54
Remanufacturing and Advanced Machining
• Surface texturing for improved paint appearance
• Plating by Laser Chemical Vapor Deposition (LCVD)
• Laser Physical Vapor Deposition (LPVD)
Among the laser cladding routes are those which melt a preplaced or blown powder
and those which decompose vapor by pyrolysis. In LCVD, the process is based on
photolysis, while in LPVD upon local vaporization. Other methods employ sputtering, enhanced electroplating, or cementation. The particle injection process is similar to laser cladding by the blown powder route, but the particles blown into the laser
melt pool remain solid. The as-created structure displays improved hardness and
wear resistance with reduced friction coefficients. In general, process variations can
be introduced to the particle delivery system, pressure delivery, and the gas shrouding systems (Steen, 2003).
Besides the methods that apply laser irradiation to cladding or powder alloying,
the laser-induced nitrogen and carbon uptake is an established method to obtain
enhanced properties of alloys and their surfaces (Höche et al., 2015). The process
of laser nitriding and carburizing is a very complex interaction difficult to describe
in detail. The entire process is dominated by local heating and the resulting surface
temperature, which determines the uptake of nitrogen and carbon. Depending on
melting or evaporation effects, different process chains are involved determining
coatings and their properties in an interlinking way. Each subprocess causes consequences for the resulting synthesis and has to be examined and weighed in order to
understand and to control the process. Just to mention the most important (Höche
et al., 2015):
• Laser absorption and local heating
• Melt and evaporation processes
• Plasma expansion into the background gas
• Dissociation and/or ionization
• Gas adsorption and absorption
• Gas atomic transport (diffusion, convection)
• Nucleation and solidification
• Solid-state phase transformation
Attempts at the production of TiN-coatings in reactive atmospheres by means of
laser irradiation were undertaken in the 1980s and 1990s, providing an enormous
improvement to surface properties (Höche et al., 2015). With a CO 2 laser, it was possible to obtain a hundred micrometers thick coatings. The surface of commercially
pure titanium (cp-Ti) after laser nitriding contains a mixture of α’-Ti and δ-TiN.
When nitrogen content of the processing gas is increased, the volume fraction of
δ-TiN rises at the expense of the α’-Ti which causes surface hardness to grow. Laser
nitriding of high-strength (α+β)-Ti alloy Ti-6Al-4V can increase hardness to moderate values in the range of 400–600 HV, improving cavitation and water droplet
erosion resistance. Values above 600 HV could significantly improve sliding wear
resistance, while abrasive wear resistance of Ti–6Al–4V can only be improved if
Remanufacturing and Advanced Machining
• Surface texturing for improved paint appearance
• Plating by Laser Chemical Vapor Deposition (LCVD)
• Laser Physical Vapor Deposition (LPVD)
Among the laser cladding routes are those which melt a preplaced or blown powder
and those which decompose vapor by pyrolysis. In LCVD, the process is based on
photolysis, while in LPVD upon local vaporization. Other methods employ sputtering, enhanced electroplating, or cementation. The particle injection process is similar to laser cladding by the blown powder route, but the particles blown into the laser
melt pool remain solid. The as-created structure displays improved hardness and
wear resistance with reduced friction coefficients. In general, process variations can
be introduced to the particle delivery system, pressure delivery, and the gas shrouding systems (Steen, 2003).
Besides the methods that apply laser irradiation to cladding or powder alloying,
the laser-induced nitrogen and carbon uptake is an established method to obtain
enhanced properties of alloys and their surfaces (Höche et al., 2015). The process
of laser nitriding and carburizing is a very complex interaction difficult to describe
in detail. The entire process is dominated by local heating and the resulting surface
temperature, which determines the uptake of nitrogen and carbon. Depending on
melting or evaporation effects, different process chains are involved determining
coatings and their properties in an interlinking way. Each subprocess causes consequences for the resulting synthesis and has to be examined and weighed in order to
understand and to control the process. Just to mention the most important (Höche
et al., 2015):
• Laser absorption and local heating
• Melt and evaporation processes
• Plasma expansion into the background gas
• Dissociation and/or ionization
• Gas adsorption and absorption
• Gas atomic transport (diffusion, convection)
• Nucleation and solidification
• Solid-state phase transformation
Attempts at the production of TiN-coatings in reactive atmospheres by means of
laser irradiation were undertaken in the 1980s and 1990s, providing an enormous
improvement to surface properties (Höche et al., 2015). With a CO 2 laser, it was possible to obtain a hundred micrometers thick coatings. The surface of commercially
pure titanium (cp-Ti) after laser nitriding contains a mixture of α’-Ti and δ-TiN.
When nitrogen content of the processing gas is increased, the volume fraction of
δ-TiN rises at the expense of the α’-Ti which causes surface hardness to grow. Laser
nitriding of high-strength (α+β)-Ti alloy Ti-6Al-4V can increase hardness to moderate values in the range of 400–600 HV, improving cavitation and water droplet
erosion resistance. Values above 600 HV could significantly improve sliding wear
resistance, while abrasive wear resistance of Ti–6Al–4V can only be improved if