Heat treatment

The size and distribution of carbide particles and grain size in cobalt-based alloys are very sensitive to the casting process. In order to achieve the required endurance strength and thermal fatigue performance of cast cobalt-based alloy parts, the casting process parameters must be controlled. Cobalt-based alloys need heat treatment, mainly to control the precipitation of carbides. For cast cobalt-based alloys, first perform high-temperature solid solution treatment, usually at a temperature of about 1150°C, so that all primary carbides, including some MC-type carbides, are dissolved into solid solution; then, they are aged at 870-980°C. Make carbides precipitate again.

Surfacing

Cobalt-based surfacing alloy contains 25-33% chromium, 3-21% tungsten, and 0.7-3.0% carbon. As the carbon content increases, the metallographic structure changes from hypoeutectic austenite + M7C3 eutectic to hypereutectic M7C3 primary carbide + M7C3 eutectic. The more carbon, the more nascent M7C3, the greater the macroscopic hardness, and the higher the abrasive wear resistance, but the impact resistance, weldability, and machining performance will all decrease. Co-based alloys alloyed by chromium and tungsten have good oxidation resistance, corrosion resistance and heat resistance. It can still maintain high hardness and strength at 650°C, which is an important feature that distinguishes this type of alloy from nickel-based and iron-based alloys. After machining, the cobalt-based alloy has low surface roughness, high scratch resistance and low friction coefficient. It is also suitable for adhesive wear, especially on sliding and contacting valve sealing surfaces. However, the wear resistance of low-carbon cobalt-chromium-tungsten alloys is not as good as that of low-carbon steel during high-stress abrasive wear. Therefore, the selection of expensive cobalt-based alloys must be guided by professionals in order to maximize the potential of the material. There are also cobalt-based surfacing alloys containing Laves phases alloyed with chromium and molybdenum, such as Co-28Mo-17Cr-3Si and Co-28Mo-8Cr-2Si. Due to the lower hardness of Laves compared to carbides, the mating materials wear less in the metal friction pair.

Porcelain teeth

Nickel-chromium porcelain teeth are actually the same as steel teeth, except that a layer of porcelain is added to the surface. It is called NP steel in the industry. It contains trace amounts of nickel and beryllium. 0.5%-2% of people will be allergic to nickel. Because metal is in contact with the gums for a long time, there will be:

1. The gums recede. There will be a gap of 1-1.5mm between the porcelain teeth and the gums, which may affect the appearance (front teeth), and at the same time, there will be food impact, swollen gums, and dental caries.

2. The gums are blue, which has been banned in developed countries.

Pure titanium can exist in the human body for a long time, but titanium alloy porcelain teeth contain only a small amount of titanium, and with today's technology and technology, titanium alloy porcelain teeth can be said to be a bit deceptive.

It does not contain nickel but contains beryllium, and the gums will appear blue (the probability is about 0.1%). When an alloy is melted from a solid to a molten metal, the melting point must be considered. The melting point of titanium is much lower than the melting points of the other components of the alloy. That is to say, when the titanium is melted, the other components of the alloy are still solid, and when all are melted After that, titanium has evaporated.