Laser Cladding Preparation On Brass Surface And Its Bionic Applications

Due to good electrical and thermal conductivities, copper and its alloys are usedanywhere. At the same time, copper and its alloys are asked for more requirements like goodanti-wear property and strength in some fields, such as ring gear of automobile synchronizer,friction pieces of hydraulic pump in construction machinery, copper crystallizer and so on.Laser cladding technique is one of surface modification techniques for copper and its alloys,it is used widely as it has advantages, such as narrow heat-affected zone, small deformation,strong bonding force and none pollution. As copper and its alloys have low absorptivity tolaser and good thermal diffusion, the paper would adopt the way of powder precoat on thecopper alloys surface to laser clad by Nd: YAG laser.The bionics research has found that soil animals, such as dung beetle, pangolin andmole cricket, have good anti-wear property when they traject the soils and dinas. Becausebody surface of soil animals own the coupling character combined with non-smoothcharacters, special physical structure and chemical composition. It can provide new thoughtsfor surface modification of copper alloys.The paper did laser cladding on the copper alloy surface on the basis of bionic theory,and got bionic units. It discussed laser process parameters how to affect width and height ofbionic units by changing the volume of current, pulse duration, frequency and defocusingamount, then obtained the best combination of laser process parameters. Three kinds of lasercladding coatings were fabricated on the brass surfaces by altering the species of alloypowders, and the microstructure morphology, phase and micro-hardness of every coatingwere analyzed. The paper also researched the anti-wear property and tensile property ofbionic samples, the samples were being stretched by SEM and XRD, then revealed thereasons why bionic samples have good anti-wear property and why break. The study resultsas follows:1) The units haven’t obvious flaws and orifices. A well metallurgical bonded interfacebetween coating and substrate was obtained. The cladding quality meets the desiredrequirements. The hardness of Co-based coating is about3.3times that of the substrate,while corresponding value of Ni-based and Fe-based coating are about5times that of the substrate. Three kinds of coatings improve the micro-hardness of brass sample apparently.2) Pulse duration is the main factor in affecting unit width among the laser parameters.The best combination of parameters is current170A, pulse duration9ms, frequency12Hzand defocusing amount3mm for Ni-based unit. The combination strength of the interfacebetween bionic unit and substrate is high, and also the combination strength of the interfaceamong layers is high.3) The average friction coefficient was in accord with micro-hardness of bionic units,and the friction coefficient of Ni-based, Fe-based and Co-based samples increasesuccessively. Weight loss of smooth sample is about4times that of Ni-based and Fe-basedsamples, and about1.5times that of Co-based sample. And anti-wear property of bionicsamples is apparently better than that of the smooth sample. Among bionic samples,anti-wear property of Ni-based and Fe-based sample are almost similar, and that of Co-basedsample is worst.4) Bionic samples obtain higher tensile strength compared with smooth sample whenthe angle between bionic unit and the tensile direction is lower or zero.