Preparation of Laser Cladding Coating Undercooling Cu-based Alloy and Co on Non-equilibrium Solidification Structure

The effect of the gradient content of Co element on the solidification process of Cu-based alloy under deep under cooling conditions was explored.The non-equilibrium solidification structure of the under cooled alloy samples were analyzed.It is found that the rapidly solidified alloy has undergone twice grain refinement during the undercooling process.Characterization and significance of the maximum undercooling refinement structure of Cu60Ni35Co5 at T=253 K were analyzed.High-density defects were observed,such as dislocations,stacking faults networks,and twinning structures.The standard FCC diffraction pattern represents that it is still a single-phase structure.Based on the metallographic diagram,EBSD and TEM data analysis,it is illustrated that the occurrence of grain refinement under high undercooling is due to stress induced recrystallization.In addition,the laser cladding technology is used to coat Co-based alloy(Stellite12) coating on 304 stainless steel substrate;the microstructure of the coating cross-section was analyzed.It was found that the microstructure of the cross-section is presented as columnar crystals,planar crystals,and disordered growth direction,so that the coating has better hardness and wear resistance.By electrochemical corrosion of the substrate and coating,it can be seen that the Co and Cr elements present in the coating are more likely to form a dense passivation film,which improved the corrosion resistance of the coating.

Fracture Behaviour of Laser Clad Fe-and Ni-base Alloy Coatings on a Cast Iron under SEMI Loading

Laser cladding technique has been applied to renovate some partially-damaged (or worn) components with Fe, Ni, Co-base alloys, hence to improve their hardness values and wear resistance successfully in previous reports. But for some punching or shearing cast iron dies damaged or worn in automobile manufacture, the renovated surfaces also bear some impact loading. Therefore, a small-energy and multi-impact (SEMI) test was designed to investigate the fracture behaviour of renovated cast iron dies achieved by laser cladding of Fe and Ni-base alloys under SEMI loading to meet above requirement. observations show that the fracture took place in the substrate near to the substrate/coating interface rather than at the interface. The tempering temperature has a great influence on the cycles to fracture of laser-clad samples under SEMl loading, i.e. the low tempering temperature of 300℃ gives a maximum cycle to fracture, while a higher tempering temperature of 400℃ has a minimum. Furthermore, the fracture mechanism has also been discussed in present study

Tribological properties of FeCoCrNiAlB_x high-entropy alloys coating prepared by laser cladding

FeCoCrNiA1Bx（x=0, 0.25, 0.50, 0.75） coatings were prepared by laser cladding to study the effects of boron on the structure and properties of high-entropy alloys coatings. The microstructure, microhardness, and wear resistance properties of the samples were investigated by scanning electron microscopy, X-ray diffraction, metallographic micro-hardness test, and friction wear test, respectively, and the mechanism of the wear behavior was also analyzed. The results showed that the high-entropy alloys consisted of BCC phase and eutectic structure, which contained FCC phase and M2B. With boron addition, the content of BCC phase increased while that of eutectic structure decreased. The wear resistance of the high-entropy coatings was considerably improved with increasing addition of horon, and accordingly, the FeCoCrNiAlB0.75 coating showed the best wear resistance.