JPH07268517A - Light weight heat resistant material and its production - Google Patents

Abstract

PURPOSE:To easily obtain a lightweight heat resistant material without impairing the characteristics of a Ti alloy by casting an Al-contg. Ti alloy together with BN and making the crystal grains thereof finer. CONSTITUTION:The Ti alloy consisting essentially of Ti and contg. Al is cast together with BN, more preferably hexagonal BN powder of about <=50mum. Adding amt. of this BN is preferably about 1 to 0.01wt.% of the Ti alloy. The Ti alloy and BN are brought into reaction in a solid phase state at about 1500 deg.C below the respective m.p. at the time of the casting. These powders are melted after the solid phase reaction and are cast. The melting is performed preferably by high-frequency melting, etc., having an electromagnetic stirring effect. The casting is preferably executed by using casting molds consisting of Y2O3, CaO, etc., which are hardly reactive with the Ti alloy. As a result, the Ti alloy casting formed with its fine crystal grain sizes is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight heat-resistant material which is a titanium alloy cast body having fine crystal grains, and a method for producing the same.

[0002]

2. Description of the Related Art It is extremely difficult to control the crystal grain size of a material having a high melting point such as a titanium alloy in shaping (molding) a molten metal as represented by casting.

Generally, in order to control the crystal grain size of a cast body, the heat flux from the molten metal to the mold is controlled to coarsen and refine the crystal grains. In addition, there is also a method in which a high melting point material such as ceramics is added to form a composite and the crystal grains are made finer.

[0004]

However, in the method of controlling the heat flux from the molten metal to the mold, when a metal material having a high melting point and active such as a titanium alloy is applied as a casting material, the moldability and the reaction surface are There was a problem. In addition, the method of adding a high melting point material such as ceramics has a problem in that the cast product is strongly affected by the addition of the high melting point material, and thus the characteristics that it should have are impaired.

[0005]

The present invention has been proposed in view of the above, and a titanium alloy containing titanium as a main component and containing aluminum is reacted with boron nitride (BN) in a solid state. The present invention relates to a lightweight heat-resistant material characterized in that it is melted and cast after refining and crystal grains are refined, and a manufacturing method thereof.

The titanium alloy used in the present invention may be any alloy containing titanium as a main component and aluminum as described above, and may further contain a metal element or a ceramic component.

The properties of BN to be added are not particularly specified, but it is preferable to use hexagonal BN powder having a particle size of 50 μm or less. This BN powder may be added as a powder, or may be added in the form of pellets by preforming. In the case of preforming, a highly volatile organic solvent such as alcohol may be added as a forming aid. The amount of the BN powder added is preferably 1 to 0.01% of the weight of the titanium alloy, more preferably 0.1%.
5 to 0.01% or less is preferable. When 1% or more of BN is added, formation of titanium nitride or boride is recognized, hardness increases, and toughness decreases. If it is 0.01% or less, the effect of BN addition is not recognized.

Further, the melting apparatus (furnace) used in the present invention
Is preferably one having an electromagnetic stirring action such as high frequency melting so that a uniform composition is obtained after melting after the solid phase reaction, but a resistance heating furnace may be used as long as it can be heated above the melting point of the titanium alloy. The crucible is preferably a water-cooled copper crucible in order to avoid reaction with an active titanium alloy, but an oxide or carbide crucible may be used.

An example of producing a lightweight heat-resistant material using the above-mentioned raw materials and apparatus is shown below.

First, titanium alloy and its 1-0.01
Place less than wt% BN powder in the melter and raise the temperature. Cold crucible levitation (CCL) melting is performed by setting the atmosphere in the melting apparatus as a reduced pressure argon atmosphere or a high-purity argon gas stream. The titanium alloy and the BN powder have a melting point of 1500 or less.
Solid-state reaction occurs at around ℃. Since this solid-phase reaction is accompanied by a large amount of heat generation, the titanium alloy is partially melted.

Further, if the temperature of the melting apparatus is raised,
The whole melts.

