EFFECT OF TESTING CONDITIONS AND OXIDATION ON WETTING BEHAVIOUR IN Al/Ni SYSTEM

The wettability tests were carried out under a vacuum at 700°C in the drop/substrate couples, where drop is pure aluminium (99.999%), substrate - Ni (99.8%) and Ni^ox (oxidized). Test were carried out using two different testing procedures: classical sessile drop method coupled with contact heating of the same Al/Ni couple (CH) and capillary purification method, where primary oxide film is removed from the surface of liquid aluminum (CP). After wettability tests, cross - sections of the samples were observed using optical microscope and SEM in order to observe phase boundaries of Al/Ni and Al/Niox couples and its phase morphology. The presence of characteristic phases of rhombic Al3Ni and irregular phase Al₃Ni₂ were observed. Tests of shear strength (push-off shear tests) and microhardness measurements of the phases were also performed. It was found that arose after contact with aluminum products of the reaction zone (RPR) on the oxidized nickel substrate is thinner than on the substrates unoxidized. Couple Al/Ni with a thin and compact RPR (reaction product region) resulting from the influence of Ni with a drop in the method of CH obtained after settling of the Al drop by CH in the oxidized nickel substrate is also the most resistant to shearing of the tested systems. The value of shear stress in this case is 63.1 MPa, and for the system Al on unoxidized nickel substrate obtained by the CP is only 33.9 MPa.

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