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Finishing plasma hardening

The essence of finishing plasma hardening (FPH) refers to increasing service life of parts and tools by applying thin-film coatings at atmospheric pressure during tubeless chemical vapor deposition (PECVD process) using liquid organoelement compounds and activation by electric arc plasma. The coating is a product of reactions of reagent vapors passing through small plasma chemical reactor.

The purpose of FPH is production of parts, tools, stamps, molds, knives, dies, bearings and other products with special surface properties: wear resistance, antifriction, corrosion resistance, heat resistance, high resistance, anti-seizing, resistance to fretting corrosion, etc.

The effect of FPH is achieved by changing physical and mechanical properties of the surface layer: increasing microhardness, reducing coefficient of friction, creating compressive stresses, healing microdefects, forming dielectric and corrosion-resistant film coating on the surface with low coefficient of thermal conductivity, chemical inertness and specific topography of the surface.

Equipment for FPH comprises a specialized current source, a unit of equipment with liquid metering device, plasma jet with plasma chemical reactor. In addition, this equipment may be equipped with a robot, positioner. manipulator, autonomous cooling unit, mobile exhaust system, coating control device, coating thickness measuring device, surface preparation equipment prior to coating.

FPH technological process is performed at atmospheric pressure and comprises operations of pre-cleaning (by any known method) and directly hardening of the treated surface by mutual movement of the product and plasma jet with plasma chemical reactor. The speed of movement is 1-10 mm/sec, distance between plasma jet and product is 5-15 mm, diameter of hardening spot is 12-15 mm, coating thickness is 0.5-3 μm. Temperature of heating of parts with FPH does not exceed 100-150 °C. Surface roughness parameters do not change after FPH. As gases, argon and nitrogen are used, starting materials for passage of plasma chemical reactions and formation of coatings are liquid technological preparations of SETOL family. Total consumption of substances does not exceed 0.5 g/h (not more than 0.5 liters per year).

Examples of FPH application: hardening of cutting tools, stamps, knives, saws, molds, gages, dies, gears, bearings, machine parts such as rollers, cams, guides, latches, clamps, pushers etc.

FPH implementation at enterprises in Russia, CIS countries and abroad shows an increase in resistance of reinforced products by 2-10 times.

Distinctive features of FPH versus analogues - ion-plasma surfacing (PVD-processes), CVD-processes, laser and electric spark hardening, epilamation and others:

• the process of hardening in the air at ambient temperature does not require the use of vacuum or other chambers and baths;
• after application of thin-film coating (not more than 3 micrometers thick), which falls within tolerances for dimensions of parts, hardening process is used as final finishing operation;
• no changes in surface roughness parameters after the hardening process;
• minimal heating during machining (no more than 200С) does not cause deformation of parts, and also - allows hardening tool steels with low tempering temperature;
• possibility of hardening of local (in depth and area) volumes of parts in places of wear while preserving the original material properties in the remaining volume;
• thin-film coating on amorphous, low coefficient of friction, high microhardness, dielectric properties, chemical resistance to acids and alkalis, transparency in IR range, close to diamond-like coatings;
• compressive residual stresses formed on the surface of hardened products increase their fatigue strength during cyclic loading (for comparison: tensile stresses occur after the grinding operation, leading to a decrease in fatigue strength);
• high adhesive adhesion of the coating to the substrate provides maximum resistance to abrasion (including – when the tool interacts with the material being processed);
• low coefficient of friction helps to suppress processes of buildup forming during cutting or sticking during stamping and pressing;
• formation of specific microrelief of surface contributes to its effective filling with a lubricating-cooling liquid when operating tools and machine parts;
• thin-film amorphous (glassy) coating formed on the surface protects the product from effects of high temperature (high temperature air corrosion tests for 100 hours at 800C);
• high hardening performance (machining time, for example, for the edges of medium-sized die cutter may reach several minutes);
• ease of cleaning and degreasing operations before hardening (no special pre-treatment);
• possibility of hardening of surfaces of details of any dimensions in manual or automatic modes;
• minimal consumption and low cost of consumables;
• low power consumption of hardening unit - less than 5 kW;
• insignificant area occupied by the equipment - 1-2 m2;
• small plasma jet with plasma-chemical reactor for hardening (weighing about 1.5 kg) can be easily fixed to the manipulator, in the robot’s arm, and also enables manual processing;
• transportability and maneuverability of the equipment (equipment weight is less than 15 kg, that of power source is less than 50 kg);
• ecological purity of the process due to absence of waste during hardening;
• minimum noise level, which does not require special protection measures;
• in contrast to hardening methods with the use of surfactants - this technology does not have special requirements for premises, there is no contact with toxic materials, no time is required to soak in solutions and dry the treated parts.

Production trials. The following types of coatings are used in FPH:

The economic efficiency of FPH parts, tools, tooling and other products is determined by increasing their resource, reducing required number for a given production program, saving tool steel, reducing scope of grinding operations, reducing time and costs related to setting presses and machine tools, possibility of intensification of operating modes.