PHASE-EQUILIBRIA IN THE AL-RICH PORTION OF THE TERNARY-SYSTEM CO-NI-AL AT 75 AND 78 AT.PERCENT AL

Phase equilibria were investigated for the Al-rich alloys Co25-xNixAl7 5 (0 less than or equal to x less than or equal to 25) and Co22-yNiyAl 78 (0 less than or equal to y less than or equal to 22). An addition o f Ni to the Al-rich Co-Al alloys significantly decreases the binary pe ritectic, peritectoid and eutectoid temperatures. On the other hand, t he temperature of the peritectic formation of NiAl3 increases with inc reasing Co addition; the maximal solubility of Co in NiAl3 amounts 10. 5 at.% at 860 degrees C. Nickel substitutes Co in Co2Al9 up to 4.7 at. %. The pseudoternary high-temperature phase (Co,Ni)(4)Al-13(h) is stab ilized by Ni addition up to 7 at.% Ni. The ternary phase Y-2 is formed by ternary peritectoid reaction from (Co,Ni)(4)Al-13 (h), Ni containi ng Co2Al9 and the decagonal phase at 880 degrees C. It shows only a li mited homogeneity range Co17Ni8.2Al74.8 to Co16.2Ni9Al74.8.