OBJECT HAVING A DUCTILE AND CORROSION RESISTANT SURFACE LAYER
This invention relates to an object having a corrosion resistant surface that is also sufficiently ductile to let the surface, or the whole object, be mechanically modified without creating cracks or other weaknesses undermining or damaging the corrosion resistance. The surface layer preferably contains at least 80% of a refractory metal, such as tantalum, and an alloy layer is created between a core element and the surface layer having the needed ductility and adhering abilities.
1 - 15 . (canceled)
16 . A corrosion resistant object comprising:
a core element being made from a first base material and having an outer surface, and,
a coating layer comprising a concentration of at least 70% of a corrosion resistant material covering at least a part of the outer surface of the core element, wherein an alloying zone exists between the core element and the coating layer, said alloying zone having a thickness from where the concentration of said corrosion resistant material is 90% of the concentration in the coating layer, to where the concentration of said corrosion resistant material is 10% of the concentration in the coating layer, from 0.1 micrometers to 10 micrometers, and where the surface of the object has been mechanically modified in such a manner that the surface of the core element, the alloying zone and the coating layer are affected by the modification.
17 . The object as in claim 16 , wherein the concentration of Ni in the alloying zone is nowhere higher than 20%.
18 . The object as in claim 16 where the thickness of the alloying zone is 0.3 to 2.0 micrometers.
19 . The object as in claim 18 where the thickness of the alloying zone is less than 1.0 micrometers.
20 . The object as in claim 19 , wherein the corrosion resistant material is tantalum or of the same group of metals such as W, Nb, Mo, Ti, Hf.
21 . The object as in claim 20 , wherein the core element is an Ni-containing metal.
22 . The object as in claim 21 , wherein the core element is steel.
23 . The object as in claim 22 , wherein the core element is stainless steel or carbon steel or a mixture thereof.
24 . The object as in claim 23 , wherein the coating layer has a thickness within the interval 5 μm-200 μm.
25 . The object as in claim 24 , wherein the coating is deposited by a CVD process at temperatures between 700 and 1200° C.
26 . The object as in claim 25 , wherein the deposition temperature depends on the concentration of Ni in the core element.
27 . A method of forming a corrosion resistant object, the method comprising the steps of:
providing a core element made from a first base material and having an outer surface,
applying a coating layer of a corrosion resistant material to at least a part of the outer surface of the core element by a CVD process at a temperature between 700 and 1200° C.,
applying said coating layer at a rate that ensures the formation of an alloying zone between the core element and the coating layer having a thickness from where the concentration of said corrosion resistant is 90% of the concentration in the coating layer, to where the concentration of said corrosion resistant material is 10% of the concentration in the coating layer, of at least 0.1 micrometers, and
mechanically modifying the surface of the object so that the surface of the core element, the alloying zone and the coating layer are affected by the modification.
28 . The object as in claim 27 , where the mechanical modification is caused by one or more of impacts, blow, strike, grinding, rolling or drawing.
29 . The object as in claim 16 , where the mechanical modification is caused by one or more of impacts, blow, strike, grinding, rolling or drawing.