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2 Si 3 N 4 Cr 3 Si Cr 2 N Cr powder Si N Cr Si 3 N 4 CrSiCrSi 2 Cr 3 Si 2 Cr 3 Si Cr 2 N  stable Si 3 N 4 -Cr 3 Si interface  unstable Si 3 N 4 -Cr 2 N interface  fast outward diffusion of N compared to that of Si Cr powder

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10 Total hip replacement Total knee replacement Hip resurfacing Metal-on-polyethylene no alternatives at present (1) Ceramic-on-ceramic Traditional bearing Low wear alternatives  High volumetric wear  Risk of brittle fracture WEAR OF JOINT REPLACEMENTS Osteolysis due to wear is the major cause of long-term failure of joint replacements Metal-on-metal the only successful bearing  Release of nanometric metal debris and metal ions (2) Metal-on-metal

11 CERAMIC surface on METALLIC joints Rationale:  Hard ceramic surface - wear resistance, low ion release  Metallic interior - no danger of brittle fracture, easy shaping Applied Ceramic Coatings - titanium nitride (TiN) Very hard: HV ~25 GPa Deposited by PVD -  weak adhesion, coating defects, no support from soft substrate  limited durability Oxinium Air-oxidized Zr(Nb) alloy: a moderately hard zirconia (ZrO 2 ) surface layer: 12 GPa Underlying oxygen-hardened substrate promotes adherence  used only against UHMWPE (high wear of ZrO 2 -on-ZrO 2 )

To produce a hard titanium nitride surface layer (similar to PVD-TiN) with good adherence to Titanium alloy substrate (similar to ZrO 2 in Oxinium) Our approach Method: PIRAC - Powder Immersion Reaction Assisted Coating before after PIRAC nitriding 12 A. Shenhar, I. Gotman, et al: Mater Sci Eng A268:40(1999) A. Shenhar, I. Gotman, et al.Ceramics Int 26: 709(2000) Environmentally friendly, not line-of- sight (possibility of coating complex shapes) Cr 2 N powder atmospheric O 2 atmospheric N 2 Ti alloy High-Cr steel container T =  C

13 N-hardened bulk supports the TiN layer and will prevent its collapse in the presence of third-body particles Unlike TiN-PVD, TiN-PIRAC is not an externally applied coating In PIRAC, metal surface transforms to ceramic (TiN) via reactive diffusion of nitrogen N-hardened Ti alloy TiN layer No delamination of PIRAC-TiN layer in bending - excellent adhesion A. Shenhar, I. Gotman, et al. Surf Coat Techn 126: 210 (2000) TiNN-hardened zone Ti alloy N N TiN-PIRAC on Ti alloy TiN and N-hardened layer thicknesses are controlled by PIRAC T-t regime

14 Number of cycles, x10 6 UHMWPE wear, mg TiN-PIRAC on Ti6Al4V CoCrMo Ringer's solution P = 2 MPa Wear of UHMWPE cup against TiN-PIRAC treated Ti6Al4V head one order of magnitude lower than against CoCrMo head No delaminating of TiN-PIRAC layer after 4 million cycles (~ 3 years in the body) TiN-PIRAC in wear simulator 5-station Hip Simulator device - unique in Israel UHMW polyethylene cup E.Y. Gutmanas, I. Gotman, J. Mater. Sci.: Mater Med. 15:327 (2004)

15 Hybrid THA in 9 dogs cemented UHMWPE acetabular cup Clinical and radiological follow up was uneventful The dogs maintained normal gait pattern until sacrificed – 3.5 years after surgery uncemented TiN-PIRAC Ti6Al4V femoral stem and head TiN-PIRAC in canine THA No radiological signs of loosening 3.5 years after surgery

16 1 mm bone ingrowth 100  m UHMWPE particles Explanted TiN-PIRAC THR No detachment of TiN layer after 3.5 years Very few PE debris after 3.5 years - low wear Bone ingrowth in TiN-coated stem 1 year after surgery - good osteoconductivity

