Electroless Ni-P-MoS2-Al2O3 Composite Coating with Hard and Self-Lubricating Properties

Abstract

The work aimed to produce Ni-P-MoS2-Al2O3 on Al-7075 alloys with multiple attributes through an electroless (EL) plating route. The effects of additives (MoS2 and Al2O3) in the EL bath on the surface morphology, topography, hardness, composition (phase and elemental), roughness, wettability, and coating thickness were evaluated. Results indicate a substantial enhancement in microhardness of the EL-coated surfaces by 70% (maximum hardness = ~316 HV) using powders, and 30% (244 HV) without powders. The maximum coating thickness and water contact angle obtained with powders were 6.16 μm and 100.46°, respectively. The coefficient of friction for the samples prepared using powders was 0.12, and for the base material it was 0.18. The compositional analysis through EDS and XRD suggested the incorporation of a hard and lubricious layer on the EL-coated surface owing to the presence of different phases of Al, Mo, P, Zn, O, and S. Therefore, the resulting coating surfaces impart hardness, self-lubrication, hydrophobicity, and wear resistance simultaneously.

Electroless Ni-P-MoS2 composite coating of Al-alloys: effect of surface textures and bath composition

“…Improved hardness and corrosion resistance was recorded for composite coatings as compared to NiP coating alone [1]. The formation of phases of NiAl, SiO, MoS 2 , NiO, Al 2 O 3 and Al 2 PO 4 confirms the formation of hard and lubricious temperature-resistant composite coating through electroless coating process [2]. Micro hardness and coating thickness improve with increase in Al 2 O 3 concentration in EL-bath.…”

“…The COF varies between 0.23-0.37 for textured samples and 0.4-0.47 for non-textured ones in hydrazine bath, whereas it varies from 0.27-0.38 for textured sample and 0.4-0.49 for non-textured samples in oxalic acid bath. It may be noted that the substantial improvement in wear resistant properties is proportional to the microhardness of the coated surfaces [2]. The textured surfaces possess higher micro-hardness with lower COF values (see figure 14(m)), which implies that the lubricity property has been achieved out of MoS 2 incorporation on the coated surfaces.…”

“…Oxalic acid imparts better performance when assigned with suitable conditions [14]. For better adhesion strength of the coatings on the substrate, proper pH (4-5) and dip time is to be maintained [2].…”

“…Some other materials used to contaminate the EL-bath for obtaining vicious properties include graphene, SiO 2 , TiH 2, SiC, BN, Al 2 O 3 , TiO 2 , CNTs, etc [20][21][22][23][24]. The urge to obtain wear resistance properties has attracted the research fraternity to use solid lubricating powders such as MoS 2 , WS 2 , CNTs, etc in the EL-coating baths [2,8].…”

“…Aluminum and its lightweight alloys with high strength and toughness have gained attention among different research industries [1,2]. Of all the available Al-alloys, Al6061 accounts for designing and manufacturing parts for aircraft, automobile, and marine sectors [3].…”