Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Reexamination Certificate
2001-01-16
2002-10-01
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
C148S278000, C148S279000, C148S281000, C148S518000, C148S530000, C427S419700
Reexamination Certificate
active
06458218
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to deposition and thermal diffusion to form a boride or carbide of a refractory metal on a substrate.
BACKGROUND OF THE INVENTION
Wear of metal surfaces, for example, in many types of machinery, is a problem for which many solutions have been proposed. Wear n many modem machines is aggravated by their high operational temperatures and loads, at which simultaneous metal oxidation, fatigue, diffusion, abrasion, or adhesion can occur. Refractory metal borides and carbides have the necessary hardness and resistance to high temperatures to resist wear.
Methods of electrodepositing refractory metals are known. For instance, such methods are disclosed in U.S. Pat. No. 2,828,251 Sibert et al.) and U.S. Pat. No. 3,444,058 (Mellors et al.). Mellors et al. disclose a method of electrodepositing refractory metals from a solution of the refractory metal fluoride in a molten alkali-fluoride eutectic mixture onto a substrate. The electrodeposited refractory metals form coating which is essentially unalloyed with the substrate. The method disclosed, however, results only in a coating of the refractory metal, and not the refractory metal boride or carbide. Furthermore, the coating is not metallurgically bonded to the substrate and it is therefore relatively less resistant to wear.
Sibert et al. disclose using a solid metalliferous form of the refractory metal to be deposited as an anode. However, Sibert et al. also disclose that, when the electrodeposition is carried out under high temperature and certain other conditions, the refractory metal forms a firmly adherent layer joined to a base me al substrate by a metal-to-metal bond. The process disclosed in Sibert et al. refers to alloying of the refractory metal and the base metal substrate, but not to forming a protective layer of a refractory metal boride or carbide.
U.S. Pat. No. 2,950,233 (Steinberg et al.) discloses a method of, firstly, forming a “cladding” layer of certain transition metals on a base metal substrate containing an amount of a transition metal-hardening element, such as carbon, nitrogen, boron or silicon, either interstitially or in solid solution. The cladding layer could be formed in much the same manner as disclosed by Senderoff et al. or Sibert et al., as referred to above. Secondly, the method requires the base metal substrate to be heated sufficiently to effect thermal diffusion of the transition metal-hardening element from the base metal substrate to the cladding layer of the refractory metal. U.S. Pat. No. 3,887,443 (Komatsu et al.) discloses a similar approach, used, however, with only V, Nb, and Ta.
The approaches disclosed in the Steinberg et al. patent and the Komatsu et al. patent suffer from the disadvantages that to ford borides, carbides or suicides, the substrate material must contain boron, carbon, or silica. This means that this method is limited to use where the substrate includes alloys containing carbon, boron or silica as a component.
In addition to methods of electrodepositing refractory metals and the elements boron or carbon on a substrate, other methods of depositing refractory metals and such elements on a substrate are known.
Finally, various approaches have been taken to electrodeposit certain refractory metals and certain other elements simultaneously from a fused salt bath. Some of these approaches are described in U.S. Pat. No. 3,697,390 (McCauley et al.) (borides of Ti, Zr, and Hf), U.S. Pat. No. 3,713,993 (Mellors et al.) (ZrB
2
), U.S. Pat. No. 3,827,954 (McCauley et al.) (borides of Ti, Zr, and Hf), U.S. Pat. No. 3,880,729 (Kellner) (TiB
2
), and U.S. Pat. No. 4,430,170 (Stem) (refractory metal carbides). In general, these approaches have been found to suffer from the disadvantage that their practical applications were problematic, as they do not generally involve stable processes. These approaches are very sensitive to impurities, and to minor variations in temperature and in the composition of the salt bath. Furthermore, these approaches do not provide a coating which is metallurgically bonded to the substrate.
There is therefore a need for a reliable method of forming a relatively uniform and metallurgically bonded layer of a boride or a carbide of a refractory metal on a substrate.
SUMMARY OF THE INVENTION
In one of its aspects, the present invention provides a method of providing a boride or a carbide of a refractory metal on a substrate of a workpiece. Included are the steps of depositing a layer of a refractory metal on the substrate, depositing at least one of the elements boron and carbon from a source other than the workpiece on the workpiece having the refractory metal layer, and heating the workpiece at a temperature and for a time period sufficient to diffuse at least a portion of the deposited refractor, metal into the substrate and at least a portion of the deposited boron or carbon into the refractory metal layer and the substrate to form a substantially uniform and metallurgically bonded layer of the boride or the carbide of the refractory metal on the substrate. The refractory metal is selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W.
In another aspect of the present i invention, there is provided a method of providing a boride or a carbide of a refractory metal on a substrate of a workpiece. The method includes the steps of depositing a layer of a refractory metal on the substrate, heating the substrate at a first temperature and for a first time period sufficient to diffuse at least a portion of the refractory metal layer into the substrate, and depositing at least one of the elements boron and carbon from a source other than the workpiece on the refractory metal layer. The substrate is heated at a second temperature and for a second time period sufficient to diffuse at least a portion of the deposited boron or carbon into the refractory metal layer and the substrate to form a boride or carbide of the refractory metal and to provide a substantially uniform and metallurgically bonded layer of the boride or the carbide of the refractory metal on the substrate. It is preferred that the layer of the refractory metal is deposited by electrodeposition.
In accordance with another aspect of the present invention, there is provided a method of providing a boride or carbide of a refractory metal on a substrate of a workpiece. The method includes the steps of providing a first molten salt bath of an anhydrous fused salt electrolyte in an inert container, the molten salt bath comprising a substantially eutectic mixture of at least one halide from the group consisting of alkali metal halides and alkaline earth metal halides and a reducing agent for a refractory metal, immersing an anode comprising the refractory metal in the first molten salt bath, immersing a cathode comprising the workpiece in the first molten salt bath, the workpiece being electrically conductive, and electrodepositing a layer of the refractory metal on the workpiece.
The workpiece with the electrode posited refractory metal thereon is heated to a first temperature in a range of about 700° C. to about 900° C. for a first time period sufficient to diffuse at least a portion of the electrodeposited refractory metal into the substrate such that a refractory metal layer is metallurgically bonded to the substrate. Subsequently, a second molten salt bath is provided in an inert crucible, the second molten salt bath comprising an anhydrous fused salt electrolyte comprising at least one halide from the group consisting of alkali metal halides and alkaline earth metal halides and a compound containing at least one second element from the group consisting of B and C. The cathode comprising the workpiece having at least a portion of the electrodeposited refractory metal diffused therein is immersed in the second molten salt bath. A layer of the second element is then electrodeposited from the second molten salt bath on the workpiece having the refractory metal layer. The workpiece having the second element electrodeposited on the layer of the refra
Linamar Corporation
Wyszomierski George
LandOfFree
Deposition and thermal diffusion of borides and carbides of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Deposition and thermal diffusion of borides and carbides of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Deposition and thermal diffusion of borides and carbides of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2999286