Microstructure And Formation Mechanism Of Plasma Arc Spray Welding Alloy DZ125 Cladding Layer

Aero-engine blades are vulnerable to wear and erosion of solid particles and early failure under high temperature and harsh environment.Because the blade manufacturing process is complex,the production cycle is long and the production cost is high,it is too expensive to completely replace the damaged blade.If the blade can be repaired,the repair cycle will be shortened and the cost will be reduced.In this paper,the cladding layer was prepared on the surface of alloy DZ125 by plasma arc spray welding technology.The influence of technological parameters on the forming and hardness distribution of the cladding layer was studied.The influence of cooling conditions on the growth of columnar crystal in cladding layer was studied.The results show that: using two kinds of spray welding materials,plasma arc spray welding is performed on the DZ125 alloy surface,and the cladding layer forms an epitaxial columnar crystal structure at the interface;as the solid-liquid interface moves forward,its temperature gradient decreases.The degree of supercooling of the components increases,and a columnar crystal changes to an equiaxed crystal in the cladding layer.The columnar crystals in the nickel-based alloy cladding layer are more easily converted into equiaxed crystals than the cobalt-based alloys.There are fine needle-shaped WC and Cr23C6 strengthening phases in the cobalt-based alloy cladding layer;the petaloid Cr7C3 phase and the bulk Cr B phase are distributed in the Ni-based alloy cladding layer,and the strengthening phase is more in the surface region of the Ni-based alloy cladding layer More,the hardness value is higher.The process test results show that the height and width of the cladding layer firstly increase and then decrease with the increase of spray welding speed and spray welding current;the cladding layer presents an epitaxial columnar crystal structure at the bonding interface,with the cladding As the thickness of the layer increases,the columnar crystals transform into turning dendrites.The height of the columnar crystal in the cladding layer decreases with the increase of the spray welding current,and it decreases first and then increases with the increase of the spray welding speed.In the cooling condition test,it was found that water cooling is more conducive to the formation of columnar crystals.The proportion of columnar crystals formed by the single-layer cladding layer under air cooling accounted for 44.5% of the cladding layer,the number of cladding layers increased,and the percentage of columnar crystals increased to about 50%;the columnar crystals in the single-layer cladding layer under water cooling The proportion of crystals is 49.87%,the number of layers increases,and the proportion of columnar crystals increases to about 78%.The hardness of the columnar crystal structure in the cladding layer is basically the same as the hardness of the substrate,which is significantly higher than the top of the cladding layer turning to the dendrite area.The hardness change trend of the cladding layer under different cooling conditions is basically the same.Under water cooling conditions,the faster the cooling rate,the more favorable is the formation of columnar crystals grown epitaxially from the substrate.The wider the hardness zone.