Ceramic-metal joints mechanical properties

The DB-procedure was optimised in respect with the kinetic requirements and the high-temperature mechanical properties of the Ni-superalloy. From the kinetic point of view, the bonding temperature should be over 1000°C when alumina and transition metals are directly bonded [6]. The bonding procedure was always carried out in high vacuum, better than 2-10 mbar (0.2 mPa). The typical thermal and axial compression cycles are presented in Fig.la. It was experimentally found that the ambient bonding temperature is 1100"C or less due to the fast creep of the superalloy beyond this. The compression for the tests was selected as 10 MPa in ceramic-metal joints and 20 MPa in ceramic-ceramic joints [6]. 

As a metal, zirconium is used in bone and muscle implant materials. The combination of mechanical properties and excellent biocompatibility makes tetragonal zirconia polycrystal (TZP) ceramics one of the best biomaterials for prosthetic joints. (Covacci et al. 1999). 

For high-temperature gas separation applications, leak-free sealing of the ITM module components and parts is essential and requires chemically resistant ceramic-metal and ceramic-ceramic seals with similar mechanical, chemical, and expansion characteristics as the membrane material. Little prior art exists for sealing and joining designs for tonnage-quantity ITM modules. ITM ceramics are susceptible to breakage and will have to be joined preferably without any joint interface property difference, possibly as a routine plant maintenance procedure. 

This combination of materials has had a profound effect upon the development of surgery for the treatment of Joint disease and prostheses are readily available, not just for the hip joint but also for the knee, ankle, shoulder and other joints. It is the good biological acceptability of UHMWPE coupled with its mechanical properties that has led to this widespread acceptance. In particular, the tribological characteristics appear to be the most satisfactory for use in a metal-polymer combination. Prosthesis designs utilising alumina ceramic also incorporate an acetabular component of UHMWPE in consequence of the low rate of wear observed. 

During the last 30 years, advances in material science have led to the development of synthetic materials that have unique properties for medical applications. Metals, ceramics, polymers, composites are the main classes of synthetic biomaterials. Metals and their alloys have been used in various forms as implants and for hard tissue repair (e.g., dental implants, joint replacement, fracture plates, screws, pins). They are mechanically strong, tough and ductile. They can be readily fabricated and sterilised. However, they may corrode in the biological media, their densities are high and their mechanical properties mismatch with bone, which may result undesirable destruction of the surrounding hard tissues. 

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