Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/20—Carburising
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/02—Pretreatment of the material to be coated

Definitions

• the present invention refers to a process for the surface treatment of an item made of or coated with Titanium, in order to provide improved mechanical properties thereto.
• the present invention further refers to items made of and coated with Titanium and subsequently subjected to a treatment according to said process and therefore provided with improved surface mechanical properties.
• the process provided according to the present invention comprises a heating step for items made of or coated with Titanium, for a preset time interval at a temperature higher than the phase transition temperature of Titanium and in the presence of an atmosphere comprising one or more inert gases and a percent of Carbon gas .
• this temperature is >850°, advantageously ranging from 950 to 1050°C.
• the pressure whereat this step is carried out is reduced, preferably ⁇ 0.5 mbar and advantageously equal to about 0.2 mbar, i.e., under vacuum beyond the controlled process atmosphere.
• the duration of the heating time essentially depends on the temperature and on the Carbon content of the atmosphere: for >25% percents of Carbon gas and >850°C temperatures the treatment times are of at least 1 hour and may extend to over 6 hours .
• the preferred percent for the Carbon gas concentration is >30%, advantageously equal to about 40%.
• inert gases Nitrogen and Argon, whereas among Carbon gases of course Carbon and Hydrogen compounds having a ⁇ 60 ol molecular weight are preferable. Two particularly effective gases are methane
• the items made of or coated with Titanium exhibit Carbon enrichment in the surface layers, an increase leading to a marked improvement of the mechanical performances of the surface .
• the effective penetration of the Carbon atoms extends down to a depth of 120 ⁇ m below the surface, with a notable content of Carbon, oxides and Titanium nitrides.
• the invention refers to all those items comprising a Titanium-base non-stick surface, treated according to the abovedescribed process. Owing solely to the wide range of employs, a listing of the viable items will be omitted. A mere few examples will be mentioned, among which valve bodies and shutters, stirrers, mixers, vessel coatings, components of machines operating on liquid or pasty fluids, conveyors, ducts and coatings thereof, machine components apt to slide one in contact with the other, slides, guides, wheels, etc.
• Titanium samples will be subjected to a heating step as hereto defined and each test piece will be measured in order to assess the effects of the treatment on the mechanical-physical performances thereof .
• Fig. 1 reports the spectra of the Ti tel quel (a) and of the sample A (b) representative of all the carburized samples at issue.
• the Carbon is found to be present in an equivalent quantity onto the surfaces of the carburized foils, and in a greater quantity than that present onto the surface of the Ti tel quel. Therefore, regardless of the time interval and of the temperature, the carburizing treatments carried out have increased the concentration of the surface Carbon.
• Micrographies taken from the samples enabled the observation that all the samples treated at 800 and 850°C, hence below the phase transition temperature of Titanium, exhibit a polygonal structure of an equiaxial ⁇ -type, similar to those of the Ti CP; the samples treated at 950 and 1050°C exhibit a different structure, with more elongated grains, suggesting a partial transformation from the a-type to the P-type structure ( ⁇ + ⁇ acicular structure) .
• the first measuring was carried out at about 10 - 25 ⁇ m from the surface, the subsequent ones from 100 ⁇ m to 1 mm thickness, then at mid-thickness (1.5 mm) and likewise starting from the opposite surface. The most significant measurings are reported in Table 1.3.
• samples G, I, L, 0, P and Q, carburized at 850 and 950°C exhibit a surface hardening equal to 400- 500 HV, anyhow quickly decreasing down to 200 HV at about 100 ⁇ m below surface.
• TQ Titanium tel quel
• the TQ sample merely exhibits a slight surface contamination from Carbon and a passivation oxide film
• sample E A significant example is represented by sample E, wherein the presence of Carbon, Oxygen and Nitrogen is detected down to a depth of about 20 ⁇ m.
• the percent by weight of Oxygen in the carburized layer is of about the 3%, always lower than that of the Carbon. Moreover, about 1% Nitrogen is present .
• the subsequent X-ray qualitative analysis of the samples confirms the presence of the abovementioned elements, in particular highlighting the presence of a nitride carbide Titanium wherein the C:N stoichiometric ratio is not lower than 0.7:0.3. The presence of TiO is also highlighted.
• the XPS analysis was carried out, thereby assessing the chemical composition of the outermost surface layers (Max. down to 60 nm) , the various phases present therein and the change thereof as a function of depth. It was observed that the Titanium is present on the surface mainly as Ti0 2 , and to a lesser extent as TiC or TiN; depthwise, the quantity of Ti0 2 decreases to the detriment of that related to the TiC and/or TiN. On the surface, the Carbon is mainly present as graphite or hydrocarbon; depthwise, the carbon-related component increases .
• Adopting a method differing from the one hereto employed, which enabled a greater data reproducibility, several measurings of the contact angle were carried out.
• the method provides the measuring of the advancing and receding angles, which appeared more stable than the static angle measured with the sessile drop method.
• the results of the contact angle measurings carried out with water are reported in Table 1.8.
• SRV-Optimol (Fretting) tribotester having a ball-plane contact geometry was used.
• the foil employed is made of Titanium, whereas the ball is made of 100Cr6.
• the test consists in oscillating (10Hz) the ball onto the foil, with a 3 mm width and applying a 20N load. The duration of the test is equal to 15 min.
• the wear strength is assessed measuring the post- test weight loss ( ⁇ P) of the materials.
• the testing conditions were selected so as to discriminate the effect of the various treatments carried out on Titanium. Table 1.9 reports the yielded results. Tab. 1.9 - Wear test results
• sample G treated at 850°C for 6h, exhibits an improvement of its tribological properties, suffering a weight loss of a mere 0.0012 g.
• valve 1 of a hand- operated type is shown. It is understood that the present applicative example is mentioned purely by way of example, and not for limitative purposes.
• This valve comprises a valve body 2 inside which a duct is formed.
• the valve 1 comprises a shutter member, in particular a shutter capable of rotating of 90°, by virtue of a handle 4, between a closing or shutting position and an opening position.
• the shutter member at issue is to be destined to a continuous use during which it should endure a certain pressure and be subjected to mechanical fatigue and to friction with the other surfaces of the valve body.
• the surface of the shutter should have the least possible wettability, so that the presence of the valve, at open conduit, does not entail excessive flow resistance.
• the shutter is foil- or plate-shaped.
• this plate is made of Titanium and it is subsequently treated according to the abovedisclosed process, e.g., alike sample D of the comparative examples .
• this member will have a prolonged strength, an enhanced reliability, and it will introduce a reduced flow resistance by virtue of the reduced friction between the surfaces thereof and the fluid engaging the valve .

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Catalysts (AREA)
• Carbon And Carbon Compounds (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Chemical Treatment Of Metals (AREA)
• Chemically Coating (AREA)

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Cited By (2)

Citations (6)

• 2000
  • 2000-12-28 IT IT2000RM000699A patent/IT1316270B1/it active
• 2001
  • 2001-12-28 AT AT01994960T patent/ATE278049T1/de not_active IP Right Cessation
  • 2001-12-28 EP EP01994960A patent/EP1354071B1/de not_active Expired - Lifetime
  • 2001-12-28 WO PCT/IT2001/000658 patent/WO2002053792A1/en not_active Application Discontinuation
  • 2001-12-28 DE DE60106087T patent/DE60106087D1/de not_active Expired - Lifetime

Patent Citations (6)

Non-Patent Citations (2)

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