Fabrication and crystallization behaviors of sputtered Ni-Cu-P films on tool steel

Electroless nickel is widely used as a hard coating for many industrial app lications due to its extreme hardness, uniform thickness, corrosion and wea r resistance. For advanced industrial applications, it is essential to prom ote the crystallization temperature of Ni-P deposits. In this study, Cu is introduced in Ni-P to improve its thermal stability. An alternative coating technique by r.f. magnetron sputtering is applied to deposit Ni-Cu-P coati ngs to solve the problem of composition control in the conventional chemica l solution method. The Ni-Cu-P coatings were deposited by r.f. magnetron sp uttering on 420 tool steel substrates with Cu + Ni-P compound targets. A no vel design of compound targets with Cu and NI-P by consideration of the sur face ratio of constituents exhibits a controllable composition in the depos ited film. The compositions of the Ni-Cu-P coating can be modified by the o riginal Ni-P deposits of the compound target along with the Cu area ratio i n the compound target. The planar uniformity of the compositions of the as- deposited Ni-Cu-P films is also achieved. All the as-sputtered (70.18-82.26 at.%)Ni-(17.17-1.39 at.%)Cu-(12.65-16.35 at.%)P deposits reveal an amorpho us structure. The hardness of as-deposited Ni-Cu-P coatings decreases with increasing Cu content. Nevertheless, the hardness of the Ni-Cu-P films is s till greater than that of the substrate. After annealing, the structure of the amorphous Ni-Cu-P deposits will transform directly into the Ni-Cu alloy and the Ni,P phase. The as-deposited Ni-Cu-P films can be hardened by prec ipitation of the Ni,P phase and crystallization of Ni-Cu. The introduction of Cu into the ternary Ni-Cu-P deposits increases the crystallization tempe rature as compared with the binary Ni-P film. The annealing temperature ass ociated with the occurrence of the peak hardness in the (82.26 at.%)Ni-(1.3 9 at.%)Cu-(16.35 at.%)P and (74.27 at.%)Ni-(12.65 at.%)Cu-(13.08 at.%)P fil ms is approximately 365 and 380 degreesC, respectively. It is shown that th e thermal stability of the Ni-Cu-P films is enhanced by increasing the Cu c ontent in the sputtered deposits. (C) 2001 Elsevier Science B.V. All rights reserved.