Microstructure evolution and lubricant wear performance of laser alloyed layers on automobile engine chains

• Size of nano grains increased with laser specific energy.
• Martensite lattice parameters increased with laser specific energy.
• Graphite increased carbon solubility and volume fraction of the retained austenite.
• Nano-hardness and elastic modulus of them are close.
• Lubricant wear volume loss decreased with laser specific energy.

Wear resistant layers on nodular cast iron chains with C–B–W–Cr powders were fabricated by laser surface alloying (LSA). Microstructure, phases and lattice parameters, were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffractometry. Micro-, nano-hardness and elastic modulus were measured with a Vickers microhardness tester and a nano-indendation tester. Lubricant sliding wear performance was performed on a ball-on-disk apparatus in ambient air using the straight line reciprocating wear form. Results indicate that microstructure of the alloyed layers changes from hyper-eutectic to hypo-eutectic, varing with laser specific energy. Nano-grain size and micro-hardness decrease while martensite lattice parameters increase with laser specific energy. Existence of graphite in the substrate increases the carbon content in the retained austenite to 1.59 wt%. Nano-hardness and elastic modulus of the alloyed layers are close. Friction and wear properties of the layers are improved by LSA compared with the substrate. Wear mechanism of them is illustrated.