Replacement of Lead stabilizer in electroless Nickel-Boron baths: Synthesis and characterization of coatings from bismuth stabilized bath

Abstract

Only a few compounds have been completely characterized as stabilizers in alkaline electroless nickel-boron plating and most of them have serious impact on health or the environment. In this paper, the effects of bismuth salts on the bath stability and characteristics of electroless NiB deposits obtained from an alkaline electroless nickel bath reduced by borohydride are presented. The objective of this paper is to propose a healthy and environmental friendly electroless NiB coating. The process of production was maintained the same as traditional NiB to facilitate the industrial adaptation. Bismuth accelerates the rate of deposition up to 10 −5 mol/L and inhibits plating from a concentration of 0.01 mol/L. The bismuth ions in the NiB bath act as stabilizer but some bismuth also co-deposits with the nickel-boron coating, leading to a coating with 3 wt% bismuth. The coating presents a homogeneous surface morphology with a 15.11 μm/h plating rate in agitated and non-replenished bath. The X-ray diffraction patterns of electroless NiB coatings stabilized by Bi 3+ exhibit a single broad peak, indicating a strong tendency to form amorphous structure. The coatings present the typical high hardness of NiB coatings (830 hv 50), with a relatively smooth surface. The wear behavior was characterized by ball-on-disc tests and a friction coefficient of 0.45 is obtained after 100 m of test with 5 N charge and an alumina ball. Scratch test results show the first damage after 16 N. NiB-Bi coatings have impressive properties and can replace lead stabilized electroless NiB in different fields.

Characterization of Electroless Nickel–Boron Deposit from Optimized Stabilizer-Free Bath

“…This might be attributed to a variation in the surface morphology: the ENB-Pb deposit presented the typical cauliflower-like structure, which led to variations in the contact area throughout the test. At the beginning, the increase in the COF was similar to that reported by several researchers [19,[34][35][36][37]. Also, it was observed that the ENB deposit's COF stabilized sooner than one of the ENB-Pb deposits, probably due to its smooth surface morphology [17].…”

“…On the other hand, as the legislation regarding environmental subjects is regularly strengthening, increased demand for completely removing lead and thallium from EN deposition baths has been seen in the metal deposition market. In addition, a few completely lead and thallium-free baths have been presented for electroless nickel-boron deposition [15,17,19,20]. One of them, developed by Bonin et al [17], completely removed the stabilizer agent from the bath and stabilized the bath by optimizing complexing agent concentration.…”

Effect of copper incorporation on phase transformation behavior of electroless nickel–phosphorous coating and its effect on the tribological behavior

“…Attempts are underway to make the electroless bath more ecofriendly by replacing toxic components with environmentally benign ones. 4 Cu incorporated in EN coating enhances its brightness/smoothness, thermal and paramagnetic stability, and anti-corrosion properties. [5][6][7][8] Cu into EN coating prompts to decrease the nodule size, and the coating appears to be smooth and lustrous compared to the conventional Ni-P coating.…”

Co-deposition of W and Mo in electroless Ni–B coating and its effect on the surface morphology, structure, and tribological behavior

“…Besides heat/thermo-chemical treatment or nitriding, recent studies have revealed that an inclusion of a third or fourth element to form poly-alloys enhances the properties of the coatings. 16–24 The inclusion of tungsten resulted in the formation of the Ni–B–W coating, 16,17 while the inclusion of molybdenum resulted in the deposition of the Ni–B–Mo coating. 18,19 A significantly higher microhardness of Ni–B–W coatings were observed compared to the binary alloy.…”

“…Other poly-alloy coatings with high hardness and wear resistance include Ni–B–Sn 22,23 and Ni–B–Bi coating. 24 Furthermore, Ni–B–Sn or Ni–B–Bi coatings were deposited from a more eco-friendly SnCl 2 /bismuth stabilized bath instead of conventional lead-based stabilizer.…”