17 5 mm PIRAC-TiN coated Ti6Al4V rat total hip components 4 mm No roughening of PIRAC-TiN-Ti6Al4V after 68x10 6 walking cycles PIRAC TiN metal-on-metal THA: rat model stainless steel PIRAC -TiN I. Gotman, E.Y. Gutmanas, G. Hunter, in P. Ducheyne (ed.) Comprehensive Biomaterials, Vol.1:p.127 (2011)

18 Ti-6Al-4V, 44 mm diameter PIRAC nitriding: 900°C, 4 h

19 Cross-section EDS line spectra of Ti-6Al-4V after PIRAC nitriding * Distance of the start point to surface is about 1.5μm Knoop microhardness of PIRAC nitrided cp-Ti and Ti6Al4V as function of distance from the surface Surface microhardness of cp-Ti and Ti6Al4V PIRAC nitrided at various temperatures Knoop microhardness for various PIRAC treatments of cp-Ti and Ti-6Al-4V alloy  Long exposures at lower tempeatures result at high microhardness; such treatments should be advantageous if fatigue strength is considered, since no coarsening of microstrusture takes place  Microhardness of Ti6Al4V alloy after PIRAC nitriding is slightly higher as compared to that of cp-Ti

20 900°C Nitriding. 4h900°C Nitriding 4h, 900°C Titanizing 1h 3 stage nitriding 900°C Nitr. 4h, 900°C Titan.1h, 800°C Nitr. 24h EDS line spectra of polished cross-section of cp Ti after different PIRAC treatment Cross-section microhardness profiles from surface to substrate of the PIRAC nitrided cp Ti Distance to surface (µm) HKN microhardness (GPa) 800°C Nitridiing.24h 900°C Nitriding.4h – – – –––– Knoop microhardness for 3 stage PIRAC nitriding of cp-Ti  2nd stage – PIRAC titanizing for 1h at 900°C results in 4 µm Ti rich layer;  3rd stage – PIRAC nitriding results in nitrogen diffusion in the Ti rich layer, produced during 2nd stage from inside - the TiN layer formed during 1st stage and from outside monoatomic nitrogen;  3 stage PIRAC nitriding can be used for faster formation of thicker TiN based hard coatings

Comparison of cross-section EDS line spectra of Ti6Al4V after different coating treatments 750ºC 8h+PVD TiN 700ºC 24h+PVD TiN PIRAC nitriding of Ti6Al4V followed by Plasma Assisted PVD (PAPVD) PIRAC PAPVD

PIRAC nitriding followed by Plasma Assisted PVD (PAPVD) No delamination. Excellent adhesion between PIRAC TiN based coating and the substrate and between PAPVD TiN layers and TiN PIRAC coating. Crack is stopped in the substrate -Ti6V-4Al PIRAC PAPVD PIRAC Nitriding: 700ºC, 48h PIRAC+ PAPVD TiN, 3 layers x 3µm Ti6Al4V TiN, 3 layers x 3µm PAPVD Ti6Al4V

23  Outer layer (point 5) is a solid solution of Co in Ti Average Thickness of Coating is μm. Cross section of PIRAC Ti coating on CoCrMo, 900°C, 4h and nitrided at 900°C, 2h in vapour. TiCrCoMoTotal Results of EDS Analysis (A) Cross-Section Image Magnified; (B) Results of A Line EDS Analysis

24  Outer layer (point 5) is a solid solution of Co in Ti Cross section of PIRAC Ti coating on CoCrMo, 900°C, 1h. Average Thickness of Coating is μm. Results of EDS Analysis (A) Cross-Section Image Magnified; (B) Results of A Line EDS Analysis TiCrCoNTotal

25  For specimen nitrided at 900°C, 2h in vapor highest peaks correspond to Ti 2 N nitride, Knoop microhardness close to the surface KHN = 820 PIRAC Ti coating on CoCrMo, 900°C, 4h and nitrided at 900°C, 2h in vapor XRD of Ti coated on CoCrMo, 900°C,4h