The materials applied to laser cladding are relatively wide. It has been successfully developed in stainless steel, dies steel, malleable cast iron, gray cast iron, copper alloys, titanium alloys, aluminum alloys, and special surfaces. And has been used in a wide range of applications, such as the following: laser cladding of cobalt-based, nickel-based, iron-based, and other self-fusing alloy powders and ceramic phases.
Laser cladding of iron-based alloy powders is suitable for parts that require local abrasion resistance and are prone to deformation.
Nickel-based alloy powders are suitable for components requiring local wear resistance, heat resistance, corrosion resistance, and thermal fatigue resistance.
Cobalt-based alloy powder is suitable for parts requiring local wear resistance, heat resistance, corrosion resistance, and thermal fatigue resistance.
Ceramic coating has high strength, excellent thermal stability, and high chemical stability under high temperature, which is suitable for parts requiring wear resistance, corrosion resistance, and high temperature resistance. And oxidation resistance of the parts.
Laser cladding can be divided into two main categories according to the cladding material’s supply method, i.e., pre-set laser cladding and synchronous laser cladding.
Pre-set laser cladding is to place the cladding material on the substrate’s surface beforehand, and then use laser beam irradiation to scan and melt the cladding material. The content is added in the form of powder, wire, or sheet, with dust being the most common.
Simultaneous laser cladding is where the cladding material is fed directly into the laser beam so that both feeding and coating can be done simultaneously. The molten metal is also supplied primarily in the form of powder, but some also use wire or sheet for simultaneous feeding.
The primary process of pre-set laser cladding is pretreatment of substrate cladding surface — pre-set cladding material — preheating — pre-set cladding material — Laser melting – post heat treatment.
The primary process of synchronous laser cladding is the substrate cladding surface pretreatment — feeding laser melting— post-heat treatment.
Process Parameters Of Laser Cladding
The main parameters are laser power, spot diameter, cladding speed, defocusing amount, powder feed speed, scanning speed, and preheating temperature. These parameters have a significant influence on the dilution rate, cracking, the surface roughness of the cladding layer, and the density of the cladding parts. The settings also affect each other, which is a very complex process, and reasonable control methods must be adopted to control these parameters in the laser, within the range allowed by the cladding process.
The higher the laser power, the more the amount of molten cladding metal is melted, and the higher the probability of porosity. As the laser power increases, the depth of the cladding layer increases, the surrounding liquid metal fluctuates dramatically, and dynamic solidification crystallizes, causing the number of porosity to increase gradually. The cracking is gradually reduced or even eliminated. When the depth of the cladding layer reaches the ultimate bottom, the deformation and cracking intensify as the power increases, and the surface temperature of the substrate rises. The power is too small, only the surface coating melting, the substrate is not molten, this time the surface of the molten layer of local pilling, hollow, etc., can not reach the surface of the melting Purpose.
The cladding speed V has a similar effect to the laser power P. The cladding speed is too high, and the alloy powder cannot be completely melted. If the cladding speed is too high, the alloy powder does not vanish entirely and does not have the effect of high-quality cladding; if the cladding speed is too low, the existence time of the melting pool is too long. Excessive length, overburning of the powder, loss of alloying elements, and high heat input to the substrate will increase the deformation.
the laser beam is generally circular. The cladding layer’s width mainly depends on the spot diameter of the laser beam, which increases, and the cladding layer becomes wider. The spot size will cause changes in the energy distribution on the surface of the cladding, and the morphology and tissue properties of the cladding will vary considerably. Generally speaking, in the small size of the spot, the quality of the cladding layer is better, as the spot size increases, the quality of the cladding layer decreases. But the spot diameter is too small, which is not conducive to obtaining a large area of the cladding layer.
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