Workshop 4: 🧪 Laser Surface Alloying¶
Industrial Workshop 4 of 7
Laser Surface Alloying
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Workshop Brief¶
Alloy a thin Cr-Ni powder layer onto a mild-steel substrate, producing a uniform, well-mixed surface layer roughly 0.5 mm deep — patchy melting leaves an uneven, poorly bonded surface.
Specifications: Powder: Cr-Ni blend · Target depth 0.5 mm · Uniform mixing
Process Theory¶
Laser surface alloying melts a thin layer of the substrate together with a pre-placed or co-fed alloying powder (here, a chromium-nickel blend), so that on rapid solidification the alloying elements are incorporated into the substrate surface, improving properties such as corrosion or wear resistance without affecting the bulk material.
Power density controls how deep and how completely the substrate-plus-powder layer is melted: too low a power density leaves powder unmelted or poorly bonded (patchy alloying); too high a power density can vaporize the powder or over-dilute the alloy layer into the bulk.
Powder feed rate must be matched to the melt pool's capacity to dissolve and mix the incoming powder; traverse speed sets the time the powder spends in the melt pool per unit length — too fast a traverse limits mixing time, while too slow a traverse can overheat and coarsen the microstructure.
Process Parameters¶
| Parameter | Range | Unit |
|---|---|---|
| Power density | 1 – 10 | kW/cm² |
| Powder feed rate | 1 – 20 | g/min |
| Traverse speed | 1 – 30 | mm/s |
Procedure¶
- Record the precision score at the default power density, feed rate and traverse speed.
- Vary power density alone and record the precision score at each value.
- Repeat, varying powder feed rate alone, then traverse speed alone.
- Identify the parameter combination that gives a uniform ~0.5 mm alloyed layer with a 100% precision score.
Observation Table¶
Table: Effect of laser surface-alloying parameters on layer uniformity
| Trial | Power density (kW/cm²) | Feed rate (g/min) | Traverse speed (mm/s) | Precision score (%) | Verdict |
|---|---|---|---|---|---|
| 1 | |||||
| 2 | |||||
| 3 | |||||
| 4 | |||||
| 5 | |||||
| 6 | |||||
| 7 | |||||
| 8 |
Graph¶
Plot Precision score (%) (y-axis) against Power density (kW/cm²) (x-axis).
Expected trend: an optimum band — low power density gives patchy alloying, excessive power density over-dilutes or vaporizes the layer.
Precision score vs power density, holding feed rate and traverse speed fixed
Calculation¶
- Relate powder feed rate and traverse speed qualitatively to the mass of powder delivered per unit length of track, and comment on how this affects layer thickness.
- State the final optimized (Power density, Feed rate, Traverse speed) combination reaching certification.
Result¶
Table: Optimized parameter set for laser surface alloying
| Power density (kW/cm²) | Feed rate (g/min) | Traverse speed (mm/s) | Final precision (%) | Certified? (Y/N) |
|---|---|---|---|---|
| 1 |
Precautions¶
- Change one parameter at a time so that the source of any patchy/uneven result can be clearly identified.
- Consider feed rate and traverse speed together, since both control the powder mass delivered per unit track length.