Research On Nickel Based Ternary Alloy Coating By Laser Cladding

Copper and its alloys are widely used in electrical apparatus and metallurgical equipment, due to their excellent electric and thermal conductivities. For example, they are the interesting materials for continuous casting mold, blast furnace tuyere and electric motor commutator et al. However, a major difficulty in the use of copper components is its poor wear resistance in severe conditions. With the superiority of metallurgical bonding, mild thermal damage to the substrate and small heat affected zones et al, laser cladding(LC) can be used to improve the wear resistance of Cu without losing other performances excessively.Ni-Cr-Si ternary alloys with two silicides enhancement phase of Cr3Ni5Si2 and Cr3 Si were synthesized on copper by LC in this paper. The microstructures of the coatings were characterized by optical microscopy(OM), X-ray diffraction(XRD), and scanning electron microscopy(SEM) with an energy dispersive spectrometer(EDS). The crystal growth in solidification process was analysed using a modification model which is combined Kurz-Giovanola-Trivedi(KGT) model with Lipton-Kurz-Trivedi(LKT) model. The results show that in Cr3 Si phase region, the number of Cr3 Si enhancement phase decreased with the increase of Ni content. Cr6Ni16Si7 would substitute Cr3 Si, when the Ni content increased to 60%(at.%). In the sublayer of Cr3 Si coatings, the high temperature gradient, rapid solidification velocity and the large dendritic tip supercooling degree induced the developed equiaxial dendrites. The small supercooling degree induced the fine equiaxed grain in upper-layer. In Cr3Ni5Si2 phase region, with the increase of Si content the volume fraction of Cr3Ni5Si2 increased. While the number of Ni2 Si and γ-Ni decreased in the interdendritic region. The typical microstructure was columnar dendrites as the lower supercooling degree.Microhardness of Ni-Cr-Si coatings was measured by HXD-1000 Vickers hardness tester. The average hardness of Cr3 Si coatings was about 1000HV0.1. Fracture toughness of Cr3 Si coatings were 3.5 MPam21 and 2.1 MPam21, respectively. Fracture toughness value of Cr6Ni16Si7 coating was higher than Cr3 Si coating, as no crack was found in micro-indentations under 1000 g load. Fracture toughness value of Cr3Ni5Si2 coatings was high. The average hardness of Cr3Ni5Si2 coatings was 700 HV0.1 with Si content add up to 20%(at.%).Wear properties of the coatings were evaluated on a CETR-UMT Multi-Specimen Test System under room temperature. The average friction coefficient of three Cr3 Si coatings was 0.45, when suffered the high hardness WC ball(HRA92). After wear, there were no noticeable features of plastic deformation in the subsurface of the wear scar in Cr3 Si coatings. The wear scar was smooth and wear loss was low. Wear loss of Cr3Ni5Si2 coatings increased when Si content decreased. Wear loss and friction coefficients of Ni-Cr-Si ternary alloys by LC were lower than that of AISI304 stainless steel. It exerted good tribological properties.