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Laser Drilling Process Yields Fewer Cracks in Hastelloy X – Part 2

laser drilling processHASTELLOY X (UNS N06002) is one of the common wrought nickel alloys used in gas turbine applications because of its high temperature strength and oxidation resistance.

The previous issue of this newsletter included initial results of a study aimed at documenting the relationship between laser and process parameters for laser trepan drilling and the common metallurgical properties of base metal cracking and recast layer thickness for Hastelloy X.

Figure 1 shows one of the main conclusions from this study. Results showed that there is a significant relationship between peak power and base metal crack length in Hastelloy X. Except for low peak power (left side of graph), the influence of pulse width is negligible. In fact, data points for the two pulse widths for the highest peak power overlap each other.

For reference, peak power (in Watts) is pulse energy (in Joules) divided by the pulse duration (in seconds).

Figure 1

Figure 1: Base metal crack length as a function of peak power for two different pulse durations. All holes were trepanned at 30 degrees from the surface.

The main objectives of the second part of the study were to test the conclusions drawn from results of the first series of tests and to refine the conclusions where required. To accomplish this, holes in the second part of the study were drilled in a thicker section of Hastelloy X sheet (3.2 mm compared to 2.25 mm in first part).

Results

The relationship between peak power and base metal cracking pictured in Figure 1 was also observed in drilling the thicker Hastelloy X. Results can be employed to control metallurgical characteristics and improve the overall hole quality for uncoated sheet metal components.

“Results… confirmed the significant relationship between peak power and base metal crack length.”

Figures 2 and 3 show micrographs of holes trepanned in 3.2 mm thick Hastelloy X at 90 and 30 degrees to the surface respectively.

fig 2

Figure 2: 3.2mm thick Hastelloy X with 869 µm diameter hole at 90 degrees to the surface. Metallurgical results are: no base metal cracks; average recast layer thickness: 14.7 µm; average oxide layer thickness: 20.3 µm.

 

fig 3

Figure 3: 3.2mm thick Hastelloy X with 869 µm diameter hole at 30 degrees to the surface. Metallurgical results are: no base metal cracks; average recast layer thickness: 25.7 µm; and average oxide layer thickness: 60.2 µm.

Next steps

A series of holes is being trepanned in Hastelloy X containing TBC (thermal barrier coating) to study the relationship between laser and process parameters and metallurgical characteristics of holes with TBC. Results will be published in an upcoming issue of this newsletter.

Have Questions or Comments?

For additional information on drilling Hastelloy X, contact LASERDYNE Sales at lds.sales@primapower.com.

If this article was of interest…

If you found this article interesting, you may also want to read the following articles from previous issues of this newsletter:

• “Minimizing Base Metal Cracking in Nickel-Based Alloys – Part 1
• “Minimizing Base Metal Cracking in Nickel-Based Alloys – Part 2