Method of producing integral, hard nitride layer on titanium/titanium alloy

DETAILED DESCRIPTION The object of the present invention is to eliminate the inconveniences of the known processes described above.
With the process according to the invention a uniformly distributed nitride layer is obtained which also coats internally (e.
g.
in capillaries).
The layer is also characterised by extremely good adhesion, high hardness (at least 2000 HV.
sub.
0.
05), good friction and wear properties, improved corrosion-proof and biocompatibility properties of the titanium or titanium alloy, and equal or improved biocompatibility properties even for titanium alloys where a depletion of the alloying element is obtained in the nitride layer.
The problem is solved in that the untreated objects are subjected in a vacuum furnace with an atmosphere consisting of pure nitrogen gas, to a temperature of 650.
degree.
-1000.
degree.
C.
and a pressure below atmospheric pressure, after which the temperature is reduced.
A high gas flow is necessary during heating to the treatment temperature.
This is in order to remove contamination layers (contamination layers=a few atom layers with absorbed carbon and oxygen which exist on all surfaces) and impurities which are desorbed during the heating process, from the surface.
This prevents them from reacting with the substrate (titanium or titanium alloy).
Such a reaction quickly produces an effective diffusion barrier, thereby preventing the formation of a pure titanium nitride layer of sufficient thickness.
Titanium and titanium alloys are particularly sensitive to the above-described effected when the reactivity is very high.
By means of the process according to the present invention a continuous, uniformly distributed nitride is formed having high purity, the thickness of which can be controlled between 0.
5 and 10 .
mu.
m, depending on the treatment time and temperature.
Titanium reacts with nitrogen gas (N.
sub.
2) and the surface is converted to titanium nitride (TiN) which is an extremely hard coating material, resistant to wear and corrosion and having good friction properties