First, let's take a look at the "temperament" of the laser cladding equipment. Let's consider the powder feeding system as a "porter". Different "porters" have different requirements for the particle size of the powder. For instance, in the air powder conveying system, it is like a "porter" that pushes the powder along with air flow. This requires the powder to "run" smoothly, that is, to have good fluidity. Generally, it is more appropriate to select powder with a particle size of 15 to 53μm, so that the powder can be steadily delivered to the cladding area along the airflow. As for the mechanical powder feeding system, it has a relatively higher "tolerance" for powder particle size, but it can't handle everything. A particle size of around 20 to 60μm is better. If the powder is too fine, just like sand that is too fine and tends to clump together, it will be uneven when being fed. If it is too thick and like a big stone that is difficult to move, it will affect the accuracy of powder delivery.

Laser power and scanning speed are like switches that "heat" the powder. High power is just like a stove with a strong flame, which can burn large powder particles thoroughly. So when using high-power laser cladding equipment, we can choose powder with a slightly larger particle size of 45 to 105μm. If the laser power is low and the firepower is small, then a powder with a particle size of 15 to 45μm should be selected. Otherwise, the powder will absorb heat too slowly and won't melt well.

Secondly, we need to consider the base material and the structure of the parts. Different matrix materials are like different "companions", and they make friends with powders in different ways. Materials with high thermal conductivity, such as copper and aluminium, conduct heat quickly, just like ice melts rapidly. In order for the powder to "get along well" with them, that is, to achieve a good combination, small-grained powder should be selected. In this way, the powder can heat up more quickly and "blend well" with the matrix. Materials with low thermal conductivity, such as stainless steel and nickel-based alloys, are like thick cotton clothes that do not conduct heat easily. Therefore, the requirements for powder particle size are not as strict, and slightly larger particle size powders can be selected.

If you want to perform laser cladding on parts with complex shapes and many small corners, it's like painting the nooks and cranny of a house. You need to use a finer "brush", that is, small-grained powder, so that the powder can penetrate those small areas and spread evenly. If cladding large flat parts, it's like laying floor tiles in a large square. It's fine to broaden the particle size range a bit.

Moreover, there are also performance requirements for the cladding layer. If you want the cladding layer to be denser, with fewer holes and defects, then choose a small-grained and uniform powder, usually 15 to 53μm is fine. Just as fine sand can fill the gaps when building a house, small-grained powder, when melted, can better fill the voids, making the cladding layer more solid. On the other hand, if the cladding layer is required to be more wear-resistant and harder, you can choose a powder with a slightly larger particle size of 45 to 105μm. During the cladding process, large-particle powder is like building with large blocks, which can easily form a larger "structure", that is, a coarser grain structure. This can enhance the hardness and wear resistance of the cladding layer. However, it should also be noted that if the particle size is too large, the surface of the cladding layer will be like rough sandpaper and not smooth enough.

Last but not the least, don't forget the characteristics of the powder itself. The fluidity of the powder is extremely important as it determines whether the powder can move smoothly during feeding. Powders with a particle size ranging from 20 to 60μm have relatively good fluidity, just like small balls that can roll smoothly on flat ground. If the fluidity is poor, the powder feeding will be intermittent, and the cladding layer will also become thick and thin in patches. At this point, you can add some flow enhancers, just like adding some lubricating oil to a small ball, or give the powder surface treatment to make it run better. Loose powder with high density is like tightly stacking more small balls together, and it contains more metal particles in the same volume. In laser cladding, 316L stainless steel powder with a bulk density of 2.0 to 3.0g/cm³ is more suitable. The powder particle size corresponding to this range is usually 15 to 53μm. With such powder, the cladding efficiency is higher and the cladding layer can also be thicker.

But to be honest, all of the above are just for reference. When actually working, experiments still have to be conducted. Just like when we taste cooking, select powders of different particle sizes to conduct laser cladding tests. Carefully observe the appearance and thickness of the cladding layer, measure its density, hardness and bonding strength. Only by trying several times can you find the most suitable particle size of 316L stainless steel powder for your process and parts at hand.

That's all for this issue's discussion on how to choose the appropriate particle size of 316L stainless steel powder for laser cladding. Welcome to contact us for further information.