A. K. Mallik and D. Basu Central Glass and Ceramic Research Institute, Kolkata-700032 Effect of processing technologies on grain size and mechanical properties of Alumina INTRODUCTION MATERIALS & METHODS SEM micrographs of samples HIPed at 1475 GRANULATION CIP (200–300 MPa) GREEN MACHINING MACHINING SINTERING Alumina + BINDER Hot Iso-static Pressing Alumina ceramics have been used as femoral heads and acetabular cup components since 1970s. There are reports of ceramic knee trials by Japanese researcher in the beginning of 1980. The ceramic HIP is used for two types of arthroplasty, a) Ceramic on Polymer and b) ceramic on ceramic. In ceramic on polymer (UHMWPE) type, the femoral head is made up of alumina and the acetabular cup component is Ultra High Molecular Weight Poly-ethylene but in the second case (ceramic total HIP) both of the components are made up of alumina ceramics. After successful technology transfer of ceramic-on-polymer HIP joint from our group, mechanical behavior of state of the art ceramic-on-ceramic HIP joints is being investigated because of its better wear properties. On the other hand ceramic femoral condyles for total knee replacements have been successful in Japan. There are more applications of alumina ceramics in biomedical field, like in spine replacement. REMOVING BINDER CONCLUSIONS CGCRI – Avure Model # Max. Working Pressure MPa Working Zone Dimensions (Diameter x Length, mm.) Approx. Unit Weight (kg) Maximum Working Temperature oC Molybdenum Graphite QIH-6 30,000 110 x 220 120 x 240 25 2000 Success of Hot Iso-static Processing(HIP) over conventional route for medical grade Al2O3 LITERATURE Properties ISO Specification CGCRI Conventional HIPed Density, g/c.c. > 3.90 >3.96 Chemical Composition Alumina > 99.5 % Alumina ~ 99.7 % Alumina ~ 99.9% Micro-hardness (Vickers’), GPa 20.0 > 20.0 > 21 Compressive Strength MPa 4000 > 4000 Flexural Strength, MPa 400 ~ 400 543.5 Young’s modulus, GPa > 350 Wear resistance [alumina pin against polished alumina disc with contact pr. of 5 MPa in distilled water medium], mm3/hr < 0.01 < 0.005 ~ 0.005 Coefficient of friction (Contact pr. – 5.0 MPa, Medium – Distilled water) < 0.30 < 0.20 ~ 0.2 Surface finish (Ra), m < 0.05 High-tech aluminas are used as load bearing implants in biomedical application, e.g. ceramic femoral head and acetabular cup in HIP joints; Ceramic knee. But there are chances of failure of these implants. The majority load bearing implant fails due to fatigue and wear. Fatigue and wear properties are material as well as design dependant. Newer design and improved material property are keys for success of these implants. Following table shows improvement of material property over decades RESULTS Comparison of Mechanical Properties of HIPed Alumina by Avure QIH - 6 Sample Grain Size microns Sintered 2 hrs at (oC) HIPed 30 min 200 MPa at (oC) Youngs’ Modulus ( GPa) Flexure ( 3 pt ) (MPa) Density HV(0.2gf) 15 sec C 1550 1475 398.82 578.91 3.9613 1996 2 C 1540 393.01 531.66 3.9532 1957 3 F 401.71 467.55 3.9735 2172 ~ 2 & ~ 5 1520 398.78 508.87 3.9741 1881 ~ 6 405.34 381.98 3.9700 2029 Literature 1600 NO 380 500 3.96 1900 Properties 1970s 1980s 1990s Bending Strength, MPa 400 500 580 Compressive Strength, MPa >4000 Fracture Toughness, MP.m1/2 4 Vickers hardness, HV 1800 1900 2000 Grain Size, microns 4.5 3.2 1.8 Density, gm/cc 3.94 3.96 3.98 Young’s Modulus, GPa 380 Hot isostatic pressed NO YES Suitable for ceramic-on-ceramic Achievements Denser Ceramic Higher Hardness Higher Flexural Strength Higher Young’s Modulous Future Goal Fabrication of Medical devices based on new processing technique - HIP K1c = 0.016 (E / H)1/2 P . C -3/2 = 2.56 MPa . m1/2 K1c = 3.3 MPa . m1/2 Optical Micrograph of Vickers Indentation REFERENCES Rietveld Analysis Rahaman et al J. Am. Ceram. Soc., 90 [7] 1965–1988 (2007) D. Basu et al, J. Am. Ceram. Soc., 90 [9] 2987–2991 (2007) D. Basu, Sadhana, 28 ( 2003) 3 & 4, 589-600 Values of Cell parameters, crystallite size and strain obtained by Reitveld Analysis ACKNOWLEDGEMENT Sample Alumina a (Å) c (Å) Volume ( A 3 ) Crystallite Size ( nm ) Strain (%) Coarse Grain 8.1151 16.6537 949.79 162.13 0.003 Fine Grain 6.7346 10.3852 407.91 60.78 0.223 Dr. H. S. Maiti, Director, CGCRI Dr. D. K. Bhattacharya, Head, Composite Division, CGCRI Dr. Suchitra Sen, Head, SEM-ESCA section Head, XRD section