JP2595534B2 - Method for producing Ti-A alloy castings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

 Purpose of the invention

[Industrial applications]

 The present invention relates to a method for producing a Ti-Al alloy casting.

[Prior art]

Ti alloys, especially Ti with TiAl intermetallic compound as the main constituent layer
-Al alloys have recently been purchased for their light weight and high strength properties, and have been used in turbocharger hot wheels and the like. Castings having complicated shapes and requiring precision, such as hot wheels, must be manufactured by precision casting. As well known, there are a centrifugal casting method and a vacuum casting method in the precision casting method. However, until now,
The precision casting technology of Al alloy was not established. The first reason is that it is difficult to prepare a molten alloy. Both Ti and Al are active metals. The former has a high melting point (1680 ° C) and its alloys have a high melting point, so high temperatures are required to melt the alloys, and multiples are required when forming TiAl intermetallic compounds. , The temperature of the molten metal tends to be abnormally high. At high temperatures, the refractory reacts with the molten metal, which tends to increase the content of impurities, particularly oxygen. Dissolution under vacuum to avoid oxidation by atmospheric oxygen,
The reaction between the molten metal and the refractory becomes more intense, which may cause sparks and blow-up of the molten metal. In any case, the content of oxygen in the Ti-Al alloy lowers the toughness and ductility of the alloy and lowers the properties of the product. Therefore, the amount must be minimized. This problem is common in casting, and in casting in a high vacuum atmosphere, gas generated by the reaction between the molten metal and the mold material remains at the end of the mold, causing defects.

[Problems to be solved by the invention]

An object of the present invention is to use a TiAl intermetallic compound as a main constituent phase.
Established a precision casting technology for Ti-Al alloys, and provided a method for producing Ti-Al alloy castings with a good run and no defects even with a complicated shape, and with a low content of impurities such as oxygen. It is in. Structure of the invention

[Means for solving the problems]

The method for producing a Ti—Al alloy casting of the present invention basically includes the following steps. A) blending Ti and Al, dissolving by plasma arc heating in an inert gas atmosphere, casting by plasma skull casting method or plasma progressive casting method, and ingoting; b) compressing the ingot with a pressure of 50 Torr or more. Re-melting by induction heating in an active gas atmosphere; and c) pouring the obtained molten Ti-Al alloy into a ceramic mold having a vacuum suctioned at the back to cast it into a desired shape. A preferred embodiment of the method for producing a Ti-Al alloy casting of the present invention comprises the following steps. A-1) A mixture of Ti and Al is melted by plasma arc heating in an inert gas atmosphere, and is cast by a plasma progressive casting method to form an ingot. Melting to form a remelted ingot, b) remelting the ingot by induction heating in an inert gas atmosphere at a pressure of 50 Torr or more, and c) removing the obtained Ti-Al alloy molten metal from the back. Pouring a vacuum into a ceramic mold and casting it into a desired shape. According to this embodiment, the content of impurities such as oxygen in the product can be further reduced. The pouring into the mold may be performed by a suction method, that is, by using a mold having a suction pipe and applying an inert gas pressure of 300 Torr or more to the molten metal to push it up, or a dropping method, that is, attaching a casting pouring gate. Using the mold
It may be done by pouring from the gate. Of course, the former has a better product yield of the molten material.

[Operation]

Melting by plasma arc heating uses a water-cooled copper crucible or a water-cooled copper mold in an inert gas atmosphere, so as with a conventional refractory crucible, such as oxygen due to the reaction between molten metal and refractory material Mixing is not a problem. In this way, once an ingot of an alloy containing a TiAl intermetallic compound as a main constituent phase is produced and used as a melting base material for casting, it is encountered when trying to directly melt a molten metal for casting. Problems are avoided. Then, when the melting base material is redissolved by induction heating under an inert gas atmosphere of 50 Torr or more using a refractory crucible, melting can be performed in a short time, so that the amount of impurities due to the reaction between the refractory and the molten metal increases. It doesn't matter much. Therefore,
Within a short time after re-melting, by pouring the molten metal with a small amount of impurities into the mold vacuum-sucked from behind,
Defect-free castings can be manufactured, with hot water running all the way to the corners of the mold.

