An in-situ high-throughput study of the Invar effect in the Fe–Ni–Co system

The Fe–Ni based classical Invar alloy and the Fe–Ni–Co based super Invar alloy are the basis for designing multicomponent alloys with low thermal expansion. In this work, we applied in-situ high-throughput experimental methods to map chemical composition, crystal structure, coefficient of thermal expansion (CTE) and magnetism in the Fe–Ni–Co system. The distribution of CTE (80~200℃) measured by the in-situ micro-beam X-ray diffraction on the combinatorial materials chips (CMC) showed low CTE regions in agreement with previous reports. Combined with the MOKE measurements, the $\bar{\mu }-\bar{e}$$\bar{\mu }-\bar{e}$ relation of the Fe–Ni–Co ternary FCC phase is found to follow the reported FCC Fe–Ni alloys in the Slater-Pauling curve. A low CTE region is centred at $\bar{e}$$\bar{e}$ = 26.7 and $\bar{\mu }$$\bar{\mu }$= 1.26 ${\mathit{\mu }}_B$${\mathit{\mu }}_B$ in the Slater-Pauling curve. The observed low CTE zone not only matches with the classical Invar and super Invar alloys but also agrees with the reported Fe–Ni–Co based multicomponent alloys with a small amount of doping (< 5 at.%) by Cu, Cr, Mn etc. The effect of Cr addition (> 5 at.%) to Fe–Ni–Co alloys on the Invar effect is further discussed in terms of the interplay between magnetism and austinite stability.