A new method is reported for fast fabrication of W–Cr alloys by combustion synthesis under Ar gas pressure of 2 MPa. The W–Cr alloy with W/Cr=1 in atomic ratio shows a hierarchical microstructure consisting of both micro- and nano-sized grains, which is proposed to be produced by spinodal decomposition. The hierarchical microstructure contributes to an improved hardness of 9.6 GPa, which is about 50% higher than that of W–Cr alloys prepared by conventional powder sintering.