KR100616412B1 - Molds manufacturing for high quality titanium cast alloys - Google Patents

Abstract

The present invention relates to a mold for a titanium casting alloy and a method for manufacturing the same, and more particularly, by effectively controlling the interfacial reaction of a titanium molten metal generally generated during casting of a titanium alloy, thereby preventing the mechanical properties of the titanium alloy from deteriorating due to the interfacial reaction. The present invention relates to a mold for a titanium casting alloy with improved environmental load reduction and improved dimensional accuracy by eliminating post-processing.

Titanium, Precision Casting, Molds, Alpha Case

Description

Mold for high quality titanium casting alloy and manufacturing method thereof {Molds manufacturing for high quality titanium cast alloys}

FIG. 1 shows an alpha case with a microstructure photograph and a hardness value change at an interface of a specimen in which titanium is cast in an Al ₂ O ₃ mold.

FIG. 2 illustrates the result of mapping the alpha case of FIG. 1 to Electron Probe Micro-Analyzer (EPMA).

FIG. 3 illustrates a transmission electron microscopy (TEM) image in the alpha case region of FIG. 2.

Figure 4 shows the ring and dot pattern obtained by removing the C2 aperture and Energy Dispersive Spectrometer (EDS) analysis results.

FIG. 5 illustrates the results of Convergent Beam Electron Diffraction (CBED) analysis on the dot pattern shown in FIG. 4B.

FIG. 6 is a schematic diagram of alpha case formation based on the analysis results of FIGS. 3 to 5.

Figure 7 shows the results of XRD (X-Ray Diffraction) analysis of SKK (Sungkyunkwan) template material developed in the present invention.

8 is a photograph showing a comparison of casting of titanium into an implant shape using CaO stabilized ZrO ₂ mold and SKK mold according to the present invention.

FIG. 9 is a microstructure photograph of an interface of a specimen cast with the SKK mold of FIG. 8. FIG.

10A is a photograph of a specimen of a titanium matrix composite material cast using CaO stabilized ZrO ₂ , FIG. 10B is a photograph of a specimen cast using a SKK mold, and FIG. 10C is a photograph of a microstructure at an interface of FIG. 10B.

11 is a microstructure photograph of a titanium specimen cast using a SKK mold using ZrSiO ₄ .

The present invention relates to a mold for a titanium casting alloy and a method for manufacturing the same, and more particularly, by effectively controlling the interfacial reaction of a titanium molten metal generally generated during casting of a titanium alloy, thereby preventing the mechanical properties of the titanium alloy from deteriorating due to the interfacial reaction. The present invention relates to a mold for titanium casting alloy with improved environmental load reduction and dimensional accuracy, and a method of manufacturing the same.

Generally, titanium casting is used for precision casting of titanium alloys and composite materials.

Titanium is known as a universal solvent in the molten state, which results in an interfacial reaction with the mold due to its strong reactivity in casting titanium alloys.

That is, the oxygen decomposed in the template is dissolved into the invasive atoms to form a reaction layer called an alpha case.

Since such an alpha case is an embrittlement area that adversely affects mechanical properties, it requires post-processing such as chemical milling to remove it, which causes environmental problems, cost increase, and dimensional accuracy deterioration.

To date, methods developed to control interfacial reactions in the precision casting of titanium alloys and composite materials are largely based on graphite, zirconia (ZrO ₂ ), yttria (Y ₂ O ₃ ), calcia (CaO), LaOF, etc. There is a method of using, a method of using a binder with a controlled silica content, and a mold casting method.

The method using graphite molds is based on the use of graphite powders proposed by Operhall [US Pat. No. 3,257,692] and inorganic powders called "stuccos". Morozov [US Pat. No. 3,389,743] using colloidal graphite and synthetic resin, and Zusman [US Pat. No. 3,485,288].

However, such a graphite mold has high energy consumption due to high purity graphite, needs to be fired for the mold only in a reducing atmosphere, has a problem in establishing a casting method and preheating with high thermal conductivity, and forms a reaction layer with carbon on the surface of the cast product. There is a technical problem.

Feagin [US Pat. Nos. 4,787,439 and 5,535,811] reported that zirconia and yttria can be used to reduce interfacial reaction layers. Lossow [US Pat. No. 4,703,806] and Horton [US Pat. No. 5,221,336] et al. And a partial coating system was developed to control the interfacial reaction.

