The up-hill diffusion of hafnium was observed during the interdiffusion of Ni-Ni3Al(Hf, B) couples. The Hf atoms diffused backwards from the original interface to the Ni3Al end, instead of moving forward to the Ni end under the concentration gradient. The observation confirmed that the Hf atoms partitioned preferentially to the Ni3Al phase by substituting for Al atoms in their sub-lattice sites.

Up-Hill Diffusion of Hafnium in Ni3Al Intermetallic Alloys. Chou, T.C., Chou, Y.T.: Materials Letters, 1986, 4[10], 423-5