Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
  • C22C32/0047—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with carbides, nitrides, borides or silicides as the main non-metallic constituents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/001—Starting from powder comprising reducible metal compounds
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals

Definitions

• the invention relates to an article based on titanium, in particular a decorative article such as a piece of clothing for the watch industry, having a high hardness and which, once polished, has a surface of intense gloss, as well as 'A method of manufacturing such an article, by sintering a mixture of titanium hydride powder (TiH2) and specific addition elements.
• TiH2 titanium hydride powder
• the invention also relates to a method for hardening and coloring a surface of such an article.
• the cladding parts for watchmaking such as cases, middle parts, bracelet links, watch dials or the like, with high hardness and high gloss, are produced from austenitic stainless steels.
• austenitic stainless steels One of the main reasons for this choice is that this type of steel can be easily stamped or stamped.
• nickel As well as cobalt are highly allergenic constituents capable of contaminating the wearer's skin, so that many countries have set up standards prohibiting the sale of articles in permanent contact with the skin, susceptible to such contamination. , especially by nickel.
• Hard articles are also known which are made from titanium carbide or tungsten carbide.
• these articles cannot be sintered without using a binder if they are to maintain good toughness.
• the currently known binders are allergenic so that the articles thus obtained are also likely to contaminate the skin of the carriers and therefore subject to the same restrictions of use as the articles based on austenitic steel mentioned above.
• the main object of the invention is therefore to remedy the drawbacks of the aforementioned prior art by providing a titanium-based article, such as a piece of clothing for the watch industry, which is ductile while having a high hardness comparable to that of a hard metal, which does not contain any allergenic element, and which, when properly treated, has an aesthetic shine.
• the invention also aims to provide a method of manufacturing by sintering such an article having a very low porosity.
• Another object of the invention is to provide a method for hardening and coloring the surface of such an article in order to increase the hardness of the latter up to a level equivalent to that of a ceramic and to give it a good metallic appearance. ie having a high gloss.
• the subject of the invention is an article based on titanium, characterized in that it is essentially composed of a mixture essentially comprising a titanium matrix and one or more addition elements chosen from the group comprising nitrides, carbides, carbonitrides, silicides, and the borides of the metallic elements of groups 3a, 4b, 5b, 6b, 7b, and 8b of the classification table of the elements, such as iron, titanium, silicon, niobium, molybdenum, chromium, tungsten , vanadium and aluminum or an alloy of metallic elements as well as aluminum oxide and zirconium oxide.
• the article according to the invention advantageously has a high hardness which varies, depending on the choice of addition elements and their quantity in the mixture, typically between 300 and 1200 HV.
• the article according to the invention is ductile and also has a high resistance to corrosion.
• sintered titanium articles are obtained which have a porosity of less than 1% and which, after polishing, have a high gloss.
• This process is thus particularly well suited to the production of decorative articles such as watch cases, bracelet links or the like.
• the article is given a surface hardness of up to 3000HV. It is also possible, depending on the nature of the gas flow circulating around the article to be hardened, to color it and in particular to give it nuances of color close to those of gold.
• Titanium hydride powder (TiH2), preferably having a high degree of purity (99.5%) and an average particle size of the order of a few microns, typically 10 microns, is conventionally mixed with a or several addition elements in the form of a powder of an inorganic material preferably having a high hardness and a particle size substantially equivalent to that of the titanium hydride powder or a mixture of powders of such inorganic materials.
• These inorganic materials are chosen from the group comprising nitrides, carbides, carbonitrides, silicides and borides of the metallic elements of groups, 3a, 4b, 5b, 6b, 7b, and 8b of the classification table of the elements, such as iron, titanium, silicon, niobium, molybdenum, chromium, tungsten, vanadium and aluminum or an alloy of metallic elements as well as aluminum oxide and zirconium.
• the titanium hydride powder typically represents 60 to 95% by weight of the mixture and preferably 80 to 90% by weight of the mixture.
• the titanium hydride can be partially replaced, in a proportion not exceeding 50% by a hydride of an element from column 4b of the periodic table, such as zirconium hydride.
• the proportion of titanium in the mixture makes it possible to influence the hardness of the article. A priori when the proportion of titanium in the mixture increases, the hardness of the article obtained from this mixture decreases. However, it has been found that by using a mixture of 80 to 90% of titanium hydride in conjunction with one of the addition elements such as those mentioned above or a combination of such elements, it was possible, against all expectations, an interesting compromise between the hardness, the machinability and the porosity of the articles produced from this mixture.