However, even when expensive mold materials such as zirconia and yttria are used, there is a limitation that the interface reaction layer due to contamination by the binder and oxygen can not be completely removed.

Degawa [US Pat. No. 4,710,481] developed a crucible fabrication method using calcia, which is known as a stable material that is economical and does not react with titanium, but it is hygroscopic in the back-up process and dewaxing process that imparts the working strength of the mold. It is not suitable for use as a molding material because of deformation of the mold.

Brown [US Pat. No. 4,057,433] attempted to minimize interfacial reaction with titanium molten metal as a heat sink by adding fluorides and lanthanides of groups IIIa and IIIb on the periodic table to the mold, but it was not very effective. It was.

In order to minimize the influence of the silica component of general colloidal silica binders on the interfacial reaction, Lim Ok-Dong [Korea Patent Application No. 10-2000-0069134] reduced the silica content from 30% to 3-10%. , But developed a binder added 3 ~ 10% of the polymer, but does not completely remove the interface reaction, there is a problem that can not obtain a sufficient working strength of the mold.

On the other hand, Choudhury [US Pat. No. 6,443,212 B1] et al., In order to completely eliminate the problem of refractory crucibles and molds, a die casting method in which a titanium alloy is cast into a mold such as Ta and Nb after scull melting using water cooling. Developed.

This mold casting method is limited to a simple shape such as an exhaust valve, and the mold material is an expensive hard material, and has a short life due to thermal shock during casting.

As such, graphite, zirconia, yttria, calcia, LaOF molds, silica binders, and mold-casting methods with controlled silica content are not suitable for economically and effectively shaping titanium alloys.

Therefore, the present inventors have studied to solve the problem that the titanium reaction and the titanium alloy and composite materials in the molten state, due to the strong reactivity in the molten state was unable to avoid the interface reaction, the oxygen and metal components decomposed in the mold titanium The products formed by infiltrating and substituting at the interface, respectively, were specifically identified and based on this, it was found that the mold itself no longer reacted with the titanium molten metal if the mold contained the reaction product in advance.

Accordingly, an object of the present invention is to provide a titanium precision casting technique which is excellent in economic efficiency without high post-treatment and high dimensional accuracy using a strong acid having high environmental load, without deteriorating mechanical properties due to interfacial reaction.

The present invention features a mold for a titanium cast alloy containing TiO ₂ and Ti _x Al produced by mixing and baking titanium powder and Al ₂ O ₃ .

In addition, the present invention is another feature of a titanium casting alloy mold containing TiO ₂ , Ti _x Zr and Ti _x Si produced by mixing and baking titanium powder and ZrSiO ₄ .

At this time, the titanium powder to adjust the content according to the size of the cast bar, it is preferable to use 0.3 to 50% by weight.

The titanium powder, Al ₂ O ₃ and ZrSiO ₄ is preferably used in the powder size range of 2 ~ 200 ㎛.

If the powder size is smaller than 2 μm, a uniform slurry with Al ₂ O ₃ and ZrSiO ₄ may not be prepared. If the powder size is larger than 200 μm, the reaction product may not be properly synthesized.

In addition, it is preferable that baking is made in the temperature range of 850-1100 degreeC.

Such a casting for titanium casting alloy of the present invention,

(a) Al ₂ O ₃ and the titanium powder may be mixed and slurried into a desired form, and then calcined at a temperature range of 850 to 1100 ° C., as another method,

(b) Titanium powder is added to Al ₂ O ₃ and calcined at a temperature range of 850 to 1100 ° C., and then a mold of a desired form can be prepared using the product.

That is, it is possible to use a mold immediately after firing or to fire a new mold using the product.

In addition, by using ZrSiO ₄ in place of the Al ₂ O ₃ It can be produced a casting for titanium casting alloy by the same method as described above.

The casting for titanium casting alloy according to the present invention will be described in more detail with reference to the drawings as follows.

First, a process of identifying the interfacial reaction between a general Al ₂ O ₃ mold and titanium is shown in FIGS. 1 to 6, and the mold of the present invention developed using the characteristics of the interfacial reaction thus identified may be 7 to 11 are shown in comparison.

