CoCr-steels

Direct Tools are sintered from one- or multicomponent metal powders. Today the focus is on one-component powders that allow making parts with properties similar to milling or EDM. Powders are made from steel, mild steel, tool steel, CoCr-steel, titanium, and aluminum. The particle size rises from 50 pm down to 20 pm. Small particles require a careful handling, as they may be respirable and explosive. Reactive powders like aluminum and titanium require a completely sealed build space and a closed material handling system flooded with shielding gas. 

Cr C Cr C chromium iton(l l) [12052-89-0] CrFe (c phase), and chromium iron molybdenum(12 36 10) [12053-58-6] Cr 2F 36 o Q phase), are found as constituents in many alloy steels Ct2Al23 and CoCr ate found in aluminum and cobalt-based alloys, respectively. The chromium-rich interstitial compounds, Ci2H, chromium nitrogen(2 l) [12053-27-9] Ct2N, and important role in the effect of trace impurities on the... 

Nanoscale debris from CoCrMo, which is also a widely used orthopedic implant material, may also induce DNA and chromosome damage as well as cytotoxicity. For instance, CoCr nanoparticles demonstrated more severe DNA damage, chromosomal damage, and toxic effects compared to micron-sized CoCr particles [8,9]. For orthopedic implants made of stainless steels, Fe or Ni nanoparticles are also possible sources for triggering toxicity and adverse effects at local or systemic levels. For example, Ni particles implanted in rat soft tissues were found to cause just allergic reactions when... 

In the methods used for the investigation of corrosion resistance, biocompatibility and bioadhesion the researchers try to simulate and imitate the natural in vivo condition of the implant. Only in the near past have efforts been made to standardize these tests. Because of a longtime decline of standardization the tests described up until now in literature differ and the results of such diversified tests are not comparable. Corrosion measurements, for example, are performed in different solutions with changing pH values and atmospheres (aerated or de-aerated). Only if different materials have been investigated in one test and under the same conditions does a comparison of their behaviour for this test seem possible. Nevertheless, regarding the differing test results, the most corrosion resistant materials seem to be the special metals (titanium, niobium, tantalum and their alloys), followed by wrought CoCr-based, cast CoCr-based alloys and stainless steel. 

Patients with total hip replacements by implants of stainless steel or of CoCr alloys who experienced difficulties after two to fifteen years due to a loosening of the prosthesis and/or allergic reactions to Cr, Co or Ni were found to have an increased content of these elements in their urine, plasma and blood. Already fifteen months after removal the contents were excessive in these fluids [9]. 

After insertion of wires of different metals into the epiphyseal region of rabbits and an exposure time of fifteen months, the histology showed different results. With materials of inert or biocompatible behaviour the cells in the vicinity of the implant were still supplied with blood, while the cells in the neighbourhood of toxic materials underwent an inflammatory reaction and died. A few elements (Cr, Co, Ni and V) have toxic effects and also have a relatively low polarization resistance. Ti and its alloys, Nb and Ta, which have a high polarization resistance, exhibit an inert behaviour. In between the materials were found which are capsu-lated. The results also show that not only the corrosion behaviour provided by the polarization resistance is responsible for the biocompatibility of the material exposed to the tissue. The steel 316L and the CoCr alloy, which have a polarization resistance similar to that of titanium, are encapsulated by a tissue membrane and their behaviour is not inert [13]. 

For turning CoCr alloys, tungsten carbide tools are usually applied. Ceramic coated carbide, boron nitride and high speed steels can also be used. Water soluble oils are applied as cutting fluids. Table lb.5 gives the turning parameters for CoCr-alloys. 

In a first approximation, the safety of couples involving different materials can be preditected by a number of experimental techniques. Table 9.3 summarizes the data obtained by several authors. Notice that the couples between stainless steel and other materials is unsafe. On the contrary, TiAlV/CoCrMo, CoCrMo/C and TiAlV/C combinations may be considered safe. However, repeated fracture of the oxide film at the conical taper region between head and stem of Ti6A14V/CoCr combinations has been associated with corrosion. Attack also occurred in... 

Black, J. and G. W. Hastings. 1998. Handbook of Biomaterial Properties. London/New York Chapman and Hall. This is a compilation of data on natural tissues and fluids and how various implantable materials interact with than. The materials covered range from stainless steels, CoCr-based alloys, titanium, and titanium alloys, to thermoplastic polymers and oxide bioceramics. Biocompatibility is discussed with each material and in a chapter on general concepts of biocompatibUity. Available online on Knovel. 

C.S. Venable, W.G. Stuck Introduced Vitalhum (19-9 stainless steel), later changed the material to CoCr alloys... 

Neural tissue response to wear debris was evaluated by applying 4 mg of particles onto the epidura of New Zealand white rabbits (n = 50, total). Five groups of rabbits were tested (n = 10, each) (1) sham operation (control) (2) stainless steel 316LVM (3) titanium alloy (Ti-6A1-4V) (4) CoCr alloy and (5) UHMWPE. The particle sizes ranged between 0.5 and 10 microns in diameter and were verified to be endotoxin free prior to implantation. Animals were sacrificed at 3 and 6 months postoperatively. Even though there was evidence of a chronic inflammatory reaction for all of the particles, it appeared localized within the... 

A wear study by McKellop et al. indicated that Poly n exhibited a 10 times greater wear rate than UHMWPE against a variety of common counterfaces, such as 316 stainless steel and CoCr alloy [19]. Because the major mechanism of wear in carbon fiber-reinforced polyethylene is abrasive wear that induces the drawing out of fibers from bearing surfaces [20], the interface strength is of critical importance in the overall performance of Poly II and similar composites. 

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