• the mixture of titanium hydride powders and of the addition element or elements thus obtained is then stirred, in a conventional manner, with a temporary binder in the form of granules, until a homogeneous mixture in the form of a paste is obtained. .
• the binder is formed from a thermal polymer or copolymer but can also be formed from wax.
• This mixing is carried out at a temperature preferably between 120 ° and 180 ° C depending on the nature of the binder used.
• the mixing temperature is of the order of 170 ° C.
• the mixture in the form of a paste thus obtained is then injected into a mold having the shape of the part which it is desired to obtain, for example a watch case, with dimensions which take account of the withdrawal of the part during the subsequent stages. of the process, shrinkage which is typically of the order of 15%.
• the injection is preferably carried out at a temperature typically around 140 ° C.
• the shaped part is introduced into an oven in which it is gradually brought to a temperature preferably between 200 ° and 300 ° C. During this heating, the binder is gradually removed by evaporation. In order not to deteriorate the shape of the part, this heating is carried out in a time typically between 2 and 9 hours and, preferably, in 8 hours. It is also important that the elimination of the binder is complete to avoid any pollution of the part by the carbon and / or oxygen of the binder, which could lead to a deterioration of the mechanical properties of the part to be manufactured.
• the removal of the binder is carried out under vacuum or in a hydrogen atmosphere in order, on the one hand, to avoid any oxidation of the binder during its removal, and, on the other hand, to increase the speed the process of removing the binder from the part without damaging its shape.
• the binder is a thermal polymer
• the latter can also be eliminated chemically, by decomposition using a vapor of an appropriate acid.
• the atmosphere of the furnace is replaced by a hydrogen atmosphere (if the removal of the binder has not already been performed in a hydrogen atmosphere).
• this hydrogen atmosphere is produced in the form of a flow circulating continuously in the furnace.
• the temperature of the part is gradually increased until the desired sintering temperature is reached.
• the sintering temperature is typically between 1,000 and 1,400 ° C and preferably substantially equal to 1,200 ° C to avoid getting too close to the temperature where the part would begin to deform.
• This heating lasts approximately 2 to 8 hours.
• the titanium hydride gradually releases its hydrogen.
• the heating rate is between 150 ° C and 250 ° C per hour.
• sintering can also be carried out in a vacuum or in an argon atmosphere.
• the porosity of the articles obtained is of the order of 3% due to the violent release of the hydrogen from the titanium hydride at the time of heating which creates a large number of pores. These pores appear in particular on the surface of the article after polishing and scatter the incident light, which prevents perfect specular reflection of the light.
• the use of such articles is therefore in this case limited to applications where the aesthetic appearance plays only a small role.
• titanium since titanium has a high reactivity at high temperature, it reacts, during heating to the sintering temperature and subsequently during sintering, with the addition element or elements defined above to form new types of titanium compounds. Different types of reaction occur depending on the nature of the addition element (s) used. Four types of reaction have been noted.
• the first type that has been noticed is a chemical displacement reaction such as: Ti + SiC ⁇ TiC + Ti x Si y (1)
• a chemical displacement reaction such as: Ti + SiC ⁇ TiC + Ti x Si y (1)
• the high reactivity of titanium is used at high temperature to dissociate chemically very stable materials and form new titanium compounds having a high hardness.
• the second type of reaction which has been noticed is a reaction with the addition of titanium to form a sub-stoichiometric titanium compound such as: xTi + TiC ⁇ TiC (1-x) (2)
• a sub-stoichiometric titanium compound such as: xTi + TiC ⁇ TiC (1-x) (2)
• the third type of reaction which has been noticed is that forming an alloy of the intermetallic type such as: xTi + yW ⁇ Ti x W y (3) This type of reaction makes it possible in particular to obtain compounds having very high hardnesses.
• the fourth type of reaction which has been noticed is that forming particles of hard materials, for example particles of tungsten carbides, embedded in a titanium matrix such as: xTi + WC ⁇ WC in a titanium matrix (4)
• This latter type of reaction increases the hardness of the titanium article and leaves enough titanium on the surface to allow a chemical reaction with other elements during a subsequent surface treatment such as a coloring treatment and / or surface hardening.