As shown in FIG. 1, there is an alpha case composed of an interfacial reaction and a hardness increase layer which are visually observed between the Al ₂ O ₃ template and titanium.

Until now, this alpha case is an environmental problem, an increase in cost, and a dimensional accuracy due to invasive elements such as carbon, nitrogen, and oxygen decomposed in a mold, especially embrittlement zones caused by oxygen. It has been known to cause degradation.

Until now, mold materials such as Al ₂ O ₃ , CaO, ZrO ₂ and Y ₂ O ₃ , which have lower standard generating free energy than TiO _2, have been used as a thermodynamic approach to suppress the reaction with decomposed oxygen in the mold. Nevertheless, the interfacial reaction could not be completely eliminated.

In FIG. 2, the result of mapping the alpha case shown in FIG. 1 to an Electron Probe Micro-Analyzer (EPMA) using characteristic X-rays is shown.

It can be seen that oxygen, which is known as a major interfacial reaction layer generating material in titanium castings cast on Al ₂ O ₃ molds, is generally detected in trace amounts at the casting interface.

On the other hand, when aluminum is uniformly distributed in a layer of about 30 μm in pure titanium having no aluminum content, it can be seen that the aluminum of the mold has a great influence on the interfacial reaction.

That is, it was confirmed that not only oxygen decomposed in the mold but also aluminum, which is a metal component, influences the interfacial reaction.

In order to confirm the phase of the detected aluminum, TEM (Transmission Electron Microscopy) analysis was performed to show an image of the interface reaction region in FIG. 3.

Figure 4a is a ring and dot pattern obtained by removing the C2 aperture to determine what phase is present in the image shown in Figure 3, it can be seen that the fine TiO ₂ present in the amorphous through the ring pattern.

FIG. 4B is a dot pattern for light and shade represented by the arrow of FIG. 3, and FIG. 4C shows the pattern index of FIG. 4B.

It can be seen that the light and dark portions indicated by the arrows in the image of FIG. 3 are the HCP crystal structure of the diffraction pattern analysis result 2110.

In addition, FIG. 4D is an EDS point analysis result for the arrow contrast of FIG. 3. As a result of the EDS point analysis, it may be confirmed that the aluminum phase is likely to be Ti ₃ Al.

For clearer phase analysis, the results are shown in FIG. 5 using a convergent beam electron diffraction (CBED) method in which the unit volume of the crystal lattice is easily identified using a focused beam without using a parallel beam.

Referring to FIG. 5, it can be seen that the portion indicated by the arrow of FIG. 3 is 61.08 Å ³ and coincides with a theoretical unit of 62.10 Å ³ of Ti ₃ Al with an error within 2%.

As described above, the interfacial reaction generated during the precision casting of the titanium alloy proved to form not only the invasive reaction product TiO ₂ by the oxygen decomposed in the mold but also the substitutional reaction product Ti ₃ Al by the metal component decomposed in the mold. It became.

6 shows a schematic view of generating such an interface reactant.

As described above, Al ₂ O ₃ generates an interfacial reaction with molten titanium, like conventional casting materials.

However, since Al ₂ O ₃ template material has advantages such as economic efficiency, dimensional accuracy, excellent work strength, air permeability and collapse property, the present invention focuses on this material and has developed a method of overcoming an interfacial reaction.

The casting mold for the titanium casting alloy according to the present invention may be manufactured by the following method according to the size and shape of the cast product, but the present invention is not limited thereto.

0.3 to 50 wt% of titanium powder was added to the Al ₂ O ₃ powder, and then colloidal silica binder was used, using a Zahn cup # 4 of ASTM D4212 to obtain a viscosity of 30 to 50 seconds depending on the shape and size of the casting. Prepare a slurry.

The wax pattern is coated with a casting material to an appropriate thickness, then dewaxed, and fired at 850 to 1100 ° C.

Figure 7 shows the XRD analysis results of the SKK mold prepared by the above-described method, the substitution type confirmed as an interfacial reaction product by the in-situ synthesis between Al ₂ O ₃ and the titanium powder of the template material It can be seen that TiO ₂ and intrusion type Ti ₃ Al are formed at the same time.

Figure 8 is a photograph showing a comparison of the specimens cast titanium in the shape of an implant as a biomaterial under the same conditions using CaO stabilized ZrO _{2 of} Sindlhauser, Germany, SKK mold of the present invention, respectively.

