The need to have available increasingly sophisticated materials, able to work in conditions sometimes exasperated, has stimulated numerous studies for the search of new materials or of particular treatments which alter the characteristics of the materials available. Among the most frequent reasons for the decay of a piece we wear, abrasion and corrosion. In the field of surface treatments the nikelchimico has proved extremely versatile for the numerous codeposizioni that can be carried out (meaning by a codeposione incorporation of particles of small size in a matrix of nikelchimico) such as Ni-diamond, Ni-boron carbide, Ni-Al2O3, Ni-silicon carbide. From the application point of view, however, the co-deposition Ni-SiC is the most widespread for its excellent behavior against wear and abrasion and for its relatively low cost.

PROCESSING
The bath of Silican has the same constituents as the bath nikelchimico, to which are added the SiC particles of sizes between 3 and 5μ. Since the deposit of SiC takes place by gravity, only the surfaces of the pieces directly exposed to the fall of the particles they will present the encapsulation, while the surfaces located parallel to the direction of fall of the granules or the lower surfaces, it will be almost free and then coated only of nikelchimico. This fact is of fundamental importance for the positioning of the parts in the bath which very often have to be set in rotation in such a way that all surfaces are to be found even if at different times in a position perpendicular to the direction of fall of the particles of silicon carbide.

PROPERTIES OF TREATMENT SILICAN
Some, such as uniformity of the deposit, the absence of the tip, corrosion resistance, are those characteristics of the nikelchimico. The Silican differs from the latter in the surface hardness and wear resistance.

SURFACE HARDNESS
The hardness of the nickel-Sic codeposto increased from 550 HV to 750 HV of nikelchimico. Subjecting the deposits of Silican to an appropriate heat treatment there is an increase of hardness up to 1400 HV (74 RC). This value is actually a dummy, as constituted by an average of the values ​​detected with the microhardometer. In fact, if the diamond pyramid of the instrument relies on a granule of silicon carbide, the value will be greater than 1400 HV; vice versa if rests on an interstice between two granules of SiC you will have a value of 1100 HV, typical of nikelchimico annealed. The table shows the value of the hardness of annealed Silican in relation to other types of treatments

Figura 6

WEAR RESISTANCE
The deposits of Silican to confer special high wear resistance. II their behavior is different depending on the type of wear which they are subjected and of the operating temperature. The following table shows some values ​​measured in conditions of wear mixed (ring-block) in the presence of lubricants at relatively high pressure: it can be noted the low coefficient of wear of the Silican.

Disk Block µ weight loss Disk Block Ni/P Steel Rc 60 0,09 102,0 0,2 Ni/P* Steel Rc 60 0,11 1,0 0,0 Ni/P+SiC* Steel Rc 60 0,13 0,1 5,1 Ni/P+SiC* Ni/P* 0,1 0,0 6,4 Ni/P+SiC* Hard chrome 0,07 0,5 1,1 Ni/P+SiC* Ni/P+SiC* 0,06 0,2 0,2 * heated for 5 hours @ 290°C

As regards the coefficient of wear, in Fig.8 shows the behavior of different types of surface treatments subjected to different loads.

Fig. 8 - Coefficient of wear and antiseizure properties of some surface treatments,
high loads, with lubricating oil.