• the hardness of the article obtained according to this process depends in particular on the nature and the quantity of the compound or compounds which result from reactions (1) to (4) between the titanium and the element (s) of 'addition.
• the atmosphere of the furnace that is to say the hydrogen
• a non-reactive atmosphere such as an atmosphere of argon or helium, or vacuum.
• Argon will be preferred.
• the replacement of hydrogen by the non-reactive atmosphere or the vacuum is done while maintaining the article at its sintering temperature.
• the duration of this replacement is typically between 5 and 80 minutes and is preferably about 20 minutes.
• the part is then cooled to ambient temperature in said non-reactive atmosphere at a cooling rate of the order of 300 ° C per hour.
• the sintered article obtained by the process which has just been described is composed of a mixture comprising a titanium matrix derived from titanium hydride and the element or elements of addition used during step (a ) described above.
• This titanium-based article has a remarkably low porosity, typically from 2% to 0.1%.
• this article has a hardness which can typically vary from 300 to 1200HV depending on the amount and type of addition element (s) added.
• the article can then be subjected to a specular polishing of its surface in order to obtain a decorative article such as a watch case, a link bracelet, a dial or the like, having a surface of high polish and metallic shine.
• the articles obtained by the process described above can be subjected to a hardening and coloring process.
• This hardening and coloring process can be carried out before or after polishing the article. Also, for example for reasons of convenience, any polishing and / or machining operation of the article can be carried out before the implementation of this hardening and coloring process so that the article, in its form almost definitive or definitive, can be hardened and colored while retaining its shine and its shape.
• the article is placed in an oven and heated to a temperature typically between 600 and 1000 ° C and preferably of the order of 800 ° C. Once this temperature has been reached, a flow of gas comprising carbon and / or nitrogen is circulated around the article to be treated for a period of the order of 10 to 30 minutes, the article being kept at temperature to which it was previously heated.
• a hydrocarbon gas such as methane, propane, butane, etc. can be used.
• the gas stream which comprises carbon and / or nitrogen is preferably diluted in an inert gas such as argon or helium.
• the proportion of nitrogen in the gas flow is typically between 50 and 100% and preferably of the order of 95%.
• the proportion of the gas containing carbon in the gas flow is typically between 2% and 20% and preferably of the order of 5%.
• the depth to which the surface is cured depends on the temperature of the article and the reaction time of the article with carbon and / or nitrogen from the gas flow circulating around it.
• this hardening and coloring process reinforces the corrosion resistance properties of the article. This reinforcement results from the properties of the elements formed in the surface layer which are similar to those of ceramics.
• the increase in the hardness of the article depends on several factors and in particular on the reaction of the compound or compounds which result from reactions (1) to (4) with the gas flow which circulates in the oven.
• TiCN titanium carbonitride powder
• TiH2, 333 g titanium hydride
• the cooled dough is granulated.
• the granules obtained are then introduced into an injection press and injected into a mold, for example having the shape of a watch case, at a temperature of approximately 140 ° C.
• the article conformed by this invention is then introduced into an oven in which a vacuum of approximately 10 ⁇ 2 millibar is then made.
• the article is then brought to a temperature of about 200 ° C by linear heating in 8 hours.
• the article is then sintered.
• the vacuum of the oven is replaced by a hydrogen atmosphere in the form of a hydrogen flow having a flow rate of 250 ml / min, and the part is brought from 200 ° C to 1'200 ° C linearly. in 4 hours.
• the hydrogen atmosphere is replaced by an argon atmosphere in the form of an argon flow. having a flow rate of 150 ml / min, and the temperature is maintained at 1200 ° C. for approximately 20 minutes.
• the article is then cooled linearly under the same argon atmosphere to room temperature.
• the cooling rate is 300 ° C. per hour and an article based on sintered titanium is thus obtained in which the titanium carbonitride has been combined with the titanium by a reaction of the type of reaction (2) above and whose porosity is less than 1%.
• the hardness measured on the article is of the order of 780HV.
• the sintered article is finally subjected to electropolishing to obtain a watch case having an intense metallic shine.
• polyacetal is used as binder and the latter is removed by decomposition in a vapor of nitric acid at 120 ° C.
• the result obtained with this variant is identical to that obtained with the previous example.