【Example】

Low oxygen sponge Ti (oxygen content 300pp)
m) and high-purity Al shot (99.9% Al), and they were blended to become Ti-36% Al, and an ingot was cast by the following method. (PSC method) Maximum output 40 with 3 Ar plasma arc torches
Using a 0 kw skull furnace, the melted raw material was placed in a water-cooled copper crucible having an inner diameter of 340 mm and a depth of 120 mm, and was melted by heating under an Ar atmosphere for 30 minutes. Tilt the crucible to 100mm in diameter
Into an ingot having a weight of about 8 kg. (PPC method) Using the same Ar plasma arc furnace as above, 200 mm inner diameter
In a water-cooled copper mold, heat and dissolve while adding the dissolving raw material little by little under an Ar atmosphere, and stub the bottom of the crucible to 47 cm.
The ingot was lowered at a speed of / hr to produce an ingot having a length of 900 mm and a weight of about 70 kg. (PPC-VAR method) The laminated ingot manufactured by the above PPC method was used as a consumable electrode, and was re-melted in a vacuum arc furnace with a maximum output of 600 A, and the inner diameter was 240 m
m in water-cooled copper crucible was cast into an ingot. (Conventional method) For comparison, put the raw materials in a CaO crucible and add Ar100To
Melting was performed by heating in a vacuum induction furnace under an atmosphere of rr. After holding for 20 minutes, a mold having a diameter of 60 mm was cast to obtain an ingot weighing about 2.5 kg. The chemical composition of the ingot produced by each method is shown in the table.
As is clear from the table, PSC method, PPC
The ingot manufactured by the PPC-VAR method and the PPC-VAR method has a low content of impurities such as oxygen, and is suitable as a base material for melting a Ti-Al alloy casting. Ceramic molds for making turbocharger hot wheels were made by the lost wax method. The molds are a suction mold and a drop mold, and each has about 20 pieces. As the template material, fused silica, zircon flour and colloidal silica were used for the slurry, and zircon sand and alumina silicate were used for the stucco material. In a 30 kg CaO crucible, the Ti produced by the PSC method was
-12 kg of an Al alloy ingot was put and melted by high frequency induction heating in an atmosphere of Ar200 Torr. Heat the above ceramic mold to 1100 ° C and immediately attach it to the casting machine,
Vacuum suction behind the mold and Ar pressure in the melting chamber is 60
Adjusted to 0 Torr. In the case of the suction method, put the mold suction tube into the molten metal,
The molten metal is pushed up by the pressure difference between the Ar pressure (600 Torr) in the melting chamber and the vacuum behind it, and is transferred into the mold. In the case of the dropping method, the induction furnace is tilted and the molten metal is poured by gravity. did. The hot wheels thus obtained were all sound castings with hot water running to the tip of the wing and were free of defects. For comparison, drop casting of the melt obtained by melting the above-mentioned conventional material was performed using a ceramic mold equipped with one turbo and charger hot wheel. . Effects of the Invention According to the method for producing a Ti-Al alloy casting of the present invention, a precision casting without defects such as underfill and pinholes can be obtained.
The amount of impurities, particularly oxygen, mixed into the product can be kept low, and the excellent mechanical properties of the material can be maintained.

Claims (6)

(57) [Claims] 1. A method for producing a Ti-Al alloy casting comprising a TiAl intermetallic compound as a main constituent phase, comprising the following steps: a) Mixing Ti and Al and melting them by plasma arc heating in an inert gas atmosphere. Then, the ingot is cast by a plasma skull casting method or a plasma progressive casting method to obtain an ingot. B) The ingot is redissolved by induction heating under an inert gas atmosphere at a pressure of 50 Torr or more. C) The obtained ingot is obtained. Pouring a molten Ti-Al alloy into a ceramic mold whose back is vacuum-suctioned and casting it into a desired shape. 2. The method according to claim 1, wherein the molten metal is poured into the mold by using a mold having a suction pipe and applying an inert gas pressure of 300 Torr or more to the molten metal to push it up. 3. The method according to claim 1, wherein the pouring into the mold is performed by a dropping method using a mold provided with a casting pouring gate. 4. A method for producing a Ti-Al alloy casting comprising a TiAl intermetallic compound as a main constituent phase comprising the following steps: i-1) Plasma arc heating in an inert gas atmosphere by mixing Ti and Al And ingot by casting using a plasma progressive casting method to obtain an ingot. A-2) Remelting a vacuum arc using the ingot as a consumable electrode to obtain a remelted ingot; b) applying a pressure of 50 Torr or more to the ingot. And (c) pouring the obtained molten Ti-Al alloy into a ceramic mold having a vacuum suction at the back and casting it into a desired shape. 5. The method according to claim 4, wherein the molten metal is poured into the mold by using a mold having a suction pipe and applying an inert gas pressure of 300 Torr or more to the molten metal to push up the molten metal. 6. The method according to claim 4, wherein the pouring into the mold is performed by a dropping method using a mold provided with a casting pouring gate.