The Metallurgical Process And Its Microstructure-controlling Of The In-situ Synthesized Metal-ceramic Coatings Containing TiB₂ By PTA

As a typical boride ceramics, TiB2 ceramics have become a reserached hot point because of its high melting point, good chemical stability, high hardness and good resistance to abrasion. But its sintering and spraying is difficult and can't achieve a heavy section, good metallurgical bonding and compact coating. Plasma-arc cladding, with simple attachments and high cladding efficiency, can be used in fabrication of the heavy section, good metallurgical bonding and compact TiB2 whisker.The TiB2 whisker is in-situ synthesized during the reaction of the alloy powders employing the plasma arc powder surfacing. The microstucture and properties have been researched by metallographical microscope, stereoscan electron microscope, X-ray diffractometer and microhardness tester. The results derived from the thermodynamic analysis and dynamic analysis show that TiB2 is the simplest product in this case. And the speed of reaction is infulenced closely by the temperature and the reactants density. The results about stucture studies show that the ceramic coatings mainly consist of the TiB2 whisker and the chemical compound of Fe and B. The lower of powders'melting point and the less of products density, the more difficult of coatings'confectioning. The bigger of welding current and the thinner of procoat, the simpler of TiB2's synthesized. The heavy section and gradient coatings containing TiB2 is obtained by multiple tracks cladding, and the thickness acheive 4.5mm, the coatings containing a lot of TiB2 whisker. The quantity of TiB2 is gradually increased and the dimension of TiB2 is gradually augmentated by the distance between the melten line and the surface, and the hardness of the coatings vary with the quantity of TiB2. The spalling of the coatings can be partly solved by changing the mass percent of Ti and B, the welding current and so on.This paper's highlights lies in acheiving a heavy section and gradient coatings containing TiB2 by PTA in-situ synthesized and concluding the metallurgical rules of in-situ synthesized the ceramic coatings by PTA. The spalling of the coatings by designing the gradient coatings was partly solved .