2-x/Sb/sub x/Te/sub 3/) and n-type (Bi/sub 2/Te/sub 3-y/Se/sub y/) alloys using mechanical alloying and extrusion and have studied the structure, composition and thermoelectric properties of these alloys. By carefully controlling every step of the process we have found that it is possible to produce rods of thermoelectric material, for both p- and n-type alloys, which have good properties. Figures of merit of up to 3.35 /spl times/ 10/sup -3/ K/sup -1/ for p-type alloys and 2.8 /spl times/ 10/sup -3/ K/sup -1/ for n-type alloys have been obtained. A fivefold improvement in the mechanical properties over conventional melt grown material has also been observed.