A new method for isolating plasma interactions from those of the laser beam during plasma nitriding

Laser-Sustained Plasma (LSP) Nitriding of Titanium: A Review

“…Black et al [111] studied the interaction between a nitrogen LSP and a CP-Ti substrate by orienting the CP-Ti substrate parallel to the axis of the CO 2 laser beam ( Figure 6c); these experiments differed from Nassar et al's [108] research (Figure 6a) where the substrate was normal to the laser beam. In Black et al's [111] configuration, the nitrogen LSP (Figure 6b) was the sole heating source since the laser beam did not irradiate the substrate, thus allowing them to isolate and study the interaction of the nitrogen LSP with the CP-Ti substrate.…”

“…Black et al [111] studied the interaction between a nitrogen LSP and a CP-Ti substrate by orienting the CP-Ti substrate parallel to the axis of the CO 2 laser beam ( Figure 6c); these experiments differed from Nassar et al's [108] research (Figure 6a) where the substrate was normal to the laser beam. In Black et al's [111] configuration, the nitrogen LSP (Figure 6b) was the sole heating source since the laser beam did not irradiate the substrate, thus allowing them to isolate and study the interaction of the nitrogen LSP with the CP-Ti substrate. When the axis of the parallel nitrogen LSP was brought within 2-2.5 mm of the CP-Ti substrate and maintained there for 5 s, the substrate melted and incorporated nitrogen from the plasma, resulting in the synthesis of TiN layers up to 300 µm in thickness on the substrate with compositional gradation of nitride concentration (Figure 7a) and faceted crystal growth on the surface (Figure 7b).…”

“…The role played by near-surface plasma during CW CO 2 laser nitriding of commercially pure titanium (CP-Ti) was investigated in great detail in the Center for Multi-scale Wave-Material Interaction (CMWMI) at the Pennsylvania State University [100,106,[108][109][110][111][112] in recent years, resulting in the development of the so-called "LSP nitriding" process that was capable of improving the wear resistance of CP-Ti in open and uncontrolled atmosphere with minimal surface oxidation. Using a combination of charge-couple device (CCD) imaging and optical spectroscopy, Nassar et al [108] characterized the near-surface plasma formed during the laser nitriding process as a function of scanning speed and off-focal distance (OFD).…”

“…(a) Schematic of Nassar et al's[108] LSP nitriding process with the substrate perpendicular to the laser beam, (b) CCD image of freestanding nitrogen LSP, and (c) schematic of Black et al's[111] LSP nitriding process with the substrate parallel to the laser beam.Figure 6a,b reprinted with permission from Ref [108]…”

“…SEM images of the titanium substrate nitrided in the parallel configuration (Figure 6c) showing: (a) longitudinal cross-section having four distinct layers of the nitrided titanium substrate, and (b) faceted crystal growth at the nitrided surface. Reprinted with permission from Ref [111]…”