The CaO stabilized ZrO ₂ is an expensive template material currently used in Europe.

As visually observed in FIG. 8, the specimen obtained with the CaO stabilized ZrO ₂ template shows the reaction layer to be removed by chemical milling, etc., while the specimen obtained with the mold of the present invention is unique to titanium in a state where only the mold is removed. It can be confirmed that there is no interfacial reaction to the extent that metal gloss is maintained.

FIG. 9 shows a microstructure photograph in the interface region of the specimen shown in FIG. 8, and it can be seen that the internal and external structures are the same without any interface reaction.

FIG. 10A illustrates a specimen obtained by casting a titanium matrix composite material (TiC + TiB) using Sindlhauser's CaO stabilized ZrO _2. FIG. 10B illustrates a specimen using a mold of the present invention, and FIG. Microstructure picture.

As can be seen in Figure 10, the same result can be obtained not only in titanium and its alloys but also in titanium-based composites.

On the other hand, Figure 11 is Al ₂ O ₃ instead illustrates the microstructure of a cast titanium specimen by using a mold of the present invention using the ZrSiO ₄ powder, the interface reaction did not take place in the same manner as in the mold using the Al ₂ O _3.

Therefore, it was confirmed that when the titanium powder was added to 0.3 to 50 wt% in addition to Al ₂ O ₃ as well as ZrSiO ₄ powder, a precision casting without interfacial reaction could be obtained.

On the other hand, in addition to the Al ₂ O ₃ or ZrSiO ₄ powder, ZrO ₂ , CaO and MgO and the like can also be used to react with the titanium powder to obtain a mold for controlling the interfacial reaction.

As described above, the cast for titanium casting alloy according to the present invention is a stable mold that does not react any more with titanium molten metal because the mold itself has previously formed an interfacial reaction product by reaction synthesis. There is no deterioration, and post-processing such as chemical milling can be omitted, thereby reducing environmental load, improving dimensional accuracy, and reducing mold processing cost.

Therefore, the application area can be infinitely extended to the integrated parts of complex shape, size and thinness, and widely applied to the automotive, sports leisure and medical engineering fields of titanium alloy and composite materials that were applied only to the existing aerospace and military industries. can do.

Claims (9)

Mold for titanium casting alloy, characterized in that it contains TiO ₂ and Ti _x Al produced by mixing the titanium powder and Al ₂ O ₃ and calcined. Mold for titanium casting alloy, characterized in that it contains TiO ₂ , Ti _x Zr and Ti _x Si produced by mixing the titanium powder and ZrSiO ₄ and then fired. The mold for titanium casting alloy according to claim 1 or 2, wherein the titanium powder is used in an amount of 0.3 to 50% by weight. 4. The casting mold for titanium casting alloy according to claim 3, wherein the titanium powder has a size in the range of 2 to 200 mu m. The mold for titanium casting alloy according to claim 1 or 2, wherein the firing is performed at a temperature range of 850 to 1100 ° C. Mixing Al ₂ O ₃ with titanium powder, slurrying the mixture to form a mold of a desired shape, shaping the obtained slurry into a mold, and baking the mold at a temperature range of 850 to 1100 ° C. to form TiO ₂ And manufacturing a mold containing Ti _x Al. Mixing Al ₂ O ₃ with titanium powder, baking the mixture at a temperature range of 850 to 1100 ° C. to obtain a product containing TiO ₂ and Ti _x Al, and forming a mold of a desired shape using the product. Mold manufacturing method for a titanium casting alloy, characterized in that it comprises a step. Mixing ZrSiO ₄ with titanium powder, slurrying the mixture to make a mold of a desired shape, shaping the obtained slurry into a mold, and baking the mold at a temperature range of 850 to 1100 ° C. to obtain TiO ₂ , A method for producing a casting for titanium casting alloy, comprising the step of preparing a casting containing Ti _x Zr and Ti _x Si. Mixing ZrSiO ₄ with titanium powder, calcining the mixture at a temperature range of 850 to 1100 ° C. to obtain a product containing TiO ₂ , Ti _x Zr, and Ti _x Si; Mold manufacturing method for a titanium casting alloy comprising the step of producing.

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