Research And Development Of Powder Used For Prepairing Failing Forging Mould Of Aeroengine Blade By Laser Cladding

As to backwards for big cracking susceptibility caused by thermal spraying powders used in the failing aeroengine pieces high-temperature forging mould repaired with laser cladding technology and problems for easy abscission of coating caused in high-temperature service environment(＞800℃),a kind of Fe-based alloy powder used in the failing forging mould repaired with laser cladding technology is researched and developed,through strain of thought of combination of alloying principle of materials with melting and solidifying characteristics during laser cladding and physical and chemical characteristics between substrate and powder,based on the mould steel(4Cr5W2SiV).The optimum formulas of the powder and effect of the technological parameters on the microstructure and properties have been investigated.The microstructure and properties of coating prepared by laser cladding are studied by means of OM,SEM and XRD.The results indicate that no cracks coating and excellent chemical metallurgical bonding between cladding coating and substrate are obtained under condition of optimum formulas(wt.%:0.3C,25Cr,1.0Ni,1.7Si,1.5B,rest Fe).The contents of slag agent B element must been controlled strictly:The optimum properties could been obtained under condition of 1.5wt.%B,Otherwise there may be many defects such as rough surface,cracks,holes and so on.Under condition of narrow laser cladding technology,other technological parameters are fixed,the hardness of the cladding coating changes within a certain of range with increase of the scaning speed.The cladding coating with good microstructure and properties ia obtained under condition of P=2.5KW,V=5mm/s,d=3mm, f=300mm,However,Since narrow laser cladding has more overlapping zones,leading to more soft band,furthermore,performance life is affected.Multi-cladding techenology of wide-band laser is a good approach to obtaining deeper cladding layers.This method is very suitable for repairing failure parts with serious wear.The optimum technological parameters of broadband laser cladding is as followed: f=315mm,P=3kW,V=3mm/s,d=3×15mm².Under the condition of optimum technological parameters,the transition of microstructure is smooth in cladding coating.The whitebright band is plane crystals in the bonding zone.Cellular crystals is obtained in the bottom of cladding coating.The microstructure from the center to the surface of cladding coating transformes from dendritic crystals and cylinder crystals to equiaxed crystals.The delution ratio is less than 10%and the character of the powder is preserved in the cladding coating. The matrix phase in cladding coating isα-Fe,a certain amount of amorphous alloys such as Fe₂B,Fe₃C,FeSi and intermetallics such as Ni-Cr-Fe,Fe-Cr,Fe-Ni are distributed on the matrix phase.Therefore,good hardness and wear resistance of the cladding coating can be guaranteed.The hardness of surface is relatively low,the hardness about 0.3mm distance from surface increases obviously,the hardness keeps smooth increase from 0.3mm to 0.9mm. The hardness has the maximum in the H.A.Z,up to 810HV0.2,then it drops quickly from H.A.Z to substrate.The wear resistance of cladding coating is 1.5 times greater than that of substrate.