Next, the obtained molten metal (molten metal) is cast (molten) into a mold that is hard to react with titanium alloys such as yttria and calcia (low reactivity).

The light weight heat-resistant material thus cast was confirmed to be a titanium alloy cast body having a refined crystal grain size by observing the structure and measuring the hardness.

As described above, the present invention has found that by casting a titanium alloy together with a small amount of BN powder, the crystal grains can be made fine without impairing the characteristics of the titanium alloy.

The method for producing the lightweight heat-resistant material of the present invention is not limited to the above method. For example, casting may be performed at a high temperature above the melting point of the titanium alloy using a resistance heating furnace capable of heating above the melting point of the titanium alloy. In addition, BN may be applied to the inner surface of the mold to cast a titanium alloy,
In this case, a cast body is obtained in which only the surface layer has fine crystals.

[0016]

The present invention will be described in more detail with reference to the following examples.

[Example 1] First, Ti-34 wt% Al
Alloy 80g, BN powder (Showa Denko's "UHP-1")
0.4 g was preformed into a cylindrical shape by a hand press and then added, and a high-purity argon gas stream (5 l / min) was added.
Cold crucible levitation (CCL) was melted in a high frequency melting apparatus using a water-cooled copper crucible.
The solid phase reaction between the titanium alloy and the BN powder occurred at 1500 ° C. and was heated to 1570 ° C. to completely dissolve it. next,
This molten metal was poured into a precision casting mold made of yttria and zirconia, then naturally cooled and the cast body was taken out.

The crystal grain size of the obtained cast body was 20 μm or less as observed by an optical microscope, and Ti-34 wt% Al (not added with BN) obtained by the same process.
It was about 1/10 of the cast body. There was no change in the texture due to the addition of BN, and the lamella structure texture of α ₂ and γ was exhibited. The hardness becomes 300 Hv due to the refinement of crystal grains, and T
It increased about 100 Hv from the i-34 wt% Al cast body. However, the bending strength of the 3-point bending test is Ti-34w.
Almost the same as the t% Al cast body, the hardness was increased without impairing the toughness.

Example 2 First, Ti-6 wt% Al-
BN powder (Showa Denko's "UH
P-1 '') 0.3 g was preformed into a cylindrical shape by a hand press and then added, and a high-purity argon gas stream (5 l
/ Min) and CCL melting was performed by a high frequency melting apparatus using a water-cooled copper crucible. The solid phase reaction between the titanium alloy and the BN powder occurred at 1500 ° C. and was heated to 1570 ° C. to completely dissolve it. Next, after pouring the molten metal into a precision casting mold made of yttria and zirconia, it was naturally cooled and the cast body was taken out.

The crystal grain size of the obtained cast body was Ti-6 wt (without adding BN) obtained by the same process.
% Al-4 wt% V About 8/10 of the cast body.
The hardness was 300 Hv and increased by about 100 Hv. It was also confirmed that the transverse rupture strength was almost the same as that of the Ti-6 wt% Al-4 wt% V cast body.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments and can be carried out in any manner as long as the configuration described in the claims is not changed. .

[0022]

As described above, according to the present invention, a titanium alloy cast body having fine crystals can be manufactured by an ordinary process. That is, the titanium alloy cast body having the above-mentioned fine crystals could not be obtained by rapid cooling in the past, but in the present invention, the crystal grain size of the titanium alloy cast body having a high melting point and severe casting conditions is very easy. It can be controlled to. Therefore, since the production method of the present invention has extremely high practical value, the titanium alloy cast body is expected to be used in a wider range of applications, and the industrial effect brought by the application of such a lightweight heat-resistant material will be extremely great. Expected to be.

Claims (2)

[Claims] 1. A titanium alloy containing titanium as a main component and containing aluminum is cast together with boron nitride,
A lightweight heat-resistant material characterized by refined crystal grains. 2. A titanium alloy containing titanium as a main component and containing aluminum and boron nitride are reacted in a solid state and then melted and cast to refine the crystal grains. And a method for manufacturing a lightweight heat-resistant material.