The Nitrotec process consists of nitriding (nitrocarburising) components, before immediately subjecting them to rapid oxidation, then quenching, finishing with the application of a protective sealant. Oxidation gives protection against corrosion, whilst the quenching and sealing give enhanced surface wear resistance and increased yield strength of materials.
Within a vacuum chamber, surfaces to be hardened are bombarded with a high energy stream of ions that penetrate the surface. This is not a diffusion process. Once impregnated into the surface, the ions (usually carbon or nitrogen) lose their energy and stop moving. The compressive stresses generated in the surface layers improve mechanical and fatigue properties, as well as corrosion and wear resistance.
Induction hardening involves using induced electrical currents to very rapidly generate heat via hysteresis, usually in a workpiece made from medium to high carbon steel. Flame hardening uses oxy-fuel burners to heat the workpiece via conduction. Both procedures use quenching after heating, often followed by tempering and/or stress relieving.
Carbon or carbon and nitrogen together, in a medium of gas, solid or liquid, are diffused into the surface of component(s), particularly those made from low carbon steels. Changes to the chemical composition of the surface (austenite) lead to high carbon content in the surface material, which when quenched transforms to a hard coating (martensite).
The surface of the workpiece is saturated with either carbon atoms (carburising plasma) or nitrogen atoms (nitriding plasma). Carburising, carried out at high temperatures, involves bombarding the surface to be coated with the plasma. The workpiece is held under vacuum until carbon atoms have diffused into the heated surface, to form hardened surface layers on quenching. Nitriding is carried out under vacuum, but without external heat. The heat to diffuse the nitrogen into the surface is provided by kinetic energy, produced when the atoms hit the surface. Hardened surface layers are formed on cooling of the workpiece in situ.
A surface treatment used to harden or clad surfaces of ferrous metals. For hardening, a laser beam with a high power density heats a small area on the surface of the workpiece, causing changes to the atoms in the lattice of the material (austenite). As the beam moves away, to another spot on the surface, the heated area is rapidly cooled by the surrounding metal (self-quenching). This rapid cooling stops the lattice from returning to its original arrangement, resulting in a very hard surface structure (martensite). For cladding, the high temperature of the laser helps bond tracks of injected powder with the surface of the workpiece.
The surface to be coated is cleaned and roughened, to provide adhesion of molten particles in the coating material when it’s sprayed onto the workpiece. The coating material is melted using thermal, electrical or thermochemical means. Molten materials (metals, alloys or ceramics) are sprayed onto a substrate material (the component) where they solidify and bond to it. Materials can be solid (wire, rod or cord) or powder, and are heated into the molten or semi-molten state by thermal, electrical or thermochemical means. The sprayed particles impinge on the substrate and flatten out into thin platelets.