• Example 2 the same steps were used as those described in Example 1 with 20% by volume of titanium carbonitride powder (TiCN, 102 g) and 80% by volume of hydride as starting material. titanium (TiH2, 296 g). There was thus obtained an article based on sintered titanium whose porosity is less than 1%. The hardness measured on this article is around 930HV. The article obtained has an intense metallic shine.
• Example 2 the same steps were used as those described in Example 1 with 10% by volume of silicon carbide powder (SiC, 32 g) and 90% by volume of hydride as starting materials.
• titanium TiH2, 333 g.
• a titanium-based article was thus obtained sintered in which the silicon carbide has been dissociated according to a reaction similar to reaction (1) above to form titanium silicide.
• the porosity of this article is less than 1%.
• the hardness measured on this article is around 900HV.
• the article obtained has an intense metallic shine.
• Example 2 the same steps were used as those described in Example 1 with 20% by volume of silicon carbide powder (SiC, 64 g) and 80% by volume of hydride as starting materials. titanium (TiH2, 296 g). There was thus obtained an article based on sintered titanium whose porosity is less than 1%. The hardness measured on this article is around 1300HV. The article obtained has an intense metallic shine.
• Example 2 the same steps were used as those described in Example 1 with 10% by volume of tungsten carbide powder (WC, 156 g) and 90% by volume of hydride as starting materials.
• titanium TiH2, 333 g.
• Example 2 the same steps were used as those described in Example 1, starting with 10% by volume of chromium carbide powder (Cr3C2, 67 g), 10% by volume of carbide powder of titanium (TiC, 49 g) and 80% by volume of titanium hydride (TiH2, 296 g). There was thus obtained an article based on sintered titanium whose porosity is less than 1%. The hardness measured on this article is around 920HV. The article obtained has an intense metallic shine.
• Cr3C2, 67 g 10% by volume of carbide powder of titanium
• TiH2 titanium hydride
• Example 2 the same steps were used as those described in Example 1, starting with 10% by volume of chromium carbide powder (Cr3C2, 156 g), 10% by volume of carbide powder of titanium (TiC, 49 g) 50% by volume of titanium hydride (TiH2, 185 g) and 30% by volume of zirconium hydride (ZrH2, 168).
• Cr3C2, 156 g 10% by volume of chromium carbide powder
• TiC, 49 g 50% by volume of titanium hydride
• ZrH2, 168 zirconium hydride
• Example 2 the same steps were used as those described in Example 1 with 20% by volume of titanium carbide powder (TiC, 98 g), 50% by volume of hydride as starting materials. titanium (TiH2, 185 g) and 30% by volume of zirconium hydride (ZrH2, 168). There was thus obtained an article based on sintered titanium whose porosity is less than 1%. The hardness measured on this article is around 850HV. The article obtained has an intense metallic shine.
• TiC titanium carbide powder
• ZrH2, 168 zirconium hydride
• the article is then gradually cooled to room temperature.
• the nitrogen in the gas flow reacts with the sub-stoichiometric titanium carbonitride resulting from reaction (2) to give on the surface a compound comprising titanium carbonitride with a new sub- carbon and nitrogen stoichiometry.
• Example 2b the same steps were used as those described in Example 1b, starting from an article based on sintered and polished titanium according to the method described above and which comprises 20% by volume as starting materials.
• titanium carbide powder TiC, 98 g
• 50% by volume of titanium hydride TiH2, 185 g
• 30% by volume of zirconium hydride ZrH2, 168.
• the article obtained after hardening and coloring has a golden yellow metallic appearance close to that of gold, and has a porosity less than 1%.
• the hardness measured on this article is around 1800HV.
• Example 2 the same steps were carried out as those described in Example 1b with an article based on polished titanium manufactured according to the method of the invention using as starting material 5% of titanium carbide (TiC , 25 g) and 95% titanium hydride (TiH2, 352 g).
• TiC titanium carbide
• TiH2, 352 g 95% titanium hydride
• a gas flow comprising 2% of methane diluted in argon was used, the article being previously heated to 800 ° C.
• the sub-stoichiometric titanium carbide which results from reaction (2) reacted with the carbon of the gas flow to form stoichiometric titanium carbide.
• the hardness measured on this article is around 800HV and its metallic gloss is intense.

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• 1995
  • 1995-03-09 EP EP95103385A patent/EP0672489A1/fr not_active Withdrawn
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  • 1995-03-20 JP JP7060735A patent/JPH07315912A/ja active Pending

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