16JR Treglio AJ Perry and RJ Stinner Surface and Coatings Technology Vol 65 1994 p 184 Applications

Table 2 outlines some of the research and development applications that have been pursued using directed beam ion implantation technology. Of the properties listed, the tribological aspects of ion implantation have received the most attention (Ref 17). In spite of the relatively shallow penetration of implanted ions (typically nitrogen), implanted surfaces have often demonstrated a high degree of resistance to wear under mild abrasive or lubricated sliding conditions. This wear resistance is especially noteworthy in alloy surfaces that contain elements forming stable nitrides. Titanium and Co-Cr alloy orthopedic prostheses for hips and knees are among the most successful commercial applications of ion implantation components for wear resistance. In use, these components, shown in Fig. 5, articulate against an ultrahigh-molecular-weight polyethylene mating surface. Tests at several laboratories have indicated that wear reductions of 10* to 100* may be realized by the implantation of nitrogen ions into the alloy. To date tens of thousands of such components have been ion implanted prior to surgical implantation.

Table 2

Surface properties modified

Substrates studied

Ions species used

Comments, references

Wear

Steels, WC, Ti, Co/Cr alloys, TiN coatings, electroplated Cr

> 1017 ions/cm2

Ti, Co/Cr alloys largest use commercially in orthopedic devices (Ref 5, 9, 17)

Friction

> 1017 ions/cm2

Dual implants give amorphous surface layer (Ref 18)

Fatigue

Ti alloys, steels

N, C > 1017 ions/cm2

Implantation effective for surface initiated fatigue (Ref

5)

Fracture toughness

Ceramics: Al2O3, TiN

Ar 1015-1017

Radiation damage critical, ion induced compressive stress helpful (Ref 4, 19)

ions/cm

Aqueous corrosion catalysis

Steels, Ti alloys, Pt

Cr, Ta, Cr plus P > 1017 ions/cm2

Ion implant can mimic "normal" alloys; amorphous and unique surface alloys possible (Ref 20)

Oxidation

Superalloys

Y, Ce > 1015 ions/cm2

Low effective doses; implanted species stay at metal-oxide interface (Ref 21, 22)

Electrical conductivity

Polymers

Ar, F 1012-10127 ions/cm2

Permits chain scissoning, doping; conductivity approaches disordered metal levels (Ref 3, 23)

Optical: Refractive index

Glasses, electrooptics

Li, Ar 1015-1017 ions/cm2

Chemical doping and lattice disorder both important (Ref 24, 25)

Fig. 5 Surgical prostheses of Ti-6Al-4V alloy of types being commercially ion implanted for wear benefits

Ion implantation is also being investigated as a means of improving the performance of certain types of coatings. Two examples are the implantation of nitrogen ions into (a) physical vapor deposited TiN coatings, such as on cutting inserts to increase their lifetimes, and (b) electroplated chromium to produce a CrN surface layer that inhibits the formation of microcracks, thus increasing the useful life of the electroplate. The latter use is of particular interest because of steadily increasing environmental concerns.

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