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The microstructure and microhardness of directionally solidified NiAl-W eutectic alloys at growth rates of 2-25 pm·s-1 were investigated by a Bridgman crystal growing facility at a temperature gradient of 300 K·cm-1.In view of the competitive growth between W dendritic and eutectic phases,W dendritic phase was eliminated,whereas the fully eutectic phase was prominent in the steady progress of the directionally solidified NiA1-W eutectic alloys.As the growth rate (V) increased,both the structure and solid/liquid interface of the directionally solidified NiAl-W eutectic alloys changed from planar to cellular.Both the fibrous spacing (d) and the diameter (a) decreased with increase in growth rate (V).The Vickers microhardness (H) of the directionally solidified NiAl-W eutectic alloys decreased with fibrous spacing (d) or diameter (a) increasing.The relationships of H to d and a were H =371.58d-0.09 and H =297.70a-0.